In Alternate drivetrain thoughts, Mark I I discussed some rear-wheel-motor ideas.
It looks like my current best drive method is still the front-fork-mounted rear-frame section, as described in First Design.
However, the rear-mounted unit is looking easier to implement as a first attempt, so I'm also pursuing that by taking apart a rear wheel to find a reliable but easy way to mount one of the middling sprockets onto the *left* side of the wheel, for test purposes. Then I can mount the motor above the baskets, and run the chain between the baskets to that sprocket. I won't have any gearshifting available for this first attempt, but it will be a working test of the motor itself.
I do still have to get the socket mounted to the motor drive shaft (formerly pedal shaft), like this:
That still requires either welding it on (not good) or drill-and-tap (best). It also requires for the rear-mounted test that I cut the pedal-bearing cylinder from the frame, entirely or just partly, so I don't have that whole frame mess to deal with mounting to the rear, just the parts I need. Decisions, decisions.
Sunday, September 16, 2007
In Alternate drivetrain thoughts, Mark I I discussed some rear-wheel-motor ideas.
Posted by M.E. at 9/16/2007 02:29:00 PM
Well, I didn't intend to put more thought into Re-Inventing the Wheel for some time, but after the comment to it, I did more pondering in between other thoughts, and my brain handed me the results on a platter just to the side of my breakfast today. It was a bit confusing, as I wasn't sure if I was meant to have such a crunchy side dish, and after cracking a couple of teeth on it while blindly munching on it all, I took a good look and realized it wasn't actually an extra few strips of bacon, after all.
Once I was examining it outside the context of hunger, I realized it is much more difficult to do than I thought it might be, but it is also likely to be a more ultimate solution to the problem at some future point. I had not really had the concept of planetary gears firmly in mind yet, either, because if I had, I would have realized I could not transfer power the way I was thinking, but would instead need to separately and simultaneously rotate the planetary gears, against the fixed center gear, in order to cause the outer rim gear to actually rotate as desired.
As soon as I had that thought, I realized I was again misconceptualizing it, and that I would need to just build the darn thing as a physical model from scrap paper or something to do thought experiments, and that I simply didn't know enough about planetary gears and such to do this yet. So this whole idea is definitely shelved until I get much farther down the developmental road.
So to speak. Ahem.
Posted by M.E. at 9/16/2007 02:17:00 PM
Thursday, September 13, 2007
I had a great brainstorm idea (which is probably going to turn out more like the results of an epileptic fit instead) while I was unmelting my brain in Jack-in-the-Box yesterday afternoon, after a multi-hour ride around town searching for books about C programming, a 15/16" star-socket, and anything else interesting and usable I might run across.
-- Take a wheel, strip it of all the spokes, put a toothed surface on the inside rim (yeah, gotta move the valvestem or make the gear work around that somehow).
-- Make a package that would fit in the cylindrical space formed by the inside of the rim, containing batteries at the bottom, motor controller in the middle, and motor/gearbox at top.
-- Take the axle with bearings (and ratchet?) and mount that thru the center of the package.
-- Make the outer rim of the package a gear that transfers the motor output to a set of planetary gears, which ride between the rim gear and this outer gear.
-- Plates on the outside with bearings as needed to hold the whole thing together, leaving enough rim exposed to use for old-stye friction brake surface without modification to the friction brakes.
Not sure how bad friction losses because of the planetary gears might be, which might be able to to be minimized with the right lubricants and precision machining of gear surfaces. Mass might also be too high to do all this.
I don't know if this would be more efficient than simply having the motor gear-drive the rim from inside directly.
All this typing just gave me one more brilliant idea that might be too complex to machine, or physically impossible, as I haven't tried to really visualize it yet:
--Make the inner (motorwheel) gear rim be *several* gearings, in rows, and the planetary gears be shiftable back and forth horizontally to engage those different gearings; I suppose the planetary gears also have to be several parallel gearings, but I cannot envision how that could work. :-( Maybe have the gearings be on the inside, and use the *motor* gear inside to transfer power differently. Not sure, don't know enough about gears yet. They're a world unto themselves, though simple in concept.
Maybe I can invent a new kind of gear that will actually do this. Or rediscover an old one, more likely. :-) Got some more research to do now. But if it *would* work, it would still allow shifting for speed control, to keep the current usage in the motor as low as possible by trading speed for torque, just like you do with the pedal drivetrain and your body.
I need a watchmaker friend, now. :-)
Anyway, that's all for maybe Mark XIII of this thing--it's more work than I could do right now, but it's a definite possible path, as the entire thing would be in a simple easy-to-swap-out wheel. I would want this to be the *rear* wheel, because it's gonna be pretty heavy, and I wouldn't want to have to steer with that kind of mass to deal with.
FWIW, I *just* remembered where I saw something similar before: Neodymics' early design idea "BMU-1". It's similar in concept, but not the same way of transferring power, as far as I can tell. Mine is probably less workable than theirs, but I really don't know enough about the mechanics of it to tell yet, as I am not an engineer, just a mad pseudo-scientist. :-)
I never did find the books or the socket. But I did find about $30 in change and dollar bills (including a fiver) just laying around in the parking lots and streets! If I was a fast rider, trying to get places in a hurry, I probably woudn't have seen any of it--I definitely wouldn't have even noticed in a car. I bet you didn't know you could get paid just for watching the ground while you ride a bike for fun.... :-)
Tuesday, September 11, 2007
A new idea has surfaced in my head during a conversation, which is to drill-and-tap (thread) a hole into the pedal shaft big enough for a carriage bolt or stove bolt to be secured into. The square under the head of the carriage bolt would fit into the square hole for the star-socket I want to use to transfer the power from the motor to the Drive Sprocket. That would keep the socket from turning except when it is also turning the Drive Sprocket shaft (formerly pedal shaft). The best part about this design is it allows maintenance, where welding it on would not--I would no longer be able to take the shaft out to do anything to the entire bearing mount area, or to move it to a different frame. This design allows all of that.
The only real catch I have is that the motor rotation has to be the same direction as unscrewing the bolt would be, so I'll have to loctite it in place. I'm sure I could find reverse-threaded bolts and such, but this makes it easier to replace if something breaks or wears. Plus I already have stuff that should fit, somewhere around here.
I also found that 1" might be too big, and 15/16 is actually probably correct, for the socket size. I mixed up my memories of which socket I had checked, and the 15/16" I have is a hex socket, not a star socket; the star was a 7/8", which is just a tad too small. 15/16" should be just about perfect.
Now I just have to find one used (I could buy one new, but I'm trying to keep the recycling theme going).
I do now have someone that may be able to help do the drilling and tapping, which I don't have the tools for. Just gotta get together.
Well, I've never really thought BEMAP was a good name for the project, but I didn't really have any other one. Many names have come up in conversation about this, some of them not very polite, and others not really having anything to do with what it is or will be for.
The best suggestions so far have been either just wierd but interesting contractions of parts of the thing, or other things related to interests of mine and the whole project idea.
Electricle™ was suggested in an IM convo by Melkorka, The Harvesting Maiden of the North™, and is the current winner.
Another was something to do with Skuld and/or her Banpei creation(s) from Ah! My Goddess!, due to her mechanical inclination and especially the often destructive results of the creations' misuse by others. No specific suggestion was made, however, and I have not been able to think of any, either.
Motor-cicle was also suggested, but it was pointed out by someone else that this would be confused with the existing gasoline versions, and that it was spelled wrong. The suggester bowed head in shame and retreated, unfortunately contributing nothing else.
Kill-kill-die-die was rejected with scorn, for obvious reasons.
ScrapCycle was considered for a moment, but not accepted.
Re-Cycle was not adopted either. Though it was clever. In musical circles, it's already used, though that doesn't preclude it's use here.
Tron's Reject didn't meet with much agreement.
I'm still up for suggestions, so please, comment them in!
I got another organ donor bike yesterday. Walked into a thrift store, and it's marked $25, and except for a rusty chain, is in good shape. Needs adjusting here and there, but it has a wider seat than mine, and has the Shimano SIS Gripshifters mine has, which I wanted another set of for the electric motor controls (but they're expensive to buy separately). I got to the register and it was rung up as $15; apparently I got there in time for the daily random special. :P
It's kind of strange. The welding, body style, and all the parts except the shifters/derailers are all the same as the two Murray's I have, but the body has Huffy *deeply* stamped into the metal down at the kickstand mount. All the stickers say "Kensington", and "made in China". The Shimano stuff all seems to be aftermarket, as they don't match the paint-crimp marks underneath them, so perhaps whoever owned it before me changed them out. I'm glad they did, though, because I sure wanted this kind.
I bought it to cut the rear frame section off and use for my Electricle™, but it's in such nice shape, and is actually a bit shorter in the seat tube than my other bikes, it fits me better than any of the others I have. So I will probably save it's frame and use *this* for the test bike, and sacrifice the other (yellow) Murray as organ donor for the rear frame part.
I'd already tried using the frame off my old white Murray Biotech, but the metal is soft and had already been bent at the rear wheel mount points long ago, which is why I had eventually given up on it--I couldn't straighten it and *keep* it straight, and the wheel would end up so out-of-true by the middle of a ride that it would rub on the brake pads, or even the frame! I thought that I could at least use it for testing, but even that is proving impractical due to the soft bent metal, thus the acquisition of the new bike for organ donor purposes.
Now I have some thinking to do before I start cutting, because I'm not sure exactly what I want to do now. :-(
Sunday, September 9, 2007
It doesn't much matter because I don't have a design to be controlled yet, but starting from some advice from 4QD, it looks like Atmel's AVR series might be the ticket to the chip to use. There is a LOT of open-source stuff out there, including some DIY programming hardware for the initial programming of the chip, and some routines to update the program with a USB bootstrap while in-circuit.
AVRFREAKS is a good place to start, from what I can see. For those that are interested, this is a comparison chart of the devices, along with data sheets:
There are versions of the AVR uC that are *designed* for PWM control circuits, both for motors and for stuff like dimmable fluorescent light ballasts. And the chips can be had for as little as $1.00 each, from some places, not to mention there are sample kits available for just shipping/handling costs. I bet I can even take some out of old equipment, because i'm *sure* I've seen these things in some of my old junk. Depends on what comes in the sample kits whether I'll bother with them or not, I guess. I'll check all that out later, once I have the bike itself physically working.
The biggest catch is that I first have to learn C, as that's what it's programming environment uses to create the code to be uploaded to it. I are not a programmer. :-( Yet.
The good news is that if I do learn how to use this uC, I will be able to do a number of other improbable projects that I could not do before, unrelated to the bike.
First up is the bike that will be converted, once I have a working design. It's a 2005 Columbia 26" Comfort Bike, with an aluminum frame. I like that the frame is strong and light, but being aluminum I can't weld anything to it (even if I find or build a steel-welder, as I don't know if I could make an aluminum-welding rig, and I really doubt I'll find one of those in someone's junkpile).
The baskets are from previous bikes--the front ones are actually rear baskets with minor modifications to fit on the front, because there never seems to be enough cargo space. Can't carry much of a load up there without seriously affecting steering, but it works for all the light but bulky groceries, like various products that come as essentially bags of air with a little product inside, ramen, powdered milk, and the like. Liquids up front are a huge no-no, as the side-to-side sloshing will quickly resonate and cause steering loss and a crash. :-( Those baskets will be replaced with panniers of some type once the motor implementation is finished, very likely a variant of these cool mop buckets from Jake Von Slatt, which are a pretty cool idea. I like the way this man thinks. You should look at the rest of his sites, too, when you're done reading this one. There are some interesting projects at his main pages, and his Steampunk Workshop is interesting and inspiring.
This is the drivetrain frame, with wheel and chain, but missing the actual pedal shaft and sprocket (which were separated for modification at the time). It's pretty grungy and rusty, plus it's bent up at the rear wheel axle mounting point, which is why the bike it came from was originally scrapped (I hit a huge pothole that was invisible in the dark, somehow only with the rear wheel as I turned a corner, and the rear wheel was yanked right out of the frame, and the frame hit the ground. Like usual, I was lucky only to get scrapes). But it will work well enough for testing purposes.
I'll find a different organ donor for the real version, likely from a thrift store or yard sale--$5 to $15 for a bike is not uncommon, if you look for them--they're not rideable due usually to rotted rubber and plastic, but that doesn't matter for this purpose, as long as the frame is not rusty or bent (in back). I simply hacksawed this part of the frame off the rest of the poor Murray Biotech, and hammered the bent parts back in shape as best I could.
This is the way the pedal levers and pedal sprockets looked before I started, with the pedals themselves simply unscrewed from them with a crescent wrench. It's still on the frame here.
This is after I used a carbide cutting wheel with my handy Black&Decker circular saw to cut the pedal levers off the pedal shaft, so that I will have a place to connect the motor's output gear to. I still have to file the motor side flat and level, I couldn't hold the circular saw steady enough to cut it perfectly, and I don't have a table saw or other large tools like that (and haven't built a table mount and mitre for the handheld one yet, either, though I probably will before I do the rideable version). I will need to make a way to weld a connecting piece between the non-sprocket end of the shaft and the motor's output gear. A spot weld would be fine for tests. Full weld would be needed for rideable version, assuming the design even works.
This is the actual motor to be used, in several views. You can see the output gear, which is a pretty hard steel (it didn't scratch much when I was scraping crud off of it with a utility blade, for instance). That gear will fit nicely inside a 1" star-type socket from a socket wrench, with the teeth moving just a bit against the socket's inside star-points. It's even better on a 15/16" socket, but because this gear has 9 teeth, and the sockets have an even number instead, I can't actually make it fit. I'd need to file down at least one tooth, and possible several, or do the same thing inside the socket, and that's tedious and difficult with hand tools, or even with my Dremel. Whichever socket I end up going with would be what gets welded to the pedal shaft above. Then when I bolt the motor down to the frame, it would be held into the socket on the sprocket, and I can turn it on and take off like a rocket. Or something.
There are bolts already intended to hold the gear assembly to whatever mating object would be driven by it, formerly the LTD's window crank, but now whatever I build for the motor mount. I'm still scrounging for parts on that, but I've got some good aluminum L-brackets, over 1/8" thick, and hard enough that I can't bend them by hand. Those, along with a few other odds and ends like a long pipe clamp I found in an old toolbox, will probably work for the motor mount, after suitable drilling of holes for mounting bolts and such. The motor feels a bit heavy, but shouldn't be an issue since I am mounting it close to and parallel to the frame--there should not be much cantilever force to yank it out of alignment even with some significant bumps and potholes.
Attached to the motor is part of the harness that includes the window up/down switch. It's spring return, and already designed to handle the current from the motor, as well as significant usage cycles, so it will certainly work for the purpose of a test deadmanswitch, until I build the actual throttle and PWM circuit for the system. Right now, I'm testing using just a 12V gelcell battery directly connected to the motor (via the switch/harness), since none of this is running for more than a minute or two at a time. Efficiency is irrelevant for these tests--I just need to see if it physically works and drives it with enough power to move me and the bike. If it doesn't do that with direct battery power, it will never do it any other practical way, either. :-)
I might be able to use higher voltages, like two cells in series for 24V, but this motor was intended for 12v use, intermittent short-period loads (rolling up a window). I am not sure what would happen at double that voltage, and sustained periods driving a heavier load than a window crank. I'll not test it unless it doesn't work the other way.
Saturday, September 8, 2007
John of TeamDroid sent me a link to this article about modifying and using the DeWalt 36v packs.
That's exactly the battery pack I've been looking at converting, for pretty much the same reasons it seems everyone else wants to do so.
I had wanted to use it as-is, so I could use it's ruggedized casing to hold everything, quick moutning points, etc, but it looks like it still has to come apart to have the charging/etc module removed if I need some higher current capabilities than it's designed for. I'm going to try to not need that much current from one battery, and instead use multiples, so that I can use it's own charge/discharge cutoff electronics to do my dirty work for me, but I'm not sure if it will work.
There is some really good info about some reverse-engineering done on the battery packs in the links from that article, and I'll be studying that to see if I can link into the existing stuff or have to bypass it all, which I'd like to avoid.
Originally, I had wanted to use some of the dozens of old laptop Li-Ion batteries I have around here, saved from the scrapheap when people replaced them because they didn't last as long as they used to, but still had significant life in the. Many of them are pretty old, though, and probably aren't worth even opening up to test the cells. Another problem is designing monitoring and control circuits so I don't blow myself up with these little grenades...er...power cells, as they're fairly sensitive to overcharging and overcurrent draw for sustained periods. Ah, I had a great plan, though it is not really practical because of the charging controller issue--it's just not worth dealing with that kind of safety problems, especially not down between my legs in the main bike frame, where I'd planned to put them. :-)
Using the DeWalt packs with their integrated controllers will help me bypass a bunch of problems with the whole battery-design issue.
I've been having an email conversation with a knowledgeable friend of mine with significantly more mechanical repair and design experience than I have, and quite a bit of thought came up as a result of it, so this post will discuss the points made in it. Depending on how the balance of advantage/disadvantage works out after further thought and comment from you, the readers, I might do something along these lines instead.
I looked at some of your design images. Why not move the motor and second gear cluster to the rear wheel? have one set (the human driven) on the right, and the motor driven set on the left?I had not yet considered that option, but there's two big reasons not to:
First, derailers have handed-ness. Meaning, they're made to be mounted on only one side. All of mine are meant only for the right side. It's why my latest blog post "Oops" had to be made, because I *knew* that but had not thought about it when making up the 3D model and the temporary physical mockup, because originally I was going to do things a bit differently with the wheel mounting frame, and thus would have had everything still on the relative "left" side of that frame, since it would have been essentially completely backwards, wheel, frame, and all. But I can't do that because I found the sprockets would end up crunching on the main bike frame when I turn, and/or chew up cabling (electrical or mechanical) that jiggles too close to it by accident somehow (since currently there's no cover over the chain/sprockets). It's possible that some of the derailers out there are meant for left-side mounting, but I haven't seen any on bikes I've actually had or worked on, or in the few bike shops online I looked at via google. Either way, if they do exist, I'd have to buy them, and that's something to avoid where possible. There's no way to modify the existing ones because of the way they work inside, as far as I can tell. Certainly *I* could not do it, as there are parts inside (made of steel) that are one-way fits, and could not be assembled in the opposite direction, even if I could take the whole derailer apart and put it back together in mirrored fashion.
If I did not intend to be able to shift the motor gears to make it more efficient for speed vs torque, to get the most out of my battery life beyond what the PWM controller will do, I would not need to worry about the derailers, and would simply need to make the chain shorter so it would have the proper tension without the derailer/tensioner on the rear. But it would still leave the second problem.
The second is that I would have to disassemble the rear wheel, and manufacture a new hub out of the existing one that could hold the spokes from the left side more toward the center, as the right side does (they're not symmetrical currently), so that there would be room to add the sprockets necessary for the left side drivetrain. Otherwise there is no place to put the sprockets to drive the rear wheel from the motor, and that is a serious flaw. :-)
A few minutes more thinking after typing up the above leads to the possiblity of only a single rear sprocket "welded" (bolted, glued, etc) in some way to the spoke mounting plate just inside the bolt/fork assembly, which would fit and clear all the necessary parts around it so the chain would not catch on things and still drive the wheel. It eliminates the sprocket ratchet, because now the chain is directly connected to the wheel, and coasting will cause the wheel to drive the chain instead of the chain driving the wheel, which has several consequences.
- An advantage of not having a sprocket ratchet is that it would allow Regen braking to work, which it will not if I use the current system, that takes advantage of the ratchet system inside the wheel's sprocket hub that allows you to coast when not inputting any energy, without rotating the input device, because energy is only fed into the wheel, never back out of it to the input device, a necessary thing for Regen. Since I'm currently using a motor with a worm-gear reduction system for testing, it's irrelevant, because it is not possible to feed energy back into the system that way, either.
- A further advantage is that it eliminates the rear derailer/tensioner, so it breaks down one part of the first objection--no need to find a left-side derailer/tensioner.
- A disadvantage of not having a sprocket ratchet is that I could not use any gearbox that has a worm gear in it, because that would lock up the entire drive train if the motor is not being powered, and my max speed would be limited to whatever the motor was spinning at.
- A further disadvantage of not having a sprocket ratchet is that the motor would always be "in circuit" mechanically, and thus always placing a physical load on my pedalling. Even though I can (and would anyway) make a switch to manually or automatically electrically disconnect the motor from the rest of the system when it is not being powered, which would remove most of the resistance/braking that would occur, it would still cause some extra resistance for the bearings and such involved--more than the sprocket ratchet in the wheel does, which is currently all I'd have to fight against. Depending on how the gearbox is attached to the motor-end drive sprocket, it might be possible to lever it out of contact with the drive sprocket so it is thus out of circuit and eliminating this problem, but that makes the connection to the sprocket more complex, since it would have to detach. I already do have some ideas about that, though, because of how I am thinking of doing this connection already.
- Another disadvantage is that not having multiple rear sprockets and a rear derailer prevents any possible rear shifting, severely reducing the amount of help I can give the motor in matching it's output to the requirements of the speed I want at any particular time, at the most efficient ratio. I would only have two speeds, because that is all the sprockets I have available on the motor drive section. Better than only one speed, but not enough for what I want to do.
If I totally trash the idea of shifting at all, and only use motors with wheel gears and no worm gears, then it is relatively easy to put all the drivetrain on the rear left side. It might come down to doing just that, but it's a bit boring because it doesn't have any real change from how I've seen many project bikes done, in that I don't recall seeing any of them yet that have a way to "change gears" for the motor separately from the pedal system, without a custom-manufactured reduction gear set on the motor itself. I don't exactly have this as a specific goal, but it'd be interesting to make this project in such a way that anyone with the desire could build it themselves from the junk they have around, too, like I am trying to. I know there will be parts I must actually make or have made with the current preliminary design, such as the blocks to go between the fork and the attached frame section, that won't be makeable with just a hacksaw, :-) but there may even be alternate solutions to *that* I haven't thought of yet.
I bring this up because of the issues you might have with steering under power. That motor might cause some interesting precession if you load it during a turn.
Possibly true, which I've thought about, but can't test until I actually finish building some basic test version of the setup. Currently, because it's a power window crank motor with gearbox, the motor will be longitudinal to the body of the bike during normal forward motion, but that will change during a turn. I don't remember which direction the motor itself turns inside it's casing to drive the gearbox, so I dont' know which direction would have more trouble turning. It's currently a pretty small motor, and has low mass, so the centrifugal / gyroscopic force isn't as bad as it could be with a larger motor, especially a pancake style one, I suppose.
I suppose I *could* prevent the motor from ever actually running during a turn, but then I have to decide how far a turning of the fork is a turn, and how much just collision avoidance, where I might actually still *need* the power input. So I don't want to do that unless the problem is so bad I can't safely steer because of it.
Friday, September 7, 2007
I had the thought originally to balance weight, etc by putting the chain drive for the motor on the left side. That won't work because of the way I have to mount the frame, which puts all the mounting points backwards for the derailers. So what you see in the images in the first Design Ideas post is now left-right mirrored from how it will be. Both chains go on the *right* side, and the motor will be on the left.
On another note, I got the pedal-axle cut, so it is just the shaft itself, no pedal levers. This makes it possible to mount to the motor gearbox now, as soon as I find a suitable coupling device. I also still have to design and make the motor's mounting bracket, and fasten it to the frame.
Hopefully I'll start getting some feedback (assuming anyone is even reading this at all), so I'll find out what really stupid thing I'm doing before I kill myself trying. :-)
The power-window motor I described in a previous post seems to function well enough after it's clean up. I took the worn-out nylon/whatever gear/cam that's driven by the motor's worm gear, and the cam/gear exposed to the outside of the gearbox case that's driven by the first gear/cam, and thoroughly cleaned all the graphite lubricants off of them, saving all that I could of that for later reapplication, and JBWelded them together, letting that cure overnight. Once I reassembled it, I now have a reduction-gear assembly that gives me enough torque to use to drive the pedal-sprockets, which will drive the chain, which will drive the wheel-sprockets that are connected to the rear wheel, and thus move the bike along the ground.
Sometime today, I have to setup the stall-current experiment to find out what current draw this motor will have at maximum, so I'll know what I must definitely limit the current draw to, to help prevent motor burnout. Unfortunately, there are ZERO specs available for this motor locatable online via any p/n that's on it. Not that I expected to find any, but it would have made things a tad bit easier. I found hundreds of places to buy new motors for the car it came from, but nothing about any specs for any of those, either, to try to use for comparison.
The two biggest things I want to achieve with this bike are simplicity of mechanical efficiency and low-cost.
The low cost I can do a lot of by using recycled parts wherever possible, since this is not a commercial venture but rather a personal transportation. :-) It'd be nice to make a saleable product, but I doubt anyone would want to ride something as ungainly as this.
The simplicity part of the first requirement is hardest to stick to, because every feature I add could double or more the complexity. The efficiency part for the current design is going to require some sort of feedback loop control via either hardware or software, taking a setpoint for speed and comparing it to actual wheel speed vs motor speed/current draw, and shifting the derailer gears automatically to maintain the lowest current draw possible for a given speed, but with the least amount of mechanical chatter switching back and forth. This feedback control loop is looking to be the most difficult part of this entire design, as I have not yet even found my starting places for it yet.
I am just about certain doing it in software would be far easier than hardware, because changing parameters for different sets of parts (like different motors) would be a whole lot easier that way. The catch is that I don't have the programming knowledge (especially with microcontrollers (uC)) to do this, and getting it right is a non-trivial task.
I would need to design the actual output hardware (power switching amplifiers, etc) first, to meet the current and voltage requirements, with certain safety cutoffs hardwired in to prevent a stupid bug from frying everything, then deciding which of several existing microcontroller (uC) boards to use (since developing one of *those* is out of my league, right now). The catch is that all the uCs are expensive. The programmers for them equally or more so. *And* I'd have to write the software from scratch, as I don't know any well-documented open source stuff available to do this sort of thing that I could use as an example. I have ideas on how to block it out, but not yet to actually write it.
I'd want a uC I could program via USB, preferably. Serial is ok, too, and very common, but many computers nowadays do not have serial ports, especially laptops! Mine does not have one (preventing me from using my drawing tablet on it, amongst other things, since the serial-to-USB adapters so far tried do not work for it). Thus, if I had a programmer that was only software in the computer, for a uC that interfaced via USB (or serial), the cost for the programmer would be theoretically nothing, because the controller developer has no hardware cost associated with the programmer to sell to users, only the software cost that hopefully is amortized into the cost of the actual uC, and then the whole thing would be pretty cheap to buy for my low-volume (i.e.: ONE uC) application. Also, if the programmer software has a simulation function, I could use that to give various input conditions to check for fatal flaw conditions of output (though I don't yet know what those would be). I have not yet looked to see how many uCs are actually made this way now, but any that are would be in consideration for this project.
I've also looked at simply buying an existing PWM controller, either software based or not, especially those from 4QD. Richard there is an *invaluable* help to me, and I wanted to be sure to credit him and his excellent technical resource site for basically providing me with the start and much of the rest of my knowledge of PWM controllers, as well as many other design considerations for other aspects of this project that I did not know where to start from, until I found 4QD. Even this entire blog entry is a result of a discussion with him, which I had not formulated into words until then.
Wednesday, September 5, 2007
This 85 Ford LTD in my driveway has power windows, but they don't work because the nylon gear inside has the tabs worn off the inside part of the cam (this is what keeps it from squishing arms and fingers hanging out the window, in theory). I guess it's previous owner liked to hold the window buttons down for a long time after they reached top or bottom, and wore them down. The motors are fine. I'd already had the motor out of one door because I was trying to find a way to fix or replace the cam for cheaper than $15/window, which x 4 is a lot of money. I gave up on that when I couldn't find the specific problem with the fuel flow, which rendered any other non-get-car-moving work meaningless.
Anyway, I've got the motor in my hand now, cleaned up a bit, and tested it on my bike's lights battery, the 12v 1400mAh gelcell.
It looks pretty much like this one, only grungier:
It runs nicely, and would be fast enough with the gearing already in it (if I could put tension on that) to likely go *real* fast on the bike. Haven't measured the current it takes, or it's winding resistance, yet, so I don't know what kind of power will be needed to drive it under load. Weighs a tad more than I'd like, at about 6 or 7 pounds, but I can live with it if it works, for the experimental parts of this.
To clean it up, I had to take it apart, and cleaned all the black oxidation and burnmarks off the copper commutator pads and the brushes (also copper, rather than graphite?). It's got a thermal cutout built into it, but I don't know at what temp it would trigger. Hopefully prior to meltdown. There is no ventilation; the motor is pretty much sealed up inside it's case--presumably to keep the water expected to come down the window glass (despite the gasketing) out of it.
The motor shaft is nice and long, but it uses a worm gear to transfer power to the crank gear. That's a problem if I want to use Regen, because there is absolutely no way to ever transfer power back into the motor itself that way. :-( Another problem is that I *have* to keep the casing intact, and actually use the gearing that's there to transfer power around, because there are no bearings for the gear end of the shaft except at the very end of that shaft, inside the casing, with an adjustment screw on the end to presumably control motor speed by friction on the shaft. That friction is easy to "disable" by loosening the set screw a turn, but the way it's all made makes this less than ideal.
The problem with the worn bits on the plastic cam means I need to degrease the whole nylon gear/cam and metal transfer cam/gear, and epoxy them together, in order to even use it for testing. That's gonna take a little time to soak and clean, cuz the graphite lube in there is really icky.
Ah, well, at least it's a test motor. And I have 3 more just like it if I need them.
Tuesday, September 4, 2007
As stated before, I need to use PMDC (permanent magnet direct current) Brushed type motors for Regen to work, AFAIK. So finding a cheap but quiet and hopefully reliable motor would be useful.
If not using Regen, then Brushless DC motors are the next choice, as they're supposed to be more efficient than brushed motors (due to less friction from not having a commutator, I think).
AC motors are right out.
Series-wound DC motors (like most starter motors in cars) are not desirable because of the extra power it will take to run it, just wasted on energizing the stator windings.
Low RPMs-per-volt is fine with me, because it means less reduction I have to do to get to the speed I really want to use to turn the wheel with. It might mean less torque, though, which I still have to figure out. I'm not good with math (I can solve an equation, but I don't really *comprehend* it).
Sources of possible motors I could recycle into this machine include but are not limited to:
-- Old big line printers, the type that feed wide paper out so fast you hardly have time to blink. There aren't many around anymore, and I'm sure some of you have never seen one.
-- Battery powered power tools. Some of the heftier ones that have a lot of torque are likely to have enough power to run this. If they're quality, it's even possible the reduction gearing could be used from them, which would be a great help. Most of the ones that work for this are bigger pro-end tools, with separate battery packs, rather than the ones with built-in batteries and such (like one little one I have here).
-- Some lawn tools. My Black & Decker electric lawnmower was AC powered, but had a rectifier and a PMDC motor in it, which would almost certainly have been big enough to do the job. Unfortunately something cracked the magnet, which got sucked into the armature windings and cut them up, resulting in what looks like the worse bad-hair day ever. If it turns out to be possible to unspool the wire off an old AC fan motor I have (without damaging the wire or insulation) I might be able to rewind it, and possibly epoxy the magnet back together, but I doubt it will perform like it used to.
-- Car window motors. I might be able to use one off this old Ford in my driveway--they don't work anyway because the crankcases for rolling them up are stripped out. That's 4 motors, potentially. But I don't know what kind of continuous power they have available. Have to take one out and see if they're marked.
-- Possibly certain old motorcycle starters, if they are PMDC instead of series-wound (because I don't want to waste the extra power energizing that stator coil set).
-- ?? feel free to add any other possibilities here.
This is how BEMAP, Mk I, is envisioned at the moment: It's made using a .3DS model from 3DM called 3DM-Bike, found on Google's search engine. The actual site the model is from is 3DM3, specifically their free models page. Unfortunately there's no author or info to credit the actual model. I modified it a bit in Lightwave 8.5's Modeler so it would look more like the bike I will eventually be modifying (Columbia 2005 26" Comfort Bike, women's style). I also had to rescale it, since the original had 72-foot diameter wheels. :-) It's just a basic representation, and doesnt' include batteries, etc, or even the connecting pieces between the front fork and the drive frame.
This is a temporary physical mockup of it, using the testbed bike I got from a friend (thanks!), along with a part of the frame and drivetrain from an old rather-worse-for-wear Murray Biotech bike a coworker gave me about 11 years ago, which is my first organ donor for the project. Obviously an actual working version won't be zip-tied together (though I might put some on just for the wierdness of the look). It also won't have the pedal cranks on it.
Your first question is probably along the lines of "why not just bolt the wheel into the front fork?" The answer is that the front fork isn't as wide as the rear fork, and thus won't hold the ex-rear wheel with sprocket set, which is needed to receive the power from the motor at the other end of the chain. Also, I still need a place to mount that other end of the chain and it's sprocket assembly and bearings. What better place than the pedal bearings, already welded nicely to a set of frames that have just the length I needed for the chain, wheel mounts, mounts for derailers, brakes, etc., that are all already made for a rear wheel and drivetrain?
So, as you can see, I've basically cut the entire rear frame off the old Murray, and mounted it onto the front fork of the testbed bike so that the axle mounting point is as close as I can get it to the original fork's axle mounting point, which lets me keep the turning control as close as I can get to the original. The motor is mounted on a frame just behind the pedal bearing/sprockets, and would have a reduction gear assembly between it and the pedal gear.
Credit goes to LongTimeLurker over at THEMAnime forums for inspiring the idea to do the front-wheel drivetrain in this way, during an IM session. If we hadn't been conversing, I wouldn't have thought of this, and would still be trying to hook the motor up to the pedal drivetrain, with all of it's potential hazards.
Of course, it's possible to just alter the original front fork to hold a rear wheel, instead, but where is the fun in THAT? No, seriously, I considered it, but I don't have the metalworking tools to do it right, without seriously compromising the strength of the fork, and risking the wheel coming off during a ride when it breaks.
I wouldn't mind *replacing* the front fork with a newly-made-for-the-purpose wider fork that *would* hold the rearwheel, but again, I don't have the capabilities to make one. And I'm not sure I can get the orignal one off the Comfort Bike to do it, either. That would still leave me with needing to make a set of mounting points for the drivetrain and motor, as well as the derailers.
The "whole rear frame" idea gives me all those mounting points, plus a place to mount the motor controller, heatsinks, etc. Even batteries would probably fit on it, but I want those in back to balance weight (in the middle frame is a possibility, depending on the batteries).
So, helpful readers, criticize away, and either help me figure out a better way, and exactly why you think it would be, or help me figure out the details to do it this way. :-) Hop to it!
Monday, September 3, 2007
1-- A way to keep as constant motor load as possible. Right now, that calls for using the drivetrain from a bike, including derailers and sprockets, to shift gears to keep as optimum a gear-ratio as possible. Unfortunately it'll be manual shifting for now, which will be difficult to do in addition to the shifting for the pedal-drivetrain, which must be used as well.
2-- At least a 10-mile range, double that if possible. 10 should be fine as long as I can charge at my destination(s), but that won't always be possible.
3-- Security: Everything must be as integral to the bike as possible, so it's harder to steal a part off of it. Looking really crappy is fine, as it makes it less attractive a target, in many cases. I'd love to be able to simply have the whole motor, controller, and batteries be quick-disconnects so I could take them into a store in a bag while shopping, but unfortunately shoplifters have caused most stores to not allow bags to be brought in at all, because the owners/managers don't want the responsibility of watching over them at a counter, and they also don't want to risk losing merchandise (both problems I understand). But since I have no way to "lock them up" other than making them as integral to the bike as possible, and then securing the bike itself as thoroughly as possible, that's pretty much the best I can do in most situations. Of course, they can always steal the whole thing, but I couldn't do much about that even if it wasn't modified, that I'm not already. (need a better bike cable/lock, though)
3a-- Alarm: Placed in a sealed part of the controller case, so if someone starts to cut the cable or whatever, it goes off. If I could get that to set off a radio-receiver alert I could carry with me, it'd be good, too, but just the noise should help. Ideally, I'd like to add a celphone with GPS tracking enabled to it that autodials 911, maybe the police would catch them and recover the bike if I did. :-) I'd probably get in trouble for that one, though.
4-- Panniers: I've got baskets right now, on all 4 quadrants. These are centered above the wheel axles, and thus cause balance problems while loaded with anything (like groceries). They need to be replaced with secure hardcased panniers, centered about the axles, with just enough clearance above ground to allow for turns and such. Maybe 5-6 inches. The tops should be about that far from the wheel tops, too. I'd like the lids to open outward, so I can latch them down to the sides, and carry tall stuff where needed. They need to be completely enclosed, and stick no farther out than the ends of the handlebars.
5-- Lights: I've already got a fluorescent lamp headlight with milkplex diffuser, converted from a filmstrip/slide scanner adapter off a dead HP scanner. It gives me a very wide area of illumination, and lets cars see me from quite a ways away, with no point source to blind them (which I'd have if I went all-LED, unless I put the same diffuser in front of them, too). Tailight is at the moment just a flashing standard bike red LED light, with trim around the edges of the rear baskets made of red EL wire out of an old case-mod PC drive cable--this is only there to let people close to me in traffic see where the edges of my bike are, if the reflectors are not in their headlight beams (common when I'm not right in front of them, like when they're passing me). The LED taillight runs on it's own pair of AAA batteries right now, and the other two are powered by a 1400mAh 12v gelcell. Haven't tested it's actual limits yet, but it runs for at least an hour with no drop in brightnesses, and the same again next day without charging up again. I'll keep the separate battery for lights even when I have batts for the motor, just so I know each will work on it's own. Gotta have lights at night, even if I have no motor. Roadkill might happen otherwise.
6-- A really comfortable seat that still allows me to pedal easily. I have tried a number of different things, but all give me the numb-cheek-stumble when I get off the bike after a couple of miles or so. Along this same line, handlegrips that are comfortable, and don't make my hands numb after a couple of miles (less on bumpy gravel and such). I'm guessing part of it might be the handlebars' angle, but I'm not sure. Different grip materials cause the problem to lesser or greater degrees, but so far none have been great. I have not yet tried casting my own from gel silicone, which is certainly an option.
7-- Regenerative braking as an addition to the friction brakes already on the bike. As I understand it, Regen would work better at faster speeds, and I know the friction brakes don't work as well at those speeds, so where one falls off the other will work better. That ought to help me slow down very quickly in the many situations that will need it. This complicates the design again, and it's not *necessary*, but I'd like to have it. If it would greatly simplify things to not have it, or would unecessarily complicate things to have it, I'll leave this out.
8-- For Regen to work, I need to use PMDC (permanent magnet direct current) Brushed type motors, AFAIK. So finding a cheap but quiet and hopefully reliable motor would be useful. If not using Regen, then Brushless DC motors are the next choice, as they're supposed to be more efficient than brushed motors (due to less friction from not having a commutator, I think).
1-- Inexpensive. Recycled items where possible. Any purchase that must be made increases the likelihood it won't be completed.
2-- Electric-Assist: The motor isn't intended to do all the work, just enough of it to allow me to move more cargo and/or faster than I could by myself, and to have a longer range. It's Phoenix, Arizona--thus most of the time it's hot, and not much fun to bike 10+ miles to work, and having to essentially take a complete shower and change of clothes before I can start working, and again once I get home.
3-- K.I.S.S. It's already more complex than I'd like, but there are features I want that I can't get with the simpler ways I've thought of. Simple operation when completed is more important than simpler design/construction. However, the more complex the design, the less likely it is I'll finish it.
4-- "Automatic transmission": At some point, I want to have the whole motor assembly control itself to match the speed I set with the throttle in the most optimum way as possible. This is in direct violation of design goal #3, but unavoidable in order to get simpler actual operation, which is more important to the eventual goal of the whole thing.
5-- Weight/mass: Needs to be as light as possible, for all the obvious reasons. Batteries are probably going to be the heaviest add-on of all of this, with panniers second.
6-- Safety: Needs interlocks on the motor so it can't run:
a-- if the motor is too hot
b-- if my feet aren't pedalling
c-- if I'm not holding the throttle in position (needs spring return?)
d-- If I'm not on the bike
e-- if the batteries are too hot
f-- if ?? Need other possible failure modes that it should cut out on, and how to make it fail in a safe way.
These are new additions to this post on 9-13-07, after some discussions outside the blog that make it obvious that I haven't made my purposes and reasonings for this project clear enough.
7-- I won't use a kit.
a-- No challenge to me if I do so. Where's the fun in that? :-)
b-- Kits cost too much
c-- Many use inefficient hub motors
d-- Many hub motors in kits appear to be brushless and thus can't even use regen, AFAIK.
e-- I've not researched too many of the ones that use part of the pedal chain to transfer power, but they appear to have the problem that it's possible to get my feet knocked off the pedals by the motor if I am not careful to keep up with it, and that could cause an accident because I'll likely lose my balance, even if the motor includes a cut-off if it goes faster than I'm pedalling--it's too late once my feet are off the pedals. I'm not the most coordinated person in the world. :P
f-- A major goal is to use recycled parts wherever possible. Basically I'll take whatever I can find and make it work, if necessary. I'm a packrat and a pretty good scrounger. Plus I have all of you to help figure this out, right? ::crickets::
8-- Re: objections to using Electric power (vs gasoline, for instance) due to limited range vs heavy weight but cheaper batteries vs expensive lightweight batteries:
a-- Range is not as much of an issue as it might seem, because this is only an assist, and won't be running the whole bike, just adding power when I don't have enough of my own.
b-- It's a little bit of an issue, in that I do need to get at least 10 miles out of it, but once I get all the right parts in there, and learn how to shift for it, it should be efficient enough for at least that. If it's a workplace as my destination, I should be able to recharge there.
c-- Once I learn how to program and build the full version of the microcontroller for all this, it'll shift itself (motor only, not pedal drivetrain), and be even better, in theory (we'll have to wait and see on the practicality of that part).
Batteries and recharging are indeed a sticky point on this, and that will be the one thing that will cost. I have temporary testing solutions, but until I have a working design for the rest of it, the final choice of batteries will not be much of an issue. :-) I have some ideas about adapting various laptop and power tool batteries, potentially with adapters that allow usage of them in their original states, which includes their current, voltage, and thermal protections intact--if I can do this, then I can use old packs that might not give as much range as I'd get with new ones, but would be free to me as people often discard them when they replace them. I've collected many dozens of them over the years and reused the working cells in them to repair other packs for my own devices before. Most were still quite usable, just not necessarily for the device they came from. This is a topic I'll have to do practical research on after I have the rest of the design physically completed, and can actually test out theories on.
9-- Why Gas Won't Work:
a-- I can't stand the smell of it
b-- It costs too much
c-- it pollutes too much directly (yeah, I know, the technology that makes the batteries and other parts for my electric will also pollute, both during manufacturing and after the parts are used up and worn out and "discarded").
d-- I'm not convinced I can repair an ICE correctly, as I've never had much luck even with gas lawnmowers, while with electrical stuff I can even re-wind a motor if I have to (hate doing it, though), and I can design and build my own electronics, etc, where necessary.
e-- Gas and oil present spillage and fire hazards, as well, in case of an accident (yes, so do some battery solutions, especially Li-Ion and Li-Poly).
f-- Too noisy. I'd like a fairly quiet ride, when I just want to go and think on the way somewhere that I will need the assist to get to or from.
g-- ICE appear to be forbidden on some, perhaps all, bike trails and parks, etc, here in the Phoenix, AZ area (valley of the sun).
10-- Not sure of the DMV status exactly, but appears to require registration, licensing, insurance, etc once a vehicle uses an ICE. Don't want to deal with all that. Plus any emissions testing, if any.
11-- I also can't easily design starters and cutoffs and such for ICEs, whereas they're super easy for electrical stuff. Since I intend the entire system to only run when I am pedalling, and cut itself off entirely when I stop pedalling, mainly for safety reasons, then those starters and cutoffs are necessary.
12-- Since the only place I can keep the bike safely is in my livingroom, well, would you want to have that smell in your house, or stains on your carpet from it?
13-- Practicality of Electric-assist bike vs Car:
a-- Carrying power: almost every thing I need to carry, such as groceries, will easily fit on the bike.
b-- Range: Almost every place I need to go is easily within my pedal-only range.
c-- Time: Almost every place I need to go is *at least as fast* to get to on the bike as by car, and often enough is *faster* on a bike during heavy traffic times, even though I am obeying all traffic control points just like cars are, because there are alternate streets and routes that allow easier movement for bikes, without me disturbing the neighborhoods (which would happen if all those cars were driving thru them). For longer distances where freeways are involved, cars will win out time-wise, as well as when they use alternate routes with low or no traffic.
d-- Special arrangements are normally very easy to make for when a, b, or c make a bike impractical or impossible, but those are not usually necessary.
e-- For those who have suggested Motorcycle or a gas-powered bike instead of electric, I would still have to use special arrangements in case a-- was the issue, as the motorcycle or gas-powered bike wouldn't move the things that won't fit on the pedal bike, anyway. Range would be increased to as far as the tank would carry me plus any gas stations, but as per point 12 above there are many reasons gas itself is highly undesirable.
14-- Weight of Electric vs gas: Batteries are good enough even now for me not to have to have the weight of the rest of the system plus rider in batteries, just to get it moving. That's an improvement over when I very briefly considered this once before, about 11 or 12 years ago, I think--the batteries were what stopped me then, as the only alternatives I knew of were NiCad or LeadAcid, neither of which is all that light or energy-dense. Li-Ion came out, but then was so incredibly expensive (some ~1Ah laptop batteries were $350-$500 or more!) that I could not seriously consider even attempting it. But now, it's far far cheaper, and better technology. Good enough for what I want to do, even if not yet optimal. Since I am already needing the assist sometimes, I don't think my aging body will wait for the batteries to get better. :P