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Friday, February 6, 2009

Drivetrain Reworked, Seat In-Progress

The drivetrain has had to be reworked considerably for a number of reasons, including those in the last post.

The whole crankshaft-thread stripping problem meant I really needed to just go ahead and use the square-end crankshaft, but that can't be done with the Roadmaster frame, as it does not have the right kind of bottom bracket, and I have no desire to cut into that frame plus another to get the right one, then weld it in. Instead, I chose to change the entire rear frame, which also lightened up the bike by about 4 pounds, by using an old brazed-together Schwinn frame from the late 70s or early 80s, I'd guess, which does have the threaded bottom bracket with the square-end crankshaft, exactly like the Magna frame (front of the bike), down to the bolts being part of the crankshaft, and using nuts to thread onto them to retain the cranks.

I still used the same ex-fork as the inter-frame stiffener and support, since it still fits about the same way (though not to the same point. In this pic the regular bike seat is still on the normal seatpost, but it won't be that way for long.

First, some new parts of the drivetrain:

I welded up the small chainring to the larger one, as that was the only secure way I could fasten it on the cranks here. Seems to work fine, and has good clearance from the frame/etc.
Next was my solution to the thread-stripping axle problem. Basically I took a broken fixed-gear freewheel (just spins, never latches) and a similar but working one to mount together on the squared-end crankshaft.

The larger chainring (orange) is the 1/2" ex-ScootNGo chainring; it is bolted between the teeth of the integrated 16T chainring on the broken freewheel. The smaller is just the working freewheel with it's integrated 16T chainring.

To mount them on the square-end crankshaft, I needed a way to adapt the large hub-sized hole in the freewheels down to the small square hole used on cranks that mount on this type of shaft. I had a number of 1/8" thick steel washers that used to be weights in the bottoms of some webcam bases. They're exceptionally hard steel for such a purpose, equivalent to the steel used on seatbelt-mounting hardware in at least some cars. To get the right sized hole, I would need to drill it out to just barely the inside flat diameter of the square shaft, then file out the corners to square it. I'd've preferred to use the threaded half of two hubs, but there was no way I could fit them both on the axle--and even if I could, I'd not've been able to line up the chains properly with the rest of the drivetrain forward of there for whichever was outboard (pedal, in this case).

Since I didn't quite get the squaring perfect (and didn't expect to), I did a little bit of rounding for the outside circumference. The washers were too large to fit inside the freewheels, so they would need this done anyway to make them small enough to fit. I just left that as the last step so I could round them at the same time. I chucked the crankshaft itself into the lathe's headstock, to use it to mount the washers on. That meant the washers would be centered on the crankshaft, and my tooling down the outside circumference would bring them into round.

After this was done, I fit one washer into the pedal-side freewheel's righthand face and welded it in. A bit of grinding to flatten the surface again and verify the welds were deep enough, and then I rewelded from the inside of the freewheel (where it would have threaded onto the hub) to the washer. Now I fit the motor-side freewheel onto the righthand face of the pedal-side freewheel, so it was against the washer, and welded this freewheel to that washer as well, from the inside of the freewheel's threaded area. Next was to line up the square hole in the first washer with the second as I fit it into the righthand face of the motor-side freewheel, and then weld that one in place. Once done, I also welded the motor-side's freewheel core to it's chainring, since it was broken and would not otherwise have turned with the motor driving it. If it had been a working freewheel, I'd've left it alone as it would've simply reduced the amount of friction in the pedal-side of the system, by not having to drive the motor chain at all with the pedals. (The motor itself is still isolated by the belt-side freewheel, so the pedals at least don't have to drive the belt or the motor itself).

Then I bolted the motor chainring onto the motor-side freewheel, and bolted the entire assembly to the crankshaft's left end, with the normal 3-chainring set on the right end (but without a crank).

The Schwinn frame has some disadvantages, such as that it is made only for caliper brakes, so I will have to weld on pivot studs for the more modern types of rim brakes if I wish to use them, and that it is a 700C frame, not a 24". The last might be an advantage, in that I can also use a 26" wheel with it, but for the brakes it is a disadvantage, in that a 24" wheel cannot be reached by calipers from the original brake bridge mounting point, leaving me either with no rear brake or having to weld on those studs. I already cut the studs off the Magna frame's rear triangle, as I have no need for them there (they were actually in the way of the original chainline on the left side), so I can use those if I do it. Another disadvantage is that it only has one rear-dropout accessory-hardpoint threaded hole, so I can't use the derailer-protector frame I took off a broken BMX-style kid's bike--it requires two to securely hold it, and with only one, it will probably just pivot in a crash and not help save the derailer.

The main frame angles and such are almost identical to the Roadmaster, so not much changes, but the seattube is about an inch and a half farther back--this means the bottom bracket is as well, increasing the chain lengths a bit. But it also means I can sit a little farther back, which is good. Also, because of the way the seatstays are designed and mounted, it would be relatively easy to cut the seattube down level with the top tube, and bend-down and reweld the seatstays to line up with the top tube. That would allow me to move the seat even farther back, if using the 24" wheel. Even if using a 26" wheel I'd still have a little more room (the width of the seattube itself) for the seatback.

One other big advantage of using the Schwinn vs Roadmaster frame is that the Schwinn has round tubes, so I can use a regular seat-mounting hardware set to hold the seat directly to the top tube, giving me a springy cushiony saddle for my bottom, already shaped to be out of the way of my pedalling legs at the front, but wide enough at the rear to fully support me in the more reclined position (which the same seat doesn't do very well in the normal upright position), and then all I have to build is the seat back, which will mount to a seatpost coming up out of the seattube. This makes it easier to get to testing the bike, as I don't have to figure out a seat *first*, then keep fixing or remaking the seat as I readjust everything else on the bike based on test results and road experience. I can wait till I have everything working, then make a final permanent seat (assuming I need a better one at that point).

I did have to do some Dremel work on the main clamp of the seat mounting hardware, so that it would fit around the top tube, which is a larger diameter than a seatpost top, and then lengthening the square shaft holes in that main clamp so the bolt can go across the tube with the slightly wider tube under it. But when done, it works pretty well, and it holds fine, even if it does make the bike look kinda funky.

Also, the chainlines would cross due to the excess chain links I didn't have a tool to remove on the 1/2" chain (motor reduction 2nd stage). That forced me to use a free-rolling pulley (jackshaft) to hold the extra chain length out of the way, which added extra friction and a LOT of extra noise of the chain rolling on the metal pulley (formerly the serpentine-belt tensioner from the LTD). This I fixed two ways, the first being to come up with a tool to deal with that.

Since I was afraid of damaging the chain I was already using, I took the longer (and slightly rusty-surfaced, but otherwise intact) 1/2" chain from the exercycle, and a small torx bit (which happens to be just a hair smaller than the pins in this size chain) from a cheap toolkit someone gave me the remains of some time ago, a hammer, and some plastic floor tile remnants. I drove the torx bit thru the tile to make a hole for the pin to go into. The bike chain tool, while unable to drive the pin all the way thru the chain, can be used to start pressing it down flush with one side and a bit out the other, which makes it easier to hold it into place on the tile. I took a hammer and gently tapped at the torx bit, lined up with the pin already partly displaced by the bike chain tool, until it was almost out the other side (just enough in to catch on the hole of the matching end when I put it back together on the bike). I did this twice, once for the end to be freed up, and once for the end of the section to be removed to shorten it sufficiently (56 links new length, formerly 61).

Above is the way it used to look, with the now unnecessary pulley above the orange chainring.
Below is the new simplified drivetrain:

And the unused pulley by itself, which I will remove when i'm sure this works better than the other, and it's definitely not needed:

The next thing I did to fix the chainlines was to remove the derailer I had been using for top and bottom of the pedal chain, and run the bottom of the pedal chain down below the motor, and run the top of the chain just inside the frame above the motor drivetrain. This still means the pedal chainline is not perfectly straight on the top, which is not great, but will still work once I put a proper guide into it. The derailer (a different one that fits better) is now on the bottom of the chain only, as a tensioner, mounted hanging from the axle bolt of the motor's freewheel/transfer assembly device. It's some old Falcon-type from a scrapped 10-speed that had had a horridly rusty chain (so stiff you can hold the whole loop of chain out and it stays that way!). But the derailer/tensioner still works fine.

There are two variations on the idea, one with the top guidewheel in the forward of the two Magna rear-dropout accessory-mounting hardpoints, and one in the rearward. I chose to do it that way because it meant I did not have to drill and tap any new holes, and it was conveniently already in the chainline's path. It seems to work better in the rearward position.

These are the two different derailers I had tried, with the more modern Shimano first, and the old Falcon last--it works better because it's simpler and flatter, and pivots in more of a straight line.

Now none of the chainlines cross in any way during normal operation, so they can't cut into each other or interfere with each other or anything else. The only leftover issue is that of making a guide wheel/pulley for the top part of the chain to keep it as straight as possible going onto the pedal-end of the chainline when under tension from pedalling, and to keep from rubbing on the frame at all (it doesn't touch, but is close, with the current temporary solution).

One thing I *don't* like about this whole thing is that with all these chains, axles, and freewheels, there's a lot of friction. Right now, it probably takes double the amount of power to drive the pedals to do the same work that my Columbia does, just from the excess friction. Since I have yet to clean out all the old gunked-up grease from everything and redo it all, there is hope that a significant part of that friction will be removed by doing that. Have to do the same thing to the wheel hubs/axles, too, but they're actually not bad, friction-wise. It's all in the drivetrain section from the motor/pedal interconnects/freewheels. If I can't work that out, I'll rethink the drivetrain to deal with it, but at the moment it does still work for testing.

Speaking of testing, I did finally get to pedal it around the yard a tiny bit (not ready for the road yet), and I also tested with the motor, using just a 12V7Ah SLA from an old dead UPS. Surprisingly, the motor does try to move the bike with me on it (moves fine without me), in lowest gear, but can't actually get started. If I pedal first, then power the motor, it will keep me going, very slowly, just barely enough to keep balanced. This means it should work just fine on 36V, and might work ok on 24V if I don't need to go fast, since it's supposed to be just an assist while pedalling, anyway. Sorry, no video, since no one would operate the camera for me to do it (and the tripod/timer operation won't work with the way I had to ride around the yard to test it).

In the process of some of the above work, and in cabling the front brakes and the two standard-drivetrain derailers, I sorted thru part of my collection of cables, controls, derailers, etc. from various bikes I've salvaged:

I found a number of cables are rusted or otherwise damaged in ways that make them dangerous to rely on, so those go in the "use for non-bike-things" bin. The others, however, make up almost two bikes' worth of cabling, half of which is now used on this Crazybike.

One thing I have to do soon is fix the slop in the steering rod. It's caused by not having the right sized spacer washers/etc. inside the eyes, so the bolts have quite a bit of play in those eyeholes. Those roller-skate wheel bearings I saved before will come in handy now, as they are almost exactly the right diameter to fit inside the eyes, and then have a bolt run thru the middle. I will need to take about half a millimeter off the inside circumference of the eyes, so the bearings will fit perfectly in there. Then I can trap the whole thing together with larger washers, and bolt it all back together again.

I also need to trim off the unused outside tab of the steering-pivot point at the handlebar stem, because it sticks out far enough to potentially catch on my knee as it passes during pedalling. Then I can round all the edges there, and see about making a shell around that section to prevent any possible pinching or damage because of it.

I have a couple of small coroplast sheets that will be used to at least temporarily cover the drivetrain areas after initial testing and tweaking, just to keep any of my clothing from catching anywhere in there--sometimes I have to wear a coat or other baggier clothes in weather colder but like we're having at night now, and I'd like to keep it all away from the greasy and destructive chains and sprockets. :-)

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