I've been inspired by another bit of one of AussieJester's projects--stabilizer wheels to let him ride at slower speeds, as well as a stable stand to hold the bike upright when stopped. Last time I was able to nearly directly take the idea and run with it almost just like he already used it (the brake-arm chain tensioner), but this time it'll have to be quite different in execution.
Because my motor would never handle the power needed to climb hills at speeds over 8 or 9MPH, and neither will my legs, I have the bike geared so I could crawl up a hill to do it. However, the bike isn't *stable* at the very low speeds (1-3MPH) that I could climb long hills at, so I would be unable to help the motor by pedalling, as I'd have to keep balancing the bike by touching the ground all the time with my feet.
So I need stabilizer wheels (or a trike design, which is the works but not possible yet) for really low speeds. I also need them to not both touch the ground at the same time, since in Arizona, a bicycle is only a bicycle under the law if it is three or less wheels in contact with the ground. As long as I keep only three of them touching, I'm safe from any legal hassles (it's already wierd-looking enough, I can imagine some problems with misunderstandings already, if someone looking for a reason to issue somebody a ticket that day picked on me).
Since I'd be riding potentially a mile or two up some hills like this, I don't want to use solid wheels, so I'm looking for a busted dolly that has good inflatable-type tires, 6" to 8", even if they have plastic hubs, as long as they have bearings in them. I have the old electric scooter wheels but the hubs are big and clunky; I think they're 10" wheels and would ride nice, but those hubs...plus the tires are relatively narrow, and wouldn't give as much shock cushion on bumps and stuff, but the dolly wheels would, since they're usually 2-3" wide.
I don't have any sort of actuators that'll do this kind of work, so it'll be just a manual lever along the center frame I reach down and pull, along the lines of the emergency-brake lever in the middle console of some cars.
The pic below shows about where they would go, and how they'd raise/lower.
Basically, the swivel point would be at the former rear dropouts of the Magna frame I'm using for the front half of the bike. They're dropouts, so they are strong enough to take the strain, even though I no longer have the seat stays that went down to them that you can see in this pic of an older revision of the bike (the batteries now rigidly fill part of the space between the top tube and the base of the bottom triangle/diamond formed by the chainstays).
The handle would go up and around the battery area, to clear them and the cabling, on the left side (even though it's the right side in this pic), so I could keep my hand on the throttle and shifter if need be.
Both wheels would be joined at that dropout, and angle out kind of like yours, so that there would be around 1/4", maybe 1/8" on either side below one wheel when the other was on the ground, without me on the bike. With me (and posssibly cargo) on the bike, it'd be less to nearly (but not) none, depending on front/rear tire pressure and front shock load. They'd pivot together as I move the one handle.
Not yet sure how I latch them in place; possibly some sort of mechanical detent device on the frame that the handle "snaps" into at full extension, with a harddisk magnet or three to hold the system in retraction when not in use.
One problem I have to deal with using midships stabilizers like this is that they probably will have to be casters--they must be able to turn with the bike, or else I could end up with the one on the ground causing sideways resistance to any turns, lane changes, etc.
If I'm lucky, they'll work as solid axles, not needing any steering/caster pivots, so they'll be built that way first. But I foresee the likelihood Murphy will smack me around for doing that, and make me build casters instead. ;-)
Wednesday, October 21, 2009
Low-Speed Stabilizers Idea
16 comments:
Alternate suggestions or improvements to anything that's been posted is very welcome, and extreme detail is preferred to brevity.
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The only way you are going to get away with not using some form of castor is to put them back at the rear wheel. At midline you are going to have to use them or forget going around a corner.
ReplyDeleteYou really don't need such heavy wheels as your talking about using though. Your really only talking about balance and not much load on them so you might look into something like the small 12" spoke wheels from kiddie bikes. They can handle what weight that would be needed and probably would be quite a bit lighter than the dolly tires with the heavier steel rims. Even the larger wheels from a old style baby buggy might work.
Lee
http://packratworkshop.blogspot.com/
That's partly why I would like to find the plastic-hubbed dolly wheels, rather than the big steel-rimmed ones. I do want balloony tires, though, simply because of bumps I'll encounter on the deteriorating sides of the roads bikes are generally relegated to. That's why I'd like to try out dolly wheels.
ReplyDeleteAs for the load, well, depending on the incline, some roadbeds are tilted quite far at their edges on some of the hills around here, especially where they curve around higher parts of the "mountains" we have. That means that at slow speeds the bike will lean over fairly hard on whichever tire is downhill, and it will actually have a significant load on it, I think.
I already have a couple of small 12" kid's bike wheels, and even the 10" scooter wheels, but I don't want to use ones that large a diameter if I can avoid it. 6" to 8" is about as big around as I think I need.
If it weren't for the bumps, I'd just use rollerblade wheels, because I have a lot of those with bearings in them. In theory, I could use shocks on the stabilizer arms, but that heavily complicates them and increases their weight even more than just using the tires.
Part of the reason to use much smaller wheels is to avoid any kind of hassles about the "3 wheels in contact with the ground" definition of a bicycle, for while I am using the stabilizers. The bigger the wheels, the more possible it would be for someone to think they are breaking that rule. Sure, they'd have to have a grudge against me or really have a bug about the bike in general, to even want to try to find something to ticket me for, but it would not surprise me to find someone like that.
Especially after someone stole those lugnuts off the motor sprocket, which could have been fatal to me in the right circumstances. (It couldn't have been simple theft, but rather deliberate vandalism--why would anyone steal lugnuts off a critical part and leave a possibly valuable PDA, neat and compact LED flashlight, and a bunch of tools untouched?)
So I believe anything possible by anyone, and I'm sure there is at least one person out there that for unknown reasons hates me quite a lot.
As far as the caster goes, yeah, I am figuring I will have to do that, just hoping I would not. Forlorn, I suppose. :)
ReplyDeleteWell, based on what you say, I will just go ahead and plan on the caster style first, then. Save me some work. ;)
See if you can do this thought experiment. One bike has a completely vertical fork. When you turn the handlebars, the wheel simply turns on the ground without raising or lowering the fork and front of bike.
ReplyDeleteNow picture the fork being horizontal. when the handle bars are turned, the wheel only raises and lowers the fork and front of the bike. What;s more, the bike tries always to turn the handlebars because gravity is pulling down on it. Too many bikes these days tend to always want to be trying to turn because the forks have the horizontal component of posture. They are somewhere between the two extremes.
That problem is why some ingenious fella way back when thought of the idea to curve the end of the fork forward. That way, when the handle bars are turned, it tends to raise the front of the bike a little, instead of lowering it. This causes the wheel to continually try to straighten itself out.
So by using caster, you might really benefit from getting a curved fork for your bike instead of trying to add casters themselves. Incidentally, I had once thought of adding outriggers like those you mention so that I could always keep my feet off the ground in an experimental weather sealable bike.
I had an old Honda car that had lots of wheel caster built into the suspension. It was the easiest car to steer. I used to say it practically steered by itself. It took no conscious thought to do it because of the excellent feedback from the self-centering steering.
I have another anecdote on how steering has affected me. i have ridden Huffys exclusively all my life. The one I had have had the good style of fork that bends forward at the bottom. They are pleasant to steer.
ReplyDeleteBut recently, a man a few streets down the road gave me a bike that has a straight fork. I was puzzled for months why I felt very uncomfortable riding it. It felt unnerving riding down the hill and having to consciously control the wobbly ride.
I talked to a smart Harvard friend who brought up the issue of wheel caster. He pointed out that wheel caster on a car improves steering feel. Then I did thought experiments on both types of forks and began to understand better.
Also do the best you can to get all the play out of the steering linkage. I drove some cars that were plagued by that problem. it made me uncomfortable trying to steer them since they tended to drift on the road. I actually took the second one for repair.
The outriggers will catch in potholes as you alluded to. They might also snag onto a curb or the pavement and tend to throw the bike to the side. Best Regards.
have you looked at the surpluscenter site? I think they have wheels like what your looking for for about $6-7 apiece. That might save you some time in building.
ReplyDeleteLee
http://packratworkshop.blogspot.com/
The problem I have with low speed is not that it doesn't steer easily, but that the bike falls over at low speeds because I cannot balance it since I am too low to the ground to use the pendulum effect as well as I can on a taller-seated bike. :)
ReplyDeleteI am pretty sure that changing the caster/trail won't fix that, though I have a curved fork I already intend to try for fixing a different problem (weight vs shock fork), once I get some more time.
Even with the best caster/trail in the world, this bike is still not going to hold itself upright going uphill at 1MPH or less. ;)
I have not looked at the surpluscenter site (don't think I'd heard of it before) yet. However, I will need to find the materials locally for no cost to be able to do this. I have a lead on some urethane foam wheels I might be able to get, if they will fit and do what I want.
ReplyDeleteI'm already working out a MkI Alpha version of the idea using kickscooter front wheels and steering tubes; been trying to post the pics all weekend but it's been too busy to finish that! Hopefully tonite.
Mike That's what I mean. The straight forks don't compensate for the pull of gravity that tries to make a bike turn and subsequently fall over. I can't be sure it is really your problem, but it sure was mine! It is why I can give my bike better steering feel when it has a lot of luggage on the rear by placing some weight on the front as well. The weight on the front increases the designed-in caster effect of the curved front fork that tends to lift the front of the bike slightly when the wheel is turned. (When the fork is turned, the curved end turns toward the ground, pushing the front of the bike upward.) So, more weight increases the magnitude of the feedback effect. This is a negative feedback that tends to keep the wheel straight. The opposite effect with the straight fork is why your straight fork made your wobble worse when you put weight over the front wheel. ciao
ReplyDeleteA caster that can swivel 360 degrees is a bit of overkill-even (frame) mounted alongside the front fork all you'd need is a design capable of swivelling to the extent the fork does. Mounted far enough back a trailing arm with some lateral flex could possibly substitute for a conventional fork assembly. Using flexible leaf springs in lieu of a conventional fork might provide enough lateral as well as vertical flex to work as a shock fork, maybe two spring segments welded 90 degrees apart, looking a bit like this: "+" when viewed end-on. The vertically oriented end would be at the front and provide the lateral flex whereas the other, horizontally oriented piece would allow for vertical flex/shock absorption. Just an idea, maybe not a good one.
ReplyDeleteJust to clarify the previous post- I'm saying *my* idea may not be that great... this next idea may reinforce that notion :) After thinking a bit more about how to use a leaf spring as a flexible means of mounting a stabilizer wheel it occured to me having 2 spring segments fastened together isn't absolutely necessary- a single leaf spring with a 90 degree twist would accomplish the same thing.
ReplyDelete-Don
First, a link to the Alpha version idea:
ReplyDeleteAlpha version
As for the straight forks, well, eventually I'll be experimenting with those, too. But I think it's not the problem in this instance--I think it's more that the bike is not fully balanced anyway, and my sense of balance is not great either, so at low speeds when I try to compensate for the wobble introduced from all the little bumps and dips, it gets worse and worse.
The non-1:1 steering ratio I have helps some, but not enough. The curved fork might also help, but it will probably not eliminate it at 3MPH or lower speeds, which is where these stabilizers will be a decent solution.
I can fix the 360-swivel of the casters by adding limiting tabs to either side of the steering tube.
I can imagine the trailing arm/leaf spring idea, but I don't think it will work as well because I think that anything that gives me any flex like that will give me too much flex, at least out of the things I have around here. Then the bike will either tend to bounce back and forth from side to side, or lean over towards one side or the other, which I don't want to happen at all.
The single leaf twisted 90 degrees partway thru is an interesting idea, and I can imagine a use for it, but I don't know how I could make one myself, especially in such a way that I would be able to build in the right spring rate, stiffness, etc. :(
The pneumatic tires are the best simple way I know of to give a slight bit of shock absorption effect for road roughness, while still giving full stiffness for leaning against with the bike weight so it doesn't tilt at all.
A little reassurance that might not apply much since mine is an upright bike is that I do most of my riding below 10 mph. I carry 50 lbs one way on my round trip, and going slower gives a better ride.
ReplyDeleteWith the upright bike, or any bike where most of the rider is above most of the bike itself, the pendulum effect makes it much easier to balance it at low speeds than with a lower-seated bike like mine.
ReplyDeleteBasically, the part of you that's above the bike can pivot like a pendulum quite easily and naturally to get the bike to balance even at very low speeds, pushing against your own lower body that is "clamped" around the bike.
It's part of why that as you add weight (cargo baskets/etc) above the BB to a regular bike, it gets harder to balance, especially at lower speeds--it now has more mass to "cancel out" your own pendulum mass.
With my bike, and other even lower-seated bikes, there's a lot less of the pendulum effect at work, as more of the bike mass is at or above my own mass. So it's much more work for my body to cancel out undulations and wobbles in the bike's low-speed travel, and takes more physical movement to cancel out the same amount of wobble a smaller movement would on an upright bike.
Of course, the more that my own mass moves side to side, the more wobble is introduced, as there is always overshoot (at least with me), and eventually it gets to where there is more wobble than I started with, and I fall over. :)
So I try my best to "turn off" my automatic balancing when I ride this bike, as it only makes things worse due to my very slow reaction time and poor balance actions. That helps, but doesn't eliminate, the wobble problems at very low speeds.
FWIW, I also thought of a radical bike-to-trike convertible, which I will have a post about as soon as I have the time to finish the sketch for it. Details aren't worked out for steering yet, but it's "interesting". Probably also impossible to build with what I have around here, but I'm tempted to try!
I think the trike idea is an excellent one. I agree about the balancing aid of being higher above the center of gravity.
ReplyDeleteI have some good news and bad news. The bad is that my eye caught the mountain bike in the shed yesterday and i noticed that the front fork is curved. That means the cause of the bad steering feel is likely something else like the handlebar assembly--either the bar itself or the neck supporting it. I might have to change those out to the classic Huffy racing types.
ReplyDeleteThe good news is that when I find out what is wrong there, I will probably like the bike. Maybe I will be able to work on it next year.
About the crazybike, have you considered a sidecar?