Straight Dope Message Board > Main Why is it easier to balance on a moving bike than a non-moving one (revisited)?
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#51
02-22-2017, 06:11 AM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
Quote:
 But how do you push sideways againt the ground, through the tires?
My preferred answer to this would be to hop on a bike and say "like so" while doing it. I'm not sure where the confusion is arising, so I can't give a more detailed answer in text.

But perhaps a thought experiment would help. Imagine an object like a bicycle, but with no moving parts: The steering fork doesn't rotate at all, and the wheels don't turn. It's perfectly bilaterally symmetrical. You hop onto the bike while it's exactly upright, and do your best to balance. We both agree that you won't be able to balance for very long... but I maintain that you will at least be able to exert sufficient control to determine which direction you fall over. Well, the same motions you make to accomplish that, on a "bicycle" that definitely doesn't countersteer, you can also make on a real bicycle.
#52
02-22-2017, 12:04 PM
 scr4 Member Join Date: Aug 1999 Location: Alabama Posts: 13,257
Quote:
 Originally Posted by Chronos My preferred answer to this would be to hop on a bike and say "like so" while doing it. I'm not sure where the confusion is arising, so I can't give a more detailed answer in text.
Then describe the simplest model for a bicycle+rider that can have this ability. If we model it as a rigid object with an additional movable weight in the middle (at the CG), would you agree that this system can only exert a small and short-lived force, equal to the mass x acceleration of the movable weight?

Quote:
 But perhaps a thought experiment would help. Imagine an object like a bicycle, but with no moving parts: The steering fork doesn't rotate at all, and the wheels don't turn. It's perfectly bilaterally symmetrical. You hop onto the bike while it's exactly upright, and do your best to balance. We both agree that you won't be able to balance for very long... but I maintain that you will at least be able to exert sufficient control to determine which direction you fall over. Well, the same motions you make to accomplish that, on a "bicycle" that definitely doesn't countersteer, you can also make on a real bicycle.
So your claim is that this lateral force, which you agree is insufficient to maintain balance, is still sufficient to initiate a turn?
#53
02-22-2017, 01:31 PM
 Machine Elf Guest Join Date: Feb 2007
I'm still tired from the discussion we had on steering two-wheeled singletrack vehicles last fall. Rather than contributing anything new here, I'll just link to my summary from that last discussion.

TL,DR: Countersteering is the only way to steer a two-wheeled (or two-skied/skated) singletrack vehicle. The countersteer may happen directly (with hands on bars), or indirectly (hands-off, shift your weight, bike leans the other way, steering geometry effects a countersteer). On (lightweight) bicycles, the countersteer is often extremely subtle (a fraction of a degree) and can be induced with tiny forces on the handlebar (measured in ounces), so it's easy to miss.

Dr. Strangelove, I will very much look forward to your rotary encoder measurements.
#54
02-22-2017, 04:15 PM
 Dr. Strangelove Guest Join Date: Dec 2010
Quote:
 Originally Posted by Machine Elf Dr. Strangelove, I will very much look forward to your rotary encoder measurements.
Ahh great, now I'm on the hook!

I hope the signal is visible through the noise. The encoder is 600 pulses/rot, which with the quadrature encoding means I get 2400 ticks/rot. So in principle, it's good down to 0.15 degrees. We'll see if that bears out in practice, and if I can manage to get a stiff enough coupling to maintain that accuracy. The project might take some time if it turns out that I have to 3D print some brackets or such.
#55
02-22-2017, 10:31 PM
 Irishman Guest Join Date: Dec 1999
Having had my own experiences with riding too close to an object and not being able to turn away from it, I now understand how countersteering is necessary.
#56
02-23-2017, 06:11 AM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
The difficulties in balance on the no-moving-parts bicycle are due to the limits of human reflexes, not to the limits of torque that can be imposed. A skilled acrobat could balance on such a bicycle for several minutes.

And I've still yet to see an explanation of the necessity of countersteering that's consistent with my experiments. We all agree that both lean and rotation of the steering column are necessary to turning a bike. The argument for countersteering is that it's impossible to initiate a lean without countersteering. I do the experiment and set things up so that I can't countersteer using the handlebars, and still have no difficulty turning. People respond that even if I didn't countersteer using the handlebars, that I must have initiated countersteering by leaning. But leaning without countersteering is exactly what they asserted is impossible in the first place.
#57
02-23-2017, 08:16 AM
 Xema Guest Join Date: Mar 2002
Chronos: Suppose you have (by any method of your choice) established a substantial left lean and thus a brisk left turn on your bicycle. You now choose to stop that turn - also rather briskly.

How do you do that?
#58
02-23-2017, 08:35 AM
 Machine Elf Guest Join Date: Feb 2007
Quote:
 Originally Posted by Chronos People respond that even if I didn't countersteer using the handlebars, that I must have initiated countersteering by leaning. But leaning without countersteering is exactly what they asserted is impossible in the first place.
The point is that a countersteer happens either directly (with hands pushing on bars) or indirectly (by leaning your body in the direction you wish to turn, which causes the bike to lean in the opposite direction, which induces a countersteer because of the self-stabilizing steering geometry.) I am confident that Dr. Strangelove's rotary encoder data will show this.

To prove this is true without a rotary encoder, we could instead build a bike with zero rake/trail: the steering axis is perfectly vertical, and the tire's contact patch is directly below, and perfectly intersected by, said steering axis. This bike would have zero self-stabilizing tendency. You could still ride it with your hands on the bars, initiating/terminating turns with countersteers (though you'd have to pay a bit more attention to make up for the lack of inherent self-stabilization). However, with hands off of the bars, you absolutely would not be able to steer this bike with body english. You'd lean one way, the bike would lean the other, and you'd continue moving in a straight line because the bike would not countersteer when you leaned it.

Last edited by Machine Elf; 02-23-2017 at 08:36 AM..
#59
02-23-2017, 09:15 AM
 scr4 Member Join Date: Aug 1999 Location: Alabama Posts: 13,257
Quote:
 Originally Posted by Chronos The argument for countersteering is that it's impossible to initiate a lean without countersteering.
I don't think it's impossible. Just extremely difficult, and not generally done.

Quote:
 I do the experiment and set things up so that I can't countersteer using the handlebars, and still have no difficulty turning.
The flaw in your experiment is that you are still allowing enough steering input to maintain balance before the turn. Which, by definition, means you are allowing enough input to make a tiny countersteer. The other flaw is that if you anticipate the turn in advance, all it takes is the tiniest counter-steer or balancing to make sure you are leaning when you reach the point you intend to turn.

Is there snow on the ground in your area? Can you do the test I suggested earlier, i.e. ride straight and then turn to the right without the front tire track veering to the left at all? To prove your point, the tire tracks should be right on top of each other, then the front wheel curves to one side, followed by the rear. And you should be able to do this upon request, so you need someone else to tell you when to turn. (Otherwise if you anticipate a turn, you can build up a lean by balancing the bike imperfectly.)

Last edited by scr4; 02-23-2017 at 09:19 AM..
#60
02-23-2017, 09:30 AM
 Quercus Guest Join Date: Dec 2000
Quote:
 Originally Posted by scr4 Is there snow on the ground in your area? Can you do the test I suggested earlier, i.e. ride straight and then turn to the right without the front tire track veering to the left at all? To prove your point, the tire tracks should be right on top of each other, then the front wheel curves to one side, followed by the rear. And you should be able to do this upon request, so you need someone else to tell you when to turn. (Otherwise if you anticipate a turn, you can build up a lean by balancing the bike imperfectly.)
He doesn't need snow (which creates its own challenges for riding), just dry pavement and a puddle (which can be intentionally created). I'd enhance the experiment by adding a couple traffic cones or other markers that the rider has to steer through, to minimize the amount of waiting for a random lean in the right direction.
#61
02-23-2017, 09:33 AM
 k9bfriender Guest Join Date: Jul 2013
Quote:
 Originally Posted by Chronos My preferred answer to this would be to hop on a bike and say "like so" while doing it. I'm not sure where the confusion is arising, so I can't give a more detailed answer in text. But perhaps a thought experiment would help. Imagine an object like a bicycle, but with no moving parts: The steering fork doesn't rotate at all, and the wheels don't turn. It's perfectly bilaterally symmetrical. You hop onto the bike while it's exactly upright, and do your best to balance. We both agree that you won't be able to balance for very long... but I maintain that you will at least be able to exert sufficient control to determine which direction you fall over. Well, the same motions you make to accomplish that, on a "bicycle" that definitely doesn't countersteer, you can also make on a real bicycle.
I don't think that you could maintain balance on something like that for any period of time whatsoever, and the direction of your fall would be determined at the time that you last had contact with the ground. As soon as your feet left the ground, or whatever was holding you upright went away, you would immediately start leaning in one direction or the other, and not be able to do anything at all to stop or reverse it. Once the center of gravity is on one side of the contact points or the other, fate is sealed, and there is no way to move the center of gravity to the other side.

Think of it as being over a single point. If your center of mass is not directly over that point, you will start to fall in that direction. What could you do to change that orientation. Is there any solely inertial move that you could make that would put your center of mass back over the center? It's the same thing with the two contact points. You are now limited in direction to fall from any direction to only two, but you still have the problem that you *will* fall in the direction that the center of gravity demands, and there is nothing you can do about that (without putting your feet down, or turning the wheel[impossible as it is fixed in this example]).With a big enough fan, you might be able to get enough air resistance to stop or reverse, or even maintain balance, but that is using outside forces, not just torque.
#62
02-23-2017, 10:32 AM
 scr4 Member Join Date: Aug 1999 Location: Alabama Posts: 13,257
Right. The bicycle+rider is an assembly that is free to pivot around the tire's contact patches. There's no way to apply torque to the assembly. One could shift the weight distribution, and temporarily apply a lateral force to the pivot, but it will be followed by a equal and opposite force as soon as it stops moving. The center of mass of the assembly stays in the same place (same angle relative to the pivot).
#63
02-23-2017, 10:40 AM
 Nolafolk Guest Join Date: Feb 2017
Balancing without wheels at all

Note that there are "ski bikes" out there that are easily controlled without gyroscopic forces. They look like typical bikes but have tandem skis instead of tandem wheels. They ride pretty much like bicycles, and if you can ride a bicycle you can ride a ski bike.

Note also that the Wright brothers knew about counter steering. Also, Kieth Code built a "No BS" (body steer) motorcycle. It's a motorcycle with two sets of handlebars, the original set and another that is attached to the chassis, not the front wheel. The challenge he issues is for anyone to ride the bike using body steering instead of counter steering. You can go to this URL for one article about the No BS bike.

Lastly, I haven't actually tried this out yet, but I don't believe counter rotating gyroscopes "cancel" each other's gyroscopic effect. My experiment setup will be a triangle of wood with two bicycle wheels, one on either side, solidly attached at the apex. Spinning one wheel adequately fast should hold the device vertical. Spinning the other wheel in the opposite direction will... Well, I'll have to try it out to see.
#64
02-23-2017, 04:16 PM
 Dr. Strangelove Guest Join Date: Dec 2010
Quote:
 Originally Posted by Chronos But leaning without countersteering is exactly what they asserted is impossible in the first place.
I asserted that it was impossible to not apply a countersteering force, not necessarily a countersteering angle--although in practice, with freely turning handlebars, the latter will basically always happen. If you locked the handlebars but installed a force sensor, you would detect a brief torque opposite to the direction of lean (due to trail).
#65
02-23-2017, 06:20 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
Quote:
 Quoth scr4: Right. The bicycle+rider is an assembly that is free to pivot around the tire's contact patches. There's no way to apply torque to the assembly. One could shift the weight distribution, and temporarily apply a lateral force to the pivot, but it will be followed by a equal and opposite force as soon as it stops moving. The center of mass of the assembly stays in the same place (same angle relative to the pivot).
Of course the center of mass doesn't stay in the same place. Let's simplify the model down to a massive assembly with a single hinge in the middle and a contact point at the bottom (of course, a bicyclist has many hinges, but one is enough). If you were on a frictionless surface and bent the hinge, the bottom contact point would slide to one side. If instead you're on a surface with friction, the reason the contact point doesn't slide is because the friction is exerting a sideways force on the assembly. And because the assembly has a net sideways force on it, the center of mass will move horizontally.

Quote:
 Quoth Nolafolk: Also, Kieth Code built a "No BS" (body steer) motorcycle. It's a motorcycle with two sets of handlebars, the original set and another that is attached to the chassis, not the front wheel. The challenge he issues is for anyone to ride the bike using body steering instead of counter steering.
And this is what I meant when I said that most experiments which purport to prove countersteering do nothing of the sort. I agree that I could not, on such a bike, make a left turn. But that's because I can't turn the handlebars left. It's not because I can't turn them right. Code successfully proved that you need to use the handlebars to steer. He didn't prove how you need to use them.
#66
02-23-2017, 06:22 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
Oh, and
Quote:
 Lastly, I haven't actually tried this out yet, but I don't believe counter rotating gyroscopes "cancel" each other's gyroscopic effect. My experiment setup will be a triangle of wood with two bicycle wheels, one on either side, solidly attached at the apex. Spinning one wheel adequately fast should hold the device vertical. Spinning the other wheel in the opposite direction will... Well, I'll have to try it out to see.
It does work, but it can put a lot of internal stresses on your gyroscope assembly, so you'd better build it strong.
#67
02-23-2017, 06:57 PM
 Dr. Strangelove Guest Join Date: Dec 2010
Quote:
 Originally Posted by Chronos He didn't prove how you need to use them.
You're essentially proposing a third mechanism. The no-BS bike demonstrates that you can't get the bike tipped over with weight shift alone. And you deny that centrifugal force is used to tip the bike (since that's the actual force at work with countersteering). What else is there?

Or, maybe, you deny that tipping the bike at all is necessary. In which case I'd wonder if you ever removed the training wheels from yours .
#68
02-23-2017, 08:18 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
You need to both lean and turn the handlebars.
#69
02-23-2017, 08:44 PM
 Dr. Strangelove Guest Join Date: Dec 2010
Quote:
 Originally Posted by Chronos You need to both lean and turn the handlebars.
Ok, so at the least you acknowledge the earlier critique of your experiment, which is that despite your efforts to only push the handlebars in one direction, you're subconsciously shifting your body mass.

Still--since turning the handlebars in one direction could only cause a centrifugal force in the opposite direction, you're suggesting that shifting your weight overcomes both this force and then some additional force to tip the bike further. But the no-BS bike demonstrates (for motorcycles, at least) that even inducing the tip is difficult to impossible. If it's not possible for even a portion of the force, then it's certainly not possible for the whole amount.
#70
02-23-2017, 09:09 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
I'll also note that the no-BS bike is a motorcycle, which is heavier than a bicycle. Countersteering might be necessary on a motorcycle, and I can't disprove that, because I don't ride one of those. I'm just saying that the no-BS bike doesn't prove it.
#71
02-23-2017, 10:48 PM
 Dr. Strangelove Guest Join Date: Dec 2010
I agree that you can't ignore weight--I've only ridden motorcycles enough to learn that the effect of shifting your weight around decreases quite rapidly as the bike mass goes up. I barely rounded a cul-de-sac in my dad's Harley, largely due to me being uncomfortable with the required countersteer. Much less is needed on a bicycle or even a lighter motorcycle, and it can be more easily induced by weight shift.
#72
02-24-2017, 12:42 AM
 Irishman Guest Join Date: Dec 1999
Quote:
 Originally Posted by Nolafolk Lastly, I haven't actually tried this out yet, but I don't believe counter rotating gyroscopes "cancel" each other's gyroscopic effect.
Why not?
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#73
02-24-2017, 05:58 AM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
Because all most people know about gyroscopes is that they act weird. Without knowing the specific details of how and why they act weird, one wouldn't know that it's all vectors, which therefore all cancel out.
#74
02-24-2017, 10:12 AM
 Quercus Guest Join Date: Dec 2000
Quote:
 Originally Posted by Nolafolk Lastly, I haven't actually tried this out yet, but I don't believe counter rotating gyroscopes "cancel" each other's gyroscopic effect. My experiment setup will be a triangle of wood with two bicycle wheels, one on either side, solidly attached at the apex. Spinning one wheel adequately fast should hold the device vertical. Spinning the other wheel in the opposite direction will... Well, I'll have to try it out to see.
Two counter-rotating gyroscopes will more or less cancel each other out (since both gyroscopes can't be in exactly the same place, they won't exactly cancel, but close enough).

But you don't really need to do this experiment for bicycles: a little googling will find that people have already built bicycles with an extra, counter-rotating wheel. They're just as easy to ride as regular bicycles, showing that the gyroscopic effect is negligible for a bicycle+rider.
#75
02-24-2017, 03:17 PM
 RedSwinglineOne Guest Join Date: Jan 2007
Quote:
 Originally Posted by Chronos You need to both lean and turn the handlebars.
Strictly speaking, you only need to lean. Turning the handlebars is how you control the amount of lean.
#76
02-24-2017, 04:24 PM
 Irishman Guest Join Date: Dec 1999
Quote:
 Originally Posted by RedSwinglineOne Strictly speaking, you only need to lean. Turning the handlebars is how you control the amount of lean.
Not exactly. If you shift the cg of the bike/you pair to the side of the forward path (i.e. lean), the geometry of the bike (i.e. trail in the front wheel) causes the front wheel to turn into the lean. Turning the front wheel is what controls where you go. Handlebars give the rider away to do that directly.

You don't even need to ride a bike to see this behavior. What happens when you put the kickstand down? The bike leans toward the kickstand side, and the front wheel turns.

Quote:
 Originally Posted by Quercus But you don't really need to do this experiment for bicycles: a little googling will find that people have already built bicycles with an extra, counter-rotating wheel. They're just as easy to ride as regular bicycles, showing that the gyroscopic effect is negligible for a bicycle+rider.
I think the point is that he doesn't believe the gyroscopic forces are canceled on those bikes. So of course they are easy to ride.
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#77
02-24-2017, 04:27 PM
 Irishman Guest Join Date: Dec 1999
Quote:
 Originally Posted by Chronos Because all most people know about gyroscopes is that they act weird. Without knowing the specific details of how and why they act weird, one wouldn't know that it's all vectors, which therefore all cancel out.
That's what I trying to suss out. What knowledge base does he have?
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#78
02-24-2017, 05:47 PM
 RedSwinglineOne Guest Join Date: Jan 2007
Quote:
 Originally Posted by Irishman Not exactly. If you shift the cg of the bike/you pair to the side of the forward path (i.e. lean), the geometry of the bike (i.e. trail in the front wheel) causes the front wheel to turn into the lean. Turning the front wheel is what controls where you go.
Not exactly. When the bike leans (to the left for example) the front wheel "wants" to turn to the left, but you don't let it. If you were to let the front wheel turn to the left, it would straighten up the bike. When you are in a constant radius turn, the front wheel is very nearly neutral. (straight) The actual turning force comes from the shape of the tire and the fact that the contact patch is now up on the side of the tire.

Turning the bars controls the lean. The amount of lean determines where you go.

The above doesn't really apply at parking lot speeds where the bike is essentially being balanced upright at all times. At low speeds the bike is generally steered where you want to go with small changes in the steering to keep the bike balanced.
#79
03-04-2017, 09:08 PM
 Dr. Strangelove Guest Join Date: Dec 2010
Rotary encoder has arrived and I have it hooked up. See my writeup here.

No useful data yet. Roads around here are too rough for useful results. Not sure I'll have time to find a big empty parting lot tomorrow, so you might have to wait a week for more, but you might find the rest of the writeup interesting in the meantime.
#80
03-07-2017, 09:54 AM
 Machine Elf Guest Join Date: Feb 2007
Quote:
 Originally Posted by Dr. Strangelove Rotary encoder has arrived and I have it hooked up. See my writeup here. No useful data yet. Roads around here are too rough for useful results. Not sure I'll have time to find a big empty parting lot tomorrow, so you might have to wait a week for more, but you might find the rest of the writeup interesting in the meantime.
Good writeup, thanks for sharing.

To cure the drift and resolution problem at the same time, McMaster has plastic gears you can buy, if you don't mind spending some money. Get a large one, bore it out if necessary, and install it on your bike's handlebar stem (you'll need to remove the stem to do this); then install a smaller gear on the encoder. Now you'll have no drift, and far more pulses per degree of steer angle. The noise issue of steering/balance corrections will still be present if you're riding on rough roads, but if you can find some smooth pavement, I think you may get some good results.
#81
03-07-2017, 06:25 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
It occurs to me that there's another confounding factor here, in that even cars (which don't lean and have trivial balance) sometimes do something resembling countersteering, to make a turn with a larger radius. And of course two-wheelers will sometimes do the same thing for the same reason.
#82
03-07-2017, 09:41 PM
 EdelweissPirate Guest Join Date: Mar 2015
Chronos, would you mind being more specific? "Something resembling countersteering?"

I suspect you mean that bicycle racers and motorsports competitors "go wide" when approaching a corner in order to describe the largest-radius arc possible within the boundaries of the road. Do I have this right?

If so, it does not resemble countersteering. Rather, it's just an attempt to use the maximum radius arc possible. This is, generally speaking, the fastest way to get around a racetrack. Depending on which side of our current argument one falls, countersteering is either a way to initiate a leaning turn quickly or the only way to initiate a leaning turn.

If that's not what you're referring to, please explain what you were referring to.

I wouldn't begin to guess what you mean by "cars have trivial balance," but the way turns affect transient suspension loading is a rich field of inquiry in the world of mechanical engineering. Unfortunately, it's often called "weight transfer" when "load transfer" would be more accurate.

(Then again, radiologists call the property of being transparent to X-rays "radiolucency," which I find nonsensical. "Transradiance" might be better, but "radiolucency" makes it clear that radiologists don't know Latin. Applied science is terrible when it comes to this sort of thing).

Again, vehicle dynamics is a field of study, even if you yourself haven't bothered to derive it from first principles. I'm not saying you shouldn't question the conventional wisdom of vehicle dynamics, but your questions imply that you think no one has ever given these things serious thought before.

I've lurked on these boards for years, so I've got a lot of respect for your opinions, especially on straight physics. So I'm surprised that you're so resistant (or maybe naïve?) when it comes to applied physics. I'm not trying to be flippant; I'm just baffled.
#83
03-08-2017, 05:34 AM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
Yes, I am referring to going wide, and it resembles countersteering in that one first turns left in order to turn right.

And when I say that cars have trivial balance, I mean that except in truly extraordinary situations, cars never fall over on their sides, and no special effort of design or operation is required to keep them upright. A mechanical engineer must of course still take into account things like differential loading on the suspension, but not to the same degree that one must take into account balance on a bicycle: A car with poorly-designed balance might be uncomfortable or wear out quicker, but a bike with poorly-designed balance probably can't be ridden at all.
#84
03-08-2017, 10:25 AM
 Section Maker:Jupe Guest Join Date: Jun 2010
This is a great discussion. I think one of the first things I ever aspired to as a young lad was to ride "no hands" on a bicycle. Never much liked motorcycles tho, too much free power!!! Trouble!!
So, 55+ years later, reading this, I "understand"..countersteering, I just never have thought about it. Its just something one does to keep the bike going where you need it too.
Usually, I have beach stuff, wetsuits and board etc carried under one arm, so the whole thing is kind of off kilter to one side, no hands or not!
If I come to a dead stop....Im going over though, without first spotting a good place to stop.

Last edited by Section Maker:Jupe; 03-08-2017 at 10:28 AM.. Reason: spel
#85
03-08-2017, 11:21 AM
 EdelweissPirate Guest Join Date: Mar 2015
Quote:
 Originally Posted by Machine Elf Good writeup, thanks for sharing. To cure the drift and resolution problem at the same time, McMaster has plastic gears you can buy, if you don't mind spending some money. Get a large one, bore it out if necessary, and install it on your bike's handlebar stem (you'll need to remove the stem to do this); then install a smaller gear on the encoder. Now you'll have no drift, and far more pulses per degree of steer angle.
I agree; that was a great writeup; thank you. While Machine Elf's idea would certainly help with drift, I worry that the increased noise from gear lash (free play between the gear teeth) would continue to swamp the results. It may well still be worth a try.

Is it possible that the drift is due to slip not between your headset's top cup (you refer to it as "the grommet on the bike") and the encoder wheel, but between the wheel and the encoder shaft? Either way, you could get a little more precision out of it by replacing the encoder's wheel with a smaller-diameter wheel. But I'm sure this has occurred to you.

Another way to address the drift is to significantly increase the normal force between the encoder and the headset top cup. In other words, I'm suggesting that you get a much bigger rubber band.

Thank you for your writeup and the time and effort involved in collecting a round of data! Let me know if I can possibly help with amplifying the precision of your test gear.
#86
03-08-2017, 11:58 AM
 EdelweissPirate Guest Join Date: Mar 2015
Thank you, Chronos, for explaining.

I would argue that "going wide" is only notionally related to countersteering: it's not a way to initiate a turn, as we both agree countersteering is, but rather a set of turns. From a steady-state linear-travel condition, countersteering causes a "high-side" and initiates a fall in the other direction. That fall is then "caught" with handlebar input and lateral acceleration, but this is a second turn after countersteering. Countersteering is the first input in a countersteered turn, regardless of whether one buys the idea that there are other, non-countersteering first inputs that initiate another kind of turn. I'm pretty sure we both agree on this.

I don't think the concept of "going wide" confounds the issue at all, and I concede I'm not sure why you think it might. But that's neither here nor there.

Single-tracked vehicles are typically modeled as inverted pendulums, which incorporates, I think, your concept of "balance." It's true that cars that are not turning don't need to be modeled as pendulums.

But it would be perfectly valid to model a car and its suspension as an inverted pendulum with centering springs (and, optionally, dampers). In fact, the vehicle dynamics concepts of "roll stiffness" and "roll center" implicitly do just that. This matters more than you seem to anticipate, because when a car rolls on its suspension, it can cause unwanted steering inputs, as can bumps encountered mid-corner. So if this incorporates your idea of balance, it matters quite a bit for both cars and bicycles. A car with large steering inputs due to roll can experience what's known colloquially as snap oversteer: "spinning out" with virtually no warning.

I admit I find your articulation of "poorly-designed balance" and "well-designed balance" a bit perplexing, but I strongly suspect we just differ on the terminology. I'd call most bicycles dynamically stable because they tend to go straight and not fall over if they have enough speed, regardless of whether anyone is riding them (this is due primarily but not exclusively to trail). Most cars would also be both statically stable and dynamically stable insofar as the trail in their steering geometry also tends to make the car go straight without any steering input.

It's still unclear to me why you think that "going wide" would confound the issue.
#87
03-08-2017, 12:39 PM
 EdelweissPirate Guest Join Date: Mar 2015
Another thought: there are plenty of activities easily modeled as inverted pendulums in which acrobats manage to stay upright for long periods of time. However, all the ones I can think of involve either very short periods of uprightness punctuated by hopping or jumping or they diverge from bicycles in an important way.

Bicycle trials riders such as Danny Macaskill (arguably the most gifted acrobat-on-a-bike ever to walk the earth) can pause briefly, but then start to fall over and must hop into the air and move the contact patch beneath their CG in order to stop the fall. Seriously, they're called "correction hops."

Similarly, slackline athletes do astonishing things, and they can briefly walk slowly without falling over. But their "contact patch" is easily moved beneath them, which is not the case with a bicycle.

Tightrope walkers seem to be able to stand indefinitely on a wire, but they have a (literally) massive pole with a high polar moment of inertia, using it like a reaction wheel, which they can then "de-react" by moving their CG slightly beyond the "perfect" balance point so they can absorb the pole's angular momentum.

Finally: bicycle trials riders, slackliners and tightrope walkers have all practiced for hundreds or thousands of hours to learn to stay upright as inverted pendulums. It's a rare skill and requires a lot of practice. And yet somehow, any kid can learn to ride a bike. If initiating a non-countersteering turn--the sort you argue are most common--requires an imperfect version of these acrobats' skills, shouldn't most people be able to pickup slacklining as easily as they learn to ride a bike? Or shouldn't they at least be less terrible at it than they are and learn faster than they do?

"I just think it happens another way, by leaning."

How does that work?

"Like so. It's hard to articulate."

Hmmm.

Our only instrumented test was inconclusive, and the experiment you described performing isn't exactly Michelson-Morley, if you take my meaning. I tried to reproduce it and failed, but it's so loosely controlled that my failure doesn't mean any more (to me, at least) than your success.

It's all well and good to reject the prevailing theory, but if you don't propose a convincing and testable alternative in its place, one is reduced to Pauli's damning observation: "That's not right. That's not even wrong."

For what it's worth--maybe very little--I still think there's merit in the wet-tire-track experiment. One could rig up a bottle and tubes to continuously apply water to both tires if puddles are in short supply.
#88
03-08-2017, 02:43 PM
 EdelweissPirate Guest Join Date: Mar 2015
Just a quick clarification: I wasn't trying to be cute by applying a dismissive quote from a physicist to Chronos, who I understand is a physicist himself. It's one of my favorite quotes, and I threw it in without thinking that it could be read as especially snarky. Sorry about that.
#89
03-08-2017, 03:02 PM
 Machine Elf Guest Join Date: Feb 2007
Quote:
 Originally Posted by EdelweissPirate While Machine Elf's idea would certainly help with drift, I worry that the increased noise from gear lash (free play between the gear teeth) would continue to swamp the results. It may well still be worth a try.
One alternative would be a synchronous belt and synchronous pulleys. Same opportunity for motion amplification and drift elimination, but without lash. Small belts can be had for a couple bucks, and pulleys for maybe \$10-\$15 each.
#90
03-08-2017, 06:14 PM
 Chronos Charter Member Moderator Join Date: Jan 2000 Location: The Land of Cleves Posts: 69,508
On "going wide" as a confounding factor: Suppose we have a bicyclist who is in the habit of going wide around turns. That bicyclist reads this thread, and decides to perform the mud-puddle experiment: He finds a nice open area with a mudpuddle, rides through the puddle, and then turns. But, as is his habit, he turns wide. If he then examines the tracks left by his tires, he might see the initial turn of his "going wide", and identify it as evidence of countersteering, even though it is not.

On the stability of cars vs. bicycles: I was not aware that cars customarily had positive trail, but I'll take your word on it. But a car could certainly be made with zero or negative trail, and still function. A bike with zero or negative trail, however, would be almost impossible to ride, except by an extraordinary acrobat.

Quote:
 Finally: bicycle trials riders, slackliners and tightrope walkers have all practiced for hundreds or thousands of hours to learn to stay upright as inverted pendulums. It's a rare skill and requires a lot of practice. And yet somehow, any kid can learn to ride a bike.
I don't know about the others, but so far as I can tell, slackline walking is easier to learn than riding a bike. I've never managed it myself, but then, I'm very poorly coordinated, and I haven't spent nearly as long on it as I did on learning to ride a bike (which also took me longer than most kids). But I've seen plenty of neophytes to slack-lining manage it after only a half-hour of practice or so: There was a bit of a craze for it when I was in college, with folks setting up lines between any convenient pair of trees.
#91
03-08-2017, 10:36 PM
 Melbourne Guest Join Date: Nov 2009
Quote:
 Originally Posted by k9bfriender Once the center of gravity is on one side of the contact points or the other, fate is sealed, and there is no way to move the center of gravity to the other side.
Actually, no. Gymnasts and divers and people who stand up (and cycle riders) do it all the time.

Bend, rotate, stand, rotate, bend.

On a roller bearing, you can rotate your c.o.g. out of plane, and restore balance.

On a point bearing, you can spin and lower and rotate your c.o.g.

(If is perhaps obvious that you can't do it at all if there is no point of contact.)
#92
03-09-2017, 04:41 AM
 Dr. Strangelove Guest Join Date: Dec 2010
Thanks for the comments, guys--I'll try to tackle most of them, and hopefully won't miss anything.

I did think about gears, but had the same thought as EdelweissPirate as far as lash is concerned. Gears are generally run with at least some small play so that the far side of the tooth does not rub; although I could apply possibly compression to prevent that, I'm not certain how well it would work.

The synchronous belt is a better idea--I actually have some handy (salvaged from inkjet printers and elsewhere), though I'd probably have to drill out the pulleys. I worry a little that the reduction might be a bit too much. Although the rotary encoder has pretty smooth bearings, the resistance might be just a tad too high for something like a 5:1 reduction, which is probably what I'd get with the typical size.

I think EdelweissPirate is correct that the next step is just a bigger rubber band. I had thought in advance that I was on the low side as far as tension is concerned; although it worked well "on the bench", it's obvious now that vibration is a problem, and more tension would likely solve that. I also have some stiff springs I could possibly employ.

The wheel and the encoder shaft will not slip--the shaft has a flat on it, and the wheel a set screw. So that at least is not going anywhere.

But between the top cup (thanks for the terminology correction!) and the headset I'm not that certain of. I haven't yet tried moving it, and for all I know it's held in place by not much friction. Something to check out.

I am sure that the drift isn't caused on the software side. I did measure this: a quadrature sensor has four possible different state transitions, +1, -1, +/-2, and 0. +1/-1 correspond to the normal "good" case where things are ticking along in one direction. The +/-2 case is bad. If you jump by 2, you don't know if you've gone forward or backwards. The 0 case is fine. In a perfect world, this wouldn't happen, but real-world sensors are subject to bounce, which means that a nice 0-1 transition might actually look like 0-0-0-1-0-1-0-1-1-1. Sometimes bounce comes out looking like there should have been a transition when there wasn't one.

At any rate, I measured these and never saw a +/-2 except when I spun the encoder really fast by hand and without the wheel. There were a fair number of 0s, but as I mentioned these are ok.

As said, I won't be able to do much until this weekend. But the weather is good, so I should be able to collect something. There are some large parking lots nearby that I should be able to use. Another thing to play with is the data rate; I'm collecting at 20 Hz now, but I could certainly go higher. Or lower; maybe part of the solution to the noise problem is to just do a low-pass filter.
#93
03-09-2017, 06:52 AM
 Machine Elf Guest Join Date: Feb 2007
Quote:
 Originally Posted by Chronos On "going wide" as a confounding factor: Suppose we have a bicyclist who is in the habit of going wide around turns. That bicyclist reads this thread, and decides to perform the mud-puddle experiment: He finds a nice open area with a mudpuddle, rides through the puddle, and then turns. But, as is his habit, he turns wide. If he then examines the tracks left by his tires, he might see the initial turn of his "going wide", and identify it as evidence of countersteering, even though it is not.
If the front and rear tire tracks are distinguishable, e.g. as by using different tread patterns, then the situation will be made more clear. A simple left-hand turn will leave tracks that look like this: the front wheel will first steer to the right before commencing the left-hand turn. If the cyclist is in the habit of running far to the outside just before starting the turn, then the mirror-imaged track pattern would appear before the main turn's track pattern.
#94
03-13-2017, 05:48 AM
 Dr. Strangelove Guest Join Date: Dec 2010
I didn't get to collect as much data as I'd have liked this weekend--my little device suffered a minor structural failure and I didn't have time to repair it. However, I did manage to collect some of me riding normally around a smooth parking lot. The data is much less noisy this time and there is a clear countersteer signal in many of the turns. See update 2.

The first turn was especially good--nice and sharp; almost a square wave. You can even see some ringing at the bottom.

None of this yet proves that countersteering is required to ride a bike, or that it is apparent in hands-free riding, but it certainly lends credibility to the hypothesis that it's both necessary and natural for sharp turns in particular. Of course this isn't a double-blind experiment so I can't say it's impossible that I did something unintentionally, but I certainly didn't do anything special while riding.

I wonder if I can find a kid to test on. Hey kids, want some free candy? Just hop on this bike for a while...
#95
03-24-2017, 07:35 AM
 Machine Elf Guest Join Date: Feb 2007
Quote:
 Originally Posted by Dr. Strangelove I didn't get to collect as much data as I'd have liked this weekend--my little device suffered a minor structural failure and I didn't have time to repair it. However, I did manage to collect some of me riding normally around a smooth parking lot. The data is much less noisy this time and there is a clear countersteer signal in many of the turns. See update 2. The first turn was especially good--nice and sharp; almost a square wave. You can even see some ringing at the bottom. None of this yet proves that countersteering is required to ride a bike, or that it is apparent in hands-free riding, but it certainly lends credibility to the hypothesis that it's both necessary and natural for sharp turns in particular. Of course this isn't a double-blind experiment so I can't say it's impossible that I did something unintentionally, but I certainly didn't do anything special while riding. I wonder if I can find a kid to test on. Hey kids, want some free candy? Just hop on this bike for a while...
Doc, don't know where you're at on this, but I downloaded a really cool app on my phone last night:

Physics Toolbox Sensor Suite

It turns your phone, with all of its sensors, into a pocket-sized data logger. You can record data from any of the built-in sensors, save it to a CSV file, and then email that file to yourself for review later. In addition to the 3-axis accelerometer (and compass, magnetometer, GPS, microphone, barometer, inclinometer, and lux sensor), phones also have a 3-axis rate gyro, which is relevant here. If you can secure your phone to the steering stem such that it's perpendicular to the bearing axis, then one of the rate gyros will report movement of the handlebars separate from the lean of the bike (of course this information will eventually be confounded with the azimuth change of the whole bike once you have established a turn rate). If you have a second phone, you can secure it to the chassis so that it records lean angle; the data files on each phone should include atomically accurate timestamps, so syncing the data in a spreadsheet later on is a cinch.

I tried a quick data file last night, and the data rate appears to be variable and not user-selectable, with a range from maybe 0.008 seconds to 0.050 seconds; I guess it's a matter of polling the sensors whenever the processor isn't busy doing something else.

Anyway, this might be an option for gathering more/different data if your rotary encoder is difficult to repair.

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