Unis certainly have seriously complex forces and motions due to the forces on the pedals but the fundamental geometry considerations wouldn’t just go away because the “joints” are not precise.
The analysis does probably get beyond the capabilities of even a reasonably well educated person fairly quickly. It would be interesting to have an engineering PhD model unicycle dynamics like they no doubt have been done for motorcycles and bicycles.
Anybody know one looking for a project?
A good study would also require collecting data using 3D force transducers on the pedals and seat so see exactly what we do when riding.
Forces are complex indeed, and whilst what was said about the “caster” effect of a front wheel on a bicycle is correct, but don’t forget that the front wheel is being pushed by the rear wheel. On a uni, to add more complexity, the wheel pulls the whole thing.
Those who have ever been able to ride a front wheel traction two-wheel vehicle (such as the VeloSoleX moped) know that it’s just impossible to ride it without at least one hand on the bar. Disengage the engine, and it behaves exactly like a bike (no hand right is totally possible despite the weight on the front wheel).
I’ve hesitated to jump in on this thread but I’m happy to discover this term “caster angle” and wanted to say thanks! In my write-ups I usually say something like “tilted behind vertical” and it’s nice to have the proper name. I’ve been trying to translate the pumping that bicycles do in a pump track to one wheel and the first part of it is absorbing the initial incline of a roller in such a way that speed is reduced as little as possible and balance is maintained on the decline side of the roller. A huge part of this is increasing the caster angle and I can usually tell ahead of time when it’s not large enough. Those cases will make me feel a little “ahead” of the wheel after the roller and result in a UPD or forward/backward balance adjustment.
Hi John, I’ve been unicycling since November 2013. Recently I’ve progressed to being able to ride about 3 miles on roads without a UPD. Can you give me some advice on handling bumps ?
I can roll over bumps by leaning back, but it immediately makes my quadriceps really tired.
Am I doing this incorrectly ?
Is there some way to lean back without getting so tired ?
I’m an engineering student…software engineering lol I can ask a couple of my mechanical engineer friends to give it a shot. iI’ll find one that rides to so it’s not as hard to explain.
I accidentally stumbled upon such an engineering thesis once, when I was searching the Net for other unicycling information. I didn’t really read the whole paper, but I think the gist was: the author(s) was trying to analyze and combine all the relevant engineering and physics information together in such a way that a “self-driven” unicycle (essentially a unicycle ridden by a “robot”) could theoretically be built. I got the sense from what I read that more problems than solutions were found… which leads to the somewhat Romantic conclusion, in our favor, that unicycling is much more easily done by sentient beings than by machines.
Not sure why you want to lean back. What we’re talking about above is the angle most riders form between the unicycle frame/fork and their upper body. Usually the frame is tilted slightly back, while the upper body is tilted forward. Having that angle allows your body to compensate more for bumps or uneven ground that it would if you were straight up.
Generally if you hit an unexpected bump, it immediately absorbs some energy from your wheel, slowing you down. By bending your body a little more forward, you bring the wheel forward. If done right, it brings your center of mass back where it needs to be so you don’t fall to the front.
But why bend forward at all, you ask, if you have to bend more for corrections? Because the body bends very well to the front, but not so well to the rear. Sometimes the same thing happens in the other direction, where the wheel gets a little ahead of you. If you’re already sitting straight up, you have to make a very awkward move to “pull the wheel back” under you. Better to have a little forward angle for when that happens.
If you’re riding on a nice, smooth, predictable surface like a gym floor, the rules are different. You can sit a lot straighter without having to worry about such things.
Meanwhile, if your quads are getting tired, it sounds like you are still over-muscling things and need to relax your weight onto the seat more.
“Imagine that your back is an extension of the seat post.”
I think this advice works for easy, relaxed riding on flat, smooth surfaces. And it is good for beginners whom would otherwise lose balance without the anchoring of he seat. More weight on the seat, however, means relatively less weight on the pedals, which can increase the chances of an ugly UPD resulting from the feet losing contact/friction with the pedals (I discovered this while learning to ride off curbs, initially thinking I needed to stay anchored to the seat). Finding balance on the pedals makes more sense to me than finding it on the seat. We all know how to balance on our feet, but balancing on our butt is not so natural. Any yoga instructors in the group?
And in order to not over-muscle things is simply plenty more of practice.. speaking from personal experience, I have tripled my distance on my 26er in this couple of days of practice and thats going through dips and bumps without any of my usual UPDs:D
I dont know..my greatest teacher is just simply experience and that is achieved by pacticing it over and over. The technical reading, I can only comprehend half of what you guys write.. until I get on my uni and experience it, only then will it make some sort of sense.
Oh, I was doing this wrong. I had the frame tilted back, but my back was still vertical. Therefore, that caused me to put too much force on my feet. I think that also slowed me down too much, so I lost momentum before hitting the bumps.
I agree. Yesterday, I was riding with my son, who is also a beginner and has a lot less saddle time than I do. I was surprised to see that he could sometimes ride over larger bumps than I could. We each got better during that ride because we challenged each other to try more technical stuff.
As I might add, my first good practice on bumps was with plenty of speed bumps. The larger the bumpier the better. You just really have to imagine you legs as shock absorbers and just simply absorb the bump, and thats where the crucial bent knee and leaning forward comes into play.
When I first practiced it, the slight hesitation of hitting the bump had me momentarily lean back, and my legs stiffened, which most likely leads to a UPD.
When you get good at that, you can easily ride over roots
.
Same goes with riding down curbs. If you hesitate from fear, you tend to lean back which youll find yourself with the uni flying/shooting fowards towards the street. Same applies with going down stairs, but with stairs you could flop fowards.
Another factor comes into play by putting weight onto the feet.
When the uni hits a bump it is pushed up against the driving leg increasing the force on the pedal. This automatically compensates for the otherwise slowing effect the bump.
When you hit a bump, both pedals will rise an equal amount because of it (not regarding the “orbiting” motion of the pedals which is expected anyway, bump or not). So assuming you have both feet on the pedals, the uni pushes up against both legs equally, the effect on forward speed being neutral. Similarly for a dip, the effect is also neutral.
A bump slows down your wheel, but not (as much) your body. Therefore a bump tends to let you fall forwards. With experience, if you see the bump beforehand, you compensate automatically. An unnoticed bump can still throw off an experienced rider.
I never noticed there were so many different widths and heights of speed bumps before I started unicycling. LOL ! I’ve got the wide shallow ones mastered now. Stairs still seem like a pretty distant goal at this time.
Killian, don’t worry. I’m not too far off the original topic, because this started with a conversation about our “back is an extension of the seat post.” I learned a lot from all of you here. I appreciate the help, and can’t wait to implement your tips during my future rides.
speaking from personal experience, I have tripled my distance on my 26er in this couple of days of practice and thats going through dips and bumps without any of my usual UPDs:D