# Re-"IT" How do you turn a gyroscopically controlled unicycle?

Just for the heck of “it”, if “it” is a gyroscopically balanced unicycle per this Washington Post article and you can’t push it down etc. per the article’s description, how the heck could you turn a thing like that? Wouldn’t a gyro powerful enough to keep a human unicycle stable be difficult to turn around corners at any useful speed?

Just curious.

http://www.washingtonpost.com/wp-dyn/articles/A49849-2001Jan11.html

http://www.delphion.com/gifcache/WO00075001A1.tif.45.s0.35.r0.gif

Maybe you could turn it by leaning… this is pretty much how you turn a regular unicycle, isn’t it?

I still hope that this isn’t what IT is, though… what a let down!!

[pure speculation]

If the gyroscopic wheel is separate from the drive wheel maybe the gyroscopic wheel stays in the same orientation while IT turns (rotates) in relation to the gyroscopic wheel.

[/pure speculation]

This link has a slightly different artist rendering, I guess nobody told the artist that ‘uni’ means one.

Gyroscopic precession, mebbe?

Actually, no. Bicycles are turned by leaning, but unicycles are turned by ummm turning. You just rotate the the thing on its vertical axis with your hips.

A gyro-uni would be quite a handfull IMO.

bicycles are turned by…well, turning the handle bars.
Leaning just keeps you from falling outward.
Next time you are on a bike, keep the handlebars straight and lean and see what happens.

It’s actually a much more complex question than has been addresed.

At slow speeds, under 20 MPH or so, the best way to turn a uni or bicycle is as described, by actually changing the direction of the wheel.

At faster speeds, gyroscopic force musses this up. As anyone who rides a motorcycle knows, trying to turn a motorcycle at speed by turning the handlebars = disaster.

One needs to countersteer. You exert slight pressure in the opposite direction you want to go. This makes the vehicle lean the other way. Gyroscopic force pulls it along an arc in the direction of the lean, turning the vehicle.

Well, if it is a gyroscopic unicycle, R. A. Heinlein’s stock is going to go up a few more points.

Scylla: Too right, which is why I can’t believe the unicycle/scooter idea is IT. I once had the misfortune of wondering what would happen if I tried to lift the front wheel of my bicycle off the ground while I was travelling at 20-30 MPH. (Answer: a crash so violent at the end of it the wheels were actually touching each other.) Considering that the action of turning while unicycling is rather similar, I’d have to say that any attempt to unicycle at 20-30 MPH is unwise unless you plan only to travel in an absolutely straight line.

One other (somewhat unrelated) point on IT being a scooter: would you be willing to toodle around at high speeds, while standing up, on something that looks like those “silver scooters” that cost \$200 last year but only \$29.95 nowadays? Forget a helmet, you’d have to wear body armor and make sure your insurance is up to date. One last thing: what are the brakes like on this thing?

Not to pick nits, but yes you do turn motorcycles by turning the handlebars at speed. You just don’t have to turn them as much.

This is pure speculation, but perhaps the gyroscope is mounted on a rotating stage. That is, the seat and wheel are fixed, and the gyroscope assembly rotates around a vertical axis (around the seat post, for example). This way, you can turn the seat+wheel by pushing on the gyroscope assembly.

I wasn’t aware that the gyroscope effect was significant in a bicycle’s handling. The idea of “trail” is a satisfying answer for me. I ride road bikes, and I use countersteering techniques, but I don’t need gyroscope theory to explain why. If I want to turn to the right quickly, I first force the handlebars briefly to the left, which causes me to get into a good hard lean to the right, then I let the trail of the front wheel pull it back to the right so I balance around the corner.

I’ve never ridden motorcycles, but from what I’ve read, the gyroscopic precession helps in getting the lean going. When you push the wheel slightly to the left, not only do you have the effect of moving the track of the motorcycle to the left of its CG, but the precession helps because the leftwards torque itself helps with the lean to the right. However, once the lean is started, precession has nothing more to do with it. The bike rounds the corner because the trail points the front wheel back to the right, just enough to keep you from falling over.

If you ever watch one of those high speed motorcycle races and get a front view of the coming around a turn, you’ll clearly see that the front wheel is turned slightly in the opposite direction of the turn.

If you’ve ridden a motorcycle, countersteering is a fact not subject to dispute.

At speed, redistributing your weight to one side or the other will not cause the motorcycle to lean. You need to countersteer to do this.

This same effect can be demonstrated by the fact that it’s easy to keep a bicycle upright while moving, but difficult while stationary.

What if the gyro was horizontal, then IT would be able to rotate freely but not lean forward/backward or to the sides. And if the gyro could be pivoted side to side (but since it would stay level IT would actually lean side to side) then IT could turn a corner like a motorcycle.

Countersteering really doesn’t apply to a one wheeled vehicle.

Not quite correct. The wheel will be pointed the opposite direction only coming into the turn. Once the lean is stable the wheel will naturaly turn slightly into the corner.

Err, yeah it does. While going in a straight line, come up on your pegs. shift your weight from one leg to the other. The bike will drop to that side. You won’t turn, but you can get your average street bike a few degrees out of true that way. I’ve really got to get a hobby.

As far as countersteering and arguements - there are two schools of thought. One, yes, you do have to countersteer. The adherents of the other line of thought are too busy crashing to put in an apperance.

Count me in as someone else who will be extremely dissappointed if the only thing bigger than the world wide web is a unicycle, no matter how cool it is.

I just watched my “Street Smarts. Vol. 2” video of motorcycle safety. The wheels stay turned in the opposite direction of the turn all the way around the curve.

It is a banked track that they showed, so I don’t if this changes things.

Countersteering on a bike is not an easy concept for non-bikers to understand.

You want to go left, you push the right hand bar downwards.(above something like 20mph)

Clever use of bike geometry by those inscrutable Japanese fellows may mke you think you are actually pushing the right hand side of the handlebar forwards but the reality is differant.

This is a similar kind of problem to conveyor belts going to the widest radius. Imagine that something happens like a length of rope get wrapped around one of the rollers, intuition says that since the radius of the roller is greater where the rope is then the belt will be deflected away from it. Any engineer will tell you that exactly the opposite happens ,the belt will rapidly move over the point of greatest radius, in fact this has been long obseverved and was used during the industrial revolution to keep conveyor and machine drive belts on their wheels.The wheels are slightly larger toward the middle than the outside, a practice known as ‘crowning’.

So what is going on ?

First thing you need to do is imagine the bike wheels not as two rubber roundy things but as two cones with curved surfaces sticking out from either side of the bike wheel.

When you push the bars in one direction you increase the distance between the contact points of the tyres, but only on one side of the tyre - this is absolutely crucial to understanding what is going on - the bike tilts toward the increased distance just as the conveyor belt does but because we have a cone this will also cause the bike to rotate toward a centre described by that cone two cones in reality because you have to take the back wheel into account.

Below around 20mph things are rather differant, to get the bike to go around a corner like a hairpin you need to lean one way and push the bike the other way, exactly the way that supermoto riders do, except that they slide all the way round at much greater speeds.

In such cases you just do not have the required precessionary forces available to do anything else and you are steering on geometry alone.

Back to the OP: A unicycle powered scooter doesn’t necessarily need the gyros themselves for stability. It could use tiny ones only for a stabilization reference for an active suspension system, with servomotors and linkages and such. A small enough gyro’s precession loads could be overcome with more servo actuation.

But I still don’t want to be on top of one when any sort of component fails.

I know I’m showing large amounts of engineering ignorance here but this is exactly what I don’t understand. Short of using a powerful inertial gyro mechanism that resists being pushed over how is a servo motor + linkage, “active suspension suspension system” of any kind going to keep a single wheeled vehicle upright. ie If I push on this unicycle scooter and it stats tipping over how is any servo motor going to keep it upright? What is the “servo motor linkage” going to push or pull on the keep the vehicle true if it’s only got one wheel.