Making an electric unicycle really self-balanced

[Karl-Oskar]

I recently came across electric unicycles, a cool and fun way fpr transportation.

The wheel balances as a Segway by applying power to the wheel. (the classis reverse pendula).

However, since its a unicycle, it does not balance sideways, and I imagine that this colud be solved with a mechanical gyro.

By controlling the gyros movement through the accelerometer that is already present, it should be possible to both balance the wheel itself, but also provide some "lift" on the pedals in order to help riders start their wheels.

When driving, the wheel itself provides the gyro effect needed to stay upright.

My questions:
How much should the gyro disc weigh + diameter and how fast must it spin in order to balance the wheel itself?

Same question in order to provide 10kg lift on one of the pedals?

 

[A.T.]

How much should the gyro disc weigh + diameter and how fast must it spin in order to balance the wheel itself?

Look up two wheel vehicles, which use gyros for lateral balance. This should give you an idea.

 

[rcgldr]

Answering an old question - gyro effects don't play a significant role. There are two ways to steer a EUC (electric unicycle), twisting and tilting. Twisting steers directly, why tilting causes the tire to steer due to camber effect.

As for stability while riding in a straight line, at sufficient speed, if the rider starts to lose balance, the riders momentum going in a slightly different direction than the EUC will tilt the EUC into the direction of imbalance, steering the EUC back under the rider to return the rider into a vertical position.

I bought a small EUC (Inmotion V8F) back in August 2021, and started off by twisting the EUC at 3 to 5 mph, extending my arms outwards, flailing left to steer right and vice versa, for balance correction and direction control, able to do laps around a tennis court on my first attempt. I moved to a long outdoor parking lot, and found my V8F became stable around 7 mph, no longer having to make balance corrections if riding in a straight line.

At that point I learned to tilt steer. Tilting at a fixed angle tends to steer about a fixed radius (the radius depends on tire profile), independent of speed, while how much to lean depends on speed (centripetal acceleration = speed^2 / radius). This requires the rider coordinate how much to tilt the EUC and how much to lean depending on speed and turning radius. Took me about 6 hours riding time to do tilt steer reasonably well (30 minutes a day, 3 days a week so about a month), and I continued to improve after that.

 

[Swamp Thing]

Maybe this is more of a classical mech or engineering topic, rather than an electromagnetism topic?

 

[A.T.]

Answering an old question - gyro effects don't play a significant role. There are two ways to steer a EUC (electric unicycle), twisting and tilting.

The question was about making it "really selfbalanced", which I understand as balanced without any steering input from the rider. While this is in principle possible by imitating what a human rider does (with some kind of robot), it should be much simpler to achieve using gyros, like some self-balancing single track vehicles already do.

 

[jrmichler]

Maybe this is more of a classical mech or engineering topic, rather than an electromagnetism topic?

And so it was moved to the Mechanical Engineering forum.

 

[rcgldr]

Self-balancing of a human ridden electric unicycle at low speed a would require a fairly massive gyro, logic and consume power, and would interfere with ability to turn. The alternative is to use a wider tire (wider tires are more responsive to tilt), like the Ninebot Z10, which has a 4 inch wide tire, and is stable around 4 mph. There really is no need for self-balancing beyond what an electric unicycle already does once at a stable speed (on my V8F with it's 2.125 inch wide tire, around 7 mph).

For some new riders, extending arms and flailing left to steer right and vice versa is almost instinctive and works at very low speeds. I stared riding back in August 2021, when I was 69 1/2 years old. After about 15 minutes getting used to how my electric unicycle responded to leaning back and forth, using a fence for support, I ventured away and was able to do laps around a tennis court on my first attempt. My wife took a video the next day. I didn't realize I was hunched over until I saw the video, which I corrected afterwards:



I moved to a long outdoor parking lot, which is were I found my V8F became stable at around 7 mph, no longer needing to do balance corrections to ride straight, relaxing my arms, and learned to tilt steer. I was doing 30 minutes a day, and on day 5, I did my first free mounts (no support). My wife took a video on day 10, at a park with a very large pathway, where I could ride reasonably well. From the headlight beam, you can see how stable my V8F becomes at around 7 mph.



My turning skills, how much to tilt, versus how much to lean, depending on speed and turning radius improved over time, with slow tight turns taking the longest for me to learn.