Electric Assist Unicycle Build
- Thread starter justin_le
- Start date
katou said:
I got to try one for the first time shortly after the Maker Faire when a bunch of unicyclists in the area met up. It was pretty fun to ride in its own way, and fairly light weight. Since you don't have the side to side swagger that pedalling provides there isn't as much opportunity to correct your side to side stability by twisting. So turning and going backwards were both much harder than on a regular uni.
They're using a one of these common style of scooter motors:
which are both cheaper and lighter than a hub motor, and combined with the large chain ratio also capable of providing plenty of torque on the wheel which is needed for the self balancing. So from a production standpoint it makes sense. The SBU is also made using a stock unicycle frame and slightly modified unicycle wheel, and you could actually knock the pegs off it and install cranks and try to make a pedal version. If someone has one and wants to try this, I would be very curious to hear their experience.
A the Faire I talked to Trevor Blackwell who was the first to document building an electric uni:
http://tlb.org/eunicycle.html
and he said he had attempted using a hub motor in some prototypes earlier on and found it didn't have sufficient torque to get the control loop tight enough, so he stuck with the transmission drive. Certainly others have opted for the hub motor route and made it work.
Justin
I will be interested in your experiences with the hub motor, I assumed that it would not stop-start-grab quick enough to make balance-control work. If you're trying it, I'm sure you have some good reasons for going with the hub motor. I've always found in building things to stop/start (mostly hobby robotics application) that the higher the reduction, the better the control. That being said, stepper motors are used for just that reason...
Always interested in hearing from one of the movers and shakers in the ebike biz,
Katou
Always interested in hearing from one of the movers and shakers in the ebike biz,
Katou
mikebikerad
1 kW
I want one! my buddies joke with me about building an electric unicycle but they are real!!! great build 
Golden Motor Canada
100 W
Have you seen this one? Made with a Magic Pie.
Check out the video..
http://www.youtube.com/watch?v=0JOgTKigxGs
Gary
Check out the video..
http://www.youtube.com/watch?v=0JOgTKigxGs
Gary
Why not a 6 year update?! This first hub motor electric uni build was simple and reliable and convinced me that non-balancing pedalable electric unicycles, really, work, great. At the time it also convinced me that I needed a higher pedal gear ratio to take advantage of the motor's output and the higher speed capbility. That lead to a small myriad of even increasingly complex uni projects with free spinning cranks, chain drives, CVT's and IGH's. Interesting in their own right, but also plagued by their own complexity.
In the end I started to miss the raw simplicity and reliability of the original fixed crank build and decided to dust it off this past week. Upgraded the controller to a Phaserruner FOC and built a small rack for holding a set prototype potted batteries with 18650 cells, but otherwise there was really nothing to do. The thing just works and is a joy to ride. Why did I leave it hanging in storage for the last 6 years!?
The Phaserunner is much smoother than the original custom-made trapezoidal drive controller that I had on it earlier. Normally that would be a good thing, but on a build like this the buzzing sound of the motor provided good tactile feedback on how hard the motor was running. Wih the Phaserunner, you have no idea unless you look at the CA display whether you're getting like 100 watts or 1000 watts of assist. So going up a hill you easily forget how much work the motor is doing and then on letting go of the throttle are in for quite the suprise when your legs have to pickup the slack or you'll go flat on your face.
It's also clear from riding around again that the throttle is not at all the optimal control input for an electric assist unicycle. You normally want to free your hands now and then for balance, and needing to be tethered to a handlbar is annoying. There are two approaches that I want to try next on this:
Torque sensor on the cranks: This would work awesome I'm sure and would natuerally let you amplify braking torque when going downhill as much as forward torque going up hill. But adding a torque sensor to a build like this won't be very easy.
Grade hill sensors: This has the advantage of potentially being much easier to implement than a torque sensor. Instead, you would have distance sensors (either optical or ultrasonic) on the front and back of the unicycle, and measure how far away the ground is from each case. That would provide the control electronics an idea the grade hill you are riding in order to produce a motor torque that cancels it out, giving increasing power the steeper the climb and regen braking on the downhills. It would also have the benefit of providing stabilizing feedback control if the unicycle does start to fall forwards or backwards.
In the end I started to miss the raw simplicity and reliability of the original fixed crank build and decided to dust it off this past week. Upgraded the controller to a Phaserruner FOC and built a small rack for holding a set prototype potted batteries with 18650 cells, but otherwise there was really nothing to do. The thing just works and is a joy to ride. Why did I leave it hanging in storage for the last 6 years!?
The Phaserunner is much smoother than the original custom-made trapezoidal drive controller that I had on it earlier. Normally that would be a good thing, but on a build like this the buzzing sound of the motor provided good tactile feedback on how hard the motor was running. Wih the Phaserunner, you have no idea unless you look at the CA display whether you're getting like 100 watts or 1000 watts of assist. So going up a hill you easily forget how much work the motor is doing and then on letting go of the throttle are in for quite the suprise when your legs have to pickup the slack or you'll go flat on your face.
It's also clear from riding around again that the throttle is not at all the optimal control input for an electric assist unicycle. You normally want to free your hands now and then for balance, and needing to be tethered to a handlbar is annoying. There are two approaches that I want to try next on this:
Torque sensor on the cranks: This would work awesome I'm sure and would natuerally let you amplify braking torque when going downhill as much as forward torque going up hill. But adding a torque sensor to a build like this won't be very easy.
Grade hill sensors: This has the advantage of potentially being much easier to implement than a torque sensor. Instead, you would have distance sensors (either optical or ultrasonic) on the front and back of the unicycle, and measure how far away the ground is from each case. That would provide the control electronics an idea the grade hill you are riding in order to produce a motor torque that cancels it out, giving increasing power the steeper the climb and regen braking on the downhills. It would also have the benefit of providing stabilizing feedback control if the unicycle does start to fall forwards or backwards.
