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 Post subject: Self-balancing one-wheel vehicle - planning stages
PostPosted: Tue Jan 08, 2013 1:27 pm 
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Location: Golden Valley
Now that the 3d printer is working it's time to move on to the next thing. I'm finally starting up my self-balancing unicycle project and I'm working through the planning stages. This will be loosely based on the Orbis Urban Mobility Vehicle. A couple of the things I already have on hand and I'll be acquiring the rest shortly.

I'll be using:
Arduino Uno - GOT IT!
Sparkfun Triple Axis Accelerometer & Gyro - MPU-6050 (part# SEN-11028)
Currie 24V 450W motor w/ 11 tooth gear - GOT IT!
Batteries - start off with some small SLAs and graduate to LiFePo4s or something.
MX350 mini dirtbike rear wheel assembly w/ 80 tooth sprocket (12.5" rim, so maybe 15" total dia.?)
Motor controller: I'm still up in the air, I may go with the OSMC, MegaMotor Plus or the Pololu 24v23 CS. The MegaMotor is preferred as it's a shield for the Arduino and it has decent power handling for a reasonable price. (I'm trying to figure out how to set it up according to the manual but it's a bit confusing. Help would be appreciated.)


I did some basic calculations and think the 450W motor should work well, tell me if I'm wrong.

450w / 24v = 18.75a
450w / 746 = .6hp
(.6hp / 2600rpm) * 62,025 = 14.54 ft-lbs
80 tooth / 11 tooth = 7.27:1 ratio
14.54 ft-lbs * 7.27 = 105.78 ft-lbs
2600rpm / 7.27 = 358rpm at wheel
358rpm * 40" circ (47"?) = 14,320 ipm (16,826?)
((14320 / 12) * 60) / 5280 = 13.5mph (15.9mph?)

I think the Ratio may be wrong. Should I be using the relative diameters instead of the tooth count? Either way, I think this should provide me plenty of oomph and a decent speed.

I'll need some help with the Arduino coding, but most of it will be there - lots of guys online have their segway clones code up, shouldn't be too hard to convert to one wheel and adjust the inputs from the IMU. Anyone that wants to be involved is more than welcome.

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Tue Jan 08, 2013 4:04 pm 
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Ratio of tooth count is fine, will give the same result as ratio of diameters.

I'm pretty sure I've seen arduino based motorized unicycle projects on places like hack-a-day, often with links to source code.

I happen to be a unicycle (non powered) rider, so if you need a test pilot....

I might suggest adapting a giraffe unicycle wheel & frame, instead of using a minibike wheel. Lighter, narrower tire. Your torque seems borderline on what I'd expect is needed (going from how tired and sore my legs get). Guess it depends what parts you have on hand. New giraffe's can be had fairly cheap.

http://www.unicycle.com/unicycles/giraf ... cycle.html

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Thu Jan 10, 2013 1:23 pm 
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Thanks for the comments!

The intent of the project is to create a one-wheeled vehicle capable of off-road travel. I intend to increase the motor size, probably to something like 1kw or more, but I'm focusing more on a proof-of-concept for now. Also, the mini-bike wheel is fairly light weight and is only $35, I can barely find an 80 tooth sprocket, let alone rim and tire for that price.

It won't be a typical unicycle either, but I'm sure your experience would come in handy. It'll have platforms for your feet and a stalk with handle bars and controls, no seat. I may add a seat later, it'd need to have a shock absorber, though. But I feel it's easier to control the attitude (pitch, yaw, angle of the dangle... call it what you will) with your arms than it is with your torso.

Eventually I'm going to purchase a Golden Motors Magic Pie 2, which is a hubbed BLDC, but I need to learn a lot more about motor controllers and running a brushless.

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Wed Jan 16, 2013 12:49 pm 
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I ordered the IMU and the MegaMoto controller last week, I'm hoping they arrive sometime soon. I also nabbed my nephew's old Scoot-N-Go scooter that I can use the rear wheel assembly and charger from. It's only a 12.75" wheel so I'm not expecting a lot of speed, but it will have loads of torque with my 450w motor. The narrow wheel might make it dificult to balance side-to-side, but it's more of a proof-of-concept then full blown development and it's on a shoestring budget.

I think I'll be somehwere around $200-250 when I'm finished.

Now I just need some help figuring out this Arduino code. I found lots of examples but it all needs to be modified to match my components, and that's where I get lost. Would anyone be interested in sitting down with me and going through what I've got so far?

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Tue Jan 22, 2013 12:26 pm 
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While waiting for the rest of my parts to arrive I decided to double check my math for my motor sizing and found a great tool for DC Motor Sizing:

http://www.robotshop.com/dc-motor-selection.html

Just put in some of the particulars of your setup and it spits out what you need. It doesn't take into account any gear ratios, but that's simple enough to do on your own.

I figured out I can propel myself up a 20 deg incline with a 2 m/s2 acceleration, or about 5.2 m/s2 on the flat using an 11 tooth gear and an 80 tooth sprocket (7.27:1) and a 450w motor.

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Thu Sep 12, 2013 8:55 pm 
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Do you have links saved for the examples and source code? I'd love to take a look at them and help out if I can.


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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Sat Sep 14, 2013 7:59 am 
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Lee,

Here's a link to the code, he's updated it but I'm not sure he's updated it for the same gyro and accelerometer I have, though he mentions it in an earlier step. I haven't read through the updated code yet, but will this weekend.

http://www.instructables.com/id/Self-ba ... text-file/

Other than altering the code for one-wheeled use I also need to adjust it for a different motor controller that is
PWM instead of his Sabertooth that uses the tx/rx pins on the arduino, and I'd need to adjust his formulas to accomodate the different accel/gyro. Another change is he mounts his accel/gyro on edge, but mine needs to mount flat on the shield because my motor controller is also a shield and will mount over the accel/gyro shield. That should be easy since it's just a matter of using a different output pin.

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Tue Sep 24, 2013 2:17 pm 
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Looking into the code by Xenon John on Instructables I found he is using the same Gyro/Accel board I have. So, all I need to do is comment out the steering functions, comment out the code he has for his serial motor driver, make some adjutments for a PWM motor driver and I should be in business. Sounds easy... if you know how to code, which I don't.

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 Post subject: Re: Self-balancing one-wheel vehicle - planning stages
PostPosted: Wed Oct 23, 2013 1:23 pm 
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Not that I'm abandoning this project, but a thought just occurred to me; instead of making a one wheeled vehicle that you still need to turn somehow, what about making a ballbot and riding it?

You could use a joystick to turn tightly or if you lean to one side and forward or back it should be able to turn on it's own. The idea has been done, but usually using something like a bowling ball. I think it's totally feasible to use something a bit softer with more grip for better traction and smoother ride. Finding/affording omniwheels and motors that can hold the weight of a person is more of a problem. I've seen people using 2-axis control and some with 3, I'm not sure which would be best. Maybe 3 axis with 6 motors to distribute the weight?

I think I'll still work on the one-wheeled thing for now and keep this one stewing.

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