Robot Scooter

[Ari423]

Now that the season is over, I was hoping I could get some advice on my Senior Capstone Project for English class (yes you read that right, English class). For my project, I designed a robotic scooter using techniques I learned from my four years in robotics. The main features are a custom single-speed 3-CIM gearbox and a manually-actuated front steering wheel. The biggest thing I'm concerned about is whether or not it will structurally be able to take the load of a person (~150 lbs) standing on it. (I know it's missing the handle crossbar, I didn't have a chance to add that in)

Some specs on the gearbox:
3 CIMs linked together by 60t idler gears
11:84 spur gear reduction, 15:36 sprocket reduction
6" pneumatic wheel
7.61 ft/s free speed, 6.17 ft/s adjusted

You can see the website I made with more details on the project (made for a less-technical audience) at arimb1999.wix.com/robot-scooter and the more detailed CAD model here.

I am very open to any criticism both for my own learning benefit and for my project grade. Thanks in advance!


EDIT: added some pictures

[TheModMaster8]

I would change the the front wheel brackets to 1/4 thick but other then that, it looks pretty sound to me.

[Chak]

Structurally, it's probably fine. After all, if you stand on our FRC robot, it'll probably survive.

I'm more concerned about electrical strength (if that's a thing). There are no motor controllers, breakers, etc. Running 3 CIMs on a 150lb robot is already a risky thing, so I figure running 3 CIMs on a 200+lb scooter can't be healthy.

Now, about the CAD model: the front wheel can't spin right now, but I'm sure that's just CAD. Also, it looks like your life would be so much easier if the front wheel is dead axle(edit: to clarify, dead axle would get rid of the front wheel brackets and a couple of bearings). I like how your CIMs are supported from the back, but I'm not sure how you're going to get them in and out if maintenance needs to happen.

[Chris is me]

I would look at the general designs of other kick scooters and consider something closer to them for the front fork and steering tube. Right now it seems like your entire deck is mounted to just a 1" span of the steering tube, which makes it hard to support. Kick scooters generally use a headset bearing on a 2" or longer tube to attach the deck to the steering tube, and they don't build a frame around the front fork / wheel at all. If you're just using ball bearings or whatever to support the thrust load of the steer tube on the deck, that might not fly.

[Ari423]

Thanks for the advice! Still open to more if anyone else has suggestions. To reply to some comments:

Originally Posted by TheModMaster8

I would change the the front wheel brackets to 1/4 thick but other then that, it looks pretty sound to me.

That definitely sounds like something I could do to add strength.

Originally Posted by Chak

I'm more concerned about electrical strength (if that's a thing). There are no motor controllers, breakers, etc. Running 3 CIMs on a 150lb robot is already a risky thing, so I figure running 3 CIMs on a 200+lb scooter can't be healthy.

I'm not 100% sure what you mean by electrical strength. As far as motor controllers and breakers go, they will go in front of the battery or under the CIMs, they just weren't CADed. I geared this lower than a normal FRC robot (17.2:1 total) so each CIM is traction limited to around 40 amps. It slowed it down more than I would have liked, but such is life.

Originally Posted by Chak

the front wheel can't spin right now, but I'm sure that's just CAD.

Yeah I did that to make the CAD model look nice. In reality, the vertical tube is supported by a bushing that allows it to spin freely.

Originally Posted by Chak

Also, it looks like your life would be so much easier if the front wheel is dead axle(edit: to clarify, dead axle would get rid of the front wheel brackets and a couple of bearings).

I agree dead axle would be easier. I chose live axle because I wanted to use the WCP pneumatic tires which are live axle only. In hindsight it would probably be easier to use the 6" AM pneumatic tires instead and run them dead axle. That will definitely be something I will look into for version 2.

Originally Posted by Chak

I like how your CIMs are supported from the back, but I'm not sure how you're going to get them in and out if maintenance needs to happen.

You are very right; I did not plan well for maintenance. I suppose you would have to completely unbolt the back plate and then unscrew the CIM that needs replacing to slide it out, but that would not be fun. I might look into enlarging the hole in the back plate to go all the way around the CIM so the CIM can be slid out for replacement.

Originally Posted by Chris is me

I would look at the general designs of other kick scooters and consider something closer to them for the front fork and steering tube. Right now it seems like your entire deck is mounted to just a 1" span of the steering tube, which makes it hard to support. Kick scooters generally use a headset bearing on a 2" or longer tube to attach the deck to the steering tube, and they don't build a frame around the front fork / wheel at all. If you're just using ball bearings or whatever to support the thrust load of the steer tube on the deck, that might not fly.

That's a good idea. I was really struggling with how to support that huge lever arm in so little space. Adding that front fork with a much longer bearing/bushing would probably work a lot better than what I have now, and it would allow for the scooter to be shorter overall. Something else for version 2.