wheel question

[bardd]

I was wondering - what will happen if we build a robot that has wheels in different size? For example, let's say we build the frame from the kit with 8'' wheels in the middle and 6'' wheels on the sides. What will happen?
I know we'll have to adjust the gear so that they'll spin at the same speed, but then the torqe will be different. Will it be substantial? How stable will the system be?

Thanks in advance.
2212!

[Kevin Selavko]

I dont think that the different speeds/tourqes of the wheels will greatly affect it, but if the robot has a center of gravity near the center then it will tip from one way to the other depending on what way you are driving. That may be able to help you with the bump though.

[Tom I]

Well I'm assuming he'd have all 3 wheels on the same level, as in the axles would be at different heights off the ground for the 6" and 8" wheels, so that all wheels touch the ground.

I don't think you'd have a torque difference, man. Think about it, in order to have the wheels spin at the same relative speed in terms of ground distance, you'll need to increase the rotational speed of the 6" wheels. Thus, if you increase the speed, you'll decrease the torque. So the 8" wheel axle will have more torque than the 6" wheel axle, but when you then consider the 8" wheel will cover ~25" of ground distance per rotation as opposed to the 6" wheels which cover ~18.8," the wheels will end up having the same relative torque because they'll have the same relative speed. Using the same drive source, if you increase power, the inverse happens to torque, and vice versa, so all in all it comes out being equal.

[David Guzman]

If you adjust the speed to match on both size wheels, you will also be adjusting the torque at the same time. A reduction in speed increases torque and because your wheel size is different (different moment arm) the force applied to the ground ends up being the same.

As long as you adjust the RPM to match the correct robot moving velocity, you will be fine.