Drivetrain First Thoughts?

[Ether]

Originally Posted by PVCMike

I am surprised to see so many people referring to Mechanum drives as being slow. In reality, yes, they are inefficient

What do you mean by the word "inefficient" in this context?

[PVCMike]

Originally Posted by Ether

What do you mean by the word "inefficient" in this context?

I mean that you lose energy through a vector other than forwards. Those mechanum rollers are rolling even when you're going straight, so you're losing energy and it could be taking you more wheel rotations to cover the same distance as a non mechanum wheel of the same diameter.

[Jared Russell]

You can model a mecanum wheel as a regular wheel of the same diameter and tread material but with 71% the coefficient of friction (assuming 45 degree, friction-free rollers. In actuality, it is >71% for F/B and <71% for L/R due to friction.).

When you aren't slipping the wheel, you get the same speed out of a mecanum wheel as you would with a regular wheel of the same diameter. It is a common misconception (and one I had believed until recently) that a mecanum wheel is necessarily slower than any other wheel.

See here for the math: http://www.chiefdelphi.com/media/papers/2390

[Madison]

Originally Posted by Jared341

You can model a mecanum wheel as a regular wheel of the same diameter and tread material but with 71% the coefficient of friction (assuming 45 degree, friction-free rollers. In actuality, it is >71% for F/B and <71% for L/R due to friction.).

When you aren't slipping the wheel, you get the same speed out of a mecanum wheel as you would with a regular wheel of the same diameter. It is a common misconception (and one I had believed until recently) that a mecanum wheel is necessarily slower than any other wheel.

See here for the math: http://www.chiefdelphi.com/media/papers/2390

Does anyone know, then, if the friction coefficients listed for AndyMark mecanum wheels are scaled in this manner? You wouldn't want to aim for 12 ft/sec and get 17 ft/sec because the values were already scaled.

[theprgramerdude]

Light cycle, anyone? Attach the arm mechanism to the center of the robot, in between wheels?

[Alan Anderson]

Originally Posted by Jared341

When you aren't slipping the wheel, you get the same speed out of a mecanum wheel as you would with a regular wheel of the same diameter. It is a common misconception (and one I had believed until recently) that a mecanum wheel is necessarily slower than any other wheel.

In theory, there is no difference between theory and practice. In practice, however...

Mecanum wheels' rollers do spin when driving in a straight line on carpet. This robs them of forward speed. Perhaps on a rigid surface like tile or concrete the "just like a traction wheel" model is adequate, but it falls short on a typical FRC field.