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Unread 16-01-2015, 15:14
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lcoreyl lcoreyl is offline
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Re: pic: McCannot Wheel

Quote:
Originally Posted by Mr. Lim View Post
I posted this because there is some disagreement whether Mecanum wheel rollers will roll when driving straight forward or backwards. Some people say they will roll, and some people say they will stay stationary.

In my experience, I've noticed that Mecanum wheels often spin faster than the robot is moving, even when driving straight forward and backwards, much like the McCannots would, except not nearly as badly. Many say that it's because the Mecanum wheels are losing traction with the carpet, but I didn't see that being 100% the case. My theory is that the Mecanum rollers do roll, even when going straight forward or backward.

I think it's fairly obvious that these "McCannot" wheel rollers will definitely roll when driven straight forwards or backwards, resulting in less than ideal robot movement.

My question is for those who believe that mecanum rollers WON'T spin when driving straight forward or backwards. How many degrees do you need to start angling the McCannot rollers until they stop rolling completely when driving straight forward or backward? 90? 45? 1? 0.00000001?

I don't know the answer to this, but I'd be curious to see what others think...
My experience has been one revolution of the 8" AM mecanum wheels translates the robot 8*pi inches forward. Measured precisely to the last decimal point (math joke!).
Unfortunately, with no team this year I can't test this myself, but I have a theory that part of what you're seeing might actually be due to the fact the circumference of the wheels have the visual breaks in them. If you have some under-utilized newbies, maybe you could convince them to convert a regular wheel (or construct something like an 8" wheel), by drawing on the marks to make them look mecanumish and then roll them around and see if it is a visual effect...



Here are some items that I highly recommend anyone with access to a mecanum drivetrain try for themselves to help their understanding:

1) draw some lines on the sides of the rollers so that it is much easier to see if/when they are spinning.

2) mechanically lock all wheels/axles so they cannot spin (rollers should be left to spin freely). push your drivetrain around.
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