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Unread 04-02-2006, 08:50
Joe Johnson's Avatar Unsung FIRST Hero
Joe Johnson Joe Johnson is offline
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Re: TO much traction??? (ifi wheels or AM wheels)

This condition is a traditional problem with 4WD with wheels in the corner.

Grippy wheels want to roll, not move sideways (the direction along the axis of the wheel).

To think about why 4WD with the wheels in the corners is a possible problem, imaging your robot spinning about the center point of the wheels that are touching the ground. The relative velocity of the wheel with respect to the ground can be broken up into 2 components: one in the direction the wheel likes to roll (that is good) one in the direction of the axle (the direction that those grippy wheel does not like to move, which is bad).

Keeping with the mental experiment, you can clearly see that the problem gets better or worse as this ratio (L/W) gets smaller or bigger. That is longer wheel bases make the problem worse (i.e. force the wheels to have to slip sideway MORE) & wider wheel bases make the problem better (i.e. require relatively less sideways slipping).

There is no "official" number on what this L/W should be but the grippier your tires, the lower the number should be to avoid hoppy turns and hot motors. I recommend trying to keep the ratio to about .5, but I have always been a fan of 6 wheel drive so I am biased...

Joe J.
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Last edited by Joe Johnson : 04-02-2006 at 08:53.
 


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