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Unread 25-10-2010, 11:09
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Re: Chainless Mecanum Drive

Quote:
Originally Posted by Ether View Post
Robot A has 1 CIM+gearbox on each side, which drives the front wheel and the rear wheel via a belt or chain.

Robot B is identical to Robot A in all respects, except that the belt (or chain) drives only the front wheel. (The rear wheels are not driven).

How would your analysis apply to this scenario?
Assuming a perfectly balanced CG:

With only two wheels connected, only 50% of the robot's weight is "over" the driven wheels (the other 50% of the weight is born by the non driven wheels which don't contribute traction since they are essentially just big bearings). For this case, the robot's max pushing force is effectively half (the mass portion of the formula to overcome static friction is halved). Since it requires less force / torque to slip the wheels, the motor connected to the wheel does not need to draw as much current, since the motor "reaches" the necessary torque at a lower amperage. However, the robot can only push with half as much force.

With only 2 CIMs in the drivetrain, a 148 pound robot geared to 9 FPS with roughtop tread (1.3 CoF) has a max pushing force that is torque limited. The motor's stall torque is greater than the torque necessary to slip the wheels. In addition, stalling a CIM draws 133 amps of current which quickly trips the robot circuit breakers. By halving the pushing force, you can make the drivetrain traction limited at some amperage. One can do this by lowering the traction of their wheels or by lowering the robot's traction overall by not driving a set of wheels / casters that support the robot weight.
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