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Unread 20-03-2010, 19:07
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Re: fine control of robot with mecanum wheels

Quote:
Originally Posted by Bill_B View Post
Can you adjust each motor's signal based on the ratio of normal forces? That is, if you know the percentages of robot weight borne by each of the corners, can you compensate for that by varying the command to each? This might also be useful for bump-climbing when the weight distribution on even a perfectly centered CG 'bot gets totally skewed.
As long as each wheel has enough normal force to provide enough friction so that it is not slipping, you want the same command applied to each wheel. The torque on each wheel gets transferred from the wheel to the ground, regardless of the normal force on the wheel, as long as the wheel is not slipping.

If a lightly loaded wheel is being given a command higher than the friction provided by the normal force on that wheel can support, and the wheel starts slipping, then what are your options? If you reduce the command to that wheel without reducing commands to the other wheels you will mess up the behavior of the bot (we're talking about a mecanum bot here). If you don't do anything, and let the one wheel slip, that will also mess up the behavior of the bot. Bottom line: you must have enough normal force on each wheel at all times in order for mecanum behavior not to be affected. That's why suspensions are used on mecanum bots: to distribute the normal load on each wheel more evenly.


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