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Originally Posted by themccannman
I don't understand how the same 4 wheels touching the ground in a static state could possibly have different amounts of traction.
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We were discussing a "good" and a "bad" mecanum drive. Who said the wheels on the "good" one were the same part number as those on the "bad" one?
And even if they were the same part number, who said they were all assembled and adjusted with the same care and attention to detail?
Differing amounts of friction in the rollers (due to wheel design, manufacturing tolerances, and care in assembly and adjustment) affects the wheel-to-floor traction of the wheels. A detailed explanation of the physics can be found
here.
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How can a free wheel be forced to spin when going perfectly perpendicular to it's direction of rotation?
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We were talking about the
rollers, not the wheels. The rollers need to spin in order for the bot to translate at 45 degrees.
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In a standard mecanum drive set up if you drive the robot straight forward the rollers on all 4 wheels will slip slightly due to the fact the ground is applying force at a 45 degree angle to their direction of rotation.
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Read Note 1 at the bottom of the post to which you were responding.
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In the case of normal traction wheels commonly used in FRC I think it's pretty safe to say the only difference in traction would be the slight change in the profile of your contacting surfaces depending on the direction of travel.
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It sounds like you are saying that the tread pattern on commonly-used FRC wheels results in isotropic friction. Was that your intent?
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I'm not trying to stir up an argument
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Understood, and appreciated.