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Re: 2583's Octocanum Modules
It's a torque thing. Here's a rough verbal sketch of what to do off the top of my head. I"m sure if I sat down and drew it out, I would find an error or nuance. But, here goes...
Draw a vector from the rotation axis of the module to the point where the cylinder applies force. Then, draw a vector from the point where the cylinder applies the force in the direction of the force with the magnitude of the force from the cylinder. Take the cross product of these two vectors. Or, if we make an assumption of planarity and only need the magnitude of the cross product, then Torque = Force * Radius * sin(theta), where theta is the angle between the vectors. This is the "lifting" torque you get from your cylinder.
To determine the torque you need to lift, do the same math, except draw the vector from the rotation axis of the module to the contact point on the ground of the traction wheel. The force then becomes the amount of weight the wheel supports. This is probably pretty close to 1/4 of total robot weight, assuming you have a center of mass close to the center of the robot. The angle between the vectors changes as well, as the weight vector is straight down.
If the torque necessary to lift is less than the torque provided by the cylinder, you aren't getting the mecanum wheels off the ground.
Hope that helps.
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Last edited by jee7s : 04-02-2014 at 18:24.
Reason: Clarity on the second calculation mentioned.
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