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Unread 29-03-2010, 21:24
fritzdejongh fritzdejongh is offline
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Re: How Do mecanum wheels handle the bumps?

Quote:
Originally Posted by JesseK View Post
This is just bad physics. The math is plain wrong as I'm interpreting it nor does it explain how a frame 'transmits' the force tangent to how the force is applied. This isn't fluid dynamics, where the pressure builds up and escapes through the path of least resistance.

If this can be proven through experimentation and then explained with clear and concise diagram, then maybe I'd consider it as valid the next time I design a robot to sit still and push a wall.
You can dissipate *energy* in a frame, but F=ma will get you in the end. Regardless of the details of your axles and struts and how the load is borne, if you have a net sideways force on the robot, the robot will accelerate sideways.

With our robot, the mechanum wheel is direct-driven by a toughbox. The motor creates torque around the axle. The rollers will convert that to a force with forward and sideways components. Our wheel is solidly attached to the axle, so the sideways force will be transmitted down the axis of the axle to the toughbox, through the toughbox mounting to a C-channel, etc. If we're not accelerating sideways, the axle is pushing back equally, with the force coming ultimately from the wheel on the other side, and by the same token, the rollers give this a forward component. For every action there is an equal and opposite reaction...

A sailboat tacking into the wind is another interesting example. The wind blows on the sail, applying a force, ignoring drag, perpendicular to the sail surface. The sailboat can then accelerate in the direction of the keel. These two projections allow the wind to blow the boat upwind.

If anyone's at the Minnesota regional later this week, we can draw some diagrams.