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model wheel over a bump

Question asked by Brad S on Jun 14, 2012

I'm looking at quick and basic modelling (for now) where a mechanism at the early stage of design wants to be tested in how it acts when a wheel attached to it goes over a bump. Imagine for example a vacuum cleaner being pulled up and over a step. At some point I'd like to include stiffness-contact modelling, but for now the wheel can be rigid and round. How would you model the wheel-step contact?

 

Since this can be reduced to 2d and block sketches can 'animate' the mechanism, I've tried giving that a go. Solidworks blocks provide tangent and traction relationships which I haven't gotten to work as shown below. Feel free to suggest a very different workflow but the following explains difficulty with my attempts. In the screenshot below, the wheel (including pink line) is a block constrained to move up and down a centreline. The other 3 blocks are potential ground surfaces. for this example you could imagine a vertical spring being constrained to the wheel and surfaces being slid right to left.

 

when the horizontal block and wheel are selected (as shown in light blue), both traction and tangent relationships are available and work fine.

For blocks with more than one line, I had to make a path within the block, to form the relationships (like a continuous surface for a cam as in the SW example). As soon as I did this traction was no longer an option, only tangent. This works on the smooth curve into a ramp shown tangent to the wheel. However if the arc radius is reduced so there is discontinuous transfer of the contact point like in a step, tangent gets stuck on the initial horizontal line (the step or ramp travels through the leading edge of the wheel).

 

thanks in advance for any help and suggestions

wheel_bump_blocks.png

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