ropes, chains & equations

Apr 28, 2004 4 Replies
T

hello all.. the recent post re: 'cosmetic roller chain' has found me experimenting.



a few things i can't seem to get right... perhaps its a fundamental misunderstanding on my part..



say i model a simple pulley.. a solid fixed disk and two weights. i can develop the model just fine and sweep in a nice 'rope' from top/center of the weights over the pulley.



if i set the sum of the two rope lengths as equal to a constant, then raising one weight should lower the other.



but, will i be able to see this in am assembly file? can i "drag" one weight and see the other move? or will mates prevent me from moving the weight at all?



no way to get physical dynamics to simulate one weight falling and one rising?


-tony


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D

Not using physical dynamics. Mates could be set up to do that, if you ignore the rope. Then you would define the rope in-context to meet the weights.

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C

It will not dynamically move but upon rebuild it will update to the new location. Simulation might crap out or not update like you want. Using animator you should be able to make a flowing AVI though.

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P

"tony" wrote:> no way to get physical dynamics to simulate one weight falling

SolidWorks' "physical dynamics" is actually "rigid body dynamics". Since the rope has a changing shape, it is not a "rigid body". You could model it as a chain of connected segments, which would more or less result in a "finite elements" approximation of the rope. The problem will then be to model the contact between then rope/chain and the pulley...

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M

Tony,

I tried to model a trebuchet and had to utilize Cosmos\Motion. With some help from the Cosmos folks, they were able to get close. But when the rope looses its shape and is no longer rigid, things fall apart. Like any complex engineering dynamics problem, the only way to approximate is in steps.

So in SolidWorks, I used configurations to represent key steps in the motion. Perhaps you can do the same with your weights.

Regards, Marie

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