Member Avatar for bhp2005

Hi, I have this homework problem that I need some help on:

In 3D: Given 2 links attached end to end with lengths L0 and L1 respectively, a point P0 that the first link starts at, and a point P1 that you want the end of the 2nd link to be at, write a function that finds the configurations of the links that put the 2nd link’s end at point P1.

I feel like I'm missing something because I don' t know where to start with it. I really don't even know what the problem is asking for. I'm hoping one of you comp. sci. or math geniuses will be able to help. Any tips/help would be appreciated.

Thanks in advance.

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  • Latest Post Latest Post by jonsca
Member Avatar for jonsca

Think of P0 as a point on your shoulder, L0 to be the length of your upper arm, and L1 to be the length of your forearm. Now, put your finger at an imaginary point in space (don't allow your wrist to rotate). That's P1. Now if you have P1 and P0 you can use something like http://en.wikipedia.org/wiki/Law_of_cosines you can get everything as a function of the angles (since you know the distance from P0 to P1 too and you can assume your upper arm can rotate at the shoulder). I don't think your professor is looking for an exact answer but something in terms of the unknown quantities.

Anyway, hope that gives you some hint without ruining all of your fun.

Edited by jonsca because: n/a
commented: Very nice analogy! +19
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