[ODE] Torquing the joint

[Nate W]

On Thu, 5 Dec 2002, Henri Hakl wrote:

> When I apply the torque it makes the body behave like a propeller, turning
> through the center of mass - but instead imagine that you have a body
> attached to a string and you spin the body in a far arc. The center of
> rotation is not at my hand that holds the string. Clearly these aren't the
> same.

The second example is not only a torque, but a torque plus a linear force
on the center of mass.  

> Another example: apply torque to your lower arm by twisting it manually in
> the middle with your other hand, and due to the nature of your body this
> torque is propagated to your upper arm. This is fun, for sure, but what I'm
> looking for is the "torque" that needs to be applied to just let the arm
> pivot at the elbow (imagine you're lifting dumbells) - and the upper arm
> stays motionless.

Now you're talking about a torque at the elbow, plus a torque and the
shoulder to hold the upper arm in place. :-)

For the articulated systems I've created so far, like walking creatures,
the joint motors have worked very well.  Have you tried that approach?

-- 

Nate Waddoups
Redmond WA USA
http://www.natew.com