# Handle Chop / Comp with constraints?

Hey,

I’m wondering if anyone has found a way to use the handle chop / comp with constraints. I’m using the IK engine to control a robot arm. It works great for the shoulder and elbow, but I want the wrist to stay parallel to the ground. Unfortunately when I build the rig again using the handle comp to create another pick point for the wrist, the constraints stop working. I guess that I could manually limit the handle chop before it goes into the robot, but I don’t know if that would mess with the IK solver.

Anyone have any insight into this other then just using straight math.

Thanks.

Posting what I’ve managed to get working (just the basic setup) in case it’s useful. Does seem that it has a mind of its own once you get past the first bone in a chain.

handle_sample.tox (2.9 KB)
(mess with the nulls tx ty tz to see it work)

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Thanks for sharing this! Its somewhat similar as to what I’m getting. I see that your putting the handles on the ends of the bones. (makes sense) I put limits on all the handles, and it kind of works, but the position of the goal still doesn’t quite match up with the handle. Its weird, I was getting the same thing on my project.

The goal position is along the path that the end effector / handle should be able to reach, so why doesn’t it go there! It might have something to do with the falloff / weight. It seems to work a little better when those are both 1.

Hmm, not sure if this observation means anything, but it’s like the handles don’t try to go to the actual position of the targets, but rather, they simply mimic the rotation that the target has relative to the origin.

In other words, for any bone/handle in the chain, imagine placing the bone’s base at the origin, then mess with the target position, and the movement seems to make more sense.

I wound up sorting it out in math. If you take 90 (the vertical angle) degrees and subtract it by the angle of the elbow you get the interior angle of the wrist. Then you need to subtract whatever the angle of the shoulder is and you get a wrist that stays parallel to the ground. Or at least its something like that i cant quite remember.