URDF transmission linkage question (MeArm)
I have a MeArm with a hip joint connected to a torso connected to a shoulder joint -> upper arm -> elbow joint -> lower arm -> claw joint.
I created a URDF to describe it and it works ok. (It doesn't have a gripper, just a resolute wrist joint for now, that isn't really my question.)
I have it working Gazebo and rviz, even MoveIt!. Here you can see the physical arm, in the position command by MoveIt and shown in the rviz:
However, my URDF is too simple! When the shoulder goes past 90, the elbow joint is affected and my position is wrong. The transmission linkages are way more complex on the MeArm than in my URDF. Note: I am an embedded software engineer, new to ROS, and not mechanically inclined.
Here you can see the error where the shoulder pulls back, not up.
So, how do I fix the URDF? Is it in the transmission types section of the URDF? I found the transmission interface page but is this a four bar transmission? How do I figure out what parameters to use? What mechanical engineering term do I search for to find other similar arms I can crib from? (I mentioned "not an ME", right?)
Also, does anyone have a super simple gripper/claw in URDF? As demonstrated by my rods-and-boxes approach, I'm fine with the simulation being an 80% approximation instead of a truly accurate description. I'd rather write the software or play with hardware than spend all my time in sim.
Thank you!
A few more images:
Good:
Not good:
