Puma 6 axis Robotic Arm with Mesa 7i80/7i40

I have been using LinuxCNC for a long time for my Mill and Lathe setup and parallel controlled stepper motors but this new project is making me a little crazy (it was straight forward on my other machines). 

I was given (in an incomplete state) a Kawasaki Robotics/PUMA 200 arm which has a Mesa 7i80 controller with 7i40 daughter cards running the servo motors.  

CORRECTION:   I believe this is more appropriately identified as a PUMA 260 arm - if that makes a difference

I have things "moving" generally with INI and HAL files from the previous owner and of the axes respond generally to control (I don't know enough about servos with LinuxCNC/mesa  but I am having all kinds of issues with Joint #1 the "shoulder" joint (the rotation, waist pillar joint in the center is Joint 0).  With a higher P value (200-300ish) the motors will hold it in position and move it up (positive direction) but when I reverse direction it stutters, pops up a follow error and estops.  I can very slowly/carefully/intermittently move the joint down but it eventually errors out.   I have a feeling that there needs to be some kind of asymmetric control of the positive/negative direction for this joint due to gravity/weight of the mechanism. 

I'm not even sure where to start here (I've been combing through some of the documentation leveraging my previous knowledge of LinuxCNC - which is a little rusty to begin with) or what questions to ask.   

Does anyone have a similar setup who would be willing to share their configuration, or maybe help me formulate some intelligent questions and find the answers. 

Thank you, 

Michael Jones

so I'm not familiar with PUMA 200, but most robots have brakes, i have had all kinds of trouble with them. I would look at them and any counterbalance system. if it has a counterbalance and the brake is on often you can get it to move up but not back down.

 
 

The system does have brakes which I have disabled (the joint free drops when it gets the follow error)

it doesn’t have a physical counterbalance that I can tell, maybe the gearbox has some sort of clutch?  

When idle, the motors are able to hold the joint in place even if I push on it.

I have a feeling that there’s something off  between the motors and encoders.   When it moves, it seems to be miscalculating the actual vs expected travel - but that’s just gut feeling.   It sometimes errors moving up, but not always.. it always errors moving down.  

Check encoder PPR, make sure the scaling is correct, then we can move to tuning.
In the meantime, upload the config files here so we can have a look, just in case something is off.

Here's the files.   I'll work on verifying the encoders shortly.  

One thing you might try is setting the PID MAX_OUTPUT to say 9.5 (95% of full scale)
As the 7I40 cannot have 100% duty cycle (the high side MOSFET bootstrap
requires a continuous PWM signal)