[Xnaron]

I've built a racking detector for my slaved axis Y gantry to protect against a racking condition. Basically if one stepper stops turning I want to issue an estop to the machine to protect it from damage. I have 1 stepper per side (A,Y). I've been using this setup for years. I added encoders to the end of each Y and A leadscrew. I developed software for an Atmega168 microcontroller to display the information on an lcd screen and allow setting of a variance trigger point. It is working well but I noticed an issue with my machine. Looking at the encoder counts I see a variance of 4 when running 48 inches. The encoders are set to 200 pulses per revolution so 48 inches = 9600 pulses. When I move 48 inches I get 9600 on the Y and 9604 on the A. This is consistent and I can see the error (variance) increasing as I move from 0 to 48 inches. To be sure it wasn't an issue with my software I swapped the encoder cables around and I see the same thing happen but in reverse (ie: 9604 on Y and 9600 on A). Does anyone know what could cause this error in the slaved A axis?

Machine details:
Y/A - Nema 34 960 oz/
2 gecko g203V drives
Windows XP
Parallel port
pmdx-122 breakout board

Here is an overview video of the racking detector. This is an older video and I have corrected any issues I may have mentioned in the video.

[manton]

Could you just drive both motors from the same axis instead? Then you would know that the same number of pulses were being sent to each motor.