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Post by dmonson on Jun 21, 2020 17:07:06 GMT
I've enjoyed my Mega V XL for a few months and yesterday had some issues where it was drifting in the x direction and messed up a cool carving. With the power shut off I moved the gantry all around to see if there was a bad spot or something or if the rack and pinion pressure wasn't even along the full length of the rails. While moving it by hand I noticed that if I went a little too fast the resistance went up a lot. I thought maybe the motor was bad, but when I looked at the electronics I noticed the power supply was coming on when I moved the motors by hand. If I moved them enough the drivers came on too! This is why the move resistance went up if moving too fast. I know that you can turn a motor into a generator so this isn't surprising. However, this brings up a couple of concerns. 1.) Is this behavior expected or should there be an isolation circuit/diode to prevent this? 2.) Is this bad on a motor driver or the motor itself? 3.) Is the best practice for manually moving a motor to unplug it from the driver first? 4.) Finally, I get the least amount of noise when I set the rack as far from the pinion gear as possible. What are the downsides of having too little pressure there?
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Post by Bruce on Jun 23, 2020 3:35:26 GMT
Moving the motors by hand turns the them into electric generators. So this is expected. When moving the ganteries by hand move then at a slower rate to avoid generating excessive voltage from the motors.
You want the closest fit of the pinion gear to the rack with no slide between the two, (power to the motors, no movement).
If there is excessive pressure of the pinion against the rack it can cause the motor to lose steps at times. If the rack is not aligned you have may have to make a few adjustments to get consistent pressure between the rack and pinion across the gantry.
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Post by dmonson on Jun 26, 2020 3:34:14 GMT
Thanks Bruce. Always something to learn. I ended up setting the rack as far from the pinion as possible to reduce the pressure, while still making sure I had no backlash. Really easy to check by grabbing the pinion gear turning it back and forth to make sure no backlash. However, for my y-axis racks, I had to squeeze the rack against the pinion like Derek shows in the assembly video. Machine is running really well now.
I do think it is best practice to unplug the motors from the box if planning on pushing the gantry around by hand for setup and alignment.
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