My LR3 (skr board) is exhibiting odd behavior on the Z axis.
The behavior is manifested on the Z stepper at the X max end of the gantry. The running g-code will send the gantry in a Z negative direction (toward the workpiece) and both steppers will work to lower the gantry, as expected. Then when a Z positive move occurs only the stepper at the X min end will raise. The other Z axis stepper does not move. Subsequent cuts thus slope downward as X increases.
If I stop the running code, and home Z it seems to behave normally.
The worst part of this is it’s intermittent - so I’m tearing my hair out trying to troubleshoot it. I’ve ruined 2 pieces due to this issue, and could sure use some suggestions.
Note: I am planning on upgrading to a Jackpot, but that’s not on the calendar yet. However if that solves this problem I”ll accelerate that upgrade.
I bet you are! That’s a tough one, particularly intermittent.
I’ve seen something similar a few times under different root causes.
First off, an intermittent connection at an extension cable can cause really weird stepper motor behavior including odd motion/no motion scenarios. To troubleshoot that, turn off your controller, pull the stepper connector at the controller and use a DMM to measure both coil resistances for each stepper as you move the extension connector by hand. Fix any intermittance you find.
(Note: disconnecting a motor when powered, including because of an intermittent extension cable, can electrically stress or destroy the TMC2209 driver)
Another time I’ve seen this, there was a controller with some kind of problem with the DIR and EN bits on the controller. You could see that by putting a DMM or scope on the pins while the machine was running and seeing that they weren’t working properly. The fix was replacing the controller.
I’ve also seen this a few times when TMC drivers and/or the controller were electrically stressed by moving the machine around by hand when unpowered.
If you ever move your machine around by hand when it is not powered, and you see your LCD backlitght light up, you’re generating enough back EMF to overstress, damage, or destroy your drivers or controller. If that happens, you may have stressed your system.
The problem could also be mechanical. While the machine is off and steppers disconnected, manually work your leadscrews up through their range of motion. If there’s any binding on either side, fix that.
A few weeks ago I had to replace the leadscrew stub on that stepper (holds that brass T nut). Why is a separate discussion…
I didn’t disconnect the stepper before I did the work…… and probably gave the leadscrew a twist or two during disassembly.
Feel pretty foolish in retrospect.
First step - I’ve ordered a TMC2209. If time allows, I’ll break out the test gear and reacquaint myself with my scope and DVM. If not, I may try troubleshooting by module replacement. Fortunately, a driver is < $10.
