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Z-axis encoder connection diagnosis

I’ve been making the first few cuts with my new build and am running into some issues with the z-axis apparently losing encoder feedback and driving the z-axis to the extent of it’s travel.

Details of my build:

  • Latest EastBaySource kit (1.5b control board)
  • Meticulous-style z-axis setup - currently just hacked together with bits of scrap ply, I’m working towards cutting a less janky version of the sled
  • Cheap air-cooled Chinese “spindle” (link)
  • Using the EBS firmware and EBS distributed version of GroundControl.

Everything works fine when just moving the sled around the board and manually positioning the z-axis from GroundControl. When I run the spindle and start making some cuts it will work for a while, then at some point GroundControl will lose track of the z-position - it continues reading a steady value while it drives the z-axis up or down, until I hit the emergency stop.

The 2 likely culprits seem to be:

  • A poor connection on the z-axis motor, triggered by vibration from the spindle. Disconnecting and reconnecting the cable at the sled does seem to rectify the issue which makes this seem likely. I’ve tried pulling the individual pins from the connector and pinching them slightly to tighten up the connection, without any lasting success.
  • Electrical noise from the spindle interfering with the encoder - I’ve read that excessive noise can be an issue with these spindles. I’m not sure where I’d begin to tackle this one, the cabling isn’t currently running particularly closely together, but… shielding? Power filters? Ferrite beads? I only vaguely understand that side of things.

It’s worth noting I have popped the encoder cap off the motor and everything looks to be intact under there. I’ve wondered whether the connector on the encoder board itself might have a bad solder joint, such that the movement of connection generally makes it good again, but I’m not sure how to get to the underside of that PCB to inspect it.

Any thoughts what my next step should be? How best to narrow down the possibilities? I have a few days to think about it while I wait on a replacement for the motor coupler I damaged today.

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Have you zip tied the cable at the sled to something to strain relieve any pull from the sled movement? The most likely culprit is the poor connection at the z motor. The encoder pulses a certain number of times per rotation of the motor shaft and the system just counts those pulses to know the mill height. If the encoder loses connection, the motor will continue to spin, but the controller gets no step feedback to count saying it is moving, so it will keep going until it gets enough steps to stop or it hits the end stop or limit.

This is my bet. Electrical noise tends to make the z-axis position move when the motor isn’t actually turning which is sort of the opposite of what you are seeing. You are seeing the signal not getting to the controller which I bet is a connection issue.

Have you zip tied the cable at the sled to something to strain relieve any pull from the sled movement?

I have done this, but only after I first encountered the problem - it was part of my first round of troubleshooting. I’m increasingly thinking I might have damaged the PCB connection by running it with the cable hanging off it for a while.

I don’t have my parts in yet, but considering next steps - I’m still suspicious of the encoder PCB, since the plug itself seems to seat pretty firmly.

Any thoughts on whether removing the encoder PCB is a reasonable option? Would it perhaps be a better idea to try to reflow the joints by heating the pins directly?

I wouldn’t be afraid to resolder the pins, but I’d be very careful about not messing with anything else. Verify that nothing on that encoder is mechanically damaged if you are inspecting it.

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