Violent GRBL Alarm 8: Homing fail: Cycle failed to clear limit switch when pulling off

I recently got my S5P 4x4 running thanks to Rob and the C3D team for working on getting me part replacement for the power pendants.

I however now have a homing issue. I’ve been browsing through the forums and seen that the error issue has been fixed with an updated controller, but I got a rev 5.

When I turn the machine back on after stopping a job, and try to initialize - the gantry violently moves and disregards the limit switches while pushing itself constantly grinding the frames. This is repeatable and I try to instantly hit the kill switch each time.

Did people who experienced this homing issue also see this behavior?

I was also able to replicate that this issue goes away after powering it down for about 20-30 minutes to let the capacitors lose their charges.

When you configured the machine per:

were you able to test the motors in each direction? Did each move as expected?

When you tested the homing switches, did each signal as the correct input?

If you aren’t, please try the beta:

Yes, ive been working with support through this aswell. Everything behaves normally until the homing error appears. All movements are as expected and limit switches under debug mode indicate when signaled.

Ive downloaded the version of carbide motion youve linked as well.

I am posting this to see if this is a new issue where it behaves violently, or did everyone else experience this as well?

I was able to run hello world and almost successfully complete my first project until homing issue and hold down complications.

I’m having this issue, too, but my machine doesn’t seem to behave ‘violently’…it’s more like it just moves onto the limit switch and then doesn’t even try to back off it. New Shapeoko 5 4x4 purchased during the Black Friday sale.

For the first few days I had no issues, then lately it started giving me this error. It’s worse if I park the machine when I disconnect Carbide Motion.

It will eventually clear if I keep repeating the initialization.

Limit switches seem to be working fine and I don’t think anything is loose. I’m not having any trouble with it otherwise and cuts are accurate and repeatable.

Will reach out to support but I would like to do some further checks to make sure I’m not wasting anyone’s time.


I also see “GRBL Alarm 8” intermittently and only on machine initialization. Details:

  • Shapeoko 5 Pro 4x2
  • Raspberry Pi 4B, Raspbian 11 32-bit
  • Carbide Motion 622

I suspect it’s a problem with Carbide Motion 622. Reason: I have not yet seen the error with the following alternate setups:

  • Raspberry Pi 4B, Raspbian 11 32-bit; Carbide Motion 578
  • HP laptop, Windows 11 Home 22H2 64-bit; Carbide Motion 618

Edit: this is a new Shapeoko 5 Pro from the Black Friday sale.

I just got my S05 PRO 4x4 setup from black friday as well and the get the grbl 8 homing error it just sits on the x axis I reached out to customer support today and hope to hear something tomorrow. Its
Friday 7 eastern but we’ll see.

TDLR: Rev 5 Controller from Black Friday Sale Bad, New controller fixed, but still Rev 5 on sticker.
@jeremym @irrealis @Wild_Wild_West

Great news @robgrz, the new controller fixed the issue. It no longer causes Alarm 8, but when I try to force it create an alarm 8 like I did with the previous controller, it now gives an alarm 6, BUT I just close that prompt and reinitialize, everything works as it should.

Now I am just waiting for C3D to get more VFD spindles to replace mine so I can get the machine back up and running!

It’s frustrating that everything didnt work initially, but im glad customer support is with me along the way.

Edit: Version 622 Carbide Motion

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