Maslow Home Maslow Community Garden Newsletter

Z-Axis encoder stops working - then the left motor gets odd, too

Hi guys,

my sleep deprivation reaches unhealthy levels as I can’t let my fingers from my new maslow. Such a great project - really cool!

Until now everything works like a charm - my frame is sturdy as rock (I have used a piece of 150 x 80 mm aluminium truss from the scrapyard as front cross bar - very stiff!), the electronics worked flawless and despite some minor trouble when it came to calibration the software runs without fail.

But yesterday evening something odd happened: from one moment to the other the z axis got crazy: I evenly told GC to return to home coordinates and X/Y axis did as expected. But z axis kept on lowering all the way down until my router sled was fully lowered. Even then it kept on trying to get lower which resulted in skipping teeth with a heartbreaking noise in my z axis gear (I have a Makita router with a self-tinkered z axis control where I had to mount the motor upside down, transmitting its torque through two gearwheels)

I immediately stopped maslow (by pressing Stop in GC) and had a look at the coordinates the firmware reported to GC. The z axis was zero - which was obviously wrong.
I opened the z axis menu and initiated a raise by 10mm. The z axis motor started working, the sled raised, but the reported z axis position in GC remained zero. Since the z axis kept on raising with a somehow uneasy running motor I stopped it manually via GC z axis panel.
I then tested the motors via GC-Actions->Test Motors/Encoders and intrestingly the first test of the LEFT (!) motor turning CW failed with a whining noise from the motor. all other subsequent tests went okay, including left motor CCW and z axis motor. Now the GC reported z coordinate seemed to function again - understandably with a decalibrated z axis, but with sane encoder responses.
I started sweating in the fear of a toasted motor controller but when I started the the test motors sequence again, all tests passed and after recalibrating the z axis everything works fine again.
I checked the connections of the z axis cabling to no avail and also all other connections seem to be fine, too.

I’m using firmware/GC v1.10 with a stock arduino board and GC on Xubuntu linux 16.04. Except the z axis gears and the aluminium mono crossbar my setup is pretty similar to the standard maslow setup.

I don’t know what happened here but I don’t like to go through this again. The skipping teeths and the whining motors are really frightening noises. So my questions are:

  • what could have possibly went wrong?
  • what could I have possibly done wrong?
  • what could the test motors/encoders sequence ‘repair’ automatically (as so it seemed to do)

And I have a feature request:

  • is it possible to implement automatic damage prevention by stopping all motors if the encoders don’t report any movement for a certain amount of time even though the motors are advised to run?
2 Likes

This sounds like a loose connector to me. When the tests pass somewhat intermittently it is usually a bad connection somewhere. I would pull out and re-seat all the connectors and then run the test again.

I can’t agree more that we need a “motor stalled” feature which will shut things down. We’ve seen several attempts to add one, but none of them have worked right. The issue is that the controller is constantly regulating the motors speed and so the voltage applied to the motor jumps around a LOT. When the motor is spinning one direction, it might actually be powered backwards for a few milliseconds when it needs to slow down. It becomes tough to discriminate a stall from normal operation. It’s clearly possible, because from a human perspective we can tell the difference, but teaching that kind of common sense to a tiny computer is tough and the attempts so far threw so many false red flags that it was impossible to use the machine…I hear the request and I will make it a priority to focus on this again.

2 Likes

Hi Bar,

confirmed, you were 100% right!

Yesterday the z-axis failed again and the root cause seemed to be a loose z axis motor connector. I had the cable attached to the sled with a strain relief to pre-empt exactly that scenario but it seems the strain relief was too loose and the vibrations of the sled made the cable slip out of the socket…

Thank you for your support!

Tim

4 Likes

Hi, I’m trying to keep threads related, so I’m adding here because I have a similar issue and loose cables wasn’t it.

My Z-axis fails the GC tests immediately, but there is a buzzing coming from the arduino. The first left motor fails test but the second and both right tests pass. In operation, left and right are fine, but the Z is dead.

Is it my motor? I just got the maslow and have only cut the sled. Z worked then and is now dead.

Thanks for any ideas.

Do you mean that the >test motors/encoder< shows a result like this?

Testing L motor:
Direction 1 - Fail
Direction 2 - Pass
Testing R motor:
Direction 1 - Pass
Direction 2 - Pass
Testing Z motor:
Direction 1 - Fail
Direction 2 - Fail

I couldn’t have screencaptured it better myself!

1 Like

Seems to me like a faulty chip on the motor driver board. The left motor and Z are on the same chip.
Did you have any incident to ‘overload’ the driver? Like the chain getting wrapped around the sprocket?

1 Like

Just to be sure I would download the latest FW/GC 1.12, wipe the eeprom and test again.
You could also swap right motor cabel with Z and then should see this (if Z-motor is ok)

Testing L motor:
Direction 1 - Fail
Direction 2 - Pass
Testing R motor:
Direction 1 - Fail
Direction 2 - Fail
Testing Z motor:
Direction 1 - Pass
Direction 2 - Pass

No, not true I guess. Swapping the cables will show if the Zmotor turns with the right motor test, but the printout will be the same.

1 Like

I’ve only cut one the final sled. So, no from my point of view.

1 Like

Swap the Z-motor cable with the right motor and see if it turns and shows pass for R. This way we exclude the Z-motor as the cause and narrow it down to the shield.

1 Like

I agree with @Gero’s diagnosis that the driver board is the likely culprit. If you send your address to info@maslowcnc.com we will send you a new one to test.

The test I would run to confirm that issue is exactly what @Gero suggests. I would plug each motor one after the other into the Left motor port and see if each one passes the test. If they all move and pass then I would say it’s the board for sure.

The other element is the cables. You may want to do your swaps first on one end of the cables and the on the other so you can make sure it’s not the z cable. Odds are it’s the motor or driver board, though.

2 Likes

I swapped the Right Motor and Z.

Now Right motor : Fail/Fail
Now Z Motor: Pass/Pass

With this i think I have a motor issue. I now notice the the Z motor is loose (i.e, the top smaller cylinder can jiggle but not separate from the lower cylinder). All other cylinders coupled and rigid on the L and R motors.

2 Likes

Wow, that does look like the motor now.

1 Like

I agree, the motor looks like the culprit to me. We don’t get a lot of bad ones of those, but it’s possible.

If you send us your address we’ll send you a new z-axis motor and a new arduino shield just to be safe.

2 Likes

Thanks! I actually ordered a replacement Z axis because I suspected this before I thought about the forums. If you want to expedite it that would be cool though. Keep the order as a donation to your efforts, but having the shield would be great.

It was for Shawn Welsh in GA. All my details are with the order.

1 Like

Does this swap motors test screw up with the calibration? I’m now getting diamonds in the upper left hand corners instead of squares using the GC calibration pattern. upper right is less so and lower left and right are less so, but still not perfectly square.

Ups, this is for testing only, without chains or sled. In production mode you should not swap cables around.

1 Like

I moved them back to the correct motors, but I was wondering if the fact that maslow thought it was moving the left motor and it wasn’t that the position is now slightly off. And I now need to recalibrate given that I’ve turned the Z motor off in GC and will manually do it until the replacement arrives.

Good question. The Maslow does not know that you swapped cables, but with tests failing, I would guess the calibration is off.