Random position shifts

Machines (Original/PRO) Controller (Buildbotics) Discussion
42

Hey John,

From where to where did you measure 69 ohms? And have you grounded your machine’s feet or not?

You could check if you have this issue:

you could check if you have this issue (without the need to disassemble the end caps shown) with the method described here. I should be noted that with the issue @TheyCallMeJohn had the the other day (he already mentioned it above), the short between inner cable and rail only popped up as a motor error on controller display after John had grounded the machine. Without this, the short does not produce a motor error and remains undiscovered, but remains disturbing the machine’s function at random moments.

I would double-check the possible issues described in the already mentioned posting, especially 7) End Nut Adjustment :

and also especially this already mentioned issue:

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43

At the X axis tube end connection I measure 1.9 ohms between the top row 2 pins (coil A), 1.9 ohms between the bottom row 2 pins (coil B) and no connection between the top row pins and bottom row pins. It’s worth noting there is a connector inside the tube about 8 inches from the stepper motor. You will need to disassemble the plastic end cap on the left side of the X rail where you are measuring the resistance to pull the wire out the right side to access the connector.

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44

Hey all,

I would say you don’t need to disassemble the plastic end caps nor to reach the connector inside the rail to find shorts between stepper wires and rails. If there is a short, you’ll measure it from outside. If there is none, the ohmic value measurements you reported of the motor coils is all you should be able to see.

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45

You do not but in this case he’s measuring 69 ohms when 1.9 ohms would be expected on one coil which is an indication of a connection issue not a dead short. My suggestion is to reduce the circuit and test at the connector inside the tube to see if he has similar results which will narrow it down further to the stepper motor itself vs the internal wiring. This also affords him the opportunity to perform the physical inspection of the wiring as you indicated might be a source of the issue.

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46

Hey Derek,

I did not understand where @eJohn measured the 69 ohms.

The method I describe here to check for shorts to rails is what I would do before measuring the coils (given the fact that the motors operate) and this method does not require to disassemble something except unplugging the stepper connectors at the controller.

Of course I would absolutely examine the flimsy connector crap that is used throughout the machine for errors – by sight also which requires disassembling. What I meant is just, what I have learned is, non-invasive diagnostic methods first, then invasive.

But considering the home losses that eJohn describes, I’m more inclined to assume fault in the area of sluggishness of the ball nut due to one of the causes linked above.

Of course, several errors can also occur at the same time for the purpose of general confusion.

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47

I used the lowest setting on my digital multimeter. With both ends disconnected I read each lead from one plug to the other. Three of them had no resistance, or zero Ohms, but the forth lead read 69 Ohm. I have bypassed that whole cable and have dry run, Z axis set 1.00 above zero, for about an hour today without an error or jitter.

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48

Hey John,

if it is one wire, not connected, that has a resistance of 69 Ω that’s not normal. Then I would write to support@onefinitycnc.com for replacement.

As I mentioned you may have had problems with the controller additionally, that can happen at the same time by coincidence.

Hope you get the machine to work reliably!

49

Have you tried verifying how your machine is grounded? This video goes into detail about the subject and how EMI and grounding affect CNC robotics.

50

Are you still getting the error code in the file logs?

51

Since installing the new controller there’s been No additional error recorded in the log.

The problem seems the X cable which connects the controller to the plug at the end of the middle X axis tube. One of the four leeds has a resistance value of 69 Ohms, the other three read zero Ohms.

52

John, my machine is doing the same thing, did you find a solution?

53

Yes, it was an open connection in the X-Axis cable. The cable is the one plugging into the controller box and the X-Axis support tube.

54

Was the connection pulled out, did you have to replace your cables. Has the situation accused since. I saw another person had a similar problem, he ended up cleaning the ball screws, thanks for getting back to me
Tim

55
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56

I’m on chat with one finite now. Now my controller box won’t even come on

57

The cable had 4 conductors and one conductor was open. I made a new cable to replace the defective one and the problem has not reoccurred.

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