Fried Zaxis stepper motor driver
Posted by RobertEdwards
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Fried Zaxis stepper motor driver October 02, 2014 08:07AM |
Registered: 9 years ago Posts: 9 |
I have posted elsewhere about problems with the Z axis not torque locking. I have found that the Pololu 4998 driver chip has failed. The strange thing is that the Z axis can be driven up and down, and apparently behaves normally. BUT, the motors do not torque lock meaning that they can easily be turned by hand when powered up. Unlike the other axes which are rock solid under power.
I have proven it by swapping Z into Y terminals to see if Z behaves. It does with good strong torque lock.
I found the problem after noticing that the Z axis would not hold its reference position. I could also hear that the motors were not running properly. The carriage weight and friction are enought to overcome the motor torque.
So, what do I do? I would like to be able to graft in a new Pololu board to bypass the on board driver. The trouble is I have no idea how to do this, interms of the main controller board PCB connections and what goes where.
Link to the driver [www.ebay.co.uk]
Does anyone have knowledge of this?
I have proven it by swapping Z into Y terminals to see if Z behaves. It does with good strong torque lock.
I found the problem after noticing that the Z axis would not hold its reference position. I could also hear that the motors were not running properly. The carriage weight and friction are enought to overcome the motor torque.
So, what do I do? I would like to be able to graft in a new Pololu board to bypass the on board driver. The trouble is I have no idea how to do this, interms of the main controller board PCB connections and what goes where.
Link to the driver [www.ebay.co.uk]
Does anyone have knowledge of this?
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Re: Fried Zaxis stepper motor driver October 04, 2014 04:23PM |
Admin Registered: 17 years ago Posts: 7,879 |
I don't think a chip can fail in that way, however the firmware can be configured to do that and often is on z to allow extra current for the second motor without overheating the driver.
The connection can be found in the schematic in the RepRap wiki. An easier hack would be to connect a pololu to the expansion port and change the pins in the firmware, although I think you will find it is behaving as intended by the firmware configuration.
Edited 1 time(s). Last edit at 10/04/2014 04:27PM by nophead.
[www.hydraraptor.blogspot.com]
The connection can be found in the schematic in the RepRap wiki. An easier hack would be to connect a pololu to the expansion port and change the pins in the firmware, although I think you will find it is behaving as intended by the firmware configuration.
Edited 1 time(s). Last edit at 10/04/2014 04:27PM by nophead.
[www.hydraraptor.blogspot.com]
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Re: Fried Zaxis stepper motor driver October 07, 2014 09:50PM |
Registered: 9 years ago Posts: 9 |
Perhaps you are correct nophead in that the chip can't fail in this way, and that the firmware actually controls this behaviour. If that is the case then it is inadequate because of the extremely low torque. I will try to interpret the firmware for this board to see how the control works, and wheter it can be tweaked to correct it.
Coding is not my thing at all, but I'll have a go at it and report on it if I find anything useful.
Thank you for the suggestion.
Coding is not my thing at all, but I'll have a go at it and report on it if I find anything useful.
Thank you for the suggestion.
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