Please Help! Stepper Motors losing Steps

Machine - Mendel Prusa with Linear Bearings
Electronics - Sanguinolulu
Firmware pre-installed - Sprinter
Stepper Motors = SY42STH47-1684A
Heated Bed - PCB MK2
Power Supply 30A @13.8 Volts
Software - Pronterface

I have been building my Mendel Prusa for the last few weeks and it has been one long struggle
As soon as I solve one problem, another one rears its ugly head!
I finally got the machine finished and tried to do a test print.
Straight away I could hear the stepper Motors losing steps, it is not just one stepper all of them are losing steps!
I have fitted 8mm Linear bearings all round and all the carriages move very smoothly so it is not a friction problem.
The stepper Motors just don't seem to have any holding torque at all, when I move the Z Axis I can make the stepper Motors lose steps by very lightly touching the 8mm Drive shaft
I wired the Stepper motors up to the Sanguinolulu Wiring Diagram on the Wiki :-

Wiring Diagram

I bought the electronics ready setup for my Stepper Motor configuration.
Any ideas before I get the Big Hammer out! :lol:

Thanks

Andy

Edited 3 time(s). Last edit at 02/01/2012 03:20PM by Normsthename.

Have you adjusted the current on the stepper drivers?

Should be set to about 1A by adjusting the pot until VREF = 0.4V for Pololus and 1.6V for Stepsticks.

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[www.hydraraptor.blogspot.com]

Quote
Have you adjusted the current on the stepper drivers?

The electronics came ready configured to the motors I bought, but I will check.
Any links to where it will show me how to do it?

Thanks

Andy

Turn the trimpot all to the left, then increase in steps of 1/8 turn until the motor doesn't loose steps. Then add another 1/8. Repeat this for every axis.

If you go too far, stepper driver as well as motor gets too hot and you waste energy. Permanent damage is unlikely, though, Pololus/StepSticks have thermal protection.

If you hear/see pauses of about half a second repeatedly, the current might be too high already, as the thermal protection kicks in. If possible, turn current down, if not possible, enhance cooling of the stepper driver chip (bigger heatsink, attach a fan).

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

nophead Wrote:
-------------------------------------------------------
> Have you adjusted the current on the stepper
> drivers?
>
> Should be set to about 1A by adjusting the pot
> until VREF = 0.4V for Pololus and 1.6V for
> Stepsticks.

Is this on a page in the Wiki?

Sounds like useful information to get in there.

I don't think so, there is something about wiring a meter in series with the coils, which is not the way I would do it. Also, as you see above other people have a different opinion of what the current should be set to.

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[www.hydraraptor.blogspot.com]

Success!
I couldn't fathom out how to measure the VREF voltage so used the method described above by Traumflug
I gradually turned the pots up until they paused and then backed them off a 1/8" of a turn.
Tried to print the test calibration 25mm cube and it printed without losing any steps
Not a perfect print but I am very happy with the quality so far without any calibration
I will try and read up how to adjust the Vref so I don't fry the stepper drivers.

Thanks for all your input

Andy

Well I spoke too soon.........
The printer is still losing steps on the Z axis sometimes.
I printed a Whistle tonight at full speed and it worked perfectly, but the next object failed.
I have wound the pot up as high as it will go without pausing but it still loses steps.
I am going to fit a Fan to blow onto the stepper drivers in case heat buildup is an issue.
I think I will also strip the Z axis down tomorrow to double check everything is running smooth
Apart from that I am at a loss......

Andy

Oil the rods with a light oil,

Turn down the starting speed and acceleration in the firmware and use 1/16 step if you're not already.

set the trimpot to 1/8th of the 270º it will turn.