DRIVERS AND STEPS

mendelevium

I have looked around trying to find out how steppers are controlled and would welcome some GOOD advise.  I  mean good, because the internet contains a minefield of very bad advise and information and you must be very careful what to take for correct or not.

Here goes...

I used a stepper SL 42STH40-1204A.  These are, as far as I know, and stand to be corrected, 12V and 1.2Amp rated.

always had drivers fan cooled.

I set up the first 3d printer using Ramps and the Polulu driver A4988 and encountered skipping of steps during print in one axis. 

Then a supplier suggested we go for the DRV8825.

When I assembled the first board with the DRV8825,  only one or two  motors would turn and severely over heat! and I mean overheat!  and start loosing steps indiscriminately.

It seems that the current limiter is open.

so what I did, I clamped the motor and set the current to 0.7 Amp. 

I found out, that the motor will start making abnormal noise over 0.7 Amp, overheat and even skip steps and go berserk.  So found convenient to clamp the motor leads and set the current to this. 

I also discovered that with the DRV8825, I hat to double the steps per mm of each axis and extruder motors.

Ramps Boards are dubious in origin and there are a lot of poor clones with poor performance.  I have now gone for the static boards, the arduino supplied by them, their DRV8825 and even the Trinsmics.  I am waiting for the stuff.

Also had two or three Mega 2500 of chinese origin destroyed at their own accord.

Can somebody give me some more guidance if I am right on track or not?

MartinH

I also discovered that with the DRV8825, I hat to double the steps per mm of each axis and extruder motors

This is correct as the DRV8825 drivers are 1/32 U-stepping with the 3 jumpers fitted, as apposed to the A4988 witch are 1/16th.

Doc_Ara

Hi

Your current setting (via Vref) should be set for approximately 90% of the rated value of your stepper. So in your case 90% of 1.2A = 1.09A

Anecdotally from the internet, the DRV8825 seems to make steppers whine in use but this does depend on the type of steppers used.

You might even be in a situation where there is not enough current to move your mechanism (sticktion, mis-alignment or whatever) and the motor is just sitting there heating up without moving.

The DRV can handle more current. On the TI datasheet is a little ambiguous with their 2.5A figure - maximum, peak current or RMS. I need a driver to handle 2A so I will be using these with a heatsink correctly fitted (not on the chip ) and forced air cooling.

Investigate the missed steps first - the A4988 is a great little chip and should just be able handle a 1.5A stepper (with adequate cooling). Are you trying to move things too fast,  are the pulses too quick for the driver, is your supply voltage to the motors high enough are your rods bent, is your gantry level (not to the bed but to the frame of your printer) etc etc

Go back to basic fault finding voltage current values, vref settings, disconnect everything you can to eliminate problems  - end up with having one driver, one motor no rod if you have to then start adding things back in.

Lastly, if you are using multiple motors with one driver check how they a joined up parallel or series -

Hope this helps

Matt

Mikelangelo

If driver overheats it will disable to cool down and then it will self reset and enable.From what you said that looks like the issue you have.Set current as suggested (90% from max rated value for motors you use) and make one serious fan to work over all drivers to cool them down.All will work just fine.

mendelevium

thanks Mikelangelo noted