Extruder stepper skipping - frustrating!

Hoping someone can give me some hints on this. I have a 1.3a board, stepstick drivers, Kysan steppers and 30A power supply. Using Sprinter firmware and Pronterface.

I have a problem where the extruder is skipping steps... mainly on curves and not consistently at the same position on each layer. It also does it when changing direction (as in when doing a complete fill, it skips at the end of each line). I have adjusted the trim pot on the stepstick from min (where it will just turn the extruder) right up to max in small increments, just to see if there was a sweet spot, but ended up where the best (least skipping) point was right at max. Extruder turns reasonably easily by hand with the hotend heated. I have found that it only takes a little bit of help (keeping some pressure turning the gear on the stepper) to eliminate the skip. I have heatsinks on the stepsticks, but they don't go above 85' F and the stepper is at about the same temperature, so it appears it's not really doing much work.

I have slowed the printing speed down to 5mm/s but it doesn't make any difference. Currently trying with ABS, but had the same problem with PLA and have tried different temperatures.

Can anyone offer any suggestions? I was going to try swapping steppers and then the drivers just to see if it makes a difference, but don't want to go to the trouble if it was obviously something else. Could changing the microstepping make any difference (currently set at 1/8)?

I've spent 2 whole days trying to sort this out, I just want to see a half decent print out of this thing!!

What is the amp rating of your steppers?

They're the ones from Ultimachine.com.....

Specifications:

Model number: 1124090
Holding Torque: 5.5Kg.cm
Rated Voltage: 4.2V
NO.of Phase: 2
Step Angle: 1.8° ± 5%
Resistance Per Phase: 2.8Ω± 10%
Inductance Per Phase: 4.8mH± 20%
Current Per Phase: 1.5A
Shaft: 5mm diameter w/ one flat
Insulation Class: Class B
Dielectric Strength: 100Mohm
Operation Temp Range: -20 ~ +40° C
Lead Wire: 22AWG / 750mm

I swapped the stepstick over last night with the one from the y-axis with no improvement.

I think Stepsticks are limted to 1A. I use 1.5A for my extruder motor ....

You can get more current by substituting a genuine Pololu fitted with a heatsink.

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[www.hydraraptor.blogspot.com]

but since the stepstick was not even getting hot, wouldn't that indicate it wasn't getting anywhere near it's full current capacity? I guess I'll order a Pololu and try it out, just hate having to wait for it to get here.

Just had another thought... would changing the microstep size to 1/4 or 1/2 or even full on the stepstick give the stepper more torque/power/current?? Just guessing here.

No the torque is the same in all the modes.

A Pololu can only handle about 1A without a heatsink. Whoever designed the stepstick decided it was a good idea to limit the current to that value so you can't overheat it, I think.

Odd that it does not get warm though. A Pololu running at 1A gets to about 50C. You can touch it but you wouldn't want to hold it for long. Also, presumably some people can extrude with 1A. Perhaps the motor is faulty.

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[www.hydraraptor.blogspot.com]

Well, I did fiddle with different step settings to see what would happen. Interesting though, the stepstick doesn't have MS3 and is not capable of 1/16 microstep, so I didn't bother putting that jumper back on. For some unknown reason, my axis_steps_per_unit for the extruder is now 386, which is about half of what it was before I started messing with the stepstick.

But....

While messing with it tonight, all of a sudden the heated bed and nozzle were not heating up at all, just cooling down. Looked at the power supply.... no power LED. At this stage I was about ready to throw it through the window!

I tested input voltage.. all good... output... nothing... DAMN!

This was a 30a supply off ebay.. from China I think.

Pulled it apart and found the fan blades had come away from the motor, popped it back on and pulled the main board out. Upon inspection, found about 8 dry solder joints. Soldered them up, reassembled and presto! it works. Fan now functions... and skipping seems to be a little better, I actually printed a small bracket to hold the Sanguinololu to the frame.

But... it is still skipping. This power supply is the one used by Adrian... as listed here...Link to ebay

Oh, and all stepsticks (they do have small heatsinks) run at about 98'F (37'C) so they're not getting anywhere near hot.

Might try and bridge the output terminals on the power supply and see if that makes any difference at all.

Going to order a Pololu soon if no-one has any more ideas....???

You could measure the VREF voltage on the slider of the current adjust pot to find the actual current. Divide VREF by 8 times the value of the sense resistor to get the current. On a stepstick the sense resistors are 0.2R so 1.6V should give 1A. That is also about the maximum VREF with a 10K pot and a 20K resistor. (5V * 10 (10 + 20)) = 1.67V

Check that the sense resistors, are the correct value and VREF is actually 1.6V when the pot is at max. You can increase the max current by reducing the sense resistors. For example soldering a 0.2R on top will give you double the current.

37C is probably about right for 1A with a heatsink though. That implies the motor is duff because looking at the spec it should be enough. Having said that I use 1.5A and ABS will always strip before the motor stalls. Clearly other stepstick owners must get away with 1A. Maybe they all use PLA.

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[www.hydraraptor.blogspot.com]

The stepstick schematic I am looking at does have MS3 and the A4988 does do 1/16 microstepping.

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[www.hydraraptor.blogspot.com]

Interesting... I must admit, all I did was look at the Pololu/Stepstick Wiki page and it shows only eighth stepping and no MS3, but, just checked the ebay page of the guy I got them from and they do have MS3 and sixteenth stepping.

I will attempt your suggestion in your previous post, thanks Nophead

ok, so I now have the printer performing rather well, no sign of skipping and running at well over twice the speed.

I installed Repetier Host and Firmware and I have to say WOW!!

This sw/fw seems to address every aspect of printing and improves on it considerably. After sorting out a couple of little issues with Repetier himself via email (to which he replied almost instantly), My first real successful print was made, and it was close to being perfect. Just a hint to anyone putting the firmware on a Sanguinololu, EXT0_HEAT_MANAGER needs to be currently set to 0 so as to not use PID for heater control. That said, he is now working on a PID simulator to allow better control over temperature. My small issues were mainly caused by being used to making changes in the firmware and recompiling/uploading to the Sanguinololu. Repetier uses EEPROM on the AtMega to allow updating certain settings such as steps per mm and the like, which makes calibrating sooooooooooo much easier as the changes are made instantly without having to recompile.

This guy is a smart cookie, can't wait to see what is going to be implemented next

Thanks for all of the help, I'm going to start pushing this thing until it starts to fail and see if I can replicate the original issue with this fw/sw.

Kalus Wrote:

>
> Thanks for all of the help, I'm going to start
> pushing this thing until it starts to fail and see
> if I can replicate the original issue with this
> fw/sw.

Can I ask if this fix sorted your extruder skipping problems?

Regards,
Dee Cee

I haven't looked back after installing the new firmware. I did push it hard, and found that my hobbed bolt was a little 'uneven' in places, so the feed wasn't at a consistent speed. But all is going well, I haven't had any instances of skipping since.

Cheers,
Kyne