Y axis high speed movement problems

Hi All,
I am done constructing my Reprap Mendel Single Color and moved onto calibrating it.
I am having problems with the Y axis motor movement. Whenever it is running at high speeds it judders in one certain direction ( will be working fine in the opposite direction). It works fine after starting up the machine and making the first print but will start juddering or pausing for the second/ third print. Most of the time it will judder and stop and obviously the print comes out complete wrong.

i turned the trimpots to feed the Y mortor about 0.79v but everything else is at 0.4v

Please let me know how i could possibly solve this.

Hi

The Y axis is the heaviest axis, and limits the speed of the printer. There will be a speed that is TOO fast. However, if it's happening at lower speeds, it might be that the axis is sticking, perhaps because the Y axis smooth rods are not parallel. As the motor speed increases, the torque (ie power) it can produce reduces, so it might work fine at low speed, but not at high speed. What speed are you finding that it judders? Is it on travel movements? You can turn the speed down in the slicing software. Is it the belt jumping rather than the motor stalling? Try tightening the belt a little. Check that all the stepper motor wires have a good connection with the screw terminals in the Melzi, and the wires aren't damaged - a poor connection may limit the current getting to the motor, and possibly damage the stepper driver.

0.8V is the correct setting for your stepper driver trimpots. This gives 1 amp current to the motor, which is sufficient; more and the motor starts getting hot.

Test the movement of the Y axis by hand. Does it move easily, or does it stick? Then test at what speed it stops, by homing the X and Y axis, and entering this in the Pronterface console:
G1 X100 Y100 F1000
then
G1 X100 Y100 F1000
so the both axis return to the start position.

Run the same code again, increasing the 'F' value by perhaps 5000 each time, up to 30000. This is mm per minute, so 1000mm/m = 16mm/s, ie pretty slow! 30000mm/m = 500mm/s, ie very fast! Speed is actually limited to 500mm/s in firmware. Record at what speed it stops moving smoothly.

If you suspect the Y stepper driver is faulty, you can test it by swapping the X axis motor wires for the Y axis motor wires WITH THE POWER OFF. It is easy to destroy stepper drivers if you disconnect them with the power on. If you're interested why, see the second section here: [reprappro.com]

Then try the movements above again. Be aware the endstops won't work on the right axis, so don't home. Move each axis to the home position before turning it on, and test the axes again with the above code.

If the problem moves to the X axis, it's possible that it's a stepper driver problem. If it stays on the Y axis, it's a frame alignment issue.

Report back if that narrows the problem down.

Ian
RepRapPro tech support

Hi Ian,
Thank you for the solution. i checked and tried to answer all your questions myself and i think i got it to work a little better now.

1) The motor is working fine. It wasnt specifically a problem with the motor it self.

2) Current is currently set at 0.8v. I got confused as to how much to set it at cause one of the archived pdf instructed a voltage of 0.4 while the updated wikisite instructed at 0.8v.

3) The rods were parallel but i checked and tried perfecting it a little bit more and now i think theres a little less resistance against the motors movements.

4) The main problem was the belt being a little slack. The judder was mainly on travel movements. The belt skips from the motor toothed pulley at high speeds. Intially the judder occured at 2000mm/m and now it starts juddering around 6000mm/m. Which is still low. The default travel speed was set to 250mm/s i set it to 80mm/s. Which is the best it can do right now. Do you have any other pointers? I bought a few seperate NEMA 17 which i am waiting on after which i can try out a different motor and see if the current one has any power issues. Please let me know if you have any other pointers to help increase this travelling speed with out skips or judders.

5) I am having a problem with setting the limits of the nozzle with respect to where it is situated on the Y glass. The nozzle / X axis is moving over the clips holding the glass with the PCB plate heater and Aluminium plate. I am calibrating the machine right now and i havent read any instruction which helps with adjusting offsets or motor limits which actually work.

Thanks,

Anil

In order to keep the nozzle from bumping into the binder clips, you'll have to adjust your endstop switches and limit the print area in your firmware. Marlin was set to 200mm x 200mm by default, but I reduced it a bit to keep the nozzle in the safe zone. I wish there was a more elegant approach than limiting my print area but oh well.

From [reprappro.com]

Quote

You can slide the Y motor back and forth to adjust the tension, lock it in place by tightening the Y motor cap screws. Adjust the tension such that the belt is tight, but not so tight that the axis begins to bind.

So, you probably need to tighten the belt. If you have used all the adjustment, set the motor at the point closest to the frame, then move a little more belt into the clamp under the heated bed.

@sheck626

I dont use clips on my bed, i use a 200x200mm 0.5mm silcon thermal pad (http://www.ebay.co.uk/itm/180930976479)
sticks the glass down nicly when hot, but comes of easily when cold. Also helps the bed heat quicker as it transfers heat better and i get the full print area available to me. Been doing this for a few months now with the same pad, works great.

Quote
Run the same code again, increasing the 'F' value by perhaps 5000 each time, up to 30000. This is mm per minute, so 1000mm/m = 16mm/s, ie pretty slow! 30000mm/m = 500mm/s, ie very fast! Speed is actually limited to 500mm/s in firmware. Record at what speed it stops moving smoothly

.

DOH! That's why I can't get my system to go faster than 30,000mm/m.

Where do I find that limit in Sprinter?

My Y-Axis is 'just barely' stutters sometimes at 30,000. But I'm only 25% on the pot, and my heatsinks are still <30degC.

Edited 3 time(s). Last edit at 04/30/2013 03:59PM by ShadowRam.

I dont know about sprinter but I am using skeinforge and its labelled as travel feed rate under the speed option.