1 Topic by rrssll

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Topic: Adjusting trimpots for motors in thermal protection mode?

I had a few successes on my Press but yesterday I was 0/3 on prints. As I get in to larger prints I'm finding that after a couple hours I hear thumping noises. I thought this was only the extruder motor but touching the z-axis I find now that it sometimes makes the exact same noise (at different times). Both the extruder and z-axis stepper motors were very hot to the touch. The lid is propped up by the door during all my prints.

More research lead me to posts [like this one about overheating motors](http://forums.reprap.org/read.php?1,140463). So now I'm going to try adjusting the trimpots per [solidoodle instructions](http://support.solidoodle.com/hc/en-us/ … Adjustment). Unfortunately that article lacks some important details. It says what the voltages should be for each axis but doesn't say where to measure them. There are articles for other solidoodle printers that show measurements between a pin on the driver chip and some other resistor, so it's not clear that this is just a measurement across the pot. The Press article also says to completely shut down the printer between every adjustment which sounds absurd (the article for their other printer says to keep it powered up).

Has anyone done this with a meter?

2 Reply by grob (edited by grob 2015-02-16 00:14:32)

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Re: Adjusting trimpots for motors in thermal protection mode?

The voltage to adjust is a reference voltage that sets the maximum current for the stepper driver chip. It's often referred to here just as "VREF" which is a bit ambiguous hehe.

You can usually measure this by measuring voltage between the signal ground (power supply negative, any pin marked "GND", etc.) and the metal body of the trimpot.

adrian made a handy table, which tells you what to use for which board, here: http://www.soliforum.com/topic/2817/ste … ref-chart/.

Adjusting the voltage to the prescribed value is a good first step to make sure nothing's out of whack and you're in the ballpark. Sounds like you might be running a little high (based on the overheating motors / drivers!), but note that the motors are actually designed to get pretty hot (60C is ok - this will feel scalding to the touch!).

If after adjustment you have further trouble, there may be a few things you can do, so let us know how you go!

SD3. Mk2b + glass, heated enclosure, GT2 belts, direct drive y shaft, linear bearings, bowden-feed E3D v5 w/ 0.9° stepper
Smoothieboard via Octoprint on RPi

3 Reply by android78

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Re: Adjusting trimpots for motors in thermal protection mode?

I adjusted mine as per the reference (1V for all except extruderm 1.5 for extruder) and am getting much nicer prints.  Prior to adjustment, mine were all over the place.
I just put the multimeter on the pads of the potentiometers themselves.  There is one side that has two pins and the other that has one.  Put the multimeter on the one on the single side and the pin that is closest to where the connectors go.  At least, that seemed to work for me.
Also find the motors getting pretty warm, but mainly the extruder motor, since it is attached directly to the heatsink for the hotend. 

Just wondering what others have found to be the best voltage settings for the stepper drivers?  Is it worth playing with them, or close enough to ideal to leave them at the solidoodle recommended voltages?

4 Reply by android78

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Re: Adjusting trimpots for motors in thermal protection mode?

One other thing to watch out for, is that the issue may be a loose connection in the wires going to the extruder motor.  It may be that the shielding is holding the wire touching until it gets hot and then giving way.
I assume that you have checked the grub screw on the extruder wheel is tight too?  When I first got my printer, the first couple of prints were ok, but then noticed the issue with extruder wheel grub screw is loose.  I think the majority of printers are being shipped with loose extruder wheels, looking on the forum here.

5 Reply by sigilo

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Re: Adjusting trimpots for motors in thermal protection mode?

Hi all, i'm trying to do the adjustment here too, but there's something i don't get, on the extruder trimpot, the maximum voltage i get is 1.123, that is when the adjustment is turned clockwise to the limit. How did you got the 1.5v?

For clarification, i have my multimeter on the 2v setting, the printer is plugged to the power and i'm measuring the pots from the single pin to the one on the right (if you look at it from the top so that the single pin is looking up and the two pins are looking down), as you suggested.

6 Reply by android78

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Re: Adjusting trimpots for motors in thermal protection mode?

What voltage do you see across the two pins on the same side?

7 Reply by sigilo (edited by sigilo 2015-02-17 23:35:36)

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Re: Adjusting trimpots for motors in thermal protection mode?

When i measure accross the two ends that are together on one side i get 1.123v as well which as i understand its the maximum, in addition, apparently i'm not the only one on this forum with the same issue, i've seen the same question popping out in similar threads.

http://www.soliforum.com/topic/9347/sol … to-fix-it/

8 Reply by trayracing

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Re: Adjusting trimpots for motors in thermal protection mode?

Check for a weak connection in the wires to the motors.  If you find one and fix it, be sure to turn down the stepper timmer before powering up.

9 Reply by sigilo

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Re: Adjusting trimpots for motors in thermal protection mode?

I have done that, all the connections seem to be just right, but i fail to see how is that related to the trimpot maximum voltage.

10 Reply by trayracing

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Re: Adjusting trimpots for motors in thermal protection mode?

sigilo wrote:

I have done that, all the connecti
ons seem to be just right, but i fail to see how is that related to the trimpot maximum voltage.

Ah right, they're having you measure ref, not sense. I don't know what SD is doing, but a common stepper setup is shown at the bottom of this page: https://www.pololu.com/product/1182. You can see a resistor and trim pot in series between Vdd and ground, with the values chosen for a useful vref range.
If the max voltage is out of whack, maybe the wrong value parts might be on your board? (especially if others have the same complaint). Talk to SD.

11 Reply by rrssll

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Re: Adjusting trimpots for motors in thermal protection mode?

Thanks for the suggestions.

@grob - seems to me the body of the trimpot should be at ground potential (and was when I checked). Otherwise you've got a big electrified component on the board that's easy to touch. Thanks for the tip about motor temperatures, that makes complete sense and I hadn't realized it.

@android78 - the directions on which pads to measure helped. I notice one of the pads has a dot next to it, marking pin 1 probably. I've tightened the grub screw - that came loose previously. I'd already also tested the motor cable and thought that was good, but I was apparently mistaken.

So here's an update on my attempt…

I measured all the pots twice then adjusted the extruder voltage 1/8 of a turn at a time until I got to 1.5V dead on. I powered up the Press and tried to run the extruder. Had to heat up the hot end before it would try (even though I had no filament in). Still got the same noise. So I shut down and tested the extruder motor cable again (I'd checked it about a week before). This time I had no continuity on one pin. I didn't believe it so I swapped the Z axis cable with the extruder cable (both ends - the motors & voltages are different) and sure enough the motor ran just fine.

Even though the break is most likely right at the motor end, I pulled the cable out so I could inspect it. This meant taking four screws off the left side panel. I recommend tying a string to the cable when you pull it out so you can use it to pull the new cable back up through the hole in the bottom of the chassis.

Anyhow, the break was right at the end. I failed at reusing the crimp connector. So I ordered this connector and these pins off digikey. Note they're by "JST" and the one in the Press is from a suspiciously similar "JSY". I couldn't find the connector for the motherboard end or the cable itself. Really I'd like to get a cable that can stand some heat and flexing so I don't have to replace it again in a month.

Parts should show up tomorrow. If I'm lucky I'll be printing again this weekend.

(Attached a closeup of the motherboard with the trimpots in their original positions for any future readers.)

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12 Reply by hotony (edited by hotony 2015-02-22 08:38:00)

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Re: Adjusting trimpots for motors in thermal protection mode?

@sigilo did you solve your trimpot voltage issue? i'm getting same results cant get it higher than 1.12v with the extruder?

13 Reply by rrssll

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Re: Adjusting trimpots for motors in thermal protection mode?

So the connector and pins I ordered worked on the cable. I had to find a crimp tool I could use though. Wish I had a soundtrack like this when I work http://youtu.be/Vptd2n5p5-I . After putting it all back together I've done a few small prints and no extrusion problems or thumping so far.

hotony wrote:

@sigilo did you solve your trimpot voltage issue? i'm getting same results cant get it higher than 1.12v with the extruder?

I was only able to adjust up to 1.5V on the extruder after turning on power to the Press. The article from Solidoodle implies that you can do the adjustments with it turned off but that seems unrealistic. The highest voltage you measure across any two pins of the pot is the maximum you can get by turning it up. A potentiometer divides the input voltage.

14 Reply by mrsnowie

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Re: Adjusting trimpots for motors in thermal protection mode?

sigilo wrote:

When i measure accross the two ends that are together on one side i get 1.123v as well which as i understand its the maximum, in addition, apparently i'm not the only one on this forum with the same issue, i've seen the same question popping out in similar threads.

http://www.soliforum.com/topic/9347/sol … to-fix-it/


You need to power on the printer aswell, the standby current is not high enough!