Debate About Stepper Motor Temp

I'm hoping to gain more knowledge, share some knowledge, and maybe provide a useful post for people to reference in the future.

I see a lot of people talking about how to cool their motors and questions about is it OK to let them get so many degrees warm. I have NEMA 17 steppers on my Prusa I2 that are 68 oz in. They are being driven by A4988 pololus. Once I learned how to set v-ref and added a second PC power supply to my printer, my axis have never missed a step. The 2nd supply was necessary because either the first cheap one wasn't delivering all the amperage it said it could or my printer was pulling more power than spec, so I now have a 2nd supply running my heat bed.

All of that said, my motors have NEVER got hot. Both of my Z motors always feel room temp metal cold. E is only slightly above Z in temp. You have to leave your finger on there for ten seconds to even notice the difference. My X and Y are just slightly above room temp. They feel like a coin you have been holding entirely enclosed in your hand for about thirty seconds. Try it, you'll see what I mean.

From reading and discussing with others there are only three reasons that I have come up with why steppers should get hot.

A. The driver (i.e. pololu) is turned up too high providing the motor with too much current.
B. The motor is too small for the application.
C. The axis the motor is attached to is providing too much resistance.

A is probably the only real reason, but people compensate for B and C by turning up the current (A).

I have read some research and white papers about micro stepping, from what I understand it is accomplished by fine control of current in the coils of the stepper motor. It applies more current to winding A than to winding B, so the shaft moves forward (toward winding . Then it brings up the current on B while lowering the current on A until they are equal. At this point the shaft holds still. Ideally this was a uniform distance to the last micro step and is fraction of the distance a full step takes. Based on this fluctuation of even a milliamp in your system could cause inaccurate step.

Can anyone add or subtract from my list? Provide commentary or other on my understanding of micro stepping?

I'm just getting started but even while I was testing the axes the X and Y motors got almost too hot to touch. I don't like how much resistance there is but that is a design flaw in my printer, if I losing the carriages for the bearings any more the nuts will fall off. I'm hoping to print better pieces as soon as I'm printing. I guess the first thing I will try is to turn the potentiometer down a little and see if that helps. Thanks for the info.

The biggest misguidance for me was the instructions from the RepRap Wiki Calibration page. It does a good job touching this subject (tuning the motor current) very first and stresses the importance of it, but to my personal disliking, it says to turn the trimpot 1/8 of a turn.

I believe 1/8 of a turn is actually quite small.. small enough for us to be able to know the difference within 50% margin of error... However, I still think that's way too much. I was able to tune my Pololus properly to keep all my motor running cool only after someone else told me even a very small turn can make quite a bit of difference - the amount of turn so small that, it actually looks as if didn't turn at all, and you just applied some force to the direction of the turn, without really feeling any kind of turning or movement..

So, compared to that, 1/8 of a turn definitely can be way too much. Following the instruction from the Calibration page - keep turning the trimpot 1/8 of a full turn until the motor starts moving, and then turn one more 1/8 step - in the beginning all my motors were running a lot warmer than they are right now. I even considered installing a fan on each motor.

As of now the extruder motor is the hottest one, but it runs under 45 C, most of time at around 40 C. Maybe I can fine tune it a little more and make it run even cooler, which will be great because then I would be able to replace my current extruder motor mount with one with the improved design, which I printed with PLA.

Yamster Wrote:
-------------------------------------------------------
>
> I believe 1/8 of a turn is actually quite small..
> small enough for us to be able to know the
> difference within 50% margin of error... However,
> I still think that's way too much. I was able to
> tune my Pololus properly to keep all my motor
> running cool only after someone else told me even
> a very small turn can make quite a bit of
> difference - the amount of turn so small that, it
> actually looks as if didn't turn at all, and you
> just applied some force to the direction of the
> turn, without really feeling any kind of turning
> or movement..

I remember writing a reply that matches that description. I also remember your name, which I'm not that good at without repetition. I think I have replied to a few of your posts and you have been in discussion on some others posts I have replied to.

So I basically told you what I have learned from you. LOL Sorry about that, but I hope it shows how much I appreciated the tips and knowledgeI have picked up from you, as well as others.

Yeah.. I'm pretty bad with remembering name and faces to begin with, so it's almost impossible for me to remember someone's online ID, which is often cryptic and/or meaningless (at least to me).

But anyway, that tip - turning the trimpot in much smaller increment than 1/8 of a full turn - really was big for me, and that's the reason I don't have 4 additional fans attached to my printer and making noise. So, once again, thank you for the tip!

appdev007 Wrote:
-------------------------------------------------------
> Yamster Wrote:
> --------------------------------------------------
> -----
> >
> > I believe 1/8 of a turn is actually quite
> small..
> > small enough for us to be able to know the
> > difference within 50% margin of error...
> However,
> > I still think that's way too much. I was able
> to
> > tune my Pololus properly to keep all my motor
> > running cool only after someone else told me
> even
> > a very small turn can make quite a bit of
> > difference - the amount of turn so small that,
> it
> > actually looks as if didn't turn at all, and
> you
> > just applied some force to the direction of the
> > turn, without really feeling any kind of
> turning
> > or movement..
>
> I remember writing a reply that matches that
> description. I also remember your name, which I'm
> not that good at without repetition. I think I
> have replied to a few of your posts and you have
> been in discussion on some others posts I have
> replied to.

Please don't let me discourage you from reposting advice. I've done a lot of it myself. That particular piece wasn't given to me, but learned the hard way. Share it.

I have just finally, in the last month, gotten to where I had unique experience to share with people. It all came by doing just what you are doing. Keep it up.

The only reason I bothered to point out it might have been me that gave you that advice was a selfish one. I had to figure that one out on my own and was wondering if I had posted unique advice and had actually genuinely helped someone. : )


Yamster Wrote:
-------------------------------------------------------
> So I basically told you what I have learned from
> you. LOL Sorry about that, but I hope it shows
> how much I appreciated the tips and knowledgeI
> have picked up from you, as well as others.

this is not rocket science

If your trying to push to much current through a small motor due to the load, this is when cooling is needed
if your just overloading the motor with to much current then it needs to be reduced

im personally to lazy to adjust mine and i just leave mine running hot, I used them like this for month and months 10 + hours a day, opened one of them up and none of the windings are even close to burning out, no darkness at all, so im pretty sure they can take a fair bit.

nechaus,

i'ts not the windings you should worry about. The magnets can take much less heat before they lose magnetism then the windings need to show any sings of heat.
But as you said, as long as it works it's fine...

Best regards

--- Lars ---

tanis Wrote:
-------------------------------------------------------
> nechaus,
>
> i'ts not the windings you should worry about. The
> magnets can take much less heat before they lose
> magnetism then the windings need to show any sings
> of heat.
> But as you said, as long as it works it's fine...
>
>
> Best regards
>
> --- Lars ---



of course, that slipped my mind completely , they should be good upto 100c for prolonged usage,
haha well if mine one day melt away from my printer, ill know i should of had a fan on it haha

That much heat has to cause something to break down at some point. Compensating for axis issues is only a temporary fix while you print new parts to fix that issue. If you plain out drawing more current than what is needed, they you could potentially be over loading your PSU and under voltage/current can result in plenty of other issues. This is especially true with reading minute voltages from thermistors and using micro stepping drivers that rely on fine current control to accomplish partial steps.

I have just recently learned that people are getting a hold of half amp motors instead of one amp plus motors. I have a confirmation from one such person that cutting v-ref in at least half makes these motors stop running hot and their initial print did not skip. If a motor was designed to get max torque at a particular amperage and that amount of torque is sufficient for your application, then there isn't any sense running them hotter.