Metal Plus Stepper Motor Overheating

[HackNFly]

I have one of the first Metal Pluses, had nothing but issues with it over the heated bed and more or less gave up on it. After more than a year hiatus I started working with it again and upgraded the heated bed to use an A/C powered keenovo heated bed. Can get up to temp in 1 minute.

Things were working mostly ok until I tried upgrading the firmware to get more than a 3 point calibration and I think that is where the problems started, I lost my old M909 settings and the Y-axis motor started skipping. Managed to narrow down that it was in fact overheating. Thought it was heated bed related, so I tried with that turned off, but the Y motor still overheats, tried swapping the X & Y and the Y-stepper and it still overheats. I finally was able to print a 0.5 in single wall test print when I lowered the Y-stepper motor down to 30% current. I also tried lubricating the slide yesterday, and loosening the Y-stepper belt. I tried printing 6 cubes and it failed, almost all steppers were hot in this case. I'm going to try lowering all the motors to 30% and trying again tonight.

Should I have to turn down the current that low to keep it from overheating? I also put back the original firmware just to rule that out of the equation.

[RetireeJay]

There are dozens of variants of stepper motors, some requiring higher current (at lower voltage) and some requiring lower current (at higher voltage). If you are sending high current into a low current / high voltage stepper, it's going to overheat.

So don't worry about it. Turn the current down until the motor runs warm or somewhat hot to the touch, but not so hot that you can't hold your finger on the motor for several seconds. The only tradeoff is if you go too low, the motor might start skipping due to insufficient torque.

The way steppers work, there is only a minor contribution to their heating due to friction or load that the motor is driving; almost the same amount of heat will be generated even when the motor is stationary - as long as it's powered up. (You can tell when the motor on a given axis is powered up because it's very difficult to move that axis by hand.)

[HackNFly]

Thank you for your response, they are the standard stepper motors that came with the pre-assembled Printrbot Metal Plus Dual Extrusion printer. I believe a Kysan motor. I'll just keep tuning the current down until I notice any skipping and turn it back up a bit.

[Mooselake]

What do you mean by overheating, and how did you determine that was the problem? Stepper motors are designed to run at fairly high temperatures. The general rule of thumb (finger?) is that you should be able to hold your finger on the motor for at least 5 seconds, assuming you have normal sensation.

Those are likely Kysan 1124090 steppers. From the datasheet they're class B insulation motors, rated at 130C. or 266F. While the case wouldn't be as hot as the motor windings at it's limit, that's still pretty toasty. You could fry an egg on them and still be within specifications.

As a practical matter you wouldn't run them that hot, from the potential burn hazard alone, but as you can see they can operate properly while very hot. The 5 sec rule will keep them in a reasonable temperature range, but if they're already there look elsewhere for your problem. Remember that by reducing the current you're also reducing the motor's power and your printer's speed and acceleration.

If the motors were actually overheating, the Rev F printrboards set the motor current in the firmware, and reflashing the firmware may have changed the firmware settings - that's one reason you want to save a copy of your settings (like in your printer notebook) after any changes. Did you know what it was before you reflashed?

And for completeness, 3 point probing is enough to determine a plane and is all you need if your print surface is flat (there's some argument that you will cancel out probing errors with more points, but they're fairly weak, since at best it'll be less than a step size's extra precision - and those step sizes aren't really all that accurate (think as much as 20% error)), and no amount of probing will compensate for a warped bed (unless you're using a (iirc) a Prusa Duet board and firmware). The Printrboard firmware only compensates for a flat surface, no warping. All that extra probing might look cool, but it really doesn't do anything useful. Better to spend that time making sure the head to bed distance is the same across the print surface with some measuring (the copier paper trick, or a dial gauge if you're more serious). It's commonly, incorrectly, called bed leveling. Autoleveling does better the closer you get to real non-auto "leveled". RJ's and my plywood bed pluses are within a few hundredths of a mm without probing required - as they (or at least the occasional moose) say probing is best left to aliens.

Kirk

[musk]

At a minimum you should revert to an official PB release of the firmware. Unless you're compiling it yourself (and know what you're doing), you're just asking for problems using non-official firmware. Make life easy on yourself and use something that's proven to work. The stock firmware and motors have never had overheating problems on the ~20 different Printrbot's I've used.

[HackNFly]

Hmm, I thought I set the appropriate board settings to e-mail me if a response had been made.

Mooselake,
I agree with pretty much everything you've mentioned, and ended up coming up with the same conclusion. The motors were hot too the touch, particularly the y-axis stepper, couldn't keep my finger on there for more than a few seconds and the motor was making a stuttering sound.
Here is a sample video
https://youtu.be/DdkpApg9r8o

I knew there was something wrong because I could easily move the y-axis if I pulled it, it was as if it was applying torque and suddenly stopped and started again. I was also highly skeptical of the temperature thing as I expect the original motors to work without overheating at the default firmware settings of 70%, but I've seen that on the forums a lot, I'd like to get it under control as I don't want to lose speed, but considering I've never had a reliable printer at this point, I just want to get it to work first.

I turned the current on all motors down to 30 last night and was able to get through the array of 6 single wall test prints fine, however trying to print one of my wooden jig design failed in the final stages. I'm going to try and up the current back to the default of 70 for all motors except the Y and try again.

At a minimum you should revert to an official PB release of the firmware. Unless you're compiling it yourself (and know what you're doing), you're just asking for problems using non-official firmware. Make life easy on yourself and use something that's proven to work. The stock firmware and motors have never had overheating problems on the ~20 different Printrbot's I've used.

This is a very logical step and exactly what I tried, forgot to mention it in my initial post. I'm a programmer by trade so I was compiling it from source, but I've reverted to the latest official firmware as I only want to be working on one set of problems at a time. I'm convinced my heated bed is a little warped, however after setting my initial layer to 0.3 mm I've had no problems with adhesion and came to the conclusion that the probing might actually be throwing me off, so I'm no longer using the probing when printing. I've managed to manually level the bed close enough to work.

I'll follow up if I get my printer working again.

[HackNFly]

Thanks for your advice. Dropping only the Y-stepper to 30% and the rest at 70% and I'm back to normal as far as printing is concerned. Partially annoyed that it overheats at the default firmware settings, but I'm happy to seemingly have a working printer now.

[Mooselake]

When you said earlier that you swapped connections and the Y stepper still overheats did you mean the same motor in both cases?

If so, it sounds like you many have a defective motor, a shorted internal winding or something similar. It might be time to order a new one (the last time I checked Kysan had a minimum $200 order) and just swap the overheating motor. Cheaper than the hassle of compensating for it, and bad motors rarely get better. FWIW, Printrbot originally shipped a different motor, and I swapped mine for Kysans some years ago. One of the replacements was defective (it had a seized bearing) and had to be exchanged.

Kirk

[HackNFly]

I swear I made this post a few days ago. Must have closed out the window early or something.

Anyways, as far as swapping the motors, no it was a full swap. It took me a few hours to do. That's why I'm pretty confident its not the motor itself as the x-axis motor in the y-axis condition showed the same issues of overheating and the y-axis in the x-axis position then ran cool.

At the moment things are working. I'm building some shelving in the garage right now to give the printer a permanent home. I was planning on creating a build chamber for it, I hope the y-stepper doesn't start overheating again. We'll see. Thanks for the help.