Stepper motors too hot!


#1

In my robot arm I have NEMA14 and NEMA8 stepper motors that are scalding hot. They melt the PLA around them. Video with some details:

nema14 spec

nema8 spec

I’m running both through A4988 drivers on a RUMBA board, max 1.5A.

Please: How do I keep the heat down to stop this problem? I don’t have room to add a fan blowing on the motors.


#2

Turn down the pots on the A4988 boards to reduce the current going to the motors


#3

I tried that. Still crazy hot.


#4

Print in ABS as it is more heat tolerant? Treating symptom not cause…


#5

How did you measure the changes to the Pot? Because you can always go lower. If you went the wrong way though you just went higher.


#6

Also you could try a small heat sink.
Like http://www.dipmicro.com/store/HSINK220D


#7

what is the model # of the NEMA 17’s?


#8

in the original message I gave the specs for both motors. neither is nema17.

Currently trying DM320T drivers, which let me limit the total amp throughput. I will also be adding the DC-DC converter to get 12v down to ~6v, as the motors demand.


#9

Well you didn’t mention the 12V. There’s your problem.


#10

It wasn’t a problem before. For example, I run these

at 12v in the same robot and they don’t get hot, but the rated voltage is 3v.


#11

Running them overspec is obviously going to generate more heat; but as far as why the 23s are within reason vs the 17’s not…

You are likely dumping the same amount of power into a much smaller volume and a lot less surface area to dissipate heat. Is there a good reason you are running them overspeced; do they not produce enough torque?

You said you ran 23’s in the same robot, but the robot seems to be form-fitting do your nema17’s, does that mean they ran outside of the containers and stuck out the sides? If so that would provide more area to cool. Even if not, it still has more surface area to cool. Each side has ~54% of the surface area on the nema 17, assuming the same depth of motor.

If you absolutely need to run these in this configuration and can’t fit aircooling, you might want to consider coolant lines; though I imagine that increases the complexity of your model significantly and increases the BOM.

Really all I can contribute based on your statements is that you have FAR less surface area for similar power drain.


#12

Continuing adventures… somehow I killed one output channel on this sainsmart driver. So I guess at VHS tonight I’ll be decyphering how to run a DM320T, which doesn’t work as easily as I’d hope.

My arm’s motors are now:

I’m looking for a solution to power all of these and the drivers and the RUMBA (5v logic). 7 separate power supplies seems like overengineering…no? What say you?


#13

If you want my honest opinion, seems like under-engineering :wink:

Is there a reason you are running so many different voltages to your motors? is this to-spec or just what you’ve found works given you were over-driving them earlier?


#14

Sorry; just realizing those were links. not sure on all the voltages, is there a reason you chose those motors?

Is that why you were overdriving some earlier to run them all on one set of rails?


#15

Those are the rated voltages on each motor’s page. I can run the nema23 and nema17s at 12v and they barely warm up. The 14 and the 08 are the problem.

I have some LM2596 DC-DC voltage adjusters w/o heatsinks. says it can handle 2a max each. I wonder if I can use one for each of the smaller motors, down to 6v.


#16

I’m amazed at the voltage disparity; yeah; dc to dc seem reasonable. At least for the 14 and 8 there seems to be plenty of headroom.

are your amp ratings all constant amp or peak?


#17

don’t take my word for it, check the data sheets. I hope for peak?


#18

Well realize that the smaller the motors the smaller and more compact the copper coils inside. And they have to distribute the heat to a smaller area. Ergo heat builds up more quickly then can be dissipated.

Also remember how steppers work. The magnetic field moves the motors only one step then it holds it there with magnetic force. Which gets converted to heat. a LOT of heat.

So actually a stepper motor produces less heat the more the motor moves. Not more.

So to reduce the heat build up dissipate the heat better or step down the current being used to hold the motor in position.

You can actually deactivate the motor in code when its not turning, but then you lose the ability to hold the arm in position.


#19

Everything you say is true… my question was “will the LM2596 drivers work to power the steppers?” If they won’t, what would you do in my place?


#20

Sounds like you could try that or run two similar voltages; if the larger motors have no problem being over worked then you can use a voltage near their optimal on one power supply and a voltage near the optimal on the smaller and just slightly under or overdrive one of them. Tie the grounds together and be cool with that. I imagine unless this is in constant use for long periods that a .3v or .6v will be too crazy