SparkFun Forums

[wookieefuzz]

Hey all-
So I've got a project with 8 steppers but I feel like running two quadstepper boards would be overkill. Of the eight, if we number them 1-8, 1 and 2 need to be run simultaneously with individual control, but the final 6 are only ever run one at a time. I was trying to figure out a way to use MOSFETs to cut off power to the motors I didn't want to run and then use the equivalent of just one stepper driver. When I wanted to use one, I could just start sending current to it.
Any ideas on a good way to do this?
Thanks in advance!

[fll-freak]

If you do not power a stepper motor it losses most of its holding torque. It can then be nudged off its current position and you lose the accuracy. If with a situation you can live with? No sense going any further if you need the holding torque.

[wookieefuzz]

Yup, no need for the steppers to hold their positions! They won't have any torque applied to them when they are stopped, anyway.

[fll-freak]

How much current per winding? How many windings?

An analog mux of some sort comes to mind. But one that could handle the current you need.

[wookieefuzz]

I'm using these guys:http://www.pololu.com/product/1204
I haven't quite figured out how much current I'm going to need running through them, but it shouldn't be anywhere near the max for these motors
I didn't really know multiplexers were a thing! Makes perfect sense now. I guess I just need to poke around on digikey for a while
Thanks!

[fll-freak]

I have one of these motors. I am using it to spin a nearly mass less sensor head. (www.fll-freak.com/blog) To keep it from skipping, I need to run it at about 75% max current. If you need torque, you will want the 0.6 amps per winding. And beware, these motors get HOT. Like 150+F hot. Like singe your fingers hot. Like don't enclose them hot. Like add a thermistor to shut them down if they get too hot hot. Did I mention that they get hot?

[wookieefuzz]

right, but do they get hot???

I actually spent a good amount of last night driving 4 of them off the quadstepper board and MAN was that a painful experience. many scalded fingers. I am also a little concerned because I am housing the steppers in some 3d printed parts and I'm worried about them melting! I'm going to run some tests on these guys today and try to get a temperature as a function of time curve and then i'm going to do the same test with a 50mm fan blowing on them to see how much that helps to cool them.
i was able to drive them through an old easydriver board being supplied with 5v and they lacked oomph but didn't get very hot. I might try giving the quadstepper board somewhere between 5 and 12v to see how that changes thing, as well. 5v doesn't run it at all and 12v makes it ridiculously hot.
I love the form factor of these motors and that they have a flat on their shaft for attaching things, but the heat is becoming a little concerning.

[fll-freak]

I am using the Pololu DRV8824 driver with a voltage supply of 12V running at about 0.5 amps per phase. It takes them about 10 minutes to get up to full temperature. I suspect that if you were to use a thermal glue to attach some small heat sinks it might run cooler. In my application they will run about 5 minutes and then be shutdown for a period of time. I too am attaching them to a 3d printed holder. The original design was a full enclosure. The new design provides ventilation and a heat sinks.

[wookieefuzz]

not sure if this image will work but I did a little temperature test and my data matches what you said. haven't tried it with a fan yet.
I was seeing temps around 65C. so right around 150F.
I ran the motor for 2 minutes which is probably about equal to the time I'm going to be doing it in my application. Not a deal breaker by any means, but surprising!
I'll let you know what a difference a fan makes.

[wookieefuzz]

embedding didnt work, heres a link to the image:
http://web.mit.edu/elicohen/Public/polo ... pGraph.tif

[wookieefuzz]

here is a comparison of using a fan on the motor vs no fan, BIG difference.

http://web.mit.edu/elicohen/Public/fanVsNoFan.tif

[fll-freak]

How big a fan are we talking? Little tiny 1" muffing fan, or an 8" PC case fan, or something even bigger?

[wookieefuzz]

50mm 5v fan (https://www.sparkfun.com/products/9648), about an inch away, blowing directly on one flat face of the motor. temperature sensor was adhered to face opposite face being cooled to minimize convection cooling the sensor itself.

[fll-freak]

Using an infrared thermometer, I find that the part of the motor near the shaft gets the hottest and that the face with the wires is the warmest. Not the most accurate survey of temperatures, but it might be of some interest to you.

How is the search for a high power mux going?