# Powering NEMA 23 stpper intended for robotic arm

I have 3 step motors here from automation direct that I intend to use with an Arduino Uno. They're NEMA 23 and heres the link to the motor's page. Specs are on the top right of the page. (http://www.automationdirect.com/adc/Shopping/Catalog/Motion_Control/Stepper_Systems/Motors_-z-_Cables/STP-MTR-23055) I dont know for sure what power supply to use. I've been looking around alot to try to get an answer but I'm still confused. If someone already covered this topic please link it to me, and sorry for being a nuisance...

Concerning the motors, I couldn't get the recommended power supply and driver (middle of the page, self-same link above). However, the "Motor Torque vs Speed" charts that came with the motor give torque values for only 32-, 48-, and 70- volt power suppliers. Does this mean my steppers wont turn with a supply lower than 32? I ask because I can easily get my hands on a couple of these 6 V "lanturn batteries" (possible even 12 V ones) to connect to the motor: http://www.o-digital.com/uploads/2179/2182-1/Lantern_Battery_6V_4R25_2_320.jpg

Could a battery like this possibly supply enough power? Maybe if I hooked up 4 or 6 of them to get voltages of 24 or 36?

I tried to calculate a good voltage supply using a formula I found here http://www.geckodrive.com/ark-4/faq.html But no luck. I goes Drive Supply Voltage = 32 * vmH Inductance

Example of a motor with 4mH inductance:

32 * v4mH = 64VDC

I dont see how they got 64 V if its simply 32X4. I guess im missing something... Besides, with an inductance of 2.36 mH for my motor, 75.52 V seems a bit high.

So basically, Im asking how i might work my may up to these kinds of voltages (32, 48, 70) using other methods (possibly mutilating a phone charger or something?). I dont have a ready made driver board like what was recommended above (I was just gonna use a solderless breadboard and SN754410ne H-Bridge) and I think the ready-made ones have some "regulators" or something built in, so I dont know what kind of voltages are dangerous for my motors, or arduino, or myself.

If there's a method to figuring this out, could you also please enlighten me so I can spread the knowledge to other possible noobs.

Lastly, if speed vs torque is a factor in any of this, I just want to add that torque is more important to me than speed. I dont even know if these motors can move their own weight. 1.5 pounds is a little much...

Any input is greatly appreciated. Thanks in advance !

If you want to run this motor at its peak torque it's going to consume 2.8A and your lanturn batteries [sic] wouldn't last long. If I were in your shoes I'd just look for a 5 to 12V power supply or perhaps a single car battery and then worry about maximizing the voltage after you've decided that you need to. Premature optimization and evil and all that.

With respect to your H-Bridge selection that's not going to work very well. You need to be able to control the amperage going into the motor or you're going to overheat it. The coil amperage is 2.8A and the resistance is 1.10 ohms so anything over 3V is going to start pushing the heat up. You can use large resistors to limit the current at higher voltages but the more appropriate method is to use a driver that will efficiently limit the current for you. This is why real stepper drives are expensive.

When you're running your motor you should expect it to get hot but not so hot that you can't withstand touching it for a couple seconds.

The docs for your motor shows that the torque is around 125 oz-in at 250 steps/sec. That means you can lift 125 ounces at one inch of distance from the center of the motor's shaft. 125/2 at 2 inches from the center, 125/3 at 3 inches from the center.... basically the math isn't that hard if you work out the design of your arm.

Thanks alot for your help. That cleared up a lot

But just one more issue. How do I figure out the "rated voltage"of my motor (which is model STP-MTR-23055)? The specs table doesn't give it, right? Do I have to figure it out myself? Is it 3V? Is that why you said any applied voltage over 3 will push the heat up?

Merci

Also, concerning current regulation, do you think my SN754410ne H-Bridge can do regulation? (I did to reading around and I'm still not clear, but I think the term is "chopping".)

Again, thanks alot.

The coils on the stepper have a known resistance and a known current limit. It's just Ohm's law to calculate the voltage.

Your H-bridge cannot do current regulation (frequently referred to as "chopping" as you've noted). I'm not aware of any easy-to-use (non-SMD) chips that will. You're probably better off to buy a pre-made driver; pololu.com has a pretty good range of products.