Stepper motors -> how to power them properly?

Greetings,


My son just finished is first robotic arm prototype with servos and a joystick using an arduino.
See the video here.


After buying really really cheap stepper motors that are too weak, I got my son a couple of better stepper motors that are to be controlled via the same arduino. I'm told they should be independently powered. I have also sourced a bench power supply to test these stepper motors. Now, we need to learn how to power them.

Later on, how do you get power to these steppers from a wall outlet?

Most likely someone here faced this kind of issue before and because it involves electricity I thought it more prudent to ask people first. Anyone can spend some time providing some guidance, something to read on maybe, that would be greatly appreciated.

Thank you kindly for you time,

Antoine & Alex in Vancouver, BC

Note:

My son (11) and I have watched quite a number of youtube videos to find the answer, including reading lots of posts. I even bought a couple of Udemy course he's started on. Please understand, though this likely will look like an easy question, its not an easy question for beginners like us. I'm learning as well in order to help him out and spend time with him. And since it involves electricity and the potential to destroy electronics which are costly (for me at least) I hope that this forum is civilized and that those that don't have anything good to say won't.

Your son is fortunate to have a good nurturing dad who gets involved with him and his projects.

This is sort of stepper 101 but stepper motors come in a few flavors like unipolar and bipolar and each type can be driven in a different way. Since the Arduino is limited in output capability when you get to a heavier more powerful motor we need a way to interface the Arduino to the stepper motor. This is what you have apparently run into. What needs known is type stepper as in unipolar or bipolar and the motor voltage and current requirements? A few popular interfaces for most hobby applications are the U2004 Darlington Array (if using a unipolar stepper) and the SN754410ne H-Bridge (if using a bipolar stepper). Those are merely examples.

Something nice is that these parts can often be found on "break out" boards which removes the necessity of mounting and soldering circuits together. Here is one such example from Spark Fun Electronics of a pre fabricated ready to use board.

This will go much better if you guys have a data sheet or any data on the stepper motor you have. That way members can provide more focused information rather than generic as I have done.

Ron

Stepper motors will not rotate when connected to fixed supply voltage.

A common type of stepper motors have 4 coils, and one wire for each coil, and one wire that is common to all coils. To make the rotate, the coils are energised in this order:-
1
1 & 2
2
2 & 3
3
3 & 4
4
4 & 1
1

etc

Energising them in the opposite order will make the motor rotate the other way.

Processors like Arduinos can control the stepping order, but an Arduino won't supply much power, so driver ICs are often used, as described by Reloadron.

I have some NEMA17 steppers and use these boards to drive them. Very convenient and very easy to use.

Mike.

Pommie said:

I have some NEMA17 steppers and use these boards to drive them. Very convenient and very easy to use.

Mike.

Click to expand...

There are also DRV8825 boards with the same pinout, which supply a little more current, if you are getting close to the limit of the A4988.

The NEMA17s normally require less than 1A (0.4 in the link above) so the 4998 should be fine. How much more current can they handle? A quick google suggests they can both handle around 2A.

Mike.

IIRC, the A4988 can handle up to 1A without/2A with a heatsink, and the DRV8825 can handle up to 1.5A without/2.2A with a heatsink.

Stepper motors should be operated at exactly at the rated current, modern drives, although using much higher P.S. voltage, maintain the current throughout the RPM range via PWM etc, in order to counter act the otherwise tapering off of torque due to inductive reactance as rpm increases, see the Gecko stepper site for sizing etc.
Max.

it appears he is using servo's not steppers...

jamie_s said:

it appears he is using servo's not steppers...

Click to expand...

Yep - servos not steppers.

jamie_s said:

it appears he is using servo's not steppers...

Click to expand...

Nigel Goodwin said:

Yep - servos not steppers.

Click to expand...

At the end of the video, he asks his son if the son wants to use steppers, the son says they are too big. So, the dad is asking how to power steppers. So, you are correct, the son is using steppers (and the son even said so in the opening few seconds of the video) but... you are not being helpful.

Pommie said:

The NEMA17s normally require less than 1A (0.4 in the link above) so the 4998 should be fine. How much more current can they handle? A quick google suggests they can both handle around 2A.

Mike.

Click to expand...

Don't confuse the faceplate size with current handling.
NEMA17 only means the screws holes on the motor's faceplate are 1.7" x 1.7". It has nothing to do with the current draw. NEMA 17 motors are commonly available from 0.4 to 2.5 amps but nothing limits a NEMA 17 to 2.5amps.

The link in the top post indicates steppers that require 12V at 0.4A. I'm assuming that these are what the OP bought.

Mike.

gophert said:

At the end of the video, he asks his son if the son wants to use steppers, the son says they are too big. So, the dad is asking how to power steppers. So, you are correct, the son is using steppers (and the son even said so in the opening few seconds of the video) but... you are not being helpful.

Click to expand...

Servos are clearly shown in the video.

Nigel Goodwin said:

Servos are clearly shown in the video.

Click to expand...

Yes, the kid said he is using a servo. The OP has NO question about what is working. Why would he? He is asking how to use the motors he bought that are not yet connected. See the link he posted in the text of post #1.

Thank you for all your responses. What my son currently has going is based on servos. The steppers I bought is what he wants to go with next.... thus my power requirement / feeding concerning those steppers. At the end of his project, he'll want to have something that plugs into the wall. I'm thinking currently using a laptop brick and may some resistances?

You need a proper 12V supply. If you're planning on running multiple motors then you need lots of amps. For 6 motors a minimum of 3A, preferably 5A. Something like **broken link removed**.

Mike.

Shaare said:

Thank you for all your responses. What my son currently has going is based on servos. The steppers I bought is what he wants to go with next.... thus my power requirement / feeding concerning those steppers.

Click to expand...

Presumably you are aware that you can't just replace the servos with steppers?, either electrically or mechanically - servos are absolute devices (you tell it to go to point A, and it goes there and stays there). Steppers are 'relative', you tell it to go so many steps from where it currently is, and in what direction, and it will attempt to do so - but you've no idea if it actually made it or not. A servo will get there, or at least keep trying to do so - a stepper will simply make an attempt, and has no idea if it succeeded or not.

I'm presuming you're just wanting to use the steppers on their own, with no additional gearing?, and no kind of external positioning feedback - it's likely to considerably inferior to servos in that case.

Nigel Goodwin
Watch the video in Post 1. The kid is clearly making a nonsense "robotic" arm as a learning experience. His dad already bought the stepper motors - TO EXTEND HIS KID's LEARNING!

If he does have a bigger project in mind, there are obviously circumstances where stepper motors are better or they wouldn't be on the market (torque vs cost, for example). Note, I have NEVER seen a 3D printing kit use servos - only steppers.

Please, let the kid experiment! Let the kid learn from his own mistakes. Those mistakes may come at a cost but the expensive mistakes are the best lessons. His wonderful father is supporting his son both financially (by buying parts) and, obviously, and technically by asking questions on this forum. Help them rather than hinder them!

gophert said:

Note, I have NEVER seen a 3D printing kit use servos - only steppers.

Click to expand...

For the obvious reasons - for 3D printers steppers are the right choice, and servos would be an incredibly poor one.

However, bear in mind we're talking to the father (not the son), who might like to know that it may not go well.