Stepper motor strength?

Hi! I've never touched an arduino but I'm wondering if it mightn't be the perfect platform to rebuild our laboratory stretch-rack that blew up (litterally) last month. Essentially we need two stepper motors, attached to screw-shafts, to stretch thin strips of plastic. Does anybody know if they'll be strong enough? could a couple of stepper motors with torque ~78.4mN.m tear apart a 10x30 mm bit of plastic bag?

Cheers! R

That sounds like the same question as "how long is a piece of string" :)

If you already have the screw mechanism and the ability to stretch the plastic sample by manually turning the screws could put a lever (perhaps 300mm long) on the screw (a spanner on a locked nut might work) and, by hanging weights from the end of the lever make an estimate of the torque required.

I suggest you get a motor with 2 or 3 times the measured torque.

Or design your project so that it would be easy to change to a more powerful motor if needed.

What, exactly, are you measuring? Is a stepper motor really necessary or would a regular geared DC motor be sufficient?

...R

Hi Robin,
Thanks for the reply! but unfortunately the old motors are of a different kind (very old and built for something else) so I can’t just take them off and test the rack-screw. I was just hoping somebody might’ve built something with steppers and screw-shafts and have a feel for how strong they are?

As for your second Q: Yes, it needs to be steppers since all scientific studies have to have meticulous control of the process (in this case the stretch-distance) if they’re to survive peer review and get published. (basically, my job hangs on it)

Cheers!
R

You have not said whether the existing (broken) system used stepper motors or even explained exactly what is broken.

If it had stepper motors can't you tell what size they are, determine how they were driven and get some idea from that of the sort of replacement required. Are there ID marks on the motors?

What part is broken?

Don't be coy. The more information you give the better the advice you will receive.

...R

Hi Robin, Slow down! I'm working on it! I couldn't get my hands on the parts until an hour ago!

Why is it broken? there was small bang and smoke started coming out of the (homebuilt) control unit when we plugged it in. The thing had been built from parts scavenged from an old machine and put together by someone who's long gone from here. I've asked around though and think the motors should be fine, I've even managed to dig up their specs, though they are unhelpfully in imperial units.

Asuming the steppers are still ok, then maybe I only need a couple of H-bridges, a couple of buttons, an arduino board and a handful of jumper wires. Does that sounds about right, or have I forgotten anything?

How do I know which H-bridge to get? or are they all the same?

and can I get away with using a mini board?

Cheers! R

Slow down! I'm working on it!

@Robin2: -1 for being too quick with helpful questions and suggestions!

R1D0: I've asked around though and think the motors should be fine, I've even managed to dig up their specs, though they are unhelpfully in imperial units.

Ok - so what are they? I mean, if you can give us the specs, we might be able to figure it out - maybe you can use the old motors with a new control system (if the motors and mechanism aren't broken, why change it?)...

Also - just because something is in imperial units doesn't mean it can't be converted to metric/SI or something like that; as someone in the States, I don't balk at specs that aren't in "imperial units" - I either use the units as-is, or I convert them as needed.

As @crOsh said, post ALL that you know about the motors.

Do NOT (repeat NOT) think of using a h-bridge to drive a stepper motor. You need to get a proper stepper motor driver board. This Pololu A4988 web page will give you some idea of what I am talking about. Obviously, without knowing anything about your motors I have no idea whether those drivers would be suitable, but they all work on much the same principle.

Also, if this is your first Arduino project get yourself an Uno as almost everything works with an Uno.

...R

Dare I ask why you should not drive a bi polar stepper with an H bridge?

ChilliTronix: Dare I ask why you should not drive a bi polar stepper with an H bridge?

A stepper driver does all the heavy lifting (in terms of the sequencing of coil pulses), it can limit the current and thus allow the use of high voltages and it can do microstepping all without requiring any effort from the programmer or the Arduino.

Using a h-bridge would be like painting the exterior of a house with a 25mm paint brush.

...R

Thanks everybody for the replies. The stepper motors are AM1524-A-0.25-12.5-57 from Faulhaber, the datasheet can be found here.

I've now managed to find most of the original bits, and the box seems to contain to boards with two pair of L297 and L297 controller+driver. It must've been one of these which started smoking. If I can find out which one I could just use two of the others. How do I find this out? nothing looks obviously burnt out, and I've never had to poke around at electrical components before.

Also, if/when I managed to interface them with an arduino, can they get enough power from the 9V that powers the board or would they need a separate power source?

Thanks all for your help, but please be patient with me, I'm slightly snowed under with students, admin, meetings and a hopeless IT dept. I'll get there though!

It looks like the L297 requires a further device to control the current in the motor.

These two features are combined in the Easydriver or Pololu A4988 stepper drivers.

Do you know which of the motor models in the datasheet corresponds with yours. There seem to be variants for different nominal voltages.

The motors should have their own power supply. Am I correctly interpreting you to say that the existing power supply for the steppers is at 9v - it seems low.

...R