Author Topic: Stepper motor has no torque  (Read 4280 times)

Offline raynerd

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Stepper motor has no torque
« on: February 28, 2013, 07:44:33 AM »
Hi guys, it's been over a year now since I wired up a stepper and over the last few nights I've been pulling my hair out.

I've wired my stepper up, 4 wire, and my controller turns it nicely, but even when I hold it by hand it just judders and stops...never mind putting any cutting strains on it! I'm using one of kwackers divider controllers to run it although the motor is actually turning a linear table axis. It has worked in the past but I'm sure it is wired correctly and I'm sure the divider setup is correct! Likewise, if my wiring was wrong, would it still turn smoothly with no load?

Could the stepper have died? - only I'd have presumed it would have totally blown if this was the case but as it is, I get perfect smooth motion when under no load. Yet virtually no torque both driving or holding.

Any thoughts, help or advice appreciated.
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Offline raynerd

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Re: Stepper motor has no torque
« Reply #1 on: February 28, 2013, 09:09:55 AM »
Not the motor, tried two with the same results but they have no markings on them. so not sure what motors they actually are. With steppers can you read into the length of the as an idea of their rating? - only these two are pretty long. Can't imagine the torque of them being so low they can be stopped with a finger!
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Offline rleete

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Re: Stepper motor has no torque
« Reply #2 on: February 28, 2013, 09:14:13 AM »
What kind of power supply is feeding them?  Sounds like low voltage/current to me.
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Offline vtsteam

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Re: Stepper motor has no torque
« Reply #3 on: February 28, 2013, 11:18:46 AM »
Yup, need specifics. Motor model and number, power supply specs. etc.

Heat and over-current can demagnetize a motor, but I bet it's something else relatively minor and fixable. Or hope so.
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Offline awemawson

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Re: Stepper motor has no torque
« Reply #4 on: February 28, 2013, 11:33:21 AM »
Chris said in his second post :

"Not the motor, tried two with the same results but they have no markings on them. so not sure what motors they actually are"

So we're not going to get specifics on the motors, but as he's eliminated the motor by substitution we're left with the driver / psu combination.

Chris, do you have an oscilloscope to watch the outputs? Possibly one of the power stage drivers has gone either short or open circuit.
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Offline vtsteam

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Re: Stepper motor has no torque
« Reply #5 on: February 28, 2013, 12:29:50 PM »
Apologies for missing that.  :wack:
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Offline sparky961

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Re: Stepper motor has no torque
« Reply #6 on: February 28, 2013, 01:18:30 PM »
Chris:

Are you able to temporarily hook the inputs to the stepper driver to a slower clock source, like switches, so that you can manually run through each of the phases?  I agree it sounds like under current, but odd that it worked and now it doesn't.  Something has to have changed, you just haven't found out what it is yet. :)

I'd double check the power supply to make sure you're getting the voltage you expect, and you might be able to hook an ammeter in series with the motor coil to see what sort of current you're getting there.

I would double and triple check your motor connection, because that's the easiest thing to get wrong.

Offline philf

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Re: Stepper motor has no torque
« Reply #7 on: February 28, 2013, 01:38:21 PM »
Chris,

If the driver is one of the 4.5A 50V type make sure  the digiswitches to set the current and microsteps are set correctly.

For some unknown reason "0" on the digiswitch means "ON" and "1" means "OFF"!

When I set my CNC up it took me a good while to work out what was going on.

Good luck.

Phil.
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