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Author Topic: help needed driving a bipolar stepper motor with dual H-bridge  (Read 4086 times)
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Delft
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hi everyone,

I'm currently working on a stepper driver for a bipolar stepper as decribed at http://www.tigoe.net/pcomp/code/circuits/motors/stepper-motors. I'm using several stepper motors from scanners/printers and a L293D dual H-bridge in the two control wire setup.
It seemed to be working today, however the torque was very low. A discontinuity in the breadboard I later discovered caused the 12v psu not to be connected. The motor was probably running on the 5v logic supply. When I did connect the power supply to pin V2, I instantly fried the L293D (Although i finally got some real action, this was not exactly what i hoped for).
I checked the wiring with the scheme, replaced the l293d and reconnected the psu, resulting in another plume of smoke rising from my desk. I must be doing something wrong, can anyone help?

thanks


(here's a video of one of the steppers at work: )


* P1020238.JPG (75.06 KB, 640x480 - viewed 85 times.)
« Last Edit: March 14, 2011, 01:07:18 pm by timcastelijn » Logged

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It's all about the current. Most likely the current drawn by your motors at 12V is much higher than an L293 can handle. You need a motor driver rated for higher currents, and you need to know what the current draw for your motors is before properly sizing a motor driver.

You can also deliver a smaller amount of effective power to your motors using PWM (the analogWrite() function) on the motor enable signals. But if you want torque, there is no substitute for an appropriate amount of high current.

If you can tell us the part numbers of your motors or otherwise measure the current draw of your motors at 12V (can you hook them up to a power supply that reads out current?) then perhaps we can suggest a more appropriate driver than the L293.

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Delft
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Hi Ruggedciruits, thanks for the advise. I couldn't find the motors specifcations on the internet, however the part numbers are below.

I did find a 10ohm and 40ohm mark on two of the motors. Does this mean that at a 12v potential the current through the motors would be (I = U/R = 12/10 =) 1,2A and 0,3A? the l293d should be able to cope with at least the 0,3A current (http://cgi.ebay.nl/ws/eBayISAPI.dll?ViewItem&item=140418184299&ssPageName=STRK:MEWNX:IT). Can I regulate the current by adding additonal resistors parallel to the psu circuit?

thanks


steppers:
- epoch t13196ah (40ohm)
- mitsumi M42SP-6TG LF (lot.no.T 55829 10ohm)
- OKI (EM-546   7X27AN2)
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Yes, for a 10ohm motor and 12V source you would be pushing 1.2A per phase, 2.4A total through the motor. Way too much for an L293.

The L293 should be OK with 0.3A per phase, but will likely get quite warm.

I would not regulate the current by adding resistors. Use PWM as I suggested in my previous post to deliver lower effective power.

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The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected
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Delft
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allright thanks,

I think I have to do some research on the forum then. Am I right this is done by applying two other PWM outputs from the adruino to the enable pins on the l293, putting a lower voltage on the enable pins, so that the l293d only lets part of the current through?
Can I also use a l298 hbridge, which is able to cope with 4A current?

cheers, tim
 
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Quote
Am I right this is done by applying two other PWM outputs from the adruino to the enable pins on the l293, putting a lower voltage on the enable pins, so that the l293d only lets part of the current through?

No, you do not want to change the voltage on the enable pins. You want to generate a PWM waveform to turn the enable signal on/off rapidly with varying duty cycle. The bigger the duty cycle the higher the average power you are delivering to the motors. Here is perhaps a too-high-level view of PWM, though I'm sure you will find more nuts-and-bolts explanations with a bit of looking:

http://en.wikipedia.org/wiki/Pulse-width_modulation#Power_delivery

Quote
Can I also use a l298 hbridge, which is able to cope with 4A current?

The L298 will give you more current capability than an L293 but it won't give you 4A. That's just a marketing number that doesn't take heat dissipation into account. See our Motor Driver Myth application note for more explanation.

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Hi !

I join this topic because i got the same motors than you and I would like to know if you have successfully controlled these motors ?

I don't have more information than you... I would like use these motors to do a 3D printer. So I would like to know what power and intensity can be managed by these motors to design the printer. I think use A4988 stepper motor driver to control these motors what do you think about this choice ?

Thank you
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UK
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I think use A4988 stepper motor driver to control these motors what do you think about this choice ?

An A4988 is a much better choice than an L298.

The Pololu website has good information about using their A4988 board.

...R
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Normally a bipolar stepper would be rated by current - however you can take a guess
on the current rating from the winding resistance coupled with the overall size which
controls the heat-dissipation.

You also learn the importance of testing a circuit carefully using a current-limited
bench power supply - invaluable for prevent disasters like this - set the current limit
and wind up the voltage watching for current getting suspiciously large, kill power
if anything looks wrong.  Test components for temperature and repeat until either
its happy or you know something is overloading.
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