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Re: AID: Motor Questions

From: Tim Moody   timmoodysympatico.ca
Date: Wed, 13 Nov 2002 08:31:15 -0800

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Yes, caught the TIP122 vs 127 problem after I sent this.  I know the L298 
datasheet shows a bi-polar stepper, but why shouldn't the four outputs be 
able to drive the four windings of a unipolar stepper (yes, I have 
identified the leads using an algorithm similar to the one you suggest.)

My question was about people's experience with continuous DC motors 
(controlled with PWM) vs. using a stepper.


At 04:52 PM 11/13/02 +0100, cis wrote:
>: Sent via the Art Interface Device mailing list: aid@interaccess.org
>: Use your "Reply All" to  reply to the list, "Reply" for private response
>
> > : Sent via the Art Interface Device mailing list: aid@interaccess.org
> > : Use your "Reply All" to  reply to the list, "Reply" for private response
> > I'm working on a PC parallel port interface to drive some 5V lights and
> > some motors.  The logic chips work fine as do the drivers for the lights
> > (L293), but I'm having problems with the drivers for the motors (L298),
> > which have been unreliable (either I blew them or they were bad).  I chose
> > stepper motors because I thought I would get more precise position control
> > without having to build any feedback mechanism, but I'm wondering if I
> > should go with something simpler and even drive it with a transistor (e.g.
> > TIP 127).
>It is impossible to drive a step motor with only one transistor
>
>do not use TIP127 that are PNP
>
>you need 4 TIP122 and 4 diodes to drive it
>see : http://www.interq.or.jp/japan/se-inoue/e_step.htm
>for exemple how to drive  with transistors
>
>but as I read your mail, I m not sure that you use well the L298
>that is more for bipolar stepper motors (you can use it
>
>if your step motor have 6 wires it is a unipolar
>with ohm meter you need to find two groups of 3 wires that give an answer 
>of some ohm
>  exemple A B C and D E F  wires
>
>
>in the A B C group , you need to find the middle point
>with the ohm meter :
>  for example you measure
>between A and D   infinite
>between A and E   infinite
>between A and F   infinite
>
>between A and B   0,7ohm
>between C and B   0,8 ohm
>between A and C   1,5 ohm
>in such a case the middle point is B
>
>do the same thing with the second group D E F
>suppose that the middle point is E
>
>now you will connect  B and E together to +VCC (5V in your case)
>
>http://www.interq.or.jp/japan/se-inoue/e_step1.htm
>give all explanation of the fonctionnement of the motor unipolar with java 
>animations
>in your case now,
>
>A is X
>C is /X
>
>D is Y
>F is /Y
>
>with the L298
>you have two bridge
>connect A and C to one bridge,
>connect D and F to the other bridge
>in that case you can use a power of 10Volt for L298
>if you let B and E in the air
>
>if you connect B and E to VCC then VCC is only 5 volt
>
>
>  Now the questions.
> > 1) I know that some of you at least are interested in PWM which I assume
> > is
> > for driving non-stepper motors.  I'm interested in comments on the
> > trade-offs between steppers and non.
>
>PWM are for driving continuous motors (it simulate variable continuous 
>voltage via a power interface)
>you can t drive Stepper motor directely with it
>
>
> > 2) I found the steppers (5V 8.5W unipolar) at Active Surplus.  Is there a
> > better source for motors?
>
>I m in france I can t help you for that, but I can say that your motor 
>seem to be performant
>if you want low cost stepper motor you can find two in old printers
>
>--
>cis@artsens.org
>
>
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