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Date: Wed, 22 Apr 2015 03:36:37 +0200
From: Bernd Walter <ticso AT cicely7 DOT cicely DOT de>
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] Stepper driver issues
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On Tue, Apr 21, 2015 at 06:12:52PM -0400, Rob Butts wrote:
> * Can you spin the rotor by hand when it's disconnected?
> 
> All three steppers spin freely.
> 
> * Have you checked winding continuity?
> 
> They all measure close to 4 ohms
> 
> * Are the windings connected properly?
> 
> I have a connector to the stepper with colored wires to each winding (a+ -
> green, a- - blue, b+ - black, b- - red).  Yes, they are verified connected
> to the correct pin (1st, 3rd, 4th and 6th) respectively.
> 
> As for trying the steppers with a 12V supply, I haven't gotten help for
> that yet.
> ???

You have a low resistence motor, which is typical for most bipolar and
says that your motor is current controlled, not voltage.
This means the voltage applied to the driver is only to quickly charge
the coils for faster speed.
The voltage over the coils when holding is much lower, so e.g. for
an 1A motor at 4 ohms it is 4 volts only.
I'm not familar with your driver, but a quick look into the datasheet
says that it can measure the current over shunt, so it should be ok.
Usually those drivers, as yours, do some kind of switching regulation
over the motor coil to get the desired current.
Those circuits can produce a lot of noise and are often very sensitive
to proper PCB layout.
They are also sensitive with the current shunts, you need low inductive
shunts, which wired resistors usually are not.
Considering the questions and problems you have it is best to get
a prebuild driver circuit board.
Those are similar to your driver hybrid IC, but completely build and since
they are more modern they can usually even work without heatsink for
a few amps load.
In the lower end Pololu makes some easy to use, which is good for most
motors in your category.

-- 
B.Walter <bernd AT bwct DOT de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.