Can't get bipolar stepper to run...

[Sideshow_Ben]

I bought the inexpensive 4-wire 12V bipolar stepper from SparkFun (https://www.sparkfun.com/products/10551) and tried to run it according to the reference page http://arduino.cc/en/Reference/StepperBipolarCircuit.  In particular, I bought the 754410ne chip and hooked it up exactly as shown in the reference page:


If I power my board off the USB and supply the motor 5V from the arduino, it runs.  If I give it Vin, it doesn't run.  If I power my board off a regulated 12V wall adapter and supply it Vin, the motor takes about 3 steps and then starts to shudder back and forth.  If I give it 5V, it takes about 16 steps and then starts shuddering.  If I supply it 3.3V, it runs fine but the arduino heats up to blazing hot.  I get that this low voltage means I'm drawing a lot of current.

What I don't get is why the motor won't run except for these few particular circumstances.

[dc42]

If I power my board off the USB and supply the motor 5V from the arduino, it runs.

That suggests your wiring is basically OK.

  If I give it Vin, it doesn't run. 

You can't use Vin to provide power to external devices when the Arduino is powered from USB.

If I power my board off a regulated 12V wall adapter and supply it Vin, the motor takes about 3 steps and then starts to shudder back and forth.

What is the current rating of the 12V supply? Is the motor driver chip getting hot? I suspect that the motor is drawing too much current for either the power supply or the chip.

  If I give it 5V, it takes about 16 steps and then starts shuddering. 

The 5V regulator on the Arduino is probably going into thermal shutdown. You are asking it to drop 7V while passing quite a lot of current (because of the motor), which equates to a lot of power dissipation.

If I supply it 3.3V, it runs fine but the arduino heats up to blazing hot.  I get that this low voltage means I'm drawing a lot of current.

It's probably the voltage regulator that is getting hot, but not enough to go into thermal shutdown this time, due to the reduced motor voltage.

If the motor runs OK at 5V, why not supply both the motor and the Arduino from a 5V USB adapter?

[Sideshow_Ben]

Thanks dc42!  That all makes sense.  I am building a clock so I eventually need to run it off of an adapter.  I figured the motor is listed at 12V so I should buy a 12V adapter but I may just harvest a 6V one from some old piece of hardware around the house and try that.

[dc42]

You need to be very careful with stepper motor ratings. 12V is the maximum peak voltage you may apply through a chopping-type driver (not the sort of chip you are using). The datasheet says the rated current for that stepper is 400mA and the resistance is 4 ohms per phase. So the maximum continuous voltage you may apply is 0.4 * 4 = 1.6V per phase. The SN754410 has a typical voltage drop of 2.1V @ 0.5A, so the maximum motor voltage you should feed to it is about 1.6 + 2.1 = 3.7V. Any more and you will overheat the stepper.

I suggest you use a 5V regulated wall wart (e.g. USB power adapter) rated at at least 1A, and put a 3.3 ohm or 4.7 ohm 1W resistor in series with each motor winding. In fact, for a clock you need very little torque or speed, so you can probably get away with 12 ohm resistors (which will reduce the current per phase to about 200mA), then you can use 0.5W resistors and a 0.5A power supply.

[MarkT]

Those low-resistance bipolar steppers are definitely not meant to be powered from
an Hbridge driver, they are designed for chopper-style bipolar motor drivers like the
A4988.

The "rated voltage 12V" is total nonsense really, these motors have a winding
current and resistance rating, and the only voltage rating is
the maximum the insulation can withstand safely, which is likely to be a lot more than
12V, probably more like 48V for something of this size.

You won't get any decent speed/torque out of the thing without a chopper driver run from a decent
supply voltage (24 or more is typical).

The datasheet has a bug, it lists the winding inductance as 3.5H, whereas it will
be 3.5mH...

[Sideshow_Ben]

MarkT, thanks!  Can I ask you guys whether it would just be smarter for me to cough up the $20 to buy a stepper driver like this one (http://www.adafruit.com/products/1438) rather than try to work this out myself with a driving chip?

[MarkT]

No, wrong driver, that's not for low impedance bipolars at all, it is for a high impedance
stepper only.  A driver that can do DC motors and stepper motors is never a chopper drive,
its just a pair of Hbridges.

Pololu's A4988 is the most popular little chopper driver breakout I believe.
http://www.pololu.com/catalog/product/1182

[Sideshow_Ben]

No, wrong driver, that's not for low impedance bipolars at all, it is for a high impedance

Wow, these motors are a lot more complicated than I thought.  So if I wanted to use an H-bridge chip or that driver board at adafruit, I'd need one of these bigger steppers like this one: https://www.sparkfun.com/products/9238 ?

[dc42]

You won't get any decent speed/torque out of the thing without a chopper driver run from a decent
supply voltage

Surely he can get enough for a clock with the chip he already has, since a clock needs very little power or torque?

[Sideshow_Ben]

dc42, I probably need some reasonable amount of toque because I'm building a fairly large gear clock.  Is is patterned off of this



but I'm having one motor drive the whole clock by connecting the hour ring to the minute ring using another set of laser-cut gears.  I'm   starting to think that maybe I should just scrap the bipolar motor and go with a unipolar one like the 42BY48H05 or 42BY48B03 sold by Jameco.  Of course, that's assuming that I can run them on either the L293D or sn754410NE chips that I now own. 

[dc42]

I'm   starting to think that maybe I should just scrap the bipolar motor and go with a unipolar one like the 42BY48H05 or 42BY48B03 sold by Jameco.  Of course, that's assuming that I can run them on either the L293D or sn754410NE chips that I now own.  

No, just buy a cheap A4988-based driver board from eBay. Make sure that it has provision for adjusting the current down to 400mA. For example, http://www.ebay.co.uk/itm/A4988-A4983-3D-Printer-StepStick-Compatible-Stepper-Motor-Driver-Reprap-Prusa-/310739187137?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item48597fb5c1.