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Adafruit Motor Shield Questions
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Adafruit Motor Shield Questions

by iHaveQuestions on Thu Jan 31, 2013 4:07 am

Hello, I've looked through the forums (although the search always gives me a hard time about using words that are too common, so excuse me if I overlooked a thread) about how to choose a stepper motor for the Adafruit motor shield, but I did not find a write-up on how to figure out what won't blow up the h-bridges (I also looked in the motorshield instructions of course, and it only mentioned not to use a stepper that can exceed 600ma).

How can I figure out indefinitely that a particular stepper won't blow up my chips?

Clearly the stepper on the adafruit website is compatible (350ma at 12v) but look at this polulu stepper motor (http://www.pololu.com/catalog/product/1208), which draws 500ma at 10 volts. The adafruit motor shield will be feeding 12v into this 10v stepper, so would this create a problem?

I'm just looking for a way to settle this confusion about steppers once and for all.



Also, can I still use Arduino pins to break-out onto a breadboard even with the motor shield installed? How would one hook a breadboard up to the Arduino with this motor shield?

Thanks!
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Re: Adafruit Motor Shield Questions

by adafruit_support_bill on Thu Jan 31, 2013 8:06 am

You should read through this FAQ first: viewtopic.php?f=31&t=26873

How can I figure out indefinitely that a particular stepper won't blow up my chips?

Make sure it doesn't exceed 600mA/phase - unless you use the techniques mentioned in the FAQ to extend that rating.

The adafruit motor shield will be feeding 12v into this 10v stepper, so would this create a problem?

The motor shield has external power terminals, so you can feed whatever voltage you want to the motors. As stated in the tutorial and the FAQ, using an external power supply is highly recommended. Using a higher than rated voltage (e.g. 12v instead of 10v) will increase the current proportionally (600mA instead of 500mA) as well as shortening the life of the motor.

Also, can I still use Arduino pins to break-out onto a breadboard even with the motor shield installed? How would one hook a breadboard up to the Arduino with this motor shield?

Yes. The easiest way to do this is with a wing shield. https://www.adafruit.com/products/196
Although a protoshield with stacking headers is another good option.
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Re: Adafruit Motor Shield Questions

by iHaveQuestions on Fri Feb 01, 2013 10:12 pm

Thanks for the link!
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Re: Adafruit Motor Shield Questions

by iHaveQuestions on Sun May 19, 2013 7:00 pm

Thanks again for your responses! I have a few more questions:

Motorshield works great via USB power or devoted arduino power. I am running one stepper motor, the stepper motor sold by Adafruit for $14. But when I try to plug my power supply directly into the motor shield (I removed the jumper and double checked the proper polarity), my stepper motor jitters out (does nothing but jitter). The power supply is a radio shack AC to DC adapter, 13.8v DC output with up to 3amps current (http://www.radioshack.com/product/index ... Id=2103959). The stepper motor should only be taking in .6 amps/phase, so this power supply should have more than enough power.

Also, the FAQ say that the practical current limit is 2amps. Is that for the entire system, or per H-Bridge (meaning 4 amps total)? So I should get a power supply with more amperage if I am to run more powerful things?

With the wingshield you mentioned above, which should allow me to breakout my arduino pins onto a breadboard, what pins will (or will not) be available for me to use? Surely the motorshield will be using some of the pins.

And what would happen if I run a DC motor rated for higher voltage (say 12v) with the power of only 7.4v? Will that mean the amp draw of the motor also be lower?

Thanks again!!
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Re: Adafruit Motor Shield Questions

by adafruit_support_bill on Mon May 20, 2013 6:24 am

my stepper motor jitters out (does nothing but jitter).

Does it jitter continuously, or only when the program tries to move the motor? Is the sketch running normally, or is the Arduino resetting?

the FAQ say that the practical current limit is 2amps. Is that for the entire system, or per H-Bridge

That is per H-bridge.
what pins will (or will not) be available for me to use?

http://learn.adafruit.com/adafruit-motor-shield/faq
All 6 analog input pins are available. They can also be used as digital pins (pins #14 thru 19)
Digital pin 2, and 13 are not used.
The following pins are in use only if the DC/Stepper noted is in use:
Digital pin 11: DC Motor #1 / Stepper #1 (activation/speed control)
Digital pin 3: DC Motor #2 / Stepper #1 (activation/speed control)
Digital pin 5: DC Motor #3 / Stepper #2 (activation/speed control)
Digital pin 6: DC Motor #4 / Stepper #2 (activation/speed control)
The following pins are in use if any DC/steppers are used
Digital pin 4, 7, 8 and 12 are used to drive the DC/Stepper motors via the 74HC595 serial-to-parallel latch
The following pins are used only if that particular servo is in use:
Digitals pin 9: Servo #1 control
Digital pin 10: Servo #2 control


And what would happen if I run a DC motor rated for higher voltage (say 12v) with the power of only 7.4v? Will that mean the amp draw of the motor also be lower?

Yes. The current draw will decrease in proportion to the voltage.
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