Stepper Motor Control

EMPTY_C

Hey all,

··· I am currently working on a project and would like to hear some insite.· I would like to rotate a brake drum using a stepper motor but with only about 1 degree at a time.· Is it possible to have the stamp control the stepper motor to do that?· I have see the 2 controllers on the site,·http://www.seas.upenn.edu/~robo2005/Electronics%20Lab%203%20v3.doc·and http://www.parallax.com/dl/docs/books/sw/exp/sw26.pdf.

···· Please let me know what you think!

MT

Franklin

You may have to add gears to get 1 degree resolution.

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- Stephen

jmalaysia

You can use gears as Franklin/Stephen suggested,· or you can look into a MICROstepping motor,· which has much greater resolution.

EMPTY_C

I figured that I would have to use the gears... no problem here.· Its the code that i am worried about.· Am i going to have the ability to take a single step each time i want it?

EMPTY_C

Any other suggestions or help?

Mike Green

The two programs that you reference are minor variations of each other. Both work by doing a single step at a time.

stamptrol

When working out the gear ratios, you might consider the steps per revolution of your stepper.

If the number of steps is not mathematically well related to the gear ratio, your ability to position the brake drum at precise locations may not what you want. However, if you're trying to position to within 1 deg with a 360 step per rev motor and a 10:1 gear ratio, you should be fine. (each step of the motor will move the drum 0.1 deg). I think inertia is going to be the hardest thing to control, depending on the strength of the stepper.

If the speed becomes too slow with the geared stepper , you may have to move to a more powerful brushed motor and measure the drum position with an external encoder.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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EMPTY_C

the drum weight i am looking at is about 117 lbs, it has a diameter of 16.50", width of 7.00" and an overall depth of 10.62. I am doubtful that there will be a stepper motor that could be used. CORRECT?

EMPTY_C

I think another big factor i need to overcome is that of the power demands. I was looking at the small circiuit that stamp works has and it seems that if i use a high torque stepper motor it would fry the uln2003. even with unipolar stepper motors to achieve a torque of 300 oz-in i would need 2 amps and a measly 6.3 volts. Is there a possible way to overcome these energy demands similar to that in the stamp works link??

Mike Green

There's no way around the energy demands if what you need is the energy to move the motor. The ULN2003 has about a 1/2A per output rating. You can parallel output pins, but it sounds like you really need a power transistor made for the job. A logic threshold MOSFET like the IRL510 could do it. You'll need to supply your own reverse diode across the stepper windings (like a 1N4001). The "Industrial Control" tutorial has some sample circuits around page 96 for relays and solenoids, but the same thing applies for stepper motor windings. They're all inductive loads. Go to the main Parallax webpage, choose the Resources tab, then Downloads, then Stamps in Class Downloads and you'll see it.