The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

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auspicious
 
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The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

Post by auspicious »

I think i'm trying to get it to turn a pound or two. Does anyone know how much of a load they can hold? I am talking about the smallest cheap $7 stepper motors from adrafruit.

With any weight, it will not spin at all... but it wont even hold the weight. it slips backwards... any ideas please? thank you. :?:

auspicious
 
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Re: The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

Post by auspicious »

dang. Is there anything like a gear box, that someone could show me, that could maybe turn a couple lbs. slowly and accurately and still hook into the arduino. (that is if the stepper is indeed a failed attempt)...

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adafruit_support_bill
 
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Re: The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

Post by adafruit_support_bill »

Those motors don't have a lot of torque for direct drive applications. If you search for "Geared Stepper Motor", you should find some options. When searching for motors, keep in mind that the motor shield can handle up to 36v and 0.6A (600mA) per phase.

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easternstargeek
 
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Re: The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

Post by easternstargeek »

@auspicious:

For problems like yours, the term "weight" has little meaning. Torque is what is important. Weight is a component of that, to be sure, but without knowing the length of the lever arm, how the mass is distributed, and the orientation of the axis of rotation with respect to gravity, it is impossible to get a clear enough picture of the problem to help.

Any motor has to do at least these things in any application:

Accelerate the load
Achieve the desired speed
Hold the load

Of those three things, figuring out the acceleration is the trickiest, because it is necessary to calculate rotational inertia, and that is not a trivial mathematical task. Most engineers will break down the system into a few primitive solid shapes, look up the "j" values from a chart, and then add them together. If you're really lucky, j values may be published by manufacturers. There is a lot of time-saving reference material out there, but making proper use of it requires a thorough understanding of rotational kinematics.

Fortunately, many of us have practical experience with this, but when asking for help, you'll get much farther by including a couple of simple sketches of your application. Don't leave out the gravity vector.

Finally, for Step Motors, you have to be careful to ramp-up the pulse frequency slowly enough for the load to catch up, otherwise the motor will stall.

Good luck with your application!

auspicious
 
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Joined: Tue Apr 26, 2011 12:44 am

Re: The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

Post by auspicious »

Thank you very much for the help. I do indeed have little experience with physics and such, though I am currently a student about to take some classes in that area.

So in the mean time, does something like this look appropriate?

It has such little info. I'm not sure if any of those gears can be "attached" to? or is it only one? if so, it doesnt say anything about how it changes the torque.... I'd really appreciate any additional input. I'll definitely be getting some more details... but how about this part in the mean time? Thanks again.

http://www.allelectronics.com/make-a-st ... ain/1.html

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adafruit_support_bill
 
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Re: The stepper motors form adrafruit, are not holding any weight, they wont turn...any ideas?

Post by adafruit_support_bill »

It doesn't look like any of those gears has a drive shaft to connect to. Looks like quite a bit of gear reduction also.

In theory, the torque increase is the reciprocal of the gear ratio. For example: a 10:1 gear reduction would give you 10x the torque (and 1/10 the max speed). In practice, there will be some friction losses in the gear train too.

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