stepper motor torque

Any good way to estimate torque for stepper motors you can't find documents for (except for buying a 600 bucks torque meter. :)

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snipped-for-privacy@yahoo.com wrote:

I once spoke to a guy who worked at a stepper motor manufacturer. He claimed they routinely tested motors by wrapping string around the output shaft. One end it connected to a known mass, the other connected to a spring balance. The difference is the torque. Load it up until it stalls.
Use two spring balances to make a simple Prony brake.
Try Google and/or here:
http://www.tpub.com/content/engine/14037/css/14037_53.htm
Pete Harrison
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snipped-for-privacy@yahoo.com wrote:

maybe a $2 spring balance, and a lever arm ? -jg
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snipped-for-privacy@yahoo.com schrieb:

Alternatives: 1. Estimate the torque generated via an FE analysis, but you would have to know: cross-sections, material data, etc. Very, very theoretical approach.
2. Measure, but time-consuming an expensive.
3. Probably the most practical approach: buy a stepper-motor that comes along with the complete documentation.
Regards, Peter.
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In comp.arch.embedded snipped-for-privacy@yahoo.com wrote:

1) Replace it by a stepper motor you *can* find documents for ;-)
2) Build your own torque-meter. Since you x-posted this from a robotics newsgroup, I'll boldly assume you know enough about mechanics to pull that off. A lever arm, a counterweight and maybe some gears should do it. If you want to measure power instead of torque, you might want to consider Joule's method of measuring mechanical work in terms of generated heat --- or drive a dynamo.
3) find a cheaper torque meter. Torque wrenches for car wheel nuts are generally a good deal cheaper than 600 bucks.
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Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
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snipped-for-privacy@yahoo.com wrote:

http://www.romanblack.com/stepper.htm
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On 19 Aug 2006 11:54:27 -0700, snipped-for-privacy@yahoo.com wrote:

Just as important as torque in some applications, is finding the upper and lower resonance frequencies. Unless this is spare-time job, get the documentation for the motor!
Stephen
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Stephen Pelc, snipped-for-privacy@mpeforth.com
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There is more than one torque of interest. There is the stall torque, which most of the replies to your query address, and there is running torque. The latter depends on the speed, generally the faster the motor steps, the less the torque, but also on the drive method: direct, R/L, or chopper drive. The drive method makes a big difference in complexity, cost, and efficiency as well as torque.
John Piccirillo
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snipped-for-privacy@yahoo.com wrote:

Having played around with turning a drum to mount on a NEMA 23 and winching a weight up and down with it, realistcally I'd have to say it's not worth the trouble.
Just bolt the motor onto whatever you want to use it for and see if it's up to the task. If it can do it slowly but not quickly, look into the driver circuit. If it can't do it, buy a bigger motor. Chances you are will be dealing with either NEMA23 of 34 size mounts so you can change the motor a lot without changing what it bolts onto (off the top of my head, I'm going to guess you could make a mounting plate with bolt holes to support either size)
Also consider using toothed timing belts. These let you have variable gear ratio, absorb vibration, and tolerate the kind of shaft misalignments you are likely to introduce in anything built without carefull use of precision machine tools. Of course you can also buy misalignment couplings...
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