Author Topic: need high torque, sensored motor @ ~100 watts  (Read 585 times)

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Offline UncleJoeTopic starter

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need high torque, sensored motor @ ~100 watts
« on: January 06, 2013, 03:58:41 AM »
I would like a high torque motor (37 oz-in @ 5760 rpm) for souping up a Scorbot 3 I bought. I really need it to be sensored to allow high startup torque and to count the number of revolutions. So far, I'm having difficulty finding such a motor.

The closest I've found are

Revolver S Stubby http://holmeshobbies.com/product.php?productid=467 (still not ready for purchase)
Team Novak Ballistic 25.5T http://v2.teamnovak.com/products/index.php?main_page=product_info&cPath=1_126&products_id=79

I've found other RC car motors, but they're usually too big.

Some alternatives I thought about are:

adding hall sensors to an existing motor - how hard is this?
rewinding a motor with more turns to increase torque (decrease Kv)
Does someone know any motors that fit my need or modifications I can do?

Thank you,
Yale

Offline jwatte

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Re: need high torque, sensored motor @ ~100 watts
« Reply #1 on: January 06, 2013, 11:19:26 AM »
Finding motors with 37 ozin at 5krpm isn't hard. You seem to have another requirement: The specific size or weight of your motor. Without knowing what that is, how can we help?
When you say "hall sensors" there are two kinds of sensors I can think of: Current sensors, and magnetic position sensors. Which one do you mean?
It sounds from your description as if you mean current sensors, for the start-up current limiting application, but then it sounds as if you mean encoders, for the revolution counts.

Offline UncleJoeTopic starter

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Re: need high torque, sensored motor @ ~100 watts
« Reply #2 on: January 06, 2013, 05:41:27 PM »
Quote
Without knowing what [the motor size is] is, how can we help?
Right, sorry for forgetting. I was kind of desperate after searching for hours without finding much. The maximum dimensions I can tolerate is 2 inches long, and 1.5" for the diameter. This motor will be used for the shoulder joint, so weight really isn't an issue as long as it's < 400g.

Actually, when I said 37 oz-in @ 5760 rpm, I was assuming I was going to use a 1:64 reduction gearbox at most, with 90% efficiency to achieve 15 N*M @ 90 rpm. If there's a higher torque motor that allows a smaller gearbox, but still achieve 1.5 rotations/second, I can use that too.

I'm not aware of the distinction between current and position sensors. From my basic understanding, Hall sensors just measure a voltage difference along a cross-section of a wire due to non-uniform charge density caused by a Lorentz force. I need the rotor position to achieve the smoothest/strongest torque. Also, I will also count the sensor transitions to determine the rotation count. I'm comfortable with microcontrollers, so the interface shouldn't be a problem.

Thanks for helping jwatte

Offline jwatte

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Re: need high torque, sensored motor @ ~100 watts
« Reply #3 on: January 06, 2013, 09:08:57 PM »
Hall sensors can measure current, by placing them atop the conductor. They can also measure position, by measuring a polarized magnet rotating on a shaft. (There are also switches, as in push buttons, that are based on Hall sensors.)
Thus, saying you need a "hall sensor" is very imprecise.
It sounds to me as if you actually want two sensors: One for current, and one for rotation (to integrate position.)

 


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