Low RPM low power high torque motors for direct drive

Electric Motors and Controllers
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CreFroD
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Low RPM low power high torque motors for direct drive

Post by CreFroD » Sat Nov 04, 2017 8:21 am

Hello! For solar-powered robot design, I need very efficient, low power motors being able to give 0,5-0,7 Nm torque at 53 RPM. The operation voltage is 6.6V. I haven't seen any brushless motors lower than 30Kv. If I understand it correctly, I need 53/6.6=8,5Kv motor. Is such motor physically possible? Can I take higher Kv motor and drive it slowly, like drone gimbals do? Would torque increase proportionally? I have seen many threads on this topic, but they were about high power (>300W) motors for helicopters/multicopters working at speeds much higher, than 50 RPM. Thank you for help!

ThierryGTLTS
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Re: Low RPM low power high torque motors for direct drive

Post by ThierryGTLTS » Sat Nov 04, 2017 10:52 am

Maxon Motor EC 90 Flat is close to you needs.

Ready to work ones and kits without axle and bearings.

Look at their Online Webshop.

Have a Nice Day..

Thierry

CreFroD
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Joined: Sat Nov 04, 2017 7:57 am

Re: Low RPM low power high torque motors for direct drive

Post by CreFroD » Sat Nov 04, 2017 11:54 am

ThierryGTLTS wrote:Maxon Motor EC 90 Flat is close to you needs.

Ready to work ones and kits without axle and bearings.

Look at their Online Webshop.

Have a Nice Day..

Thierry
Thank you. But these motors have too much power for my application. And cost.

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sn0wchyld
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Re: Low RPM low power high torque motors for direct drive

Post by sn0wchyld » Thu Nov 09, 2017 8:40 pm

CreFroD wrote:Hello! For solar-powered robot design, I need very efficient, low power motors being able to give 0,5-0,7 Nm torque at 53 RPM. The operation voltage is 6.6V. I haven't seen any brushless motors lower than 30Kv. If I understand it correctly, I need 53/6.6=8,5Kv motor. Is such motor physically possible? Can I take higher Kv motor and drive it slowly, like drone gimbals do? Would torque increase proportionally? I have seen many threads on this topic, but they were about high power (>300W) motors for helicopters/multicopters working at speeds much higher, than 50 RPM. Thank you for help!
yes, there shouldn't be much issue driving a higher kv motor at those lower speeds, though it will require a more robust controller than a low kv motor (less inductance/back emf = harder for the controller to 'control' the motor.
There's also little issue driving a motor at below its rated power level - in your case, ~4W vs 90W rated for the aforementioned unit.
You could also use a gymbal motor, that may be a better option overall. 4W shouldn't be an issue, and you should be able to find one that can provide your desired torque levels.
A servo motor with its 'end points' removed may also be a good option. You can use a voltage divider in place of its pentameter to trick its brian into continuously rotating. A simple arduino program can use the pentameter's actual outputs to get an accurate position feedback too, feed that through a simple PID controller and bias the voltage divider accordingly and you have a simple and (possibly, idk how much a .7NM servo costs) cheap closed loop position control.

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