Low RPM low power high torque motors for direct drive

Electric Motors and Controllers
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CreFroD   1 µW

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Low RPM low power high torque motors for direct drive

Post by CreFroD » Nov 04 2017 8:21am

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   100 mW

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

Post by ThierryGTLTS » Nov 04 2017 10:52am

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   1 µW

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

Post by CreFroD » Nov 04 2017 11:54am

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   1 MW

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

Post by sn0wchyld » Nov 09 2017 8:40pm

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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usertogo   10 W

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

Post by usertogo » Jul 05 2018 8:36am

CreFroD wrote:
Nov 04 2017 8:21am
solar-powered robot design
Is this project ongoing? I also got myself two 'hoverboard' motors (350W max. each) for this purpose... Its for a small prototype that will initially be challenged to clean my sidewalk...

mechhead   1 W

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

Post by mechhead » Jul 19 2018 8:12am

you can get plenty of gimball control motors for drones the larger ones have a 80mm dia stator and come in very low kv forms wound with fine wire, not good for high power levels but high efficiency 3 phase brushless motors that will turn slowly on your low voltage with a cheap sensorless controller. They often use the same frame and magnets as the high powered drone motors but are would with many more turns of single fine strand wire they are designed to point cameras and can get quite large for the larger camera support types capable of rather large holding torque and fairly slow rotation, probably ideal for your setup you may even be able to hack a gimbal motor controller to provide continuous rotation at variable speeds or use a cheap 24v ebike sensorless controller to drive them

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