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Author Topic: high torque-low voltage geared BLDC motor  (Read 581 times)

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Offline thandarTopic starter

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high torque-low voltage geared BLDC motor
« on: April 08, 2014, 09:39:11 AM »
hey everyone,
Im designing a robotic arm and looking to combine a 12V or 24V bldc motor with a suitable gearbox in order to give me torque up to 500Nm. Do u think thats posible? if so can u suggest any particular geared motor?
I dont know if it is allowed in this forum but can u also suggest me some online shops for motoros and gearboxes? thanks in advance  ;)

Offline jwatte

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Re: high torque-low voltage geared BLDC motor
« Reply #1 on: April 08, 2014, 10:22:29 AM »
For equipment as heavy duty as 500 Nm, you will not find "hobby" style stores that carry these.
You will have to look at industrial supply companies that specialize in motion control.
Also, for that level of torque, you may need to look at AC induction motors, as permanent magnet based motors may not be available that can achieve that.

How fast do you need the shaft to spin at? Achieving 500 Nm at 1 rpm is going to be a lot simpler than achieving 500 Nm at 100 rpm!

It may be that the power you need requires you to go to electric vehicle type motors. These typically require drive voltages higher than 24V -- the Nissan Leaf runs at 400V, and has 280 Nm of torque. But, again, what speed you need is an important factor.

Places that sell this kind of equipment can be found on Google -- just look for "motion control."
Expect to spend many thousand dollars for the motor, and as much more for the control/inverter circuitry.

Offline thandarTopic starter

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Re: high torque-low voltage geared BLDC motor
« Reply #2 on: April 08, 2014, 11:23:58 AM »
at first thanks for the immediate response.

speed isnt a problem for me, I wouldnt mind to get that torque even at 3rpm or 1rpm as u said. Im looking for bldc cause I wanna have the motor as compact and light as possible. and I wanna keep the voltage low cause Im planning to use batteries to power the robot

Offline thandarTopic starter

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Re: high torque-low voltage geared BLDC motor
« Reply #3 on: April 09, 2014, 05:45:04 AM »
well budget isnt a problem at this stage  :P
about specifications the things I rly care about is high torque, low voltage and as small size as possible. I've calculated that Power of 150W-200W would be efficient. Im open to suggestions

Offline jwatte

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Re: high torque-low voltage geared BLDC motor
« Reply #4 on: April 09, 2014, 10:49:16 AM »
If I remember right, 1 Watt is 1 Newton-meter per second. If we put that calculation in, you'd have to gear a 200 Watt motor so it spins at 0.4 rotations per second to deliver 500 Newton-meters.

There's nothing wrong with BLDC motors as such. They are very popular in hobby RC circles, for example. AC Induction motors are also compact. They work on a principle similar to BLDC, except they don't need a permanent magnet but instead generate the counter-magnetic field through induction. If you want lightweight, I think coreless motors may also be lighter-weight than brushless permanent magnet motors.

I don't know if a gearbox that goes from 12000 rpm or whatever to 0.4 rpm will be available off the shelf, as I'm not a mechanical engineer who does motion control for a living or buy these things very often :-) I checked a reputable supplier like Maxon, but they only go up to 120 Nm in standard products with planetary gearboxes, and less with spur gear boxes. Perhaps check the automotive industyr for a suitably strong gearbox?

Offline thandarTopic starter

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Re: high torque-low voltage geared BLDC motor
« Reply #5 on: April 09, 2014, 12:25:55 PM »
well theoretically a 200W motor rotating with 4rpm could give about 480Nm. That would do  :P
but as u said I cant find such a gearbox on the shelf...
should I use harmonic drive instead of a planetary gearbox??

thanks for the advice, I'll check the automotive industy and review the AC induction motors
 

Offline Tommy

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Re: high torque-low voltage geared BLDC motor
« Reply #6 on: April 09, 2014, 04:07:52 PM »
Quote
if so can u suggest any particular geared motor?

thandar, not sure about your application, but I'v had a notion of using these type motors(link below)
with an electric brake(a must for that type application) and encoder(also a must have) for an arm type device.

http://www.robotmarketplace.com/products/NPC-B81HT.html


Tommy

 

Offline gerard

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Re: high torque-low voltage geared BLDC motor
« Reply #7 on: April 10, 2014, 09:04:18 AM »
Quote
if so can u suggest any particular geared motor?

thandar, not sure about your application, but I'v had a notion of using these type motors(link below)
with an electric brake(a must for that type application) and encoder(also a must have) for an arm type device.

http://www.robotmarketplace.com/products/NPC-B81HT.html


Tommy

this motor barely passes 100Nm
even heavy duty ampflow gearboxes ahave a failure point of 400Nm

for 500Nm you will need some industrial grade motors and gearboxes
nothing even close to light 'light'

Offline jwatte

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Re: high torque-low voltage geared BLDC motor
« Reply #8 on: April 10, 2014, 10:11:50 AM »
Quote
theoretically a 200W motor rotating with 4rpm could give about 480Nm

That's not what my math says, but my math could be wrong. Could you show your formula so I could figure it out?

Offline thandarTopic starter

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Re: high torque-low voltage geared BLDC motor
« Reply #9 on: April 10, 2014, 11:40:44 AM »
at first thank you all for you answers
@ tommy even if torque was sufficient this kind of mechanism doesn't fit with my designs. ofc its my fault cause I haven't made clear the exact purpose of my arm.

@jwatte I used this formula (Torque (N.m) = 9.5488 x Power (kW) / Speed (RPM)) for my calculations but there is a possibility to have been misguided :P what u think?

Offline jwatte

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Re: high torque-low voltage geared BLDC motor
« Reply #10 on: April 10, 2014, 02:09:50 PM »
I think you're right -- I had the rpm/omega conversion wrong. That takes the necessary gearing to something like 3000:1 (depending on the RPM of your motor.) With a gearbox that an withstand 540 N.m. That's into performance car/motorbike territory...

 


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