# Small motor, low speed, high torque



## rob2011 (Aug 16, 2011)

Hello, i'm new to the board, and i'm planning to build a small neighborhood vehicle, kinda like a golf cart. It's going to weigh about 800-1000lbs, top speed could be 10mph or less, and range 3-5miles between charges.

I would like it to have lots of torque for going uphill. So my questions are:

- am i right to think DC motors would be best, because of high torque from standstill?

- if so, which kind? brushed or brushless?

- can i use reverse with a simple switch setup?

- I've seen golf cart motors, and a 5HP is about USD600. And i've seen RC motors like this
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5139
which has 7kW max power, and it costs USD100. Why is that? It's also very light. There must be some drawback. 

- Anyway , i'm looking for something very light and that doesn't need to run at high RPMs. any suggestions?

thanks


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## DawidvC (Feb 14, 2010)

Small motor, low speed, high torque: - pick two .

Unfortunately you won't have all three in the same motor.
If you are really interested in getting as close as possible to your (nearly) impossible specifications, do have a look at rcgroups.com. They do produce torque and power near to what you are looking at, if you can live with the high rpm's they run. They have some outrunners doing 8000rpm that otherwise fit the bill.

Another solution (also DIY) would be to look at some of the high-power diy wind generators built from ex-washingmachine motors. That would becloser to what you are looking for, but you will have to make your own controller.

BTW, a brushless dc motor is a form of ac motor, and have nothing but the name on common with dc motors (OK guys, no debating, just simplifying)

In general, the torque of any electrical motor is related to the rotor diameter, so the larger the rotor diameter, the more torque you get, *IF* all else stay the same.

Regards
Dawid


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## rob2011 (Aug 16, 2011)

Hmm, i think i understand. Then i'm willing to use a bigger, heavier engine, to get good torque at low RPM. Or maybe i could use a reduction, but that would add weight and complication.

I'm planning to use 2 motors with about 5Nm of torque each, using direct drive to each half axle. 

One issue i have when browsing motors is that they never tell how much torque they produce. Is there a way to estimate that?


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## ken will (Dec 19, 2009)

how about some of these:
http://www.golfcartcityonline.com/golf-carts-for-sale/mechanical/motors/


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## sonicj (Mar 17, 2010)

if it is about the size of a golf cart, sticking with golf cart components might be in your best interest. 

complete Graziano rear end with brakes $130

club car regen motor $169 shipped
-sj


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## rob2011 (Aug 16, 2011)

Thanks Ken. I've seen ome of these motors and the thing is, i don't know how much torque they have, they just say some are "high torque". 

There's also those ebikes hub motors, and some of them have a pretty impressive torque.

There's an online calculator at ebike.ca that shows that the BMC V2 can generate 150lbft at 5km/h. THose motors are wide, but they are only about 5cm thick. looks pretty interesting, anybody have any experience with them?


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