# BLDC Motor Reccomendations



## MT_DEWSKY (Oct 24, 2015)

Hey everyone,

I'm currently an EE student and part of a SAE Supermileage team. I've been researching motors over the past week or so. Our team needs two new motors to drive our electric car. We currently have a set-up of 24V system, and about a 3200rpm gearbox. We're looking for a motor that has at least 86% efficiency and is at $350 or under. 

I've found a few places that could potentially work, but I can't contact the companies to get specifics. The motor can have a controller but it must be removable. It's a requirement that we build our own. I've found motors similar to this: (http://www.anaheimautomation.com/pr...ess-motor-item.php?sID=369&pt=i&tID=96&cID=22).

Any help, ideas, experience, or links would be incredibly appreciated. 

Thanks.


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## kennybobby (Aug 10, 2012)

You will need to define the vehicle requirements before it is possible to pick a motor. See for example this thread, http://www.diyelectriccar.com/forums/showthread.php?t=89694


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## MT_DEWSKY (Oct 24, 2015)

So I did some calculations and I also used the two links for calculators. Attached is what I have for information. Our gear ratio is 10:96. We'd like to find something that is able to be run off of the 24-28V supply we have now. We can use two motors to drive the wheel if needed as well.


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## kennybobby (Aug 10, 2012)

Assuming that the 220 lbs includes the pilot, then it looks like you need 1.1 hp to travel at 35 mph, and 2.3 hp for the given acceleration rate.

The other requirement you need is the duty cycle, or length of time it must operate and survive without over-heating or melting down, etc.

Until we know the duty requirement, let's just assume that a 1.5 hp motor could operate continuosly at 1.1 and could be run short term peak at the 2.3 hp, in order to meet the kinematics.

1.5 hp is 1120 Watts, so with a 24 V battery you would need 1120/24 = 47 Amps nominally. 2.3hp = 1715 Watts/24V = 72 Amps needed for the acceleration phase, and 1.1hp = 820W/24 = 35 amps needed to run at the 35 mph steady-state speed. Assuming flat land, no hills or wind. The electrical current values along with the duty time can be used to size the battery pack.

You already somehow have a gear ratio selected (bicycle chain and sprockets?) without knowing the vehicle torque requirement, but Paul's calculator indicates that you need 21 ft-lbs at the wheels. So using your 10:96 ratio, 21ftlbs*10/96 = 2.2 ft-lbs at the motor, and from the calculated wheel speed @ 588 rpm, so 588*96/10 = 5644 rpm at the motor. So now you have some minimum motor specs of what you need: a nominal 1.5 hp motor able to produce 2.2 ft-lb of torque at 72 amps, and run 5700 rpm on 24 Volts.


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## MT_DEWSKY (Oct 24, 2015)

We currently have a set-up from the previous year. The old motor was a DC brush motor and we are looking at getting a more efficient motor. The gear ratio is what was used last year. I'm having a hard time finding a BLDC motor that will match our set-up. This link is what was used last year(G43-500): http://www.ampflow.com/four_inch_high_performance_motors.htm

Here's our power source: http://www.headway-headquarters.com/24v10ah-diy-headway-battery-kit/


The weight includes the pilot. The duty cycle will be decided by the driver on whether to coast or accelerate. We're shooting for maximum mpg-e in a competition. Last year pulled less than 20A with the brush motor.


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