# How did you determine your motor size?



## storx (Nov 24, 2013)

I am not asking about the calculations you can use to determine motor sizes and such.. i am just curious how others determined the motor they used in their project or conversion.. I am asking this because i think i am overestimating the amount of power out of an Electric motor i need to drive an 3 wheel reverse trike down the road.. 

I have been thinking kw to hp numbers all this time thinking i would need something between 50-100kw to power my bike.. but i am coming to quick conclusion that this is not the case.. I recently bought an 2012 Chevy Volt for 12.5K out of a bold move to reduce driving cost after totaling my last car.. and i didnt know the electric motor in that car is only 110kw peak pushing a nearly 4,000lb car down the road at no slouch rate.. when i do the math that is about 36lbs/kw ratio.. 

My goal weight on the build is around 800lbs or less for the bike, so if i went off the same principle as the volt for similar acceleration, i would need something around 22-23kw only... hmm 

How did you determine your motor size for your project?


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## IchibahnSLC (May 22, 2015)

If I'm to be honest I happened on my fb1-4001a . Got it for $180 so yeah...


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## bigmouse (Sep 28, 2008)

Keep in mind that power is only part of the equation.

Power = torque X speed. The beauty of electric motors is that they have full torque at zero speed.

Any torque at 0rpm is 0kW. Your power it determined more by the voltage you can supply than it does with the motor. The motor is all about torque. For an electric motor, torque is roughly equal to current X some constant (torque per amp) factor. So as long as you have that current flowing, you'll have that much torque, no matter what speed.

In short, your Volt has plenty of torque, so it feels fast, even with only 100kW peak power.

Anyway, my motor selections have always been based on the torque capability of the motor, not the power. I just make sure I size the battery and controller to get the amount of torque I want up to whatever RPM I want.


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## dcb (Dec 5, 2009)

you kind of do have to look at the calculations...

you need to have a reasonable guess on the aerodynamic and friction drag of your vehicle at different speeds, this tells you how much hp you need to achieve a given speed, and top speed (assuming you gear it right) on a level road with no wind for a given horsepower.

Acceleration is a function of power and weight (and gearing).

With gearing you can trade top speed for acceleration, but acceleration is limited by tire slip, especially in a reverse trike, so there isn't any point in delivering much more torque to the rear wheel than it can handle if you are thinking about a single speed (it will only reduce your top speed). More calculations...

But the actual motor selection for me was a cheap 60hp ac motor for a motorcycle...


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## storx (Nov 24, 2013)

dcb said:


> you kind of do have to look at the calculations...
> 
> you need to have a reasonable guess on the aerodynamic and friction drag of your vehicle at different speeds, this tells you how much hp you need to achieve a given speed, and top speed (assuming you gear it right) on a level road with no wind for a given horsepower.
> 
> ...


Which motor did you use that was a cheap 60hp ac motor?


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## dcb (Dec 5, 2009)

it was an ac24ls, a couple hundred on ebay, but sorting out the controller is another matter (which requires some calculating, or get a match set) as are suitable high voltage batteries, etc. A brushed controller is much simpler to sort out. You can also surf evalbum.com for motorcycles to see what other people use and what sort of performance they report, and add some fudge for being a trike.

http://www.evalbum.com/type/MTCY


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