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Discussion Starter · #1 ·
So I’ve recently been given an electric motor to sell for scrap. Prior to this I’ve been daydreaming about a three wheeled hot rod running a Ford six cylinder, however this motor has me thinking. I already got the motor(not sure if it works not sure if it’s powerful enough). The motor is down in my garage and it’s late here but I figured I’d ask what stats should I be looking at for a sub 1000lbs vehicle capable of highway speed or better?

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2 major components to "how much power do I need":

1 - Enough to overcome rolling resistance of the tires squishing. That largely comes down to the vehicle's weight. At highway speed for most vehicles this is still 50% of the power required (but drops off rapidly above highway speed). At 1000lbs, yours will be much smaller than half the power.

2 - Enough to overcome air resistance. This largely comes down to the vehicle's frontal size and shape. This is a cube function, so, to go 2x as fast requires 8x as much power. Smaller vehicles (less air to push out of the way) require less power, and slipperyer vehicles (air has an easier time sliding around) require less power. Presumably your 1000lb vehicle will also be quite small and not shaped like a brick.

For minimally acceptable acceleration and the ability to go up hill, you want about double the power available that is required to reach your max speed.

For reasonable acceleration, you want about quadruple the power required to reach your max speed.

Any power above that starts to feel a bit sporty.

Here's a calculator to use:

Set your acceleration to 0 to find out your base power requirements to reach a top speed.

You'll want to change your:
- Mass
- Coefficient of Drag (wikipedia this for a similarly slippery vehicle)
- Frontal area (wikipedia again if you can't visualize it)
- Velocity (it defaults to highway speed)
- Acceleration (set it to zero)

If you're too lazy, my rough guess is you'll need somewhere around 14 horsepower or 10kW for highway speed So, ~60 horsepower (40kW) to not feel like you're towing a boat anchor to get there.

Next, motor specs. This is a bit tricky, because motors are rated for a particular use case. They're often capable of 10-20x what their continuous rating says they are, for short bursts. They're often capable of much higher voltage than their specs say too. For example, 48v 20hp forklift motors are fairly easily given 400v and soak up 400hp in a drag race if you want them to.

But a good starting point is, show whatever you do know about your specs and interpret from there after.
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