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Old Jan 24, 2013, 07:01 AM
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Joined Jan 2013
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Thrust and movement

Hey guys, I have a trolley with a mass of about 80kg on castors (125mm, able to handle up to 100kg), and I want to make this a propellor powered car.

What I want to know though, I have a 3.2kw Brushless motor with a KV rating of 230, along with a 19x10 prop. I'm running the whole electrics system off 24v with a maximum supply-able peak current of 480A, My ESC is rated at 100A.

How can I know whether this setup will be able to push my system or not? 3.2kw of motor seems one hell of a lot as I have built go karts and other such projects on just 500w successfully.

The trolley has to be air powered.

Cheers, Harris
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Old Jan 24, 2013, 02:51 PM
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Denver, CO
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Best to make it simple. Find out how much force is needed to move the trolley. Then find out how much thrust the 19x10 prop will put out. Depends on the prop design, but typical of a 19x10 is around 17 to 18 pounds of thrust between 7000 to 7500 rpm.
At 24 volts, and 230kv equals about 5500 rpm. So might be nice to gear it, to get a little more rpm. It should not come close to the power rating of the motor, unless used with a larger prop.
I don't have numbers on a 19x10 at such low rpm, but I figure it would move the trolley.
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Old Jan 24, 2013, 09:01 PM
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What would be the best way to calculate the required force? I don't really have any form of force measuring equipment. If the trolley was literally being dragged along the floor, I could use the coefficient of friction equation but i'm not sure how to calculate this using castors.

Anyone know how?

Cheers,
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Old Jan 24, 2013, 09:24 PM
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I'm not too up on mechanics but I know that the hardest part will be overcoming the static friction.

Knowing that F=uN (u being coefficient of friction)

The coefficient of friction for a ball bearing is apparently around 0.0015,

N=mg with no vertical net force so n = 80*9.81 = 784.8N

Now knowing that the only main opposing force is friction (not accounting air resistance which is pretty mega), Fr = 0.0015*784.8 = ~1.2N which seems awfully small!
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Old Jan 25, 2013, 02:32 AM
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If you can easily push it with one finger, it should be fine. That is unless you have very strong fingers.
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