no load amps

[antslake]

I have a King of Shaves P1 running a wire drive and a x640 prop, suppo 2200kv, what should I expect to see for no load amps when spinning the whole assembly? Is this a good way to test if you have something binding? I am at 10amps on 4s, I think like 40k rpm's, but I have to double check that.

[NativePaul]

While it is a way to check for binding I wouldn't recommend it. Running out of the water unloaded is a good way to burst the motor and (if your strut uses lead-teflon bearings or you use a teflon liner in your stuffing tube) running it without water lubrication is a good way to melt the teflon seizing it up, winding up the flex, ripping the stuffing tube out and burning up your ESC.
I undo the coupler and spin the shaft by hand.

[Jesse J]

He is running wire drive, but risk to the motor may remain...
However,with an out runner, what is the data indicating that it will hurt the motor? Aren't they used in airplanes that occasionally in a fullspeed dive may reach near unloaded conditions??
Who has actually witnessed or knows of an instance that this test has damaged the motor?

And yes spinning by hand unconnected to motor is how I do it to.

[Fluid]

An unloaded motor is very inefficient, and will get hot very fast. High heat is never a good thing. Outrunners have rpm limits which are usually lower than a corresponding inrunner, this due to the high centrifugal forces on the magnets attached to the thin, flexible rotor. (BTW, max rpm is under 32,000 in the PO's setup.) Combine high heat with high rpm and the risk of failure is increased. But the real answer is - why do it? What is the advantage? What usable information do you gain? None whatsoever. Like texting and driving, just because you can doesn't mean you should....



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[m4a1usr]

what should I expect to see for no load amps when spinning the whole assembly?

You would see the IO for the motor, plus some amperage for the friction related components. But I wouldnt do it over 10 volts since thats were the motor IO is calculated from. However, having stated that it truely serves no purpose since you dont have a baseline to compare it against.

On the other hand, if you were building kits or RTR boats it would serve as a guide or range where they should be before getting packed up and sent out to customers. Could be a quality control tool for a business.

John

[antslake]

Good advice guys. Yes Jesse, I am running a wire drive currently, but I wanted to see the difference between wire and flex, which one drew more would be an indication of resistance and efficiency. I only do it for a second so I can't see it heating up and ceasing. Everything is greased, and I run a bearing in the strut. Using 10the volts makes sense, and I should limit my tests to operating rpm's.

@ fluid. My outrunner has seen 60,000rpm and held together thank God. Running rpm is 40k or under. I never understood the purpose of making high kv outrunners. Outrunners are torque monsters and should be taking advantage of. I have blown magnets off an axi motor in my plane once.