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Mar 08, 2002, 09:11 AM
Involuntary Beta Tester
Thread OP

Brushless Motors Efficiency Questions


I'm new to electrics and I've been playing around with P-Calc.
When I enter the parameters of my current motor, gearbox, batteries and get amp and flight duration sorta close to what I'm experiencing. My motor is 480 Wattage, 2.08 gearbox, and 7.75 X6 prop (Wattage prop), 8 cell 600AE

When I change the motor in PCalc to a Hacker B20 the amps go way up.

I had the impression that brushless motors are more efficient and a guess I was expecting more duration with a little more power. Instead I get 1/4 the duration because the amps are so high.

Can anyone enlighten me?

Thanks

Kelvin
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Mar 08, 2002, 10:01 AM
Supersonic Engineering
GordonTarling's Avatar
Which wind B20 are you using and what gear ratio?

Gordon
Mar 08, 2002, 12:28 PM
Involuntary Beta Tester
Thread OP
I havn't bought a brushless motor, I'm just trying out PCalc.

Thanks

Kelvin
Mar 08, 2002, 01:28 PM
Registered User
Quote:
Originally posted by kelvin
I havn't bought a brushless motor, I'm just trying out PCalc.
I think what Gordon means is that there are many different Hacker B20 motors. Which one/s are you trying in PCalc ? I.e. what 's the rest of the motor name.

People use brushless motors for all sorts of reasons. You can usually get more power OR more duration depending on which motor you choose and how you set it up. They are not simply drop in swaps that automatically improve everything without you having to think about it.

Steve
Mar 08, 2002, 08:59 PM
Involuntary Beta Tester
Thread OP
I've set up PCalc with the closest motor I think mine is a Graupner 480 7.2v. Batteries are set to 8 600AE, gearbox ratio 2.08 (prop gear 25 teeth, pinon 12), prop APC 8X4. I get about 7.7amps, 4+ minutes of duration, prop rpm 8771, static thrust 15.4.

If I only change the motor to a brushless, e.g. Hacker B20 31S it gives me more static thrust and prop rpm but reduce times due to the higher amps.

I guess I expected something like improved duration and more power.

Thanks

Kelvin
Mar 09, 2002, 12:51 AM
Registered User
Kelvin.....in P-calc,..for a given prop,you can adjust the amps down to whatever you want by changing (usually higher ratio) the gear box ratio, it varies by the gauge winds and S or L models,usually , what is optimum for the average brush motor is gonna pull way too many amps on the low turns Hacker's, increase the ratio, then you should see the thrust per amps numbers improve ...........................kw
Mar 09, 2002, 09:11 AM
EDF Head
Haldor's Avatar

Re: Brushless Motors Efficiency Questions


Quote:
Originally posted by kelvin
When I change the motor in PCalc to a Hacker B20 the amps go way up.

I had the impression that brushless motors are more efficient and a guess I was expecting more duration with a little more power. Instead I get 1/4 the duration because the amps are so high.

Can anyone enlighten me?
Well you really comparing apples with oranges here as you have missed one thing - motor kv and the resulting difference in rpm. The Hacker you entered into PCalc have a much higher kv than the Wattage so therefore it will try to spin the prop much faster hence higher amps as it needs more power to do so.

Here is what you do - enter your current Wattage combo and find the prop rpm of that system. Then with the same batterypack and prop find a Hacker that do the same rpm. Then you'll see less amps due to the Hacker better efficiency.


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