ORIGINAL: rmh
a simple example which demonstrates the BIG difference in electric vs IC engines:
Electric has MAXIMUM torque at zero rpm - from then on, torque remains same or decreases
IC engines have max torque ONLY when engine rpm reaches the point whre the flow of fuel charge is optomized resulting in maximum pressures in the power stroke.
From then on, torque decreases -at some rate- depending on engine design
So?
well , max torque occurrs at only one point somewhere in the rpm curve on an IC (design parameters determine this point)
BUT
You start with it on the electric and can potentially reach it again at any usable rpm - depending on power supply/ speed control/design limitations, ability to provide current needed .
The corker is that you also can apply a braking force to the propeller AS DESIRED-if you have proper motor control
This is accomplished by using back electromotive force (Back EMF) which is accomplished simply by shorting out the power leads (oversimplification here) and the motor -which is trying to generate power - , generates into a ''short'' which becomes a brake .
Couldn't be sweeter.
(This technology is about 100 years old by the way - but batteries have-up till now been incapable of producing sustained power in a light package.)
Don't believe it?
I guess the post itself got lost.... from the power/torque/power curves in my previous post, you can see that the above statement is just wrong. I work on motors and motor drives every day, from itty bitty DC motors up to 700HP Vector control AC drives.......what we are talking about here is fixed magnet motors, or brushed motors. Back EMF, properly called counter EMF, is a purely induction motor phenomenon. DC motor with a field current: short the field and they run away in speed with little torque. I've done it, plenty of times. Golf cart service companies provide a kit to do this, they call a 'scat' kit. That's not how you slow down the electric models. You just back off the voltage. This is why you can't believe everything you read in a hobby magazine, written by the average modeler. It's hit or miss when you get accurate, factual information.
The ESC's in use in models are essential voltage controllers; period. No brakes, no back flow of current. Braking is called a regenerative drive, by the way.
The graph curves are why some manufacturers have computer tuning built into the ESC, to compensate for weight/prop/speed envelope. Better than IC? Depends on who you talk to; I know motors very well and I fly glow. Electrics are certainly simpler. At the Advanced line in Muncie, this year, there were two "flameouts". Both were fried ESC's. No glow engines failed. For the record, YS does not sponsor me in any way. I just prefer IC engines. Seems it brought me SOME success this year. But the power is a curve, not linear, and not max torque at zero only, and down from there. Nor does it remain constant.
Brian
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Edited to fix the quotes to what I think was intended.... Bruce