Quote:
Originally Posted by Metallover
hmm, yes I was thinking brushed, but induction would work too. But it all comes down to if a neodymium magnet is stronger or weaker then an electromagnet of the same size. If you could get an all electriC motor to work, you wouldn't have to worry about temps as much because there are no magnets to demagnatize. You would have to worry about things melting like plastic and insulation. That means in theory if you have a very powerful esc then you could put as many volts as you want and gear as highas you want until to either reach the escs limitations or you start melting stuff...
It whole probably have to be induction because brushes would wear out fast. Another peopem would be efficiency. It would have to be very powerful to be as efficient as two motors.
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Neodymium is actually stronger than an EQUAL size electromagnet. Remember, most of the magnets in the motors we use are really small. You couldn't pack much electromagnet in that size. :)
Electromagnets have a limitation based on the characteristics of the steel that is used to carry and concentrate the field. There is a point at which the steel carries the maximum amount of magnetic flux that it can carry, and it won't carry any more. This is called "magnetic saturation", and when that point is hit, the electromagnet doesn't get any stronger.
So, you could make a pretty powerful electromagnet-electromagnet motor, BUT, it would be larger than an equal power permanent magnet motor and would be a little less efficient. What would happen at maximum output (instead of demagging) would be that it would get hotter and hotter (very quickly) when the steel saturated, until the windings failed. This is what happens with Cobalt magnet motors -- the cobalt magnets won't fail until over 1000 degrees (F) -- but the windings fail long before that. Plus, a much larger magnet is required because cobalt doesn't have the power of neodymium -- so the motor is larger and heavier for the same output power.
SO, therefore, today you just can't make a more powerful motor than a DC brushless in the size we use (sub 5 horsepower.)
The maximum power output of a motor ALWAYS comes down to efficiency... efficiency is really the "holy grail" of motor design, because the losses always become heat in the motor, and you must shed that heat to produce power efficiently ... And if you think about it, you can output twice as much OUTPUT power on a 90% efficient motor as you can on an 80% efficient motor.
We in the industry are always looking to increase the efficiency -- to keep the temperature down when running huge amounts of power into the motors.
Patrick