I understand all this, and the limits set up in the radio are fine, but setting an ABSOLUTE LIMIT to Duty Cycle - enforced in firmware - would reduce the possibility that the receiver (or, in my case, robotic brain) would send the model, uncontrolled, in to a concrete wall.
Because, if the MMM glitches out, chances are the model will just freeze. If my robot controller glitches out, then there is a GOOD possibility that the model WILL fly.
A PWM Duty Cycle limit would be very useful for me, efficiency be dammed.
Not to mention, if you have kids and you want them to try out your pimp ride, wouldn't it be nice to just limit the high end to kid safe speeds?
Quote:
Originally Posted by BrianG
There are only two ways to limit the voltage to the motor:
1) Through chopping off the excess voltage. This is known as linear regulation and is extremely inefficient because the excess voltage X current flow = power needed to be dissipated on the FET. So, if you drop the voltage from 6s to say 4s, that's a 7.4v drop. At even a low 20A, that's 148w! So that's out.
2) Through PWM. This involves sending narrower pulses to the motor. So, if you send 6s pulses (22.2v) at 10% duty cycle ("DC"), the motor is seeing an average voltage of 2.22v. 50% DC = 11.1v, and so on. This is what gives you efficient variable speed capability. The trouble with limiting the DC, as others have noted, is that everything runs better at full voltage. So, despite the somewhat less efficiency of limited DC, this would be the only practical option.
So, to get what you want, it would just be a matter of setting your throttle EPA to something less than 100%. Or, you could use programming on the ESC instead, but it's just easier to use the radio (and allows you to change on the fly).
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