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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Thanks for the technical response. Are you a sparkie in real life? I am but just dont get into this part of it. I do realize that these things run better at full voltage, but thats about 50mph on everyones vehicles. I would assume less then 5 percent of someones run is always at full voltage. There just isnt enough street or track to keep them at WOT all the time. So sounds like it would be a simple programming change for the controller, but chaning epa on radio might be easier. I have never played with that feature, I guess I need to look.
What about an extrenal transformer between the batts and the controller? Maybe something like the Castle BEC with variable voltage output, but on a much greater scale? SAy 200A of handling power instead of 4A
This would be a great feature for the new E-revo as a user could dial his power output based on experience. I highly doubt the new traxxas 2.4 gig radio is going to have an epa setting.