Quote:
Originally Posted by BrianG
Thomas, I think we (or at least I) would like a more technical explanation about how timing, punch control, and start power settings work.
For example, when I mash the throttle at a stop, the transmitter goes from neutral (~1.5ms) to WOT (~2ms) in a blink. However, how does the ESC respond to that, and what do those settings do internally to the ESC to affect that?
I see it like this:
Timing: Is this kinda like advancing the timing on a 1:1 car; where the motor signal pulses are more or less "ahead" of the rotor position to get it to spin faster?
Punch control: Does this take the instantaneous change in throttle input and ramp it up over a longer time instead, kind of like an integrator in an op-amp? So, even though the trottle goes from neutral to WOT in 1ms, the ESC ramps that up over say 50ms.
Start power: I really have no idea here. Is this some sort of current limiter? Or does the ESC send larger PWM pulses to the motor to get it running?
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BrianG --
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Timing Advance
Let's see. Timing advance is just like the timing on a 1:1 car -- In an internal combustion engine, it takes some finite amount of time for the flame front to burn through the gasoline/air mixture in the combustion chamber, so the spark plug is fired early -- to make sure that by the time the piston is at top dead center, the fuel is mostly burned, and cylinder pressure is near maximum -- making the most power.
In an electric motor, there is an effect called inductance -- inductance is a resistance to change in current in a circuit -- so current ramps up and down, and doesn't change instantaneously. At low timing, the controller is actually centering the current ramp on the switch of coils, so that the efficiency of the motor is highest. But-- it is also possible to advance the timing even more, which increases the amount of current drawn by the motor (and therefore torque) -- however, this also increases (significantly) the amount of current drawn by the motor when the rotor is in a position where it doesn't generate torque efficiently, lowering efficiency.
So timing is a trade-off of torque generation (power) and efficiency. Above a certain amount of timing advance, and the rotor actually starts generating REVERSE torque for a short period, and then efficiency drops very quickly.
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Start Power --
Start power is the maximum amount of power that the STARTUP algorithm is allowed to apply to the motor PRIOR to detecting that the motor has started (or the position of the rotor.) The higher the start power, usually the quicker the startup algorithm can successfully start the motor, but the more power might be wasted (read "extra motor heat") in starting the motor.
Remember, these are sensorless motors and controllers- - prior to startup the controller doesn't know the position of the rotor, and must "tickle" the rotor to detect rotation and position of the rotor. The higher the power in the "tickle" the quicker rotor position can be detected.
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Punch Control --
Punch control is the maximum RATE of change on the throttle. So, as Brian explained, if you go instantly from zero to full throttle, the punch control will integrate the throttle over a very short amount of time (much less than a second) to limit the huge surge currents drawn by the motor at very very low RPM. So at very low punch control settings, the throttle follows the stick as closely as possible. At high punch control settings, the throttle is "smoothed" a little more, and driveability is usually improved.
Hope that helps!!!!!
Patrick