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BrianG
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Join Date: Nov 2005
Location: Des Moines, IA
12.23.2008, 01:47 PM

MM and MMM settings explained


The following explanation is an excerpt from a different post originally by Pdelcast, edited slightly:


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 --

Sensorless: 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.

Sensored: In sensored mode, start power limits the amount of current allowed at startup -- startup is the first few times the motor turns. This allows the motor to develop some EMF before the throttle is allowed to ramp up quickly.

If you use a little throttle at the start, you probably won't notice any difference.

Where it really makes a difference is in drag racing -- high start power will allow a faster spool-up of the motor. BUT -- it's dangerous as it is more likely to damage a motor.


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Punch Control --

Punch control is the maximum RATE of change on the throttle. So, 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

Last edited by BrianG; 01.21.2010 at 01:27 PM.
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