mmm settings
 

hey there guys. got my mmm combo up and running yesterday. i was just wondering about the startup power thing. currently have it set at medium. does anyone here run it at high and what kind of difference does it make. what are the main advantages/drawbacks.

im running a pair of 2s trakpower 25c 4900mah lipos.

thanks for your help

If you click the "?" next to it, it'll explain it and what each setting is for.

I use High start power because my lipos can handle the load and IMO it reduces cogging and gives me more juice off the line (not like I need it, my tires can never keep traction at any speed).

any one else care to explain. im using trakpower 4900mah 25c continuous, 50c max burst discharge lipos. would these be ok on high startup power?

High start power is generally used when there is a dnager of cogging, auch as in a crawler or with low kv motors which are hesitant to start spinning from a standstill- same apllies to a truck with very tall gearing.

Thats my understanding anyway- I set my start power to low in my gmaxx, and it rarely coggs, just occasionally hesitates once in a blue moon before it takes off like a rocket as I bury the throttle. :smile:

Motor Start Power
 

Motor start power is basically how much energy the speed control sends to the motor from a dead stop. The higher the setting, the more power the motor tries to pull. How much energy it does pull is completely dependent on the batteries abilities. I generally recommend running this as low as necessary for your needs. If you need more power off the line, increase the setting; this can also help with certain types of cogging where the motor requires more energy to start. Our motors generally run well on medium or low. If you're happy with the power, then there's no reason to increase it. The only thing you gain is quicker take offs, and sometimes eliminating cogging. The down sides are lower run times, higher motor and battery temps, and sometimes higher ESC temps as well.

**But remember, this puts a larger strain on your battery and motor** The extra energy can only come from the battery, so the more you pull from the motor, the less run time you get and the harder you push you the battery. Setting the start power too high on an insufficient battery can damage the battery over time, or cause it to puff up more than my belly after the holidays.

As a rule of thumb, error on the side or lower timing. If you're not having troubles with the motor starting up smoothly or insufficient torque off the line, leave it on medium or even set it to low.

Hope this helps clear things up a bit, but if you have more questions, please don't hesitate to ask.

Thomas Porfert
Castle Tech Support

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?

Great questions, I would like to know the answers to these as well!

Please see Patrick's reply 2 posts down, he breaks down every setting in easy to understand wording. He's a master at taking complex ideas and explaining them in a simple and comprehensive way. Learned more from him about electronics than any book I've ever read!

Better yet, just post the firmware source code and we'll figure it out. :wink:

J/K, but I had to try. :smile:

Thanks in advance for getting that info though. I always like to understand how things work, not just accept that they do and that's it.

Once you get the lowdown, I'll add the info to the sticky thread that already contains information about various aspects of BL that Patrick already talked about.

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

Thanks Patrick! Also added this information to this thread.

Kinda like pre-ignition on 1:1 cars?

It might be better to write the setting unit in actual time scale, say xx ms, than in percentage, so that the user can actually KNOW(instead of GUESS) how much effect the ESC is doing. :yes:

That would definitely be nice. My MGM ESC does it's "Soft Start" in seconds, maximum is 1.6 seconds :surprised: It's a good way to keep the wheels on the ground, tires attached to the wheels, and keep your Traxxas R/C from coming apart, though even with Soft Start I still smoked a Revo :slap:

Great explanations. Thanks.

HK3948: I have been using high start because I had problems with cogging before all the firware upgrades and I never changed it back. I used a Neu MM and TrakPowers like you.

Sorry Himalaya, Punch control just isn't simple enough for us to display a time scale.

Punch control is non-linear, and designed to keep control of RMS currents. So, for example, it will ramp slower between 10% and 35% than it will between 75% and 100% throttle, even though they both change by 25%.

We could probably display the full-throttle range time, but that would be misleading to the end-user, as ramp times would typically be MUCH quicker than the worst-case.