Timing advance and gearing as BL tuning tools:
Let's look at each separately, and then how they would work together.
Advance in a brushless motor works on the same principles as it does on a brushed motor, and also very similar to a combustion engine. That is: when you advance the timing up from zero on a brushed motor, it does several things UP TO A POINT OF DIMINISHING RETURNS:
1) Raising the advance raises the Kv of the motor.
2) Raising the advance in some cases can make the motor feel punchier
3) Raising the advance generally increases motor temps
But as above - the first two of those three things will only increase up to a certain point, and beyond that point, the Kv can actually go DOWN, and the punch can go down as well with excess advance. Motor heat will generally go up in small increments up to that same point, and the next setting up can show GREATLY increased motor temps.
Timing advance is a dynamic thing, meaning there will always be an "ideal" setting to get the best mix of rpm and torque relative to motor heat, but that "ideal" figure is different for each motor, track layout, surface, vehicle, and gearing. It's even different for each state the motor is in while you're driving - as in hard acceleration out of a hairpin to a straight, slow throttle ramp up out of a sweeper to a straight, and medium/low throttle modulation through chicanes and S curves. So essentially, any time you're changing the throttle position on your Tx, the "best" advance level for the motor changes as well.
So how do you "tune" the advance to get the most from your motor? You use two main parameters and one minor one in race conditions:
1) Motor heat
Heat is caused by the efficiency level of the motor, as in - 200 watts of electrical power are going into the motor from the battery and throught the ESC, and 150 watts of power are being transfered as physical work onto the spur gear of the car. 50 watts of power are being lost due to the efficiency level of the motor. (which the tech heads will instantly recognize that this example motor is running at 75% efficiency) Those 50 watts lost are created/expelled by the motor as heat. So the lower the efficiency level of the motor (more heat/less work) the more heat it creates and the hotter it gets.
Increasing the timing from a starting point of zero can in some cases (explained more fully below) INCREASE the overall efficiency of the motor, and cause it to be cooler at the end of the run. But generally, you'll see increased temps with each notch higher advance level. What you want to look for here, is relatively small increases as you go up, and then that next setting that causes a DRASTIC temp increase. This is your "point of diminishing returns" for that particular motor/gearing/car/track/driving style/traction situation. Generally it's best to run one (high level competition) or two (club racing) settings below this point as an optimal place for the motor with a little safety factor.
2) Motor "feel"
Upping the timing from zero, you'll also notice the motor feels more punchy, and has a touch more speed (with the GT ESC, it's about 1/4 to 1/2 a 64p pinion tooth per setting speed difference) than the last lower setting. The same process as above will reveal for each motor/gearing/car/track/driving style/traction situation a certain point at which the motor will actually be slower and less punchy than the next lower advance setting. Generally you'll find that the "point of diminishing returns" as far as track feel goes, will match up fairly close to the excessive temperature difference point.
3) Battery capability
This is a minor point compared to the first two, but in some situations (mod) it can make a BIG difference on the track. Increasing timing advance generally increases the apm draw of the motor. This in turn increases the load on the battery. The higher the amp load, the lower the battery voltage goes, and the lower the voltage the slower the motor is. I've seen many occasions with NiMH packs and even a few with lesser Lipo packs that upping the timing advance doesn't change the motor temps much, but the punch suddenly goes WAY down. What's happening here is that the motor is simply asking for more current than the battery can provide, and the voltage is dipping WAY down under heavy acceleration loads. Again, a minor point but worth mentioning.
Very rarely do broad generalities work for electric systems, but here are some basic guidelines in real-world settings to go by:
1) Generally the faster the motor (lower turns, Higher Kv) the LESS timing advance it will tolerate before getting to it's "point of diminishing returns".
2) Generally the slower the motor (higher turns, lower Kv) the more it "likes" and responds well to higher levels of advance.
3) Generally the longer and more open or "sweepy" the track is, more advance can be used.
4) Generally the shorter and tighter the track is, less advance is better.
So as real world examples - If we're running a tight technical track with a mod motor, generally plan to use very low advance settings. For a long sweepy track with a 13.5 motor, generally plan to use higher advance settings.
Originally Posted by Casper
Ok. That is a good reason. Thanks for the further explination!
Excuse the stupid question as I am new to this BL stuff.
I think I understand the DRRS stuff and the reason for the low setting and I think I agree with that (got to do some track testing)
On timing with a brushed motor more timing made for a softer bottom end and higher top end. Is that still true for a BL motor?