Im curious why we use brushless motors in RC? Is it important to have have maximum torque at 0 rpm with an decreasing slope? Isnt the point to understand your RMS velocity on a track and select a motor and FDR that aligns peak efficiency of the combination to the track?

An asynchronous motor is built for horsepower and the torque curve is the exact opposite of a synchronous motor. Wouldn’t that be a better place to start your hunt for speed?

I understand that if you calculate your rms torque for a track and its skewed towards low rpm synchronous is the way to go and Asynchronous for an application skewed towards higher rpm.

Isnt the point to align the efficiency curve of the motor to the application needs?

i think the critical thing about motors that doesnt get discussed much....that I would like to mention to create context is continuous torque is not what allot of people understand it to be.

you want torque to change velocity. Current creates torque and torque creates acceleration. If it takes 2 or 3 times the current to accelerate versus maintain a speed how come we cant dump 2 or 3 times the current into the motor continuously and just have more torque or more speed all the time? (Assume torque controls speed)

this is why most data that gets published (rarely in RC) shows 2 torque/speed curves and maybe an efficiency curve. One curve (peak or intermittent)is 2 to 3 times higher than the second one. A continuous torque curve (which is what you need to use when selecting the right stuff for an application) is really a peak curve restricted by the motors ability to dissipate heat continuously without exceeding its specifications. Its called a thermal time constant. If a motor is selected and the track you are running on requires and average speed/torque right in the middle of the efficiency curve isnt less heat being wasted and you are spending most of your time in the most responsive portion of the motors capability?

I only explain the torque curves because there is allot of anecdotal data people use to justify a selection....which is ok...and I even recommend things this way sometimes when i dont have something to measure. In robot design we use allot of basic physics that I dont think allot of people are exposed to this combination of information in RC or at least I havent seen it applied. im not here to really prove something to the world but understand if there is a difference. Also when I say robot I mean anything that is controlled by a servo with high/low inertia mismatch and a requirement for high/low dynamics. Robots is a catch all.

It’s been only brushless since I got in hobby in late 2010. I do own a few running brushed but not for any particular reason other then they came that way, liked how the ran. So I only know the stories of the old brushed days. Simple reason I’ve come to understand it’s they are overall simpler and far less maintenance then the old brushed motors. Hopefully those with experience from the brushed days will respond.

Most of your question I know I don’t understand what’s being asked.

Yea, sorry. i do appreciate the intel but i should have used English. i said synchronous and Asynchronous. The best way to understand it in the real world is an AC motor versus a DC motor. The torque curves are polar opposites. The DC motor creates an electromagnetic field that is synchronized to the rotor of the motor and can be very dynamic but typically has a low rotor inertia so its better for full stop and start. An Asynchronous motor has a higher rotor inertia and the pulses that rotate the rotor maybe faster or slower than the poles on the motor. (Slip)

im glad it doesnt sound insane. if your track keeps your motor at an average speed closer to max than minimum having a torque curve that is fat at max makes sense and vice versa of course. Cogging should be an issue in a race car at least its level of importance should be lower than the conversion of current to torque and minimizing heat.

I know its easier to minimize cogging with a very high speed switching frequency but then you get more heat waste. Have you seen a drive or an ESC that maybe switches from 16k to 4k? if you can change the switching frequency without a noticeable bump you may be able to stay asynchronous and just close the velocity loop faster at low speed and cooler at high speed.

agreed. The synchronous motor has great 0 speed torque but how many people are competing at low speed? I guess the first place to start is by looking at the RMS power for a standard track. If the average speed is above 50% just go simple AC motor (or asynchronous non permanent magnet brushless motor).

do you know how sinusoidal the waveform is? Is it more trapezoidal? I know that if the power circuit creates a waveform other than what the motor is designed for you get waste in the form of heat.

There was much more tuning opportunity with brushed motors than there is with brushless (windings, timing, shimming, air-gap, brush hardness/cut, spring stiffness, commutator diameter, armature stack, etc..). It was common for a guy who liked a 12-turn to have 3-5 different windings (single through quad strand windings) of just 12t. Some used actual Dynos to tune their motors. It was more than a little crazy. They were also just as powerful (modified, stock is on a different level now) even with nimh batteries. Ever since batteries went up over 3,000 mah, we’ve had an excess of power available. Brushless has pretty much saved electric racing for its ease of use and maintenance.