[jonmrodriguez]

As far as the profit margin, one barrier to just building this yourself is the NRE for a suitable brushless motor controller that does speed control, handles unknown and varying load torque, and does motor braking. Or do you know of an existing alternative controller?

[jonnycowboy]

They are using off-the-shelf brushless motor controllers (from what I can gather) and off-the-shelf brushless motors. There are many makers of ESCs with your requirements including from the now-ubiquitous HobbyKing, both sensored and sensorless (for RC car applications) including this one: http://www.hobbyking.com/hobbyking/store/__17234__Hobby_King... which will do variable engine braking as well.

[skdoo]

Our motor control ESCs, remote control electronics, battery management systems, and software are entirely custom. Off-the-shelf RC parts aren't smooth, reliable, safe, or quiet enough.

[khafra]

JohnnyCowboy's concern about early motor failure from the sideloading--do you have estimates on the mean mileage between component failures, and how much replacements would cost?

[jonnycowboy]

My bad, I misunderstood your comment that you were using "(relatively) cheap brushless motor controllers".