Tip brakes (and tail rotors) consume additional power. Differential collective has very little effect on power consumption.
The blades on the two rotors of a coaxial are set so that they always cross at a specific azimuth, to minimize vibration. This rules out the use of a rotor brake, since the brake would slow both rotors.
From the Department of Demented Designs
Where the lights are never turned off ~ because the light never really came on.
This is a concept for yaw control on a coaxial rotorcraft. It does not brake or consume additional power and it does not require differential collective.
Unfortunately, it does not maintain a fixed blade crossing at a specific azimuth.
OTHER: Miscellaneous - Thoughtless Idea - Coaxial Transmission w/ Yaw Control
Dave