Comment Re:Gyroscopic precession (Score 1) 262
Um.
You're going to get this effect (under braking or acceleration) no matter what orientation the flywheel is using. In one case it will be precession, in the other it will be a straightforward angular acceleration. The vertical axis might work better when your speed is constant.
When you apply the brakes with a vertical axis flywheel, you are accelerating that flywheel which means an application of torque. The frame of the car will experience the opposing torque, providing a twisting force in one direction or the other, depending on which direction the flywheel spins. Drawing energy off the flywheel to accelerate the car will twist you in the opposite direction.
Counter rotating flywheels would probably solve the problem.