[Azimech]

For the car or the truck? I've updated post #21 with my idea why a failsafe in a car wouldn't always work.

There is an additional problem. If the car brakes are designed to engage when power is lost, you'd need to control that force. If a truck loses all it's air at once, all wheels will stop turning instantly. So when those brakepads start to push the disc, an equal opposite force minus the amount of force for a safe deceleration is needed to prevent locking up. That, is a lot of power and would mean an enormous backup capacitor or a large battery. But since the argument was about the complete loss of power, nothing can be regulated.

This could work however, if all wheels are electrically driven, and the motors work like generators when applying the brake pedal, with a failsafe that the generators would focus a defined amount of their power on a large heatsink for a brisk but controlled deceleration. For a normal application using conventional technology, this is economically unfeasible and very heavy. The force a braking system can develop is more than twice a car engine can produce. For an electric motor to have the same braking ability as a conventional system, you'd have to have a very large, very heavy motor relatively to the rest of the vehicle, so you'd need additional braking capability: disc brakes.

So for the stuff to work safely, you'd have conventional disc brakes with a hydraulic pump and a 4-way computerized brakecommand servo, and 4 generators that pump their power through a relay to a huge heatsink that can absorb the power of a that huge slowing mass.

All that as an alternative to normal operated hydraulic brakes? Call me a luddite.