A mechanical energy accumulator, suitable for being mounted in a vehicle has a spherical housing with three pairs of flywheel assemblies mounted therein. Each of the pair of flywheel assemblies is rotatable in opposite directions about a respective axis. Each of the axes are perpendicular to one another. At least one permanent magnet motor is mounted within the flywheel assemblies. Each of the flywheels of the flywheel assemblies has a double conical flywheel base, a motor-generator suitable for driving the double conical flywheel base, and a flywheel lid covering the motor-generator. The mechanical energy accumulator may be mounted in a shell having an expansion member. The mechanical energy accumulator has a strong side and a weak side due to varying retention strength of windings therearound so as to create a controlled burst.