The inertia of a flywheel depends on the shape of the flywheel and its mass. the energy stored is then = inertia x angular velocity^2.
as the velocity is squared it means that making adjustments to the speed has a greater effect than changing the mass...
So the development of the system would bring us down the road of reducing the mass to an acceptable level while changing the shape and increasing the flywheel speed to a maximum...
By doing the maths we figured that the flywheel weight could be reduced to 5kg and be capable of storing more energy just by changing the shape of the flywheel (having more material at the edge) and increasing the gear ratio.
Learning process!!!!