Help with a DC motor safety device idea

Hello all,

I have an idea to use energy stored in a capacitor to drive a small DC
motor in the event of power loss to the system.

Will something like this actually work?  How would I determine the size
of capacitor needed?

I assume that I would charge the capacitor each time the motor runs
normally, so in the event of power loss after a loading cycle, I would
be able to then activate a switch, and used the stored energy to
complete a singl unloading cycle.

Any ideas would be greatly appreciated.

Mike