I'm sorry, I just tried your circuit and the capacitor is charged by the battery and no L1 (motor) flyback goes to capacitor.

Luc

this is boost  converter diagram .....place  L1  with DC motor...and change single diode into bridge recifier

This is a great experiment but I can see the inefficiency of the current configuration.
A better solution would be to use a bank of caps instead of a single cap and increase the switching so the motor is being powered more often than every 360 degrees. I would also do away with the remote motor powering the switching since that is an extra draw not needed.

The more caps you can include and the more switching the better, you can liken it to a conventional petrol engine. The more cylinders you have the smoother it runs.

I will use 4 caps to explain. (but you could use more)

4 caps will require 8 switches. 4 switches for dumping and 4 for powering the motor.

Now instead of your power/dump cycle being how it is currently you can adjust it to every 90 degrees
 (360 / 4 cycles = 90)

You would need to build a distributor plate that sat at the rear of the motor to fix the 8 switches to.

Every 90 degrees the battery would supply the motor, as the motor rotates it would engage/ disengage the switches via a cam fixed to the shaft of the motor.

You would need to have the switches fixed in pairs with the leading switch in each pair being the dump and the second switch in each pair being the supply to motor.

Picture a clock, you would have a switch just before 12 o’clock  and a switch just after 12 o’clock and repeat at 3, 6 and 9 o’clock.

As the cam approaches the 12 o’clock position, it activates the dump switch  just as it passes it activates the power switch. As it travels to toward the 3 o’clock position one of the caps would be collecting EMF. As the cam hit’s the first switch at the 3 o’clock position it would dump the charge to the battery. As it passes the 3 o’clock position it would activate the power switch and the cycle starts again.
The more switching that can take place the smoother the motor will run and less torque lost, the maximum switches used would be governed by how quickly the caps can charge during a cycle.

You may even be able to increase the power available by including an alternator/generator driven by the motor. Perhaps charging a second battery whilst the first is in use.