The Siren Board

Thought this was a novel approach for a clutchless vehicular coaster siren. The person behind CAM sirens designed a brush lifting mechanism to allow the rotor to coast after power was removed.

Drawing and patent description

Here is one that just sold on Ebay:

I had a CAM Model 4 that I sold a few years ago. It had a different method of moving the brushes away compared with this one. The commutator was at the front of the motor, between the armature and the siren rotor. The brushes were mounted to curved supports which were pushed via a crescent-shaped bar against the commutator by a large solenoid in the base of the siren stand. I could never get it to work correctly.