The objective of our design project was to increase the functionality
of the Zappy scooter produced by Zap, a manufacturer of electric vehicles
located in Santa Rosa, California. The Zappy is designed with only
one control device, a finger-activated switch to turn the motor on
and off. It has no speed control. This design limitation results in
a sudden high rate of acceleration once the motor is activated causing
a substantial current draw, making the scooter difficult to control
and steer. The manufacturer suggests that to mitigate these performance
deficits, the user should manually push off to begin moving the scooter
before activating the motor.
To make the scooter more user friendly, we developed a variable
speed throttle device similar to those used on electric wheelchairs.
Design considerations included the following.
1. For marketing purposes, the new throttle circuit would have
to be easily installed by the user to replace the stock relay.
We chose to design a DC motor control based on a DC chopper circuit
because it met these design considerations.
2. The new system would have to be capable of the same top speed
as with the stock system to maintain the product's benefits for
3. The system would have to be inexpensive to fabricate.