7 3/8 x 9 1/4 T echnical / Build Your Own Electric Vehicle / Leitman / 373-2 / Chapter 7
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Build Your Own Elec tric Vehicle
releasing the pedal means the motor is off (no creep). Pressing the pedal to a certain point sets a certain motor voltage, which means a certain speed. Pressing hard gives you a constant rate of acceleration (because the controller is in current limit; constant current 5 constant torque). Release the pedal, and it simply coasts (unless you have regenerative braking, in which case you can configure what it does).
DC Motor Controller—The Lesson of the Jones Switch The easiest way to vary the DC voltage delivered to a DC motor is to divide its steady, nonvarying DC component into smaller pieces (see Figure 7-1). The average of the number or size of these pieces will be a resultant DC voltage that the motor “thinks” it is receiving. At the top left of Figure 7-1, the value of the voltage delivered to the motor is
Vmotor 5 ((ton)/(ton 1 toff)) 3 Vbattery 5 (ton/T) 3 Vbattery 5 KdcVb
(1)
This equation shows that the voltage delivered to the motor is proportional to the amount of time the pulse is on versus the total length of the period. As toff >> ton in the left-hand graph, the average voltage (V) the motor receives is only equal to a small
Figure 7-1 Summar y of Jones switch PWM chopper controller characteristics.
