Speed Control For R/C Models

EE JULY/AUGUST 1987 by P Techer 1 The speed and direction of rotation of a motor in a radio controlled model aeroplane or boat is generally controlled by pulse width modulation of the supply voltage to the motor driver stage. In the present circuit, shown in Fig. 1, bistable FF, is set up rather unconventionally to func- tion as a monostable multivi- brator, whose period is set with R,-C1-P1. This period deter- mines the toggle point at which the motor"s direction of rotation is reversed. Output Q of FF2 goes high when the pulse at the D input (PWM signal) is shorter than that at the CLK input (signal from FF1). This causes Ti to actuate Ref, so that the motor direction is reversed. The PWM control signal applied to the cir- cuit is also fed to N2, whose out- put pulse width is the differ- ence between that of the input signal and that from FF1. The pulse width at the output of N2 therefore increases as the rel- evant control handle on the transmitter is moved further towards eith...