A joystick-based PWM control system for an electric wheelchair with integrated safety features

Department of Mechatronics, Nelson Mandela University, Gquberha, 6013, South Africa

^* Corresponding authors: s219101426@mandela.ac.za, farouk.smith@mandela.ac.za

Abstract

This paper presents a fully integrated control system for a two-motor electric wheelchair, using a thumb-operated analogue joystick to generate differential wheel velocities via pulse-width modulation (PWM). The system’s design emphasizes smooth speed control and safety: it includes soft-start/stop ramps to prevent mechanical shock, an obstacle-detection alert when reversing, and a battery monitoring cutoff to avoid deep discharge. A microcontroller (Arduino Uno) reads the two-axis joystick (10-bit ADC, neutral ~512) with a center deadband to eliminate drift, then applies a nonlinear mapping to determine proportional PWM commands. High-current H-bridge drivers (BTS7960) power two 24V, 250W DC drive motors, handling up to 43A continuous. An HC-SR04 ultrasonic sensor is mounted at the rear to scan for obstacles during reverse motion; it triggers an audible buzzer if an object is detected within a preset distance (1 m). The battery subsystem comprises two 12V batteries in series (24V total) with an Arduino-monitored voltage divider. When battery voltage falls below the critical threshold (sensed as ~5V at the Arduino input), an NPN transistor (TIP120) cuts power to prevent over-discharge. Extensive experiments were conducted: for example, commanding 100% forward PWM results in a smooth acceleration profile (taking ~2–3 seconds to reach steady velocity). Torque output versus PWM level was characterized using the motor’s torque constant. Obstacle sensor tests confirmed reliable echo returns from 0.5–2.0 m, with alarm beeps that intensified as distance decreased. Battery discharge trials demonstrated consistent voltage droop under load, confirming the cutoff at the intended level. All safety features responded correctly during testing. The system achieves safe, intuitive control of a powered wheelchair and meets design goals for user comfort and reliability.