Joystick Control Vehicle with Remote Override

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Joystick Control Vehicle with Remote Override

Designers: Eranga Devasurendra, Grant Harwell, Walter Reggel, Brian Rinne, Jide Emiola, Brad Hammond, Brent Hand, Juan La Rota, Alva Kepple.
Client Coordinator: Sonya Parker

 

This project was designed for a 22 month-old girl who was diagnosed with cortical blindness and hypotonia.  Cortical blindness is a term used to describe an apparent lack of visual functioning, in spite of anatomically and structurally intact eyes. The cause is assumed to be that the visual cortex of the brain is non-functional.  The little girl is unable to crawl or walk due to hypotonia in her hips.  Her mother also has a heart condition which limits the amount of time she is able to carry her.  Her mother contacted us after seeing a vehicle that had been modified for a child with cerebral palsy on the news, requesting a vehicle with the ability to self operate using hand joystick controls instead of foot pedals.  Furthermore, the parent needed to be able to operate the vehicle using a remote control that overrides the joystick control.

TECHNICAL DESCRIPTION

 

Furnished equipment included a toddler truck, battery charger, and owner’s manual.  The first design aspect was steering, and it was proposed to use RC servo motor and speed controller.  The advantages included operating voltage 4.8 to 6 Volts DC, it was readily available and inexpensive, and included a Feedback system for positioning in one package.  It provided sufficient torque for steering a ¼ scale car models (HS-805BB 343 oz-in) and can have additional gearing if necessary. RC servo motors have a standard interface that may be linked directly to a receiver for remote control.  Disadvantages included the fact that the positional control signal is a pulsed signal, which required an additional interface between the potentiometer signal and the servo.

The second design component was the control system for remote control.  This was accomplished by connecting the motor speed controller and the servo motor to a receiver and local control from the joystick pots through an interface board.  Switch over is accomplished by using a three channel receiver, in which channel one links to the servo, channel two to the speed controller, and channel three to a switch module or forward speed controller.  The speed controller powers a relay whose contacts connect the output of the local interface board. PWM signals to the servo and speed controller when powered, and with the relay not powered the relay contacts connect the PWM signals from the receiver to the servo and speed controller.  Local control is through an interface board that converts a potentiometer signal into the proper PWM signal.  A combined switch and signal pot interface to a single board computer takes the pot signals and the receiver PWM signals and creates a PWM from the pots.  It also does the switching based on the on/off module connected to the receiver.  The finished product is shown in Figure 17.  Total cost = $1061.

17 - joystick control vehicle
Figure 4.  Joystick control vehicle with remote override