A 4-directional controller for motorized wheelchairs.

Step 1: Construction Overview

Materials:

2"x4" plank (at least 8" long)
3 conductor cable
8x 3-pin molex connectors
3x 2-pin molex connectors (or 6-pin)
Molex pins
1/8" female audio mount
4-channel IR obstacle avoidance sensor module
Digital I/O box for wheelchair
9-pin D-sub. connector (Connector for I/O box)
Project box
16x machine screws (#10 x 1")
16x internal threads (#10-32)
Velcro tape
Double sided tape
Heat shrink tubing (1/2")
Clay

Tools Used:

Table saw
Band Saw
Drill press
Mill
3D Printer
Heat gun
Sandpaper
Wire stripper
Molex crimper
Hammer
Phillips screwdriver
Scissors

Safety:

To avoid eye damage, wear safety glasses while cutting wood with the table/band saw. Practice caution and precision while using the heat gun and drill press.

Step 2: Prepare Connectors

3-conductor cable:

Cut the 3-conductor cable to a length that will fit the wheelchair, allowing the cable to wrap from the back housing to where the controllers will be. Using the wire stripper and molex crimper, expose the internal conductors and crimp the molex pins on them. Insert the crimped pins to their corresponding molex connectors (male/female). After testing the connections, use the heat gun and shrink tubing to protect any exposed wiring.

9-pin D. Sub:

This project was based off an Invacare Mk5 wheelchair. The digital I/O box for this chair uses a 9-pin d.sub. connector to interact with the wheelchair. Use the connector specified by the wheelchair manufacturer. Using the wire stripper and molex crimper, add female molex connectors to the connector not used by the I/O box. Using the soldering iron, connect the emergency stop wire to the 1/8" audio mount. This will allow the use of a button to reset the controller if something goes wrong.

Pin out for the Mk5:

Forward
Reverse
Left
Right
Attendant Overide (Not used)
Emergency Stop
+5v
Common (-)
+15v (Not used)

Step 3: Prepare IR Mount

Using a 3D printer, print out a node for each IR sensor. Files have been provided in .SLDPRT, .STL, and .IGS format.

Using the table saw, cut the 2"x4" planks to 4" segments. You will need one square per IR sensor. Drill a 1.5" hole in the center of each square. Center the sensor puck on the square and mark where the screws will be. Use a bit that is at least .200" to bore out holes to mount the IR puck. A hammer can be used to insert the internal threads from the bottom of the wooden puck.

Adjust the table saw and cut a 1/2" channel for the IR sensor wire on the bottom of the wooden mount. Use a belt sander or band saw to round the edges of the wooden puck, then sand the whole mount smooth.

Place the IR sensor into the 3D printed mount and secure with clay. Lower the mount and sensor into the center hole of the wooden puck and secure with screws. Doubled sided tape was used to cover the bottom, but velcro works as a less permanent alternative.

RE__IR_Sensor_Pucks.zip
Download

Step 4: Prepare Project Box

Mill out a window for the IR control board so that the LED indicators are visible and the IR adjustment pots are accessible. Drill a hole for the 3.55 mm jack, as well as holes on the end that are slightly smaller than the connector wires. The box will act as a clamp when tightened. Add velcro or double sided tape to the bottom of the box for mounting to the wheelchair.

Insert the 3.55 mm jack and secure with its corresponding nut. The jack will be wired to the emergency stop and ground pins as indicated by the wheelchair I/O interface. This will allow an operator to reset the controller should a signal malfunction.

Connect the d-sub wires to the I/O terminals and the IR wires the their respective channels. Close and tighten the project box.

Step 5: Connections and Testing

Connect the IR sensor cables to the sensor with the molex connectors and the the d. sub to the I/O interface. Connect the I/O to the wheelchair controller accessory port or as indicated by the chair manufacturer for external controllers.

Turn the wheel chair on, but keep the driver profile on joystick control, power should still be supplied to the IR sensors for fine tuning. Alternatively, use a DC power supply to provide 5v to the sensor box. The LEDs will turn on when the sensors are detecting an object, in this case a hand. Using a screwdriver and keeping the area above the sensor clear, adjust the power output using the potentiometers on the sensor board until the LED for the channel being adjusted is on the boundary of turning on. Wave your hand over the sensor, this is the maximum range that the sensor can detect without a false signal. Adjust further as needed.

Connect the emergency stop button through the 3.5 mm jack, and set the wheelchair to accept alternative control. See the manual or contact the manufacturer to determine how this process works.

Mount the sensor to a lap tray or other configuration and test for correct movement. Continued adjustments may be made to the sensor range using a screwdriver. Congratulations, the chair should now have proximity control.