Building a custom remote for someone with muscular dystrophy

Krishna Basude
Nov 1 · 5 min read

When I was still at UC Davis, I really wanted to get into a specific lab that dealt with helping paralyzed and injured individuals control everyday tools using brain and muscle signals (EEG and EMG). The professor connected me with someone who had contacted the lab about a project.

The man who contacted the lab is named Tim. Tim has advanced muscular dystrophy, which confines him to a motorized wheelchair. He can speak and operate his wheelchair, but cannot move his arms. His wife Denise takes care of that for him. The only way he can control his wheelchair is through slight movement of his fingers, essentially his entire range of motion.

Tim was an avid RC car racer. His wife Denise would help him build the cars and he would race them at local meets. However, he was having trouble operating the remote for the cars. His fingers just didn’t have the strength to fully move the trigger and wheel on the remote.

Example of an RC car remote. You accelerate and reverse with the trigger and steer with the wheel (Spektrum)

I visited Tim and got a remote and car from him for testing. I also measured his range of motion with a ruler to see how far he could move his fingers. For him, the easiest way for him to move his hand was back in forth like in this picture:

Depiction of Tim’s finger movement. He could move in the direction of the arrows for a full range of only about 5–7cm.

Talking to the professor, we knew that using EMG or EEG signals were probably not necessary. I knew that I was going to use a 3D printer to make some custom switches. And I decided that I would use a laser cutter to create a plate that Tim could rest his hands on to operate the switches.

After opening up the remote and pulling a few things apart, I realized the switches were literally just potentiometers! These potentiometers were connected to a board inside, which reads the current passing through the switch and emits a radio signal to the car’s transponder. By rotating the shaft, you change the resistance of the pins.

Picture of backside of potentiometer connected to remote

I used a multimeter to find the max and minimum resistance for both the acceleration and steering potentiometers. I searched online for pressure sensing resistors and other sensors to find the best kind of design for Tim, even trying to get a hold of the special joystick he uses to operate his wheelchair. I realized though, that I could easily utilize the potentiometers straight from the remote to make something plug-and-play.

I starting drawing some concepts, and used calipers to make measurements of the potentiometer. I then used SolidWorks to create a 3D model of my prototype. It took some trial and error to get the parts to fit right. My first prototype looked like this:

First switch mount prototype!

I found the spring from a small variety pack I got at Ace Hardware. The metal part you see is the shaft of the potentiometer, which fits snugly in the lever piece. I tested out the mechanism and it worked great. The cool part is that in either direction you turn in the lever, the spring compresses the same way and restores the shaft to the center!

After many many hours of prototyping and printing, I got to this:

Final inner mechanism of switch. Sorry for the blur!

This picture gives a better sense of how the mechanism works. The lever has a flat portion at the bottom that presses down on a beam, which turns freely and compresses the spring. I used a little tape to hold the spring down, in case Tim or Denise wanted to adjust or change the spring.

I used CorelIDRAW to create a switchboard design to mount the switches on. I then used the school’s Trotec laser cutter to cut out the design on a plate of acrylic and ended up with a result I was pretty happy with:

Acrylic mounting board after cutting and engraving with Trotec laser cutter. (It says Autobot Tim, which is a play on Tim’s email!)

I tapped holes in the covers of my switch mounts and countersunk the holes for the screws on the bottom of the plate to give it a more finished look.

I encountered a few problems with the thin wires in the remote coming loose. I had to get some new wire from the lab and solder that onto the boards and to the batteries. After a few hours of soldering and assembly, I got to this:

Assembled switch board with covers on each mechanism. The remote was screwed together and then zip-tied using the holes on the right. The slit on the left cover is longer than the switch on the right for better range of motion.

I couldn’t wait to show this to Tim. I wasn’t even sure if it would work for him… but I think it definitely worked out in the end:

Tim was so happy. He even sent an additional email thanking me, telling me how this made him feel like a kid again after not being able to race for more than 10 years. He later used this remote to win 4th place in race later in the year!

This experience helped solidify why I wanted to pursue a career in medical devices. Helping people surmount health obstacles and achieve things that they couldn’t before are two goals that I will use to guide my career path going forward.

Feel free to reach out with any comments or questions about my project at skbasude@gmail.com.

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