Wheelchair Hack Lets Two-year-old Explore On His Own

[Shea’s] son [Alejandro] was born with Spinal Muscular Atrophy which limits his ability to move. The ability to explore one’s environment as a toddler is really important to development so [Shea] and his wife have been looking into assistive technology. Their health insurance paid for a medical stroller when he was nine-months old and has told the family they need to wait five years for a powered wheelchair. Rather than wait, [Shea] took it upon himself to hack a wheelchair his son could control.

He found a used adult-sized motorized wheelchair on eBay for about $800. Not cheap, but way more affordable than a brand new unit. This type of chair is made to be controlled with a joystick, an option not available to his son at this point. Foot control was an option if he could figure out how to build an interface.

After unsuccessfully trying to repair a broken digital kitchen scale [Shea] was inspired to reuse the sensors as pedal inputs. [Alejandro] has limited foot strength and the sensitive strain gauges are perfect for picking it up. Above you can see the sandal-based interface he built. The two feet working together affect steering as well as forward and reverse. The pedal system is connected to the wheelchair using a Digital to Analog converter chip to stand-in for the original analog joystick. After the break we’ve embedded a video of [Alejandro] exploring the outdoors in the finished chair.

In this case it’s fortunate that [Shea] has the skills to build something like this for his son. We hope this will inspire you to donate your time an know-how to help those in your own community who are in a similar situation. This really takes the concept of The Controller Project to the next level.

37 thoughts on “Wheelchair Hack Lets Two-year-old Explore On His Own

  1. I think this is the first time a Hack a Day post brought a tear to my eye. This dad deserves recognition for both the technical aspects of the project plus the caring and love it represents. Great job.

    On a technical note – he may want to put an accelerometer in the chair to override the controls if the chair hits something. A specific challenge in this type of design is that when the chair hits an obstacle his boy will end up putting more pressure on the controls causing it to accelerate more. This dad seems damn good at building this so he probably already figured that out.

    1. He has considered it, but not implemented it yet.

      From the text, “The controller PCB also includes a 3 axis accelerometer. The pedals are very sensitive and are capable of moving the wheelchair with only a few grams of force. I was concerned that driving the wheelchair on bumpy surfaces could potentially cause unwanted forces to be applied to the pedals creating oscillations and instability in the system. The accelerometer was included to to offer the possibility of applying an intelligent damping algorithm to prevent this. At the time of this writing this has not been implemented or necessary.”

      1. Didn’t catch that. See, he already got it. Good for him.

        A low pass filter in the control software could work to smooth out those bumps at the expense of a little lag in control response. The filter wouldn’t necessarily need to be symmetrical. It could react to increases in speed a little slower. A profile with a slower climb in speed with a rapid ability to slow down could work.

        My main worry would be a bigger crash that tilts the chair or even topples it over. Either event could put extra pressure on the accelerator causing further problems.

        It sounds like he is already thinking this through. I am very impressed with this guy as both a dad and an engineer.

        1. The chairs control module has a “built in” system like that. Its called “tremor damping”. It looks like dad integrated the new drive control into the old joystick. If he got his hands on a programmer for the chair he could fine tune the system that way.

  2. A couple of comments:

    Would it make more sense to have the LED PCB at a different location to
    actually provide some visual feedback?

    I would use avoid using Lexan or plexiglass material as pedals.
    Countersinking screw mounts can cause more stress and can lead to
    cracks. May be fiberglass would be more flexible and less likely to

    1. Cast lexan or acrylic can handle the stress very well. The extruded junk from the hardware store is already so full of stress points it doesn’t perform very well and likely would crack over time. I agree that you shouldn’t use those.

      Good Lexan is used for all kinds of high stress applications. I have a router table insert that is made from a cast lexan plate that puts up with HUGE stresses. (I am not always nice to my tools.)

        1. Most applications I have seen have the Lexan or acrylic cast into the main shape then the mounting holes are drilled and tapped. When the forms are cast or molded the material is extremely strong and handles stress well.

          Most Lexan or Plexiglass materials you find in hardware stores are formed by an extrusion process. This stresses the material and significantly weakens it. After extrusion it cools and locks in these stresses. This causes cracks and breaking in the long (or short) run.

          High quality materials do not have these issues and can handle far more abuse before breaking.

  3. Are things like this commercially available already? If not, I would encourage patenting the idea. The working prototype is there. I’m sure all the design diagrams are in order. 3 days work and some slight lawyer’s fees, and you could easily sell the design.

    1. If he doesn’t want to go down the Patent route it may also be good to open source the design. There are some good groups out there that do open source hardware work. They would probably take this in without hesitation and everyone could get the benefit of the group effort on the project.

      If he wants to make money off the idea I am not against that at all, but this may be an alternative to keep the ideas out there for people to use if he doesn’t want to do that.

  4. Well done! I volunteer with a group called the TETRA Society which helps with assistive technologies for those needing the expertise to adapt, modify, build or otherwise make stuff work better.
    There are branches throughout Canada/US. Search for TETRA.

  5. Shea your an amazing person and somehow I think we will be hearing from Alejandro as well in the future seeing he has so much love and intellect surrounding him.
    Sitting in the office with tears in my eyes, thanks for sharing this with the world.

    [i]”We hope this will inspire you to donate your time an know-how to help those in your own community who are in a similar situation”[/i]

    It has and I will try my best to apply my technical skills to bring the quality of life up for my fellow humans

  6. I imagine a future where it will be common for people to control motorised vehicles using their feet.
    On a serious note, I am always taken aback by the cost of assistive equipment. Granted there are no/few economies of scale, but there must be a considerable amount of profiteering going on too. For people who do not have the competences required to tackle something like this, I imagine it could easily start to feel bleak.
    Oh, and props for using the phrase “sandal-based interface”.

    1. Hmm… yeah, they’re very pricy, but not sure it’s necessarily profiteering.
      I imagine there’s a LOT of failed prototypes, and a lot of fees for certification on products, as they probably count as medical things? Also, you need a lot of testing to make sure there’s no bugs in an electric wheelchair that’ll make the thing go full-throttle into a road and kill the user, or run over a child… Plus a lot of insurance against liabilities against those kinds of accidents.
      Plus, they must need staff with a lot of skills, so they need to be paid above average.

      1. This is so true. Medical software, especially, is requires extremely rigorous testing. Sometimes I think this industry is over-regulated. Of course, I’m sure some would disagree, especially those who have been harmed during procedures or by medical equipment, etc. It seems like a delicate balancing act is needed to balance regulation of companies who may want to take short-cuts — vs — an overly litigious society that is quick to blame and sue. But I digress…

        This is an awesome achievement and goes to prove how fast innovation can work in an environment motivated by love and caring rather than profit.

  7. As a professional wheelchair tech for a small DME company im blown away by this build. I have installed a lot of the “top of the line” drive controls on chairs, ranging from sip and puffs(using breathing in or out to control driving), fiber optic systems, proximity switch systems mounted in head rests or foot board(similar to this design) and this design exceeds a lot of the build quality in those setups…..

    Im also insanely impressed with how dad integrated the rehab stroller seating onto the power base. I have never even thought of attempting something like this. It gives you all the adjustment for growth and corrective/supportive positioning without the size and weight of a full blown power system like the one that would have come mounted from the factory. The additional space saving leaves room for the bulky vent and suction machine which is always an issue with “manufactured” seating systems.

    Shea you are one hell of a father and i would love to help you out with parts or or tips if the need ever arises. I honestly wish half of the parents of my clients where so hands on as you. My job would be eliminated but i know the lives of the children being helped would be so much better.

  8. Shea is an amazing father and a truly gifted engineer. He not only cares deeply about Alejandro, but about all of the parents and their children dealing with SMA.

    What’s even more profound about this all, is that Shea has no formal training in electronics or programming. The biggest autodidact I’ve ever met. Heart of gold. Hope he gets some funding to make this available to other families in need.

    1. Yes, the fact that all of you techies have Bern touched by this dad’s love for his child shows you have heart.
      You are not all about making money, but generating ideas. Some have offered safety measures, parts, your expertise. That is generous. It is this gener
      ous spirit that brings a tear to my eye. Without this, We have no cure. So, you are contributing to the cure for SMA. Thanks.

  9. Good to see how a father can go to any extent to tackle his son’s disability. Such things inspire people the most. You know what, the best thing is FDA approves the first gene therapy for spinal muscular atrophy to treat children younger than 2 years. This source will help you to know more.

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