DIY Electric Powered Wheelchair

When studying Mechanical Engineering at UC Davis we were required to participate in a Senior Design Project. For my project, I chose to work on a DIY Electric Powered Wheelchair that anyone could build. Myself and two of my classmates used our engineering background over the course of two quarters to design the following wheelchair. I created the instruction manual attached in the last step as a way to document our build in hopes that anyone could follow our steps. This Instructable summarizes the document and showcases the performance of the chair.

Step 1: Project Background, Needs and Specifications

Project Background

Current electric wheelchair users constantly have to deal with high insurance prices and long wait times when it comes to purchasing and repairing their electric wheelchair. Specifically, our sponsor Pamela had to wait several months just to have her caster wheel assembly replaced. For someone who requires their chair for a main mode of transport, this is unacceptable. Additionally, the wheelchair manufacturers have been creating chairs with lower specs (torque, average speed, etc.) while insurance companies are raising the costs to own such a chair.

The goal of the project was to avoid these negative setbacks and also prove someone could build their own electric powered wheelchair in their garage using basic tools such as a chop saw and drill press. The scope of our project included producing a working drive-train and frame that would provide a solid foundation for our sponsors, WHIM Unlimited, to develop a fully working and refined electric powered wheelchair. We hope this assembly guide will provide the necessary framework for others to build their own chair, ending the longtime dependence on inconvenient health and insurance companies. This guide is by no means includes a final product, but rather a proof of concept and a framework for others to build off of to fit their own personal mobility needs. For more information, please visit whimunlimited.com.

Project Needs

Based on our meetings with our sponsors, we determined our chair would need to exhibit the following:

• Powertrain Needs:
  1. Powerful motor,
  2. Ability to climb road curbs
  3. Good acceleration
• Body Needs:
  1. Stable and sturdy
  2. Maneuverable
  3. Meets ADA specifications
• Overall Needs:
  1. Safe
  2. Modular
  3. Easy to build
  4. Easily obtainable parts
  5. Long lasting

Project Specifications

Based on our project needs, we created the following project specifications:

• Powertrain Specifications:
  1. 3 MPH up a 4 degree incline
  2. Can go up a 10 degree curb (bump)
  3. Accelerate from 0 to 5 MPH in under 2 seconds
  4. Max speed of 8 MPH (wheelchairs on the market average about 4 MPH)
• Frame Specifications:
  1. Max size of 30"x42" (ADA)
  2. Chair height of 15" to 25" off the ground
  3. Can handle a 500 lb load
  4. Turn radius < 44" (taken from ADA chair dimensions)
• Overall Requirements:
  
  1. Use standardized parts (minimize custom parts)
  2. Easy to build (no complex geometries)
  3. Adaptable to the user

Step 2: Bill of Materials

As stated previously, we wanted our materials to be readily available and easily accessible for anyone to find. The reasoning behind this was to avoid long downtimes or having to go through a supplier that has a monopoly on selling specific parts (i.e. only one set of motors that works and only one supplier who offers them). This would also allow someone with a chair in need of repair to go to their local hardware store or order a part online and replace the faulty one quickly on the chair themselves or with a little help. Thus long down times would ideally be eliminated.

As part of our project, we researched different suppliers to find our initial sources for the parts, but we also found alternate suppliers and parts in case the primary source disappeared. The overall cost of the chair was roughly $2000 as compared to chairs on the market that range from $1000 to $6000+. Our chair is on the lower end of this price range, but it offers the specifications one would find on a more expensive model. Overall, our cost could be reduced with various design improvements and material changes, but again this was meant to serve as an initial prototype and proof of concept.

Step 3: Tools Needed, Custom Parts, and Gridbeam Cut List

As Mechanically Engineering students, we had access to a full machine shop capable of creating all the custom parts to our hearts content. Unfortunately, the average person doesn't have this luxury, thus if we took advantage of these tools then it could get quite difficult for someone to follow our instructions. For this reason, we chose to work with tools that the average person may have laying around in their garage.

A majority of our build was made using only a chop saw and drill press, however we did have to make a few custom parts. These included the driveshaft, motor mounts, and driveshaft coupler parts. We felt these parts required the most stability and reliability possible, so we chose to make simplified custom parts. We then created drawings for these parts so someone could go to a local machine shop or makerspace or even contact an online service to have them made.

We were able to use only a few custom parts thanks to our choice of framing material: Gridbeam. This material is best described as 2" square tubing with 7/16" mounting holes every 1". Unfortunately, the material is fairly heavy (~5 lbs/foot) but it does make assembly fairly easy once the cuts have been made.

Step 4: Caster Assembly

During the summer before my Senior year, I had the privilege to work at Aerojet Rocketdyne as Visual Planning Intern. Long story short, we would take advanced rocket assemblies and create a virtual build of the model so the technicians on the floors had something easy to follow when assembling the parts. Basically, I created Ikea/Lego-like instructions for rockets. Seeing as the wheelchair needed a set of easy to follow plans, I created a guide by applying the same skills I used during my internship. The finished result is a clean, easy to follow list of steps that doesn't require a B.S. in Mechanical Engineering to follow.

We created our entire assembly using Solidworks. I then planned out the best way to assemble the parts, and create the virtual build by putting together vector drawings using Adobe Illustrator and InDesign. The first assembly we decided to build is the caster assembly. The caster wheels make it a little awkward since they rolled around fairly easily, so it's best to have some help or somewhere to put the assembly as it comes together. Make sure all the Gridbeam pieces are square to each other before tightening the bolts.

Step 5: Motor Assembly

The next assembly to put together is the motor assembly. This one is a little trickier to put together and required some finessing in order to get the motors, driveshaft and motor mounts to all line up. Luckily none of the fasteners are permanent so if you mess up there's nothing to be worried about.

Step 6: Final Assembly

Once the caster and motor assemblies are together it's time to put it all together. Both assemblies are fairly heavy and awkward in size so it helps to have at least two people to put them together.

Step 7: Controlling the Chair

Our chair utilizes the open sourced Arduino and two H-Bridge shields to control the electricity to each motor. We also use a USB host shield and a cheap USB joystick to provide an intuitive control scheme. For batteries, we used two 12V lead acid batteries hooked up in series to provide a total voltage of 24V. We found this to be more than enough power and control for the prototype, however the Aruidno code needed to be refined further before the chair could be used for everyday use.

Note: I mainly worked on the overall chair design and documenting how we assembled the build. One of my other teammates worked on the actual Arduino code, but I believe he just researched code that other people had used with the H-Bridge shields. Again, we were Mechanical Engineers so learning/writing code from the ground up wasn't really really in our scope. Apologies if the lack of refined controller code is what prevents you from making your own chair.

Step 8: Testing the Chair

As part of our project, we needed to prove our chair met the specifications we outlined at the beginning of our project. We also participated in a Senior Design Showcase put on by our school where all our classmates also showed off what they had worked on for two quarters. Everyone at the showcase was impressed with the maneuverability and ruggedness of our chair and we didn't shy away from showing it off. Attached are some videos of our initial benchmark tests along with footage from our showcase. By the end of our project, we were happy to have something that actually worked and had a fun time showing it off and playing with it.

Step 9: Design Recommendations, Add-ons and Accessories

Seeing as our course was only two quarters and we had a finite budget, we didn't get to fully develop the chair like we would have. It's obviously missing a chair and other elements to provide a smooth and comfortable ride. We iterated through our design countless times but there's always room for improvement. Again, this is mainly a proof of concept and initial crack at a problem, so there are many things that could improve the chair.

Step 10: Maintenance Guide

No machine works well just by itself, but instead requires maintenance to prolong it's life. Our wheelchair is no exception. Although we were done with the project a few weeks after it was built, we still were able to forecast which components would require upkeep in order to have the best performance possible. These suggestions are mainly based on the manufacturer's suggestions for the parts, and we don't know for sure if problems would arise with other parts.

Step 11: Assembly Document

Overall, this project was my first time applying my coursework to an actual, real world problem. I hope if you choose to follow this Instructable that you share with me your hardships or any suggestions for improvements you may have. At the start of this project, we wanted to make the chair easy for anyone to follow, but at the same time allow others to adapt it to their own needs. Thank you for taking the time to read through my Instructable, and I hope you enjoyed it as much as I did making it and the DIY Electric Wheelchair contained herein.

Comments

[Kyaevus]

Hi! I was wondering if you think this could be adjusted to make a smart drive-like device to attach to a manual wheelchair? And if so do you think I could swap out the two wheels for one? Thanks!

[jtaggard]

Hello. It’s probably possible to add a smart drive device to an existing manual wheelchair. You’d likely need some sort of coupling between the wheels and whatever motors are attached and a way to fix them to the frame. I think you would still need two motors though, as one motor would make it harder to control and make turns. There are ways around this with a differential or similar mechanism, however this could get real complex and real expensive pretty quickly.

[FIRED GUY]

HI SIR I AM A STUDENT IN INDIA I WANT TO MAKE A FULLY AUTOMATIC JOYSTICK CONTROLLED ELECTRIC WHEEL CHAIR BUT THE PROBLEM HERE IS THAT I HAVE ONLY 10 000 RS IN MY POCKET MONEY THATS LIKE AROUND 132 DOLLARS SO CAN I GET A BUDGET VERSION FOR THIS JOYSTICK CONTROLLED WHEEL CHAIR

[jtaggard]

Hello. $132 US is not a lot of money for this type of project. The motors along will take up most of this cost. Your best bet would be to find some old motors that are strong enough that someone is getting rid of or even just a used electric wheelchair that someone is donating. Then just attach an Arduino or similar microcontroller and motor driver / relay to power the motors. The Arduino would be able to control the driver or relay based on inputs from a joystick.

[psycho.69dave]

3 months ago I asked a question about changing your design slightly adding larger wheels to enable the wheelchair to climb stairs and cross any terrain such a snow or sand. And still no response of course most of the other people that ask questions never received response either so I guess I'm not special in that respect.

I'm looking for an electric wheelchair that I can build myself that will climb stairs, that will be able to cross sand without sinking in and several inches of snow. I feel a track system would be best instead of wheels.

Is it possible to adapt your chair to climb stairs?

[FIRED GUY]

HI BROTHER IF YOU WANT IT TO CLIMB STAIRS THEN YOU WILL NEED TO ADD A RUBBER CRAWLING TANK CHASSIS

[jtaggard]

Hey there friend. Sorry the past several months have been quite busy so I haven’t had a chance to respond. I think an electric wheelchair that can climb stairs would be better with a tread drivetrain. I believe I’ve seen something like this before with this sort of capability so a quick google search might give some good examples. Tread would also be a better option for off-road capabilities I think. You could go the bigger wheels route, however you may not be able to reach the desired speeds (I.e. the Mars rovers can handle multiple terrains but have to go very slow to avoid damage). As for your batter question, yes it could be possible to have a second set to swap in to extend range. Keep in mind this will add weight to the chair so that might impact the performance. If you do go this route, my suggestion would be to solder in some quick connectors of some sort (see aviation pin connectors) to make it easy to swap between the batteries. You’ll also want to make sure the polarity on the batteries is always correct when reconnecting to make sure you don’t short anything out and damage your electronics (I’ve learned this the hard way unfortunately). Sorry for the delayed response, but hope this helps.

[psycho.69dave]

I have thought about building a electric wheelchair for a very long time, so my question is this. Can I make the tires larger / wider than bicycle tires to use on sand or snow. I would love to be able to use it through nearly every type of terrain.

Second question. Can more batteries be added with a separate on off switch so once the regular batteries run low, you can switch to the charged batteries to go further. I know 20 miles seems like a lot, but that means you can only go 10 miles in each direction before you have to recharge again. Twice the battery power would give you the full 20 miles each way.


Living in the country limits the use of any kind of electric wheelchair or mobility scooter.

[wkyung2711]

Can I have the Arduino code and circuit diagram?

[jtaggard]

Hello. I did not work on the electronics portion of this build so I do not have the specific code or circuit diagram. I believe there should be examples online though that do the same thing we did. Essentially, the motors are all attached to an h bridge controller with the high voltage batteries plugged in. This keeps the batteries and motors all on one circuit. The joystick is then attached to a usb shield on top of an arduino and the arduino has its own 5v-10v power supply (we used a rechargeable phone battery bank). The arduino then has some of the pins outputting signals to the h bridge controller to tell the h bridge which motors to turn on or off depending on the joystick orientation. Hope this helps a little, but again I suggest looking online as there are many projects that use a similar method to control motors.

[shigida]

Sir! Thankyou very much for sharing us this project.Just I am trying to repair my old wheelchair.The motors are in good condition.Only I have to change the whole electronic parts.So I am looking for good motor H-bridge controller and Joystick.Would you mind telling me which type of H-bridge controller and joystick you used.I tried to read from your list.But I can`t.

[jtaggard]

Hi and thanks for the read through. Unfortunately I did not work on the electronics part of this build so I don’t know what h-bridge controller we used. I did find this article though that I think could help: https://octopart.com/blog/archives/2018/05/choose-an-h-bridge-to-drive-your-dc-motor. You’ll want to make sure the controller can handle the voltage your motors run at though so you don’t limit the power your motors can run at and don’t blow the board. As for the joystick, I believe we just used a standard Logitech usb one and found some code online to map the joystick axis to the different motor functions. For use on an everyday wheelchair though I’d suggest a smaller joystick probably.

[toankfc1998]

Sorry .Can you give me the drawing please

[jtaggard]

Hello. All drawings are already included on Step 3. Let me know if something is missing.

[Wheelchairabhi]

How can be possible the turning of this wheelchair to left or right
Please explain the process

[jtaggard]

Again, I didn't design the electronics side of this project, but my best understanding is as follows. The motors are connected to an H bridge which then is connected the the Arduino. This allows the Arduino to control the high powered circuit that's needed to drive the motors, but not be overloaded and just send the signal telling which motor to turn on or off. The H bridge allows the motors to be individually run, meaning you can rotate just the left motor to turn right and just the right motor to turn left. Additionally you can run different combinations of motors forward or backward to turn in place, spin, or do other things.

[Robert Zingher]

I am 460 lb and want to add BLDC motor and controller to a manual wheelchair. Please determine for me what BLDC torque I need? Also please explain the conforming BLDC hub motors and controller with joystick?

[jtaggard]

Hi. You're going to need to determine how fast you want the chair to go and under what conditions (i.e. flat ground, incline, etc). From there you can determine the torque needed to get the chair moving from a standstill and how long before it gets up to speed. There are lots of sites out there that can help with formulas / equations for calculating this (try this as a start https://www.orientalmotor.com/technology/motor-sizing-calculations.html). For the motors we connected them to an H bridge shield for the Arduino. This lets the Arduino running on low current control which motor gets which high current (running on a separate circuit). The code then maps the joystick movement to the correct motor powering. This is a common use case so there should also be example Arduino code that you can adapt

[CherylT71]

hi! may i ask what motors did you use? im also doing an electric wheelchair project and wondering which motors are generally used thanks!

[jtaggard]

We searched a lot and there weren't many suppliers of the type of motor we selected. However, we were limited by the specifications we wanted for the wheelchair (i.e max speeds, ability to go up certain inclines without sacrificing power, etc.). So if you don't need as much torque then there are cheaper options out there. Mainly just do the calculations to determine what torques you want based on your desired speeds for different situations. We steered away from hub motors since their specs didn't match up with what we needed, but this may not be the case for your project