Introduction: Wheelchair Bracket
The purpose of this is project is twofold.
1. 3D print a bracket that will screw into the track feature of a permobil wheelchair. This bracket can be used as a template that can be modified to connect anything needed to the wheelchair. I had been wanting to make a basic bracket just to see if I could easily connect to the wheelchair and this was the perfect opportunity to try.
2. The second purpose was to build a tray table for John's iPad so that he wouldn't have to bend over to use it. In this case, use the bracket to hold a standard 3/4" pvc pipe. 3D print an iPad holder to use as a tray.
Tray tables for wheelchairs already exist, but this one is made specifically for John and is much cheaper. I also like the idea of being able to print my own bracket so that I can attach anything I want to the wheelchair.
This was a very quick project. I spent maybe an hour designing the 3D printed parts, using Tinkercad to draw it, and building it with pvc pipe I already had laying around. If I was looking for perfection I would likely re-do it, but since I have other things to work on and this works as is, I'll keep it for now.
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Step 1: Sketch
The bracket is going to screw into the unitrack of the Permobil. So, the holes the bolts go through must line up with the unitrack. You can't just eyeball it when drawing in Tinkercad.
I've found that it's easiest to start with a sketch where I can calculate out all the measurements. For instance, I know that my holes have to be spaced an inch apart (on center). But the default for Tinkercad is to measure to the object's bounds not to the center. So, if I sketch it out first, I can calculate all those measurements and save time when drawing in Tinkercad.
I want to be able to slide a 3/4" pvc pipe into a tube that's connected on to the bracket. As a guess, I decide that the tube should be 1/8" thick. A hole size of 1-1/4" should easily accomodate the pvc pipe. The pipe should be the same height as the bracket.
Step 2: Draw the Bracket With Tinkercad
Tinkercad is free software on the web. Just sign up for an account and you can use the very user-friendly CAD application.
First thing I do is change to english units and bring down the ruler.
Then just drag over the pieces, adjust them to size, and move them using the ruler to follow the measurements made in the sketch.
For instance, to start, bring over the rectangle. Change it's dimensions to a X=3, Y=1-3/4, and Z=1/4. Then move it to 0,0,0. First piece done!
For the holes bring out the cylinder with the gray stripes. The gray stripes indicate that it will be a hole. Size it to X=1/4, Y=1/4, Z=1. Then move it to Z=-.25. Make 3 more copies of it by simply copying and pasting. Now move them to 1:X=1/4, Y=1/4, 2:X=1/4,Y=1-1/4, 3:X=2-1/2,Y=1/4, and the last one to X=2-1/2,Y=1-1/4
The part of the bracket that connects to the wheelchair is done. Now, just add whatever connector piece you want to be able to attach whatever you want to the wheelchair. In my case, I want to add the tube that the pvc pipe will slide into.
Again build to the dimensions of the sketch. Bring out a solid cylinder and center a 'hole' cylinder within it. You can either use the align tool, or you can just move the cylinders using the ruler to make sure they are centered. I make the 'hole' cylinder much taller so that I don't lose it within the solid cylinder. Once they are aligned I group them together. In this case, in order to sit on the bracket you need to tilt the cylinder by 90 degrees. Select the cylinder in Tinkercad, then grab the little triangle to rotate the cylinder.
Now to put it on the bracket, again you can either use the align tool, or use the ruler to set the X,Y,Z location right where you want it.
Once everything is together you can select all the parts and group them together.
After I'm done I export to a .STL file. I have a library near me with a makerspace that prints 3D prints - it is very convenient.
Step 3: Draw the Tray in Tinkercad
I used much more guesswork for this piece.
I knew the general size I wanted, but didn't have to be as precise with measurements.
Initially, I wanted to be able to slide a pvc pipe into the back of the tray and then use 'bolts' to hold the pipe in place. I found an instructable that showed how to create a bolt using a ISO metric thread shape. You can find this shape in Tinkercad under Shape Generators: Featured. I made holes on my tray using the same metric thread shape. When I got the print back, though, I think it just wasn't a clean enough print and the bolts wouldn't screw into the holes. Maybe it was because the I put the threaded holes in my cylinder shape. In any case, I decided not to retry and instead just glued pvc pipe into the tube of my tray.
Step 4: Put It Together
Connect it all up using 3/4" pvc pipe.
The pvc pipe just sits in the tube of the wheelchair bracket. A bolt is used to position the pvc at the right height. I used pvc cement to glue the tray to a straight piece of pvc pipe. Then I just kept using connectors and pvc pipe until I was able to position the tray in a good spot for John.
Since I was using what I already had around the house, a lot of the connectors were 3-way connectors, but if I were to do it from scratch I'd use 90 degree elbows instead.
Judges Prize in the
Assistive Tech Contest