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Kitten wheel harness – part I

February 20, 2015

A friend of mine recently found a home for a disabled kitten, whose hind legs are paralyzed.

The poor thing wants to play and move around like any other kitten, so he drags himself around with his forelegs. He doesn’t get far, and he scrapes and wounds his legs in the proces.

My friend posted on Facebook that she hopes to raise enough money to buy the critter a wheelchair, or more accurately a wheel harness.

But commercial harnesses are awfully expensive, so that prospect didn’t seem promising.

At work I’ve been working on a 3D printed armor for a child with Osteogenesis Imperfecta, a disease that causes bone malformation and frequent fractures. So I thought to myself, I have a 3D printer, why not build a wheel harness for the kitten and be done with it?


I did a quick google search with the search phrase “cat wheel chair”, and found lots of images, most of which seemed like improvized designs with huge heavy frames and wheels.

But one design caught my eye. It seemed quite elegant and minimalistic, and had the advantage of a lot of clearance and space between the wheels, which is important for avoiding low obstacles.

This seemed like something I can build. And while I’m at it, why not publish and release the 3D files so that anyone can build a cheap one too?

I also decided to make it adjustable, since the kitten will grow and need the harness to become longer and wider with time.

Materials and methods (and stuff)

After sketching around for a bit in Blender, I came up with this design. If it looks familiar, it’s because it’s an almost shameless copy of the one above, with a twist 😀

Cat Wheel Harness Initial Design

Cat model used for this illustration made by Gwinna, downloaded from Blendswap.

After completing the general design and having a 3D model to play with it, I went shopping. I bought an aluminum bar 20mm wide and 3mm thick (and 3m long, since they wouldn’t sell any less). And I also bought an aluminum pipe with a diameter of 8mm (and a 1mm thick wall), again 3m long. Each 3m piece cost around 35NIS (around 9$ / 8 EUR ).

I also bought a pair of wheels and screws for attaching them to the bar. The wheels have a diameter of 8cm and a nice almost “offroadish” tread. The pair cost 15NIS (4$ / 3.5 EUR).

The last item I needed to buy was the actual harness, so I went to the pet food store, and asked for the smallest dog harness they’ve got. This cost 40NIS (10.5$ / 9 EUR).

Now I needed to finalize and 3D print the connectors – two for connecting the longitudinal pipes and the transverse pipe, and another two for connecting the wheels to the longitudinal pipes. The remaining two pieces are for connecting the harness to the frame.

3D printing

I have a 3D printer at home for a few months now, and I haven’t used it nearly enough yet. The problem is finding interesting things to do with it, and I have lots of ideas, mind you, but most of them require more time than I actually have. The wheel harness was a wonderful use for the printer, and the first really useful thing I’ve done with it.

My printer is an open source Prusa i3 Hephaestos, which is a damn good printer kit that wasn’t easy to build (even though I built it during a short printer building course). Challenging though it was, it was well worth the cost and effort.

As I’m still something of a newb with hands on printing at home, I’ve been having trouble printing with ABS (heated bed and special sticker notwithstanding). So I decided to print the harness parts with the much friendlier white PLA I’ve got mounted on the printer.

Printing Parts for the Wheel Harness

This went along rather smoothly, except for the frustratingly difficult removal of the supports on the harness connector (the long round pieces in the middle). A Scalpel, pliers and scissors were used alternately until the damn thing agreed to come off.

Of course I had to reprint the whole bunch 3 times, because I discovered various bugs every time (bar canal too narrow, screw hole diameter too small, fragile parts, etc).  I adjusted the models after every test, and ended up with a design I’m happy with, until I can test it on the actual kitten and see if it actually works in real life.

Cutting, drilling and bending

I visited the local makerspace, XLN Tel-Aviv community laboratory, and used their disk saw, vise and drill press to cut the pipes and bar to the desired lengths, and to drill holes where needed.

I cut the pipes into 20cm, 15cm and 10cm pieces, and decided to try it first with two 20cm (length) pipes and one 15cm (width) pipe. The bar was cut into 16cm long pieces.

I drilled 6 holes every 1cm on the top 7cm of the bar, and another hole at the center of the bottom 2cm.

The vise and hammer came in handy for bending the bar into the desired shape. I bent the middle 7cm (after drilled bit at the top) in a ~30 degrees angle, then bent the bottom 2cm long bit back the opposite direction until it was parallel with the straight upper part.


The aluminum bar before bending and drilling a hole for the wheel at the bottom 2cm. This piece was discarded due to the appallingly inaccurate drilled holes (something that was avoided afterwards by making initial dents to guide the drill).


Assembly was pretty simple, and required only 4 X M4 nuts and bolts, and two sharp edged M5 screws. The bolts need to be rather short, around 10mm long. I didn’t have any short M4 bolts, so I used my rotary tool (Dremel copy) to cut ’em the 2cm long bolts I had. I used a pair of double edged velcro strips to attach the harness to the frame, and the rest was pretty straight forward, as the printed connectors do most of the work for you.

This is the result of all this work, and in a few days I’ll hopefully get to see if it actually works, and maybe give a little kitten his mobility back.

When I’ve fixed all the bugs with the design, I’ll release the 3D files and instructions so that anyone can make this cheap, quick wheel harness for their disabled pets.

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  1. Cathy permalink

    Wow!! This is amazing!!! Your inventiveness is needed right now!…
    Would you be interested in helping another kitten? There is a kitten foster home in Langley BC, Canada (near Vancouver) that needs some help. is a foster home that broadcasts a 24hr livestream feed and has become very popular with 1000s of people watching the cameras from all over the world and over a million fans on Facebook. They recently saved two feral kittens, one of which is missing most of his back legs. He was very sick and on death’s door and in just a few days has fought his little heart out not only to live, but to walk and play like the kitten he is. Shelly, the foster mom, has put out an appeal to anyone who is interested and able to help create a wheelchair for him. If you are at all interested please, PLEASE, contact Shelly!!

    Some links so you can see how amazing this kitten is…

    • Thanks Cathy 🙂
      Will look into it in a week when I’m back from a short vacation abroad.

      • Cathy permalink

        Thank you for responding 🙂 As luck would have it, a local company has volunteered to help as well as a local high school that has a 3D printer. After looking through more of your posts I realize that you live halfway around the world which would probably be a logistical nightmare if you were able to help!! Your friend’s cat seems quite please with your invention!
        Thanks again for your response. I hope you enjoyed your vacation 😀

      • Sure 🙂 Glad that you’re getting help and I hope it works out. I do have to say that Benji eventually ended up disliking the chair, especially since he hates being harnessed at the front (regardless of the rest of the apparatus).

        We’ve been getting much better results with his physiotherapy training by simply using a rear harness and a leash to train him in spinal walking.

      • Cathy permalink

        Thanks! It’s good to know about Benji’s preferences and physio. The more info the better, I’ll be sure to pass it along 🙂

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  1. Kitten wheel harness – part II | BioBlogical - BioLogic's 3D & Design blog

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