This is a pet wheelchair that I designed and built for a friends small dog. It should work for cats as well, but that has not yet been tested.

Items needed to purchase:
4 - 608 bearings
2 - bolts 1/4-20 x 2" long
2 - nylock nuts 1/4-20
18 - 10-24 set screws
approximately 24" of aluminum tubing 1/2" diameter

The quantities of parts needed to print are:
2 - wheels
1 - tube engagement - 4 degree - left
1 - tube engagement - 4 degree - right
2 - belly & Leg supports
2 - front harness clips
2 - rear supports
2 - Wheel Support - Angled (or 2 Wheel Supports which are straight)
There are 2 options for the wheel supports. If the dog likes to run and play, I recommend the angled wheel supports, but there are non-angled wheel supports if necessary.

Once all the parts are printed, you will need to attach press the 608 bearings into either side of the wheels, and then attach velcro to a harness for the dog and make a sling of some sort based on the type of paralysis your pet has. The "Belly Leg Support" part has several attachment points to use for attaching the sling to the wheelchair.

When fitting the wheelchair to the pet, you will have to determine at that time how long to cut the aluminum tubing to best accommodate the size of the pet. The entire chair assembles easily with the setscrews using an allen wrench, and a regular set of wrenches to attach the wheels. Make sure when attaching the wheels that you don't tighten it too much so that the wheels don't turn.

Also, make sure to use a 10-24 tap to tap the holes where the setscrews go, otherwise it will crack the plastic. You can do this easily by using the tap in an electric drill. It's very fast and quick to complete this.

https://youtu.be/nnb8IwKyPqI