This cart was designed to provide mobility to a chihuahua that was born without front limbs, it provides stability and mobility.
Additional to the 3d printed parts you will need 8 roller skate bearings, 3 80mm skate wheels and superglue
The model can be adapted to different heights modifying the center bridge part
***
Update: A second option to have the front tires not turn has been added (original design) because some dogs that dont have good balance fall to the side when the front wheel spins. This option requires the dog to learn to lean back to turn (not that difficult) as you can see in the video