I have included 3 designs- small dog, medium-large dog and quad cart.For smaller dogs, the frame is made from flat aluminium bar 20mm wide available from hardware stores. Assembly is with standard nuts and bolts. For larger dogs, the frame is made from 15mm copper water pipe and joined with pipe fittings to suit. Annealed tube in coils should be strong enough. Hard drawn tube is stronger but more expensive. Aluminium or steel tube can also be used but fittings may be hard to find. Final version can be assembled using epoxy glue. Hold together with plastic tape till then.
Wheels/ axles/ axle mounting
Hardware stores have wheels off the shelf. These are usually too heavy or too flimsy. I recommend wheels from a modern stroller or pram which are light and strong. Axles also available from same source. Wheels may also be mounted with single bolts on each side if desired. Axles are mounted to a mounting block secured to the frame with nuts and bolts. For smaller cart use solid sheet metal or plywood or Perspex. For larger cart, use stronger material such as plastic from a household chopping board. Multiple holes may be drilled so height can be adjusted up or down. If plastic is used, suggest carving out a groove to fit tubes for a stronger fit. Heat tube and press in to melt plastic to shape.
This is a major weight bearing point. Two types are described. A ring support made from heavy gauge wire or light tube (brake lines are suggested by others), suitably bent to shape and heavily padded. Attached to top frame so as to be a rigid structure. Another type is a fabric sling with holes cut for legs with or without gender specific cut-outs. Attached to frame by slipping over fixed bolts. Holes to be reinforced with extra material and metal eyelets. Lifting handles are recommended especially for larger dogs. Beauty is that dog can be inserted like a pair of shorts and lifted in to place. Useful for heavier dogs. If required, feet can be suspended off the ground in fabric slings attached to the rear frame
A strap of webbing is attached to the very front of the cart and passes under the chest and secured on the opposite side with clips, touch-fastener closures or bolts with holes in webbing. Strap should be padded to prevent chaffing.
Frame may need to be adjusted for length or width. Small cart can be adjusted by overlapping two sections of bar and bolting offsets together at two points. Tube carts can be adjusted by having a section of the frame made from a larger diameter tube and sliding one section inside the other and securing with bolts or self tapping screws.
Quad carts are inherently unstable. Top frame MUST be smaller than bottom frame. Outriggers are recommended if stability is an issue. See designs of commercial carts for ideas. Front wheels must be caster type to allow manoeuvrability. These may be mounted using same method as rear axles but the mounting block should be horizontal. Height adjustments are possible if the pivot of the caster is converted to a long bolt which can be adjusted up or down. Sling type leg supports are probably required. DO NOT ATTEMPT TO SUPPORT WEIGHT OF ENTIRE ANIMAL ON A CHEST SLING. It will cause breathing difficulties.Balance point is critical for rear wheel carts. Weight bearing point should be approx three quarters of the way from shoulder bar to axle line. Too far back and the cart will tip over backwards. Too far forward and too much weight will be on the shoulders. Basic tools are all that is required. You may need to buy a simple cheap pipe bender and a tube cutter each under $10.
I bought a used baby pram from eBay for $0.99. From it I got wheels, axles, casters, tube, fabric, straps and padding. Try the Freecycle network for freebies. Google it! Local councils have clean-up drives in some areas. Be daring. Go out at night with a balaclava on and scrounge till it hurts.
Wheelchairs and carts should only be used on injured or disabled animals after seeking competent veterinary advice. This advice may or may not be accepted as some vets spout phrases like “quality of life” and “we accept Amex and Visa”. The instructions and drawings supplied are not guaranteed to suit the particular uses desired by the user. It is the responsibility of each pet owner to make their own decisions regarding their suitability for use in any particular circumstance.
© Copyright 16 November 2006. May be used by permission if you love a furry friend and do not ever, ever charge a fee for this information. Further information and drawings are available from Virgil at firstname.lastname@example.org