Bridgewood : Mark I Glider pony cart

Mark I Glider pony cart

For my current Mark III Glider design please see http://www.bridgewood.org.uk/glider/

Back in 2009 I had some requests for more information about the Mark I cart that I used at the Preston indoor pony day, and so I took some more pictures and tried to explain how it all fits together. - Tanos.

This page describes a simple, lightweight cart I've built for ponyplay. The parts are all readily available from DIY centres (eg B&Q) and bike shops (eg Halfords), and you only need a hacksaw, vice, drill, and metal files to build it. (If you hover your mouse pointer over any of the pictures you can see a bigger version, and there's another page with them all on too.)

The first small picture shows all the pieces laid out, behind the length of 4inch PVC water pipe which I use to carry them in. The construction methods are inspired by hang gliders (hence "glider"), and it's just made of stretched fabric and steel tubes that bolt together. The cart only weighs 9.8kg, so it's very portable - for example, to isolated areas of forest.

Starting from the back, the wheels are standard "28 inch" hybrid-style wheels from a bicycle shop, with knobbly tires but a larger diameter than most mountain bikes. This size is also called "700C" or "622mm". Next the two 20mm square-section steel shafts, with padded handles made by wrapping black duct tape round many times. Various bicycle handlebar tapes are also available but ordinary duct tape works surprisingly well. The tubes are finished off with black plastic plug-in end caps. All of the tubing needs to be steel with wall thicknesses of 1.0mm or 1.25mm. You can buy very thin steel tubes for curtain rails etc but they are far too weak to use.

The fabric seat is stretched between the two 20mm circular-section steel crossbars about 50cm apart. I bought the fabric at a surplus material shop by asking for something to repair a deck chair, and it's actually for making outdoor awnings. The seat can either be sewn with a machine, or just wrapped round the two crossbars once the cart is assembled and held in place with several loops of duct tape (which sticks extremely well to itself.) The crossbars are in turn bolted to the shafts using machine screws and wing nuts, and this is easier if there is a little slack in the length of the seat. I've used wing-nuts throughout as it's easy to check they've not loosened while you're using the cart. I used 60mm long, 6mm diameter M6 "machine screw" bolts and wing nuts, and cut some of the bolts shorter for use in different places.

Next the wheels are attached to the crossbars by eight forks, which support both sides of the wheel hubs. The points where the forks bolt on to the crossbars are 15cm apart, which is wider than the wheel hubs. This means the forks meet at the hubs at an angle side-to-side as well as front-to-back. These angles make it harder for the cart to flex or buckle. Each end of each fork is flattened with a vice before it is drilled, so the end can be bolted flat against the crossbar or against the wheel hub. The two flat ends need to be made at right angles. I use a flat metal file to tidy up and round off the ends, especially any sharp bits.

The L-shaped flattened ends of the false-axle are attached to the two bicycle wheel hubs with the same hub bolts used for the forks. The false-axle provides additional strength, and plays the role a normal axle does with most other types of paired wheels.

Finally, the footrest is made of two vertical and one horizontal piece, and hangs from the shafts. The flattened ends of the verticals are drilled and bolted onto the shafts just in front of the forks. To stop the footrest pivoting too far forward or back I bent the flattened top ends over the shafts to make small L-shapes. It may take some experimentation to find a comfortable length for the verticals, and I made the flattened bottom ends 2 inches long with two pairs of holes drilled to allow some adjustment.

When the cart is assembled, I have the shafts below the crossbars so the pony is lifting the front joint from below rather than pulling it up from above. That joint experiences the biggest stresses, and this arrangement reduces the risk the bolt threads will be stripped and fail.

I start with the crossbars and shafts on the ground, and assemble the cart upside down so I don't need to support the crossbars somehow while I put the forks and wheels on. It's worth leaving all the nuts and bolts loose until all of them are in place. The first few times I find I have to make one or two of the bolt holes slightly larger with a thin round metal file. It's also necessary to check the wheels are straight and aligned before finally tightening everything up.

Before climbing aboard, the shafts must be held by someone or weighted down, as you are very likely to tip backwards if you lean too far. I find it's easiest to get the pony to hold the shafts horizontal while I climb on or off the seat, rather than them trying to raise or lower the cart with me aboard. In particular when lowering the cart, the weight they're trying to hold increases suddenly as the driver is tipped forward.

Once finished, the seat is about 75cm off the ground, and for most ponies the shafts will be roughly horizontal in use and almost level with the driver's centre of gravity. This is the most efficient arrangement as it minimises wasted effort spent pulling up or down rather than forwards. Ideally, the cart would have huge penny-farthing style wheels so the axles lined up with the shafts too, but they're not easily available. However, the big 28 inch bicycle wheels do help, and are also good on rough ground as they smooth out peaks and troughs. Not surprisingly, these are the design principles of traditional hand-drawn rickshaws.