Bridgewood : Mark III Glider pony cart

Mark III Glider pony cart

Back in 2009 I had some requests for more information about the cart I used at the Preston indoor pony day, and so I took some more pictures and tried to explain how that Mark I Glider fits together. I continued developing the idea, and by 2011 I had produced the Mark III Glider described below, which features a lower seat for increased stability on woodland rides but retains the lightweight, easy-to-make "glider" philosophy. - 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 plus 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 11kg, so it's very portable - for example, to isolated areas of forest.

Starting from the back, the wheels are standard "28 inch" hybrid-style quick-release wheels from a bicycle shop, with knobbly tires but a larger diameter than most mountain bikes. This size is also called "700C" or "622mm". Quick-release wheels have a long thin removeable axle bolt, rather than fixed stubby bolts that cannot easily be removed or extended. Then comes the storage tube made from 4inch black PVC water pipe. 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 which are held about 86cm apart by the two sidebars, also made of 20mm steel tubing. The seat is 49cm wide and 120cm in total length including the ends folded back round the crossbars. I originally 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, 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), or fastened with leather-working rivets as I have here. The front crossbar is 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.

20cm lengths of threaded steel rod are used as axle bolts and passed through the bicycle wheel axles. These bolt to the ends of the shafts and to six 15mm square-section forks, which support both sides of the wheel hubs. The front and back crossbars are slightly different in size to accommodate the inner and outer pairs of forks/shafts.

To stop the bottom of the cart flexing, there is a 14mm steel tube acting as a false axle and attached to the shafts near the true axles of the wheels. I've used round tubing with the ends flattened in a vice, but you could use more square-section tubing instead.

Finally, the footrest is made of a tube with a length of chain passed through it, with snaplinks on each end of the chain to attach it to eyebolts on the underside of the shafts. This is easily adjustable, and can also flex on very rough surfaces where a solid footrest could ground. As well as increased comfort for the driver, the footrest makes it easier to push back on to the seat and get the driver's centre of gravity balanced over the line of the wheel axles. Maintaining this balance minimises the weight on the pony's arms and increases their endurance.

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 sidebars on the ground, and assemble the cart upside down so I don't need to support the bars 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 up so the seat is horizontal while I climb on or off, 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 50cm off the ground - about 25cm lower than the Mark I Glider. The most efficient arrangement would unify three components: the driver's centre of gravity would coincide with the axles of the wheels and the shafts would pull forward from this point. This is the most efficient arrangement as it minimises wasted effort spent pulling up or down rather than forwards. Not surprisingly, these are the design principles of traditional hand-drawn rickshaws. Ideally, the cart would have huge penny-farthing style wheels to achieve this threefold unity, 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. Attaching the shafts to the wheel axles also satisfies one of the three conditions.