Bicycle trailer from scrap metal




Scrap metal

This pile of junk metal, scavenged from the side of the road before an inorganic rubbish collection, has been turned into a useful trailer system for a bicycle. The pile includes an ironing board, part of a shelving system, a tube chair, a magazine rack, small wheeled trolley, and some light reinforcing rod. It's in various stages of decay, but overall is sound and perfectly useable.

On the right is my Henrob 2000 welding/cutting torch that I've had for many years (Henrob info page). It runs at a much lower pressure than typical gas torches (very economical) and will weld dirty and rusty metal without cleaning or flux. Because it uses so much less gas I need to keep only small oxygen (1.6 cu metre) and acetylene (1.0 cu metre) bottles for even large jobs

Charging

The intention is to make a modular system. The wheels are attached by four bolts with wing nuts and are transferable to another trailer base, which will save both materials and cost. This is the first base made - a long cargo hauler, shown here while the 6 volt gel cell for the LED lighting is under charge. The next will be a smaller weatherproof box for carrying tools and equipment.

Acetylene

The previous link is the unfinished, but roadworthy, base loaded up with a small acetylene bottle in a wooden cradle. This is how I transport my welding bottles to and from the local gas supplier. This bottle weighs around 21kg (1500psi), the oxygen bottle is much heavier, 40kg (12000psi). I've carried two kids around with no problems at all (apart from my legs !!), and they weighed over 75kg together

Details

Assembly is very straight-forward, and based around the shelf frame. First the 1" angle is welded to it to fix the wheel bogey to. Next the cross-braces at the front half for the coarse mesh of the magazine rack. Then the tow bar and two small brackets for front and rear LED lights. Lastly some 10mm steel bar hooks for any rope tying or elastic hooks. Pictured is one of the hooks and the lockable pin (a steel disk welded to a short length of 1/2" rod) connecting the bike to the trailer. This is a convenient way to hitch/unhitch the trailer

Trailer forks

The forks on the wheel bogey are made from the tapered chair legs and the thicker edge rods of the magazine rack. The cross brace is part of the trolley. A loop is added to one side of the fork to hold the wheel in, just in case the nut ever comes loose

Bike side of trailer

The bicycle side of the tow bar is made from a section of tubing from the ironing board and more bits from the chair. It's bent slightly so that the rotating joint can be directly behind the back wheel. A small strut stops any twisting imposed by the trailer

Swivel joint

Ideally I'd like a small ball and socket joint for the bike-trailer connection, but my lathe isn't set up properly, so I've made do with this. The two 1/4" plates allow horizontal movement for turning (which is about an 8ft circle, about the same as the bike on its own). The second part of the joint takes care of any leaning of the bike or bumps the trailer goes over. A heavy bolt is passed through a 1" square tube. The head of the bolt is welded on the bike side, the tube free to rotate around it. So far this seems to work very well

Cold zinced

Once all the parts have been put together, it's given a grind and a wire-wheeling to remove loose rust, paint flakes and scaling from the welding. It's then painted with phosphoric acid rust fixer, which is later hosed off. Areas around the welds are wire-wheeled again and sprayed from an aerosol can with cold zinc. Most of the frame is sprayed with aluminium paint, some parts are (or will be) brushed with black enamel

Lighting

LED lights are used throughout, as they are very efficient compared to filament bulbs. The store-bought lights that came with the bike will either be rewired to run off the gel cell or replaced with more efficient circuits. White LEDs are very bright, consuming little power, compared even to the store-bought LED lights. The front lamp I made uses 1/14th of the power (8mA vs 110mA) yet is just as visible and at a wider angle. The LED faces backwards into the mirror and shines like a torch, whereas the store-bought ones rely on the LED lens. Typically those ultrabright LEDs have around a 20 degree viewing angle, which I don't consider suitable for road use. The back reds (trailer and under the rack) are also low-current white LEDs. The one under the saddle is the other inefficient store-bought. Underneath the trailer rear light is a forward-facing white reflector, for even better visibility. I found that local bike shops have, for some reason, boxes of surplus reflectors that they don't want and were quite happy to give them away by the handful. The front lamp for the time being has mylar film over it. When I get time I'll make a proper housing with a perpsex front. Click here to see how I made the front light for the trailer out of bits and pieces around the workshop White LED lamp

All finished !!

The cost has been very reasonable - NZ$50 for a pair of new wheels, $20 for welding gas, $20 for bolts and other small bits and pieces like the rust-proofing, paint and cutting/grinding discs. Less substantial trailers I've seen on the web from US suppliers would have cost typically $1000 and up to import. As far as I know there is or was only one trailer manufacturer in NZ, who sells a child buggy for around $900

Eventually I decided to change the bike from a purple girl's one to a blue boy's one. A few reasons - (a) it's a girl's bike - I'm not a girl (b) black wires and cables don't stand out so much against a royal blue background (c) the stand needed a proper welded fixture rather than the crappy screw-on one supplied (d) after fitting the new saddle Buns Of Mild Steel the frame had to be lowered a couple of inches to make it more comfortable (e) bits and pieces had been tacked on ad hoc and it was time to fix them on properly. Think the trailer will stay silver for good visibility

Previous to the major overhaul of the bike itself, the trailer was fitted with a gas bottle holder that has its centre of gravity below the axle. It is now difficult to overturn and therefore much safer