This sidecar was built to transport my 3 year old son on the local cycle paths.

It was constructed from a steel angle frame, with a wooden bodywork and plastic screen.
It was designed to pivot against the bicycle frame so the cornering and riding were less affected by the addition of the car.
The design was reminiscent of sidecars which were commercially available in the 1940's.

Safety.
The sidecar was fitted with a harness to help the passenger stay safely in place.
A guard was also fitted to the side of the bicycle rear wheel to stop potential accidents between the child and the spokes.

Please note that being in the UK I mounted the sidecar on the left. If you cycle in a country where they drive on the other side of the road, you should consider switching the sidecar to the other side.

Step 1: Making the Frame

The frame was made from 25mm steel angle 3mm thick. The angle was cut to the dimensions shown in the CAD sketch.
The frame parts were clamped in place using some wooden off-cuts and cable ties, then welded together.

Step 2: Adding the Wheel

The sidecar wheel was a standard 20" bicycle front wheel. The mounting was slotted to allow some degree height adjustment, but this could be ommited if you know what bike you are going to attached the sidecar to.

The wheel mount was positioned midway along the frame edge and welded in place.

The outer frame was a piece of 25mm steel strip bent in the vice. This was bolted to the main frame to allow the wheel to be removed more easily.
Once the outer frame was bolted in place, the outer wheel mount was clamped and welded to complete the wheel fixing.

Step 3: Building the Bodywork

The bodywork was made from plywood. 12mm thick plywood for the base and top deck. 4mm plywood for the curved sides. The overall dimensions were 850mm long, by 300mm wide and 300mm high. Some metal brackets were used on the inside to help keep things square.

The top and bottom deck were cut to the same profile. They were spaced apart by a vertical post with the top deck moved forward by 5". The rear panels were also cut from 12mm thick and a hole cut to allow access to a small boot.

Once the basic box was complete an opening was cut in the top where the passenger would sit. This cut left the thin 4mm sides exposed to damage; so some 12mm ply off cuts were glued inside the sides, to give re-enforcement.

Step 4: Finishing the Bodywork

The wheel arch was two semi-circles of 12mm plywood with some 4mm ply bent over the top and secured with screws and glue.
The wheel arch was not secured to the outer frame so that the frame could be removed to service the wheel without having to remove the whole arch.

To finish, a screen was cut from polycarbonate and mounted using a strip of wood planed to the required angle. Some automotive body filler was used to blend in the edges and fill in any small gaps. The sidecar was painted in bathroom emulsion.

The seat was two sheets of 12mm plywood, covered in 2" of foam with some material folded over and stapled in place underneath.

Originally the body was mounted on springs to the chassis, but this gave unwanted oscillations, so the springs were replaced with soft rubber bushes.

Step 5: Attaching to Bicycle

The pivot was a simple bar held in four mounting blocks. Two blocks on the bicycle and two on the sidecar. The sidecar pivot blocks were made adjustable to allow sidecar tracking to be set.

The sidecar pivots were blocks of aluminium. One was slotted and the other had a single pivot bolt, to allow for adjustment of tracking. The blocks were cross drilled to take the 12mm pivot bar.

The bicycle pivots were steel blocks welded to steel strip.
The rear mount was drilled to fit the rear axle nut.
The front mount was mated with an aluminium block which was notched to help it locate on the chain stay. The notch had some old rubber inner tube glued in it, to prevent damage to the cycle paint.

To give clearance for the pedal closets to the sidecar, the sidecar was mounted with its front mount touching the rear mount on the cycle. This position was held using split pins and washers, but an alternative would be to use 12mm threaded bar for the pivot, with some nuts to hold the sidecar position

Step 6: Finished Images

Here are some general images to show the sidecar with the bike.

Modifications ?
A threaded bar instead of a pivot would be a simpler mounting and would allow fore and aft adjustment of the sidecar position - although this would not be as quick to release.
The sidecar could have been a little longer to give more growing room. It was designed to fit in the boot of our car, but longer would have been better.
The wheel mounts could have had slot which was open at the Bottom. This would give the simplest wheel removal without the need to unbolt the outer frame part.

More sidecar details can be found at : http://www.steves-workshop.co.uk/vehicles/sidecar/sidecarindex.htm