Load-carrying Bicycle Trailer

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The trailer consists of two axles.

1. A 1m wide forward axle with a 16in bicycle wheel at each end. This axle is designed to maintain lateral-stability. It is made with a 20mm outer diameter seamless steel pipe (2.5mm wall thickness) and weighs about 1.5kg.
2. A 60cm wide rear axle with a pair of 14in bicycle wheels at each end. It is a load-bearing axle. It is made with a 16mm diameter solid steel rod and weighs about 1kg.

We modify a stock 14in or 16in wheel in the following way:

1. The spindle and ball-bearing housing are removed, leaving just the hub that binds the spokes.
   
2. A sleeve is made using a 48.3mm outer diameter, 7.14mm wall thickness (schedule 160) seamless steel pipe section about 24mm long.
   This section is bored (about 12mm deep) to fit outside of the hub at one end and at the other end it is bored out (about 12mm deep) to fit a sealed ball-bearing.
   2 such sleeves are made, one for either end of the hub.
   Each sleeve weighs about 50g.
3. For the double wheel case, 3 ball-bearings are used for a pair of wheels. One goes between the 2 wheels and one each goes on the outsides of the wheel pair.
   The interconnecting sleeve is a slightly different design. It's actually 2 sleeves made the same way but only 18mm long. They are bored only 6mm deep on the ball-bearing side to fit half the ball-bearing. Their outer diameter is also reduced by 6mm.
   The 2 sleeves are fit into both sides of the ball bearing's outer casing. An additional outer sleeve of 36mm length and about 3mm remaining gauge encases these 2 sleeves.
   This design serves to align the wheel pair while providing an inter-wheel spacing of 36mm.

All structural elements (for pulling, steering, strengthening and frame-building) are made using rectangular  cross-section (40mm x 8mm), hollow (2mm gauge) steel beams. Weight is about 1.6kg/m.

These beams are strengthened at their attachment points with iron plate segments. A 4mm thick iron plate segment fits inside the beam and two 2mm thick plate segments sandwich it from the outside. The 3 plates and beam section are aligned, bored through with 2mm holes and riveted. (This  keeps weight low while providing strength where needed).

The 2 pulling beams are aligned and spaced about 70mm apart.
The 2 rear axle steering beams on are aligned with the rear axle line and placed close to the ends of the axle. Their non-axle ends are placed outward, away from the back of the trailer.

The 2 forward axle steering beams are aligned with the forward axle line, placed close to the ends of that axle and their non-axle ends are placed  inward, towards the bicycle frame location.

The 2 axles are then passed through the 4 aligned holes in each case, then the locations of the beams are adjusted and fixed. Finally, the wheels are bolted in from the outside.

The chassis is attached to 2 load-bearing points in the bike frame:

The rear wheel spindle. This connects to the ground via the wheel spokes and rim, directly.

The seat-post. This connects to the ground at both front and back, wheel-ground interfaces through the bike frame. This is an indirect connection.

The frame design promotes keeping the weight of the load, balanced along the center-line of the trailer. This helps reduce tyre-road friction, hence increasing speed.   The base frame rests primarily on the center of the rear axle, on the sides of the lateral-stability axle and the seat-post of the bicycle. It then has  narrow forward extension from the seat-post to the handle.
The useable length of the trailer-frame is about 2m which is good for long, thin loads such as pipes or beams.

Slope

Carrier Shape

Carrier detachment and add-ons.

The trailer’s dimensions have been designed to be transported in the trunk of a small car.