Introduction
I have already built 4 steel and aluminum tube solar mono-wheel trailers (mostly scrap materials), ultra-light fiberglass tube mono-wheel trailer, 2-wheel trailer from a wheelchair.
This year, I needed to build a new trailer for the needs of my association, a trailer that could carry solar panels and a banner for the association. I opted for a single-wheel model.
For an eco-responsible design, I chose bamboo as the base material for the tubes.
Technical Description
The structure
I used the same structural principle as my previous trailers:
– the tubes are associated in a trapezium,
– a fork for a 20-inch wheel is associated with the trapezium (recovery in a bicycle workshop) ,
– metal inserts allow the trailer to be attached to the drawbar,
– the drawbar is a model marketed by a trailer manufacturer,
– a kickstand is added (very useful when you need to detach the bike).
It is recommended to make your constructions from sections of dried and steamed bamboo. Unfortunately not having a deadline for this project, I cut the standing bamboos, choosing very straight stems, and I started construction right away.
Trapeze construction
The lower tube must have a sufficient internal diameter to accommodate the 20-inch fork.
The upper tube has sufficient length to accommodate the solar panels (145 cm).
The tubes are first associated with each other using a fiber epoxy resin which hardens in 7 minutes (the portions of bamboo that will be glued in this way must be sanded beforehand).
Then strips of fiberglass textiles are wrapped around these junctions and are coated with a brush in liquid epoxy resin.
I then use wide tape to compress the textile against the tubes, the excess resin is thus evacuated.
This transparent liquid resin becomes dry to the touch in a few hours (6 to 8 hours depending on your temperature). It only reaches full strength after 7 days.
Kickstand
It is made with a relatively light steel structure, it is held by a steel cable, and a small tensioner raises it when riding.
Solar equipment
For the needs of the demonstrations of our association, I installed 2 solar panels of 100 Wp (6 x 5 cells) and a CTK-EV 300 solar regulator.
Summary
The weight of the bamboo structure with its stand is 4.5 kg. The fork used is a 700g steel fork. Using an aluminum fork could save 350g.
The wheel I have with its 45mm tire is not very light: 1.7kg. One could easily save at least 300g by choosing a lighter wheel and a thinner tire.
The Bob Yak drawbar used weighs 1.2 kg. An Extrawheel trailer drawbar would save 500g.
Currently, the total weight of the trailer without panels is 7.4kg.
Point to watch
I will be monitoring the progress of the freshly picked bamboo stalks as they will dry out over the next few months. Will we observe a retraction of the material and a weakening of the junctions? The future will tell…
Anyway, if necessary, I can always add fiberglass + resin textile strips in places that require it.
Evolutions
The dimension of this trailer is mainly related to the dimension of the banner it has to carry.
If I were to build such a trailer for travel, I would probably make it shorter, the wheel would be completely covered by the latest solar panel. A plywood shelf would be added to the lower tube to allow for hanging and carrying luggage (watertight cylindrical bags).
