Edge Collective

Bike Trailers

Developing an easy-to-assemble, low-cost bike trailer design, in collaboration with the Somerville Bike Kitchen.

Design goals and approach

We've been working to develop an easy-to-assemble, low-cost bike trailer design, sourced from readily-available parts. The hope is to make it easier for people to transport cargo using bicycles.

After some experimentation, we've currently settled on a design that uses:

recycled bicycle wheels (current design uses 16" 'kids' bike wheels; we're working on a design for larger bike wheels
a bike frame made from 1/2" electrical conduit (inexpensive / easily sourced)
a hitch trailer attachment made from a length of braided vinyl tubing
a widely available bike hitch mount
custom steel 'dropouts' (the wheel supports)

Electrical conduit can easily be sourced new, and sometimes scavenged. Bending it properly requires a custom tool (described below) which is widely available (and likely something that can be borrowed). The dropout design can likely be replicated using a drill to cut holes and slots in $1 electrical box covers from Home Depot; but we're currently using an online laser-cutting service to make the four required dropouts for about $3 each (details below).

We're planning to add more detailed build instructions soon, but the below description gives a general flavor of the current design.

Approximate cost

Approximately $35 to $45 per trailer (if using recycled bicycle wheels, and assuming a future hitch design will cost less than $10)
plus an additional $20 to $60 one-time purchase of a special 1/2" emt conduit pipe bending tool (if you can't find one to borrow)

A more detailed parts list is below.

Trailer Version 1.0


Assembled bike trailer frame, using recycled 16" wheels; the main bike frame is constructed from a single 10' length of 1/2" electrical conduit.


Closeup of the custom 'dropouts' for the trailer. THe design files can be sent to a metal lasercutting service for production (details below).]

Parts list


Two 10 ft lengths of 1/2" metal 'emt' electrical conduit (@ $7 ea from Home Depot) = $14


Two 'short' dropouts (@ $3 ea) and two 'long' dropouts (@ $3.30 ea) from sendcutsend.com (see below for design and ordering details) = $13


Eight #10-24 x 2" bolts, with nuts (4 for $1.38 at Home Depot) = $3; Five #10-24 x 2.5" bolts, with nuts (2 for $1.38 at Home Depot) = $5


Two borrowed or recycled 16" 'kids' bicycle wheels (free)


A 6" length of 7/8" braided vinyl tubing (sold in lengths of 10' for $25 at Home Depot; so 6" is about $1.25)


Burley Bike Trailer hitch on Amazon for $10

Common tools


Phillips-head screwdriver


11/64" drill bit


Phillips-head screwdriver


Pliers

Special pipe-bending tool


1/2" conduit pipe bender -- $20 on Amazon, $60 at Home Depot, free if borrowed


How to use a pipe bender: https://www.youtube.com/watch?v=r3h97SfQYYI

Making the dropouts

The bike frame design has an 'inner' wheel support bar that is higher than the 'outer' support bar, leading us to design a longer 'inner' dropout, and a shorter, 'outer' dropout.


The wheel mounts have an inner support bar that is higher than the outer support bar (by one pipe diameter).


The different heights of the inner and out support bar are compensated by different dropout lenghts, in order to keep the wheel axle level.

We designed the 'short' and 'long' dropouts in openscad. (The original .scad files for "version 0.3" of the droupouts can be found on github: version 0.3 can be found on gitlab)

You can upload the ".dxf" files linked below to sendcutsend.com, specify 0.125" (3.2 mm) stainless steel, and they'll send you back the laser-cut metal.


Short dropout. DXF file (for production); SCAD file (for reference or re-design)


Long dropout. DXF file (for production); SCAD file (for reference or re-design)

Making the hitch

Base Design & Variants

As of 12/23, we've been experimenting with a standardized 'wheel base' design that uses a single, 10' length of 1/2" conduit as a stable 'frame' around adult-size (26 in) bicycle wheels. The idea is that this 'base' can then be modified to be used as a bicycle trailer, or a simple garden / city cart.

We'll be posting updates as this design solidifies.