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
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| Assembled bike trailer frame, using recycled 16" wheels; the main bike frame is constructed from a single 10' length of 1/2" electrical conduit. |
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| 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
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| Two 10 ft lengths of 1/2" metal 'emt' electrical conduit (@ $7 ea from Home Depot) = $14 |
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| Two 'short' dropouts (@ $3 ea) and two 'long' dropouts (@ $3.30 ea) from sendcutsend.com (see below for design and ordering details) = $13 |
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| 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 |
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| Two borrowed or recycled 16" 'kids' bicycle wheels (free) |
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| 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) |
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| Burley Bike Trailer hitch on Amazon for $10 |
Common tools
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| Phillips-head screwdriver |
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| 11/64" drill bit |
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| Phillips-head screwdriver |
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| Pliers |
Special pipe-bending tool
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| 1/2" conduit pipe bender -- $20 on Amazon, $60 at Home Depot, free if borrowed |
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| 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.
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| The wheel mounts have an inner support bar that is higher than the outer support bar (by one pipe diameter). |
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| 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.
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| Short dropout. DXF file (for production); SCAD file (for reference or re-design) |
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| 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.
Somerville Bike Shop Bike Trailer Workshop Dec 2023
