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Engr114 bicycle trailer fabrication
In 2004, HSU Whole Earth Engineering-114 students assisted Bart Orlando in a project to fabricate a bike trailer for the Campus Center for Appropriate Technology (CCAT). The trailer consisted of a welded frame of 1 inch steel box tubing. It was strong enough to carry an ~135lb woman and able to turn on a dime. Students learned how to design a simple trailer frame and hitch, cut box tubing with a Saws-all, remove burs with a file and pedal powered grinder, weld steel, paint steel and safely tow a bike trailer for the first time.
Both men and women took turns learning to use a wire feed arc welder to join the steel struts of 1" box tubing. The tack-welding of the frame was facilitated by using a template consisting of a 4x8' steel sheet and angle iron guides. However, the underside of the trailer would make a good template itself if it were fitted with welded guides for strut alignment and inscribed with measurement specifications. In this way, the process of trailer replication would be facilitated by mimicking  the biological process of Transcription: The Synthesis Of RNA. 
The trailer hitch consists of a steel eye-loop, on the end of the trailer tongue, which is tethered (with a length of a used bike tire inner tube) to a car tow hook that is welded to the frame of the bike. All degrees of freedom necessary for a trailer hitch are provided by using this elastic tethering system.
by Bart Orlando