For my Engineering Design and Communications class we were assigned a final group project of helping someone in the community with an engineering need. My team were was tasked with building a a hand powered cart for a special ed class in a local middle school. After much collaborative brainstorming we chose a design that we felt would meet the specification and be possible for us to construct.
The design used two salvaged bikes that were flipped upside down a chair built in between.
due to time constraints and that the bike was a prototype, a few design elements had to be scrapped or changed. Here you can see that the each hand peddal powers each wheel directly without a derailer for changing gears. This simplified construction greatly, but requires a little strength to get started from a stand still and doesn't allow that great a range of speed. The gear hub was also tightened down so that the peddels could be turned in reverse for backwards movement, but it also meant that if you let go of the handles they would continue to spin with the wheels.
You can see where the brakes were relocated in case you lose control of the handles
To accomidate drivers of different leg length, an additional pad was included and stored here on the back
Another problem we ran into was in the use of the trailing rear wheel. When designing the bike we were not fully away of the special dynamics of the front wheel and the many factors that contribute to its self stabilizing effect. By turning the bike upside down we changed the angle of attack that the steering axel had, creating an unstable system. To compensate, we replaced the large reer wheels with casters that worked, but gave a much bumpier ride.
We learned a lot on this project, and although we were dissapointed that we could not hand off a finished project to the client, we knew that the design process would not end with us, and that future EDC teams will pick up the project from where we started.