January 21, 2014
At the end of last semester, the team decided that we were going to build a tricycle for competition. We wanted to do something we had never done before and were excited by the promise of a bike that every member of our team could ride. Although our previous vehicles have fit all of our team members, they required quite a bit of practice to ride.
Today, we met to determine the configuration of our tricycle, informed by the Hellbent Cycles Tricycle Design Primer. First, we discussed whether we wanted front or rear wheel steering. We all agreed that front wheel steering would improve our handling, especially at moderate to high speed. This is reflected by the fact that all cars, trucks and bikes are front wheel steering. In fact, the only commercially produced rear-wheel steered vehicles we could think of were forklifts. Next, we discussed wheel configuration - tadpole (2 wheels in front) vs delta (2 wheels in back). Although the delta configuration is simpler to manufacture, the tadpole configuration has better handling and manueverability and moves the center of gravity of the vehicle farther forward. We decided to move forward with the tadpole design.
We discussed front vs rear wheel drive for the tadpole tricycle. We determined that the extra chain length required for a rear wheel drive outweigh the extremely increased mechanical complexity of a front wheel drive which would need a differential and a multi part axle. We also plan to put front wheel brakes on the two front wheels.
We also discussed the fairing configuration of the vehicle. Although we know that a full fairing would be more aerodynamic than a partial fairing, the full fairing adds weight and manufacturing complexity. Although we would like to stick with the monocoque frame we have built in the last two years, we have not yet decied on a full or partial fairing. This decision will be made in the next week using data from aerodynamic simulations. Some team members also expressed interest in alternate fairing materials such as fabric. This may be explored but will not be pursued for the competition vehicle.
Next, we discussed ideal rider position. Several team members looked in past design reports where we had looked into optimization of seat angle. We found that our prior testing indicated that a seat angle of 40-50 degrees was ideal to allow for riders to see over their knees, output maximum power and remain comfortable. This led into a discussion on adjustability to compensate for riders of different heights. We determined that although it would be simpler to have fixed pedals and add padding to the seat for different riders, we cannot commit to this until we know the shape of the fairing. Instead, we will design adjustable pedals so that if the fairing configuration requires them, we can build them.
Finally, we talked about wheel size. From the aforementioned paper, we learned that smaller wheels resist 'tacoing' where the round wheels fold under side loads similar to a taco when lifted by the eater to be eaten. For the front, we decided upon small 16-20" wheels. In the back, we will likely go with 20" or 26" wheels. Although the larger wheels would allow for a smoother ride and easier gearing, the increased durability of the 20" wheels may push us towards them.
Overall, we had a very productive meeting and are looking forward to the semester ahead. Tomrorrow, we will break into task forces to do detailed design on the subsystems. We plan on performing detailed design over the next two weeks.