Vehicle Concepts
Concept #1: Titanium Honeycomb Frame
Titanium honeycomb was selected as a concept material for several reasons. Titanium honeycomb is remarkably lightweight and incredibly rigid. The stiffness of a titanium honeycomb panel combined with its low density makes it a perfect candidate for a frame material. The weight of a tandem frame and roll cage made of titanium honeycomb would be roughly five pounds and would deflect minimally with the weight of two riders (~320 pounds). Since the honeycomb comes in standard sheets and the inner core is laser welded at every seam, it can be easily cut to the required shape with minimal reduction in structural strength. One cautionary note is the sharpness of cut edges when working with this material, so we will need to be extra careful when handling the fabricated pieces and take measures to reduce the risk for injury.
In industry, titanium and aluminum honeycomb panels are used to manufacture lightweight craft that will be subjected to considerable strain/stress. The aerospace industry uses honeycomb in aircraft and aerospace for structural framing and wing support. Honeycomb has also been used in Formula One cars to re-enforce the vehicle nose cones because of the material's superior damping and impact properties. By using such materials in a frame, road vibration and noise are also reduced.
The team has determined this particular design to be the most unique of the three concepts considered, and thus would like to use this design to fabricate the actual 2011 NAU HPVC vehicle. Aluminum honeycomb is also under consideration as a backup, should titanium honeycomb be unavailable for donation or too expensive to purchase. The vehicle will include lean steering and a recumbent back-to-back rider setup. A concept drawing of the honeycomb frame design is shown in Figure 1.
Figure 1. Titanium Honeycomb Frame Concept
Concept #2: Carbon Composite Frame
Carbon composite has been selected as the possible second frame material concept for its strength, weight, and durability. Carbon fibers can be molded into any shape or form that would allow our team to create a uniquely shaped vehicle frame.
In industry, carbon composite is used to manufacture lightweight body panels in automotive and structural aerospace applications. It is also used in many consumer products, such as fishing rods, sports equipment, and bicycle frames and components.
Our team has selected the carbon composite frame as a second choice because, as mentioned previously, composites are difficult to work with, messy, and the epoxy resin needed for bonding is a cumulative toxin when inhaled. The process needed to create a quality mold is very time consuming, and laying-up the carbon composite on the mold requires skill and knowledge of the material. We also do not have an autoclave at our disposal at NAU, so we would need to sub-contract the curing operation to a local contractor. Due to the limited time that we have to fabricate a vehicle, this option is not time efficient, but would still produce a unique vehicle frame. This vehicle design will include lean steering and a recumbent back-to-back rider setup. A concept drawing of the carbon composite frame design is shown in Figure 2.
Figure 2. Carbon Composite Frame Concept
Concept #3: Chromoly Truss Frame (2010 Mystax Cetus Modification)
The SAE 4130 chromoly truss frame concept is the third frame option chosen by the HPVC team. This frame design was used on the 2010 Human Powered Vehicle, the Mystax Cetus. The frame is made from thin-wall chromoly tubing welded into a truss design. Since chromoly is relatively easy to weld, this frame is very versatile for mounting components and easy to modify. The current 2010 vehicle will be shortened, a roll bar removed, lean steer linkage added, and the rear seat flipped and repositioned to fit a second rider in the back-to-back setup.
This concept is the third option and will only be used if there is insufficient funding to fabricate concepts one or two. While the truss frame design is unique, it is the heaviest of the three concepts we've considered, weighing roughly sixteen pounds in its current condition on the 2010 vehicle. A concept drawing of the modified truss frame design is shown in Figure 3.
Figure 3. Chromoly Truss Frame Concept