Open Source Car/Manufacturing Instructions

Design Rationale

The basic requirements for the OS Car are: Two passenger capacity, Ultra-high fuel economy (50+ MPG, city, 100+ MPG, highway), Ultra-long range (1000+ miles), Low Cost (less than $12,000), Ease of Construction (1000 hours of construction time. Can be constructed by one person in 1000 hours with a vertical mill, band saw, disc sander, grinding wheel, air compressor, welder)

Given these requirements the basic attributes chose for the OS Car are:

• Reverse Trike Layout
  The reverse trike layout was chosen because it allows for side by side seating, an aerodynamic rain drop shaped body, and safe handling. A two-wheeled vehicle with tandem seats resembling a motorcycle would have less frontal area and probably less wind drag, but would simply not be practical to drive. A four-wheeled vehicle could be made with a rain drop shaped body, but would have extra drag from the two rear wheels which would protrude from the body. The reverse trike design may seem novel, but has been used successfully for over 100 years in cars from the Egg to the Aptera. Other benefits to the reverse trike layout are lower weight and cost due to the obviation of one wheel and a differential.

• Hybrid Hydraulic Powertrain
  A hybrid powertrain is a requirement for achieving high fuel efficiency in city driving in order to: 1. Exploit the low brake specific fuel consumption (BSFC) of a very small displacement engine which cannot create enough power by itself to provide sufficient acceleration of a vehicle. 2. Allow for regenerative braking where kinetic energy of the vehicle is recaptured and stored. Hybrid electric powertrains are most popular in hybrid vehicles produced by the major OEMs, but using a such a powertrain in the OS Car would require either very expensive lithium-ion batteries, or very heavy lead-acid batteries. A hybrid hydraulic powertrain would not require any batteries for energy storage and would instead use a relatively lightweight and low cost accumulator.

• Tubular Steel Space Frame
  A tubular steel space frame design was chosen for the space frame because it will be lightweight, stiff, strong, relatively inexpensive, and easy to construct. Although aluminum tubing would allow for a lighter design, its cost would be unacceptably high. A composite monocoque is and alternative to a space frame design, but a monocoque would require costly molds, and would require a large amount of time and a fair amount of skill to construct.

Bill of Materials

Mazda NB donor vehicle

(with weblinks to sources)

Instructional Video

A to Z on the Fabrication

3D CAD files

Metal parts