Wednesday, March 16, 2011


Factory Five and Grassroots Motorsports design contest entry.
These are initial designs for a spec racing car design competition. The specs are as follows (as far as I can remember)
  • square section tube frame
  • Composite shell
  • Mid engine, rear drive layout
  • 95" wheelbase
  • 2.5L 4 cylinder boxer engine from a donor Subaru Impreza WRX
  • 1800 lb curb weight
  • Under $15k for complete kit (donor car not included)
The main constraints are price and weight. Obviously you can't get away with a composite carbon shell for $15k (or can you? China?) So the shell should meet the target weight assuming less expensive materials.
The drive train components and frame currently are estimated at 900lbs.
The remaining components are the responsibility of the designer(s)

  • Front and rear shell (less than 100lbs each)
  • doors? (way less than 50lbs each)
  • side windows (Lexan)
  • windscreen (Lexan or salvaged from donort)
  • rear window (Lexan or salvaged from donor)

  • Dash panel 
  • gauge cluster
  • steering wheel 
  • seats (14 lbs each for Recaro Profi)
  • harness 
  • pedals 
  • misc linkage
Other bits

  • Driving lights 
  • head and tail lights 
  • signals 
  • rear view mirror(s) 
  • front wing 
  • other wings or aero elements not included in the shell
Since this car is meant to be a 'track special' or spec racer, and cheap, there will be no luxuries built in.
In order to keep the price down, it's a good idea to re-use as much of the donor WRX as possible.  The engine is to be a 300+ hp Subaru EJ257 turbo, variable intake valve timing, 16 valve 4 cylinder boxer. The builder has to pull it from a donor car, so it's really up in the air as to what you can do with the engine. The 3L boxer six from the Legacy is only about 20mm longer and could probably handle a pair of intercooled snails and about 600bhp. And water injection..
I'm using a pretty simple and free vertex subdivision modeler called Wings3D, and will be doing all of the rendering in good old PovRay raytracer.  Subdivision modelling is not a new concept, but it is different from NURBS and Bezier based models I'm used to. 
All of the models are being kept in GitHub to avoid previous data loss disasters:

There the models will evolve and any interesting scenes will be stored for rendering.
Here's Wings3D at work on a prototype:

The environment is very basic, with point, line, surface and body modes having contextual menus. I like it so far, especially for an open source non-commercial piece of software. It's written in C and Erlang, and has an Erlang console interface which I have yet to use.
At this stage the prototype is evolving based on my limited experience with subdivision modelling. Free form modelling is primarily done by moving geometric elements (individual or selections of lines, points, faces, objects) in such a way that you end up with a shell of the desired object which can be sub-divided into quadrilaterals that appear smooth. The above model is the result of 2 subdivision passes. Extra geometry is added in the form of bevels to maintain surfaces which I don't want rounded.
See basics of smoothing polygons here:

The prototype above is a first pass in an iterative process. I don't know if I like it, or it will be light enough, or will even fit on the frame. It actually looks way too large, like a Lancia with a V12 in the back. I do want the front and rear shells be one piece, and open front and rear like a big clamshell (see the Ford GT40 and other 60s race cars). This should make molding and fitting those parts simple, as you don't need separate fenders, hood, valance, etc.
It has some ripples that are the result of my removing the headlight bevels, as they didn't smooth well. I will experiment with different smoothing algorithms, and start over with new models frequently.
I welcome any ideas, input, suggestions. Gullwing doors? No doors at all?