Trev is built around a structural tub chassis fabricated from composite sandwich panels. Low-mass non-structural body panels are fitted to the tub to form an aesthetic and aerodynamic body.
The technique used to build the UniSA prototype is summarised in three articles in AutoSpeed magazine:
The construction technique is simple and effective.
The original design had the battery in the front of the car. Team Trev made some modifications for the 2010 Zero Race:
The 2001 tub model (Tub_2011.skp below) makes the following improvements to the design:
The tub design is almost finished. Still to be done:
The original Trev tub was made from Ayrlite 2016 20 mm thick aluminium honeycomb panels, with 290 gsm fibreglass skins. The floor and front compartment were reinforced with two layers of 170 gsm Kevlar, at 0 and 45 degree angles, to give the tub sufficient stiffness and toughness.
Polypropylene honeycomb is a much cheaper alternative, is non-conductive and perhaps quieter, but is slightly heavier. Team Trev is using polypropylene honeycomb for their African Solar Taxi.
The diagram below illustrates a simple right-angle fold.
The desired final shape has two panels at right angles to each other. The two panels are marked out on a board with a gap between them. The width of the gap is a t, where a is the desired angle, in radians, and t is the thickness of the board. For a right angle in 20 mm thick board the gap is pi/2 x 20 mm = 31.4 mm. Folding the panel will close the gap on the inside of the fold.
The process for more complicated shapes is similar. Use the dimensions from the inside surfaces of each panel, and draw the panels onto the board with gaps between them corresponding to the fold angles.
The following images show the the tub templates. The corresponding SketchUp models can be downloaded from the bottom of this page. You can export DXF drawings from the SketchUp models using a DXF and STL export plug-in.
Each of these template sheets fits on a 1200 x 2400 board. The folds are designed for 20 mm thick board. The red strips indicate regions where the skin must be removed on the bottom of the board; the blue strips indicate regions where the skin must be removed on the top of the board. (For those that remember Origami: the red strips are mountain folds and the blue strips are valley folds.) Dimensions can be determined from the SketchUp models.
We have not yet finalised the design of the rear of the car, behind the rear seat. This will partly depend on the design of the rear swing-arm.
The vertical walls to the side of the front seat are not parallel to to centreline of the car. When these panels are folded, the inner face of each wall will be in the correct location but the outer face of the wall will have a slight gap at the front and a slight overhang at the rear. The gap can be filled, and the overhang can be trimmed off.
Once the panels have been marked out:
For tight angles, applying a fillet of microballoons into the corner can make it easier to apply the fibreglass tape.
There are several possible techniques for fixing components to the tub:
The photo below shows the mounting for the rear swing arm.
[photo to be added]
In the next version, the mounting for the rear suspension will be lower. We also need to incorporate some means of isolating road and motor noise from the chassis.
The front suspension is mounted to vertical steel plates which also fold underneath the tub.
[photo to be added]