Electric Car Project
I'm starting to acquire the materials necessary to build a single-seat, electric commuter car. It will be an open-wheeled, reverse trike with 300Ah worth of prismatic, lithium iron phosphate batteries. It will use an AC31, AC electric motor running at around 84V. This means I will need 26 LiFePO4 batteries. The chassis is designed to be built in three sections that can be bolted together. The front section contains the front suspension unit, the battery box and vehicle electronics. It will be built around an after market front suspension designed for classic, Type1 Volkswagens and is available from Red 9Design in the UK. The middle section will be a composite tub made of epoxy-aluminum honeycomb panels ( 20mm-single ply 2016 panels from Ayres Composite Panels USA) sheathed in Kevlar with 1" marine plywood bulkheads. This technique (minus the plywood) was used by a University of South Australia team to build their "Trev" electric vehicle. The rear section will be a swing arm unit for the rear wheel which will be belt-driven by the electric motor. This unit will be based on a modified version of the rear drive section of the XR3. The body will be made using standard, foam- fiberglass techniques employed by many kit car designs. One major difference with these is that I want to make the body in three separate sections which can be independently removed for vehicle inspection and maintenance. Here's a sketch of the vehicle I have in mind. Entry will be made by a canopy section that swings to the side like the entry for a Messerschmitt KR200. The car will have a removable, polycarbonate top that can be stowed in a rear boot above the drive unit. The cg of the car will be biased toward the front axle for good lateral stability and a small amount of under steer.
I've deliberately refrained from making detailed plans at this point. It's been my experience that when one does a project of one's own design from scratch, modifications to the original idea will always have to be made anyway. It's therefore better to try to try anticipate all the problems you might have with the idea further down the road, and to come up with a general design that can be easily modified later. This keeps things somewhat intentionally vague at he beginning, with the details falling into place as the thing is actually built. I would use the analogy of a chess game: Try to think as many moves ahead as you can, but keep your strategies flexible to account for the unforeseen. I started this project by studying the plans for the Doran, Tri-Magnum, XR3 and Vortex. I've incorporated several ideas from each of these vehicles and the Trev into my design. These plans also contain discussions of the physics of three wheeled cars which I found very helpful. Having owned and driven a KR200, I'm very comfortable with driving on three wheels. For an excellent description of the joys and sorrows of building three wheeled electric cars, I highly recommend viewing Nap Pepin's website in which he describes modifying a BugE to use lithium batteries and later making a scratch-built three wheeler he calls the Lithium Hawk.
At his point I've ordered the front suspension, the seat and the materials for making the tub. I expect to begin the tub in July. I'll post pictures as I fabricate.
The composite panels have finally arrived and I'm now fabricating the center section of the vehicle or "tub." The panels are easily cut with a circular saw and can be bent after using a router to remove a section of surface ply so that the panel may then folded inward along the routered section. The internal aluminum honeycomb crushes as the panel is folded and bend angles from 0 to 180 degrees may be made with this technique. Application of a couple of layers of fiberglass along the inside edge of the fold holds the bend in place and reinforces it.
A routered section of the Ayres panel exposing the internal aluminum honeycomb. I used a length of 2x4 aluminum tube as a fence to keep all cuts straight.
The panel is folded along a routered section. The wider the routered strip, the more the panel can be bent. This panel will be formed into one side of the tub.
The aluminum tubes are great for holding the folded panel in place. Tapered popsickle sticks make good shims to get the angle just right.
Two layers of fiberglass tape are epoxied to the inside seam of each fold.
One side of tub fomed and epoxied in place.
Both sides of the tub are epoxied into place on top of another panel section. The tub is 32.5" wide and 55" long.
I'm continuing with the tub. I''ve decided to use 1.5 inches worth of marine plywood instead of 1 inch. The Red 9 suspension is here and so I've started to design the front end around it.
Tub with plywood bulkheads and racing seat. The duct tape will be replaced with carbon fiber reinforcement and the whole thing will be sheathed in kevlar. Two doubled-walled, aluminum tubes will run down the sides of the tub for some side impact protection (a sample of this tube is shown inserted in a hole in the front bulkhead).
Up-side-down tub with aluminum tube reinforcements and kevlar sheathing in place. The gray tubes are conduits for the rear brake line and electrical cables. The bottom is painted with black epoxy.
I'm still working on the tub. Things are going more slowly since school started but I'm making steady progress.
Tub with brake pedal assembly, throttle and roll brackets installed. The dual master cylinders are visible on the front of the bulkhead. The side tubes are secured to the bulkheads with custom brackets.
Another view showing the pedals and the aluminum tread plate floor. The motor will be partially recessed into the rectangular hole in the bulkhead. The round holes are for speakers. The interior will be finished with aluminum panels and carbon fiber.
I spent the summer welding up the front end out of mild steel and finishing the bulkheads by sheathing them in carbon fiber. I plan to finish up the front end during the fall.
This is the front end /battery box thus far. The front bulkhead is attached to the rear of the box through brackets containing rubber isolation bushings. The silver part in the middle is the frame for the Red 9 front suspension. The wishbones for it are propped up on either side.
This is the front side of the rear bulkhead. The grills on either side are the speakers.
This is the otherside of the rear bulkhead.