This instructable gives an overview of building two small cars from the ground up, both powered by electric bike motors. The build includes chassis, fibreglass body, steering and drive train. The cars are designed for efficiency to extract the maximum performance from a 1hp motor and were used to compete in an electrathon competition. It can be built for around $1500 including motor, controller and the latest lithium batteries and will go flat out around 50km/h for 1 hour before recharging.
Similar in size to a gokart, Roadbot 3 and Roadbot 4 have streamlined bodies, minimal frontal area and low rolling resistance tyres. They are powered by brushless DC electric motors and a lithium battery packs.
They were built to compete in the Perth EV Challenge in Western Australia by the River Raiders team.
Step 1: Planning and Models
After doing some drawings and measuring up the drivers, a scale foam body model is made from polystyrene foam and a full scale ergonomic study is made from plywood. The shape of the sides shows how the vehicle profile will look and identifies a couple of places we can shave a bit off the cross sectional area.
This year we are using 20” wheels and are building 3 and 4 wheel cars. The 20” rear wheel, down from 26” in previous years allows a more reclined driving position which reduces the frontal area. The 20" wheels are also stronger for side loads than large bike wheels (note a bike does not apply side loads to a wheel when cornering) but have a slightly higher rolling resistance however at speeds over about 30km/h, reducing wind drag becomes more important than rolling resistance.