This Instructable provides an overview of the design and construction of a small electric go-kart or microkart with brushless motors, lithium batteries, independent suspension and a composite deck chassis, built from new components for under $1500. By keeping the design as light as possible, this microkart maximises performance from 6.5hp and its tiny size exaggerates the 40mph top speed.
SKIP TO BUILD STEP 1 - DRIVE TRAIN or continue reading below for more background info about the project.
My overall goal was to produce an electric go kart for under $1500 that showcases current motor and battery technology, is suited to on or off road use, great to drive and challenges a few of the standard approaches to kart design along the way.
Some friends are building electric gokarts by taking a sprint kart (fixed gear racing gokart) and replacing the 2 stroke engine with an electric drive train. This is a quick way to make an electric kart, but unless you already have a racing kart you need to first buy a kart which would blow my price goal. I also wanted to further develop the go kart concept in a few other areas including size, chassis, suspension and independently driven wheels.
Size - to keep weight as low as possible, provide greater options for racing in carparks and indoors and make for easy transport in the boot of a car rather than a trailer, this design miniaturises the already miniature, hence the name microkart. This will extract maximum performance from the small electric drivetrain.
Chassis - structurally racing gokarts are flexible enough to lift or at least reduce the pressure on the inside rear wheel when cornering to counter the effect of a solid rear axel. In this design the rear wheels are driven independently with a motor for each wheel so the chassis will not need to flex for cornering and all four wheels can remain on the road. In addition the electrics are mounted inside the chassis instead of on top for protection and a cleaner look.
Suspension - go karts don't usually have suspension which is fine on a smooth kart track, parking lot or in a warehouse, but to find more places to drive it, improve performance and to provide a smoother ride off road, the microkart is designed with suspension. While it does appear to go against one of the principals of the go-kart which is keeping the design as simple as possible, the challenge is to do it cheaply and simply using easily available components.
Independent drive - ultimately I want to produce a 4wd gokart to maximise acceleration on and off road with each wheel independently powered by its own electric motor. To reduce costs and complexity (avoiding CV/universal joints at the front) I will be driving the rear wheels. Independent drive should extract more grip than a solid axel as well as saving the weight of the axel. It also opens opportunities for the future for developing a traction control system.
So on with the build....
One third of the gokart budget, $500 was allocated for the motors and controllers. Higher power motors designed for electric bike use were chosen as providing the optimum combination of power, price and packaging. Two 2000W or 3hp brushless electric motors from Cyclone Motor were purchased online for $159USD each and two brushless electric motor controllers from Golden Motor for $95 each. The motors included a 7 tooth sprocket for standard bike chain. A little over the $500 budget (particularly as the prices don't include delivery costs) but well priced considering the cost was less than $100 per hp.
Getting the power to the rear wheels uses a standard bike chain driving a recycled bike sprocket on each rear wheel. See the step on wheels for more information on mounting bike sprockets on the rear wheel hubs.
Electric Motor Source Guide
There are three main groups of electric motors that are practical options for a go kart.
1. Radio control plane or car brushless motors.
The RC community were great innovators in making their own high power small electric brushless motors for RC aircraft and now there is a huge range of options of ready made motors and controllers. They provide the highest power to weight ratio electric motors available and are very cost competitive, but they are not the most durable, are typically very high revving thus need higher gear ratios for karts, need to be de-rated for use in go-karts to avoid overheating and they are not well suited to start stop or slow speed operation. Hobby king is a good starting point to find a high power RC brushless motor. Instructables user Teamtestbot has a good primer on using RC hobby motors here https://www.instructables.com/id/The-New-and-Improv...
2. Electric bike motors
These are also cheap and readily available, particularly in the 200w to 500w range to suit e-bike regulations. They are provided in kits that are easy to wire up and they are designed for higher torque and slow speed operation. While 200w to 500w would be OK for a kids gokart, there are a few sources of e-bike motors up to around 5kW or 7hp. Cyclone Motor, Golden Motor and Kelly Controls are suppliers of higher power e-bike motors.
This project uses two 2kW or 3hp brushless electric motors from Cyclone Motor. These are ideal size and well priced to suit the project. Cyclone use Kelly controllers for their motors, and while I have found Kelly controllers to be fine on previous projects, Golden Motor cruise controllers have a good range of features at a better price, thus we are using two 48V 50A continuous (100A peak) controllers from Golden motor on this project.
3. Small electric car motors such as etek type motors often sold for small electric car conversions
These are ideal for a go-kart conversion using a larger gokart frame and suppliers such as Motenergy which has replaced Etek motors is a good example. These motors are typically 10hp plus. The disadvantages are that the motor, controller and battery are all going to be more expensive and while they will fit a regular gokart frame well, they could start to be a bit bulky for a microkart. EVPower.com.au supply a 10kW Motoenergy motor for $615 or a 30kW Motenergy for $918 excluding taxes and delivery and a controller is going to cost you a similar amount.
There are a few other sources such as old forklift motors, industrial starter motors but these tend to be hit and miss to source, and can be heavy and / or may not be suited to continuous use in a gokart.