Battery - For the Mock-up I have used three 12 Volt sealed lead acid batteries in series, this gives me a power supply of 36 Volts. These are only 7 amp hr batteries and would probably only run the kart for 15 – 20 minutes. I will either use a Lithium iron battery or a 15 amp hr batteries for the final build. Lithium ion is much lighter but far more expensive.
Motor - The motor is a MY1020 brushed DV motor rated at 36V and 850 W. This should be plenty powerful enough for a kids go kart. I estimate the kart should have a maximum speed of about 20 miles per hour.
Controller - The controller takes all the power in together with the inputs from the various devices on the go kart and then provides electrical power to the kart as required. It uses power electronic devices to do this. The speed control is done by pulsing MOSFETs, which are basically power transistors. This type of control is called pulse width modulation (PWM). This basically switches power to the motor on and off really fast and this rate at which this happens controls the speed of the motor. This switching is controlled by an integrated circuit which gets signals from devises on the kart such as the accelerator. If you are a young engineer thinking about what to study you could do a lot worse than Power Electronics as this field is so important for electric cars and various types of renewable energy.
Ignition Switch - The ignition switch, the switch simply needs to be closed for the motor to run. When you close the switch you can hear a relay close in the controller.
Accelerator - The accelerator is a Hall Effect device with three wires, power ground and signal. As you depress the pedal the voltage on the signal wire changes and the motor speeds up.
Speed Selector - The speed selector is another 3 wire device. It works by connecting either yellow or green wires to the black ground wire. When the switch is in the middle position neither wire is connected and the speed is at the fastest setting. I am using a three position Double throw Double pole switch for this device.
Brake Switch - The brake switch is really really important. It cuts out the motor when the brake is pressed. A kart has left foot braking so there is a risk that you could accelerate and brake at the same time and have an accident or cook the brakes. The switch has to be made to cut out the motor. I have simulated it using this simple switch but on the kart I will either use a magnetic switch or micro switch. The controller has several other brake switch connections which I am not using.
The controller also have a battery indicator which shows the voltage left in the battery, I have not decided whether to use this yet.
Below is a schematic diagram of the wiring system.
I hope to get back on the lathe next and make-up the sprocket and brake disc adaptors.
Keep spannering, Tom