Mechatronics

The go-kart mechatronics system is designed as a modular system, consisting of several subsystems that are responsible for different tasks. There are six major subsystems: Power Distribution (PD), Main Control (MC), User Interface (UI), Throttle-by-Wire (TBW), Brake-by-Wire (BBW), and Steerby-Wire (SBW). The “x-by-wire” system design approach has been gaining popularity in the automotive industry which is to replace conventional mechanical and hydraulic control systems with electronic signals. The elimination of traditional mechanical components could increase control stability, increase design flexibility, reduce cost, and improve efficiency. In our go-kart drive-by-wire design, all subsystems except the PD use an STM32 Nucleo development board on a standalone PCB as the electronic control unit (ECU). Like modern vehicle design, communication is achieved using the controller area network (CAN) to allow efficient information exchange between nodes. These modular control systems are integrated with the original go-kart chassis in a nonintrusive manner and are easy to understand, build, and modify.

Power Distribution Subsystem

The autonomous go-kart is powered by six Nermak Lithium LiFePO4 deep cycle batteries, each with a voltage of 12V and capacity 50Ah. The batteries are mounted on the two sides of the go-kart, with wired connections across the chassis. Four batteries are connected in series, leading to a net voltage of 48V, which is used to power the main drive motor. Meanwhile, a buck converter is used to step down the voltage from 48V to 12V, which is then used to power up the motors in the SBW and BBW subsystems for autonomous control.

Main Control Subsystem

The MC handles all the driving requests from the high-level end and sends out those commands (throttle, steering, brake) on the CAN bus. It serves as an interface between the go-kart mechatronic system and the end user. Three different operation modes are supported: manual, remote, and autonomous. In the manual mode, input is read from the steering wheel, throttle, and brake pedals of a driver just like in any conventional vehicle. In the remote mode, the operator uses a Spektrum DX6 2.4GHz radio to send the driving commands, which are received by the MC using an AR6200 receiver. In the autonomous mode, the command is transmitted from a highlevel computing unit such as a laptop or a specialized onboard computer, through a USB to TTL communication.

User Interface Subsystem

The UI is a customized PCB mounted on the side of the driver’s seat. It allows the user to select the desired operating mode using the toggle switches. Meanwhile, it collects real- time go-kart state information, including its speed, steering, and brake and display them on an LCD panel. It plays no role in mechanical control and is solely used for user monitoring and interaction.

Throttle-by-Wire Subsystem

The UI is a customized PCB mounted on the side of the driver’s seat. The TBW controls the go-kart’s main drive motor. The TBW’s Nucleo receives the desired speed from the CAN bus and sends out the measured speed. Speed measurement is achieved using a hall effect wheel speed sensor mounted close to the go-kart’s rear shaft. Speed control is performed using a closed PID loop. The output of the Nucleo is a PWM signal with a varying duty cycle which is then converted into a 0-5V analog voltage. This analog voltage is passed into the Alltrax SR48300 DC Motor Controller for speed control. Another design is a remote kill switch which allows the operator to remotely cut off the power if an emergency occurs. This is implemented using a remote relay that can disconnect the switch to the motor contact which instantly stops power delivery to the main power. This part is independent from the MC and will continue functioning in a worst-case system failure.

Steer-by-Wire Subsystem

The original unmodified go-kart platform uses an alloy shaft to connect the steering wheel and the front wheel. Steering is made possible entirely through the driver’s torque input. In order to provide an autonomous mode, a motor must be added to actuate the steering. Several design ideas have been composed: one attempt was to mount the motor parallel to the steering shaft and use a belt or chain for motion transmission.