Final Design

The vehicle’s steering system’s rotational speed and torque on this go-kart must be equivalent to a normal human driver. The steering system is made up of the following components to allow it to rotate the steering rod as fast and strong as a human driver:

A BLDC motor and gearbox fastened to a plate affixed to the front support, a gearbox, and a pulley and belt system. The BLDC and gearbox were placed parallel to the steering shaft which then drove the steering rod by a pulley and timing belt system. The brushless DC motor itself produced a steering torque of 2.6 Nm at 5657 RPM. After combining with a 100:1 gearbox it can reach a theoretical torque of 130Nm and a speed of 30 rpm. The assembly put together is shown in Figure 1.

The steering motor of the go-kart was a NEO BLDC motor, as seen in figure 2. It is normally used in a robotics competition called FRC. It conforms to the design requirements of 50 Nm steering torque force and a minimum speed of 25 RPM. Meanwhile, it is well documented so the Triton AI team can easily control it . The motor is geared to provide 2.6 Nm of torque and rotates at a speed of 5676 rpm. The motor's working voltage is 12 volts, and its stall current is 105 amps. As the motors voltage is the same as the battery and most electric systems on the go-kart use 12 volts the motor's 12 volt input is appropriate for this case and is easy to integrate into the circuitry. This motor will be added with the REV controller and encoder to allow position control.

The MAXPlanetary System is a cartridge-based modular planetary gearbox designed from the ground up for NEO-class motors. Building on the ability to iterate and adjust designs easily, the MAXPlanetary System consists of lubricated cartridges allowing for swapping gear ratios on the fly and with ease. It allows users to configure a single-stage planetary using one of three different reduction cartridges or build multi-stage gearboxes through stacking individual cartridges together. All of the cartridges have a failure torque higher than 230 Nm which makes it a perfect fit for this project.

Because the long time for identifying components during this quarter, the team did not have a chance to implement the electromagnetic clutch. This section is to documentation for the following team.

The purpose of the electromagnetic clutch is to allow the steering system to have a disengagement mechanism. As seen in the figure 5 below, the clutch consists of two parts, the driving section and the driven section. When the power is off, the driving section is mounted rigidly on an actuator that provides the rotational actuation, and the air gap between the two parts allows the driven section to rotate freely. When the clutch is powered on, the coil stator in the driving section will generate the electromagnetic magnetic field that pulls the driven one and closes the air gap. The friction of the material makes the driven section rotate with the motor. In the final design, the driving section is attached to the BLDC motor, and the driven section connects to the steering shaft via a pulley system. When the go-kart is powered on, the computer will take control of the steering system to have autonomous driving. After the disengagement is activated, the clutch will be powered off and separate the two sections. Therefore, the human driver can turn the steering wheel manually without fighting with the high gear ratio of the gearbox.

In the braking system the main objective was to relocate the current actuator mount for autonomous only control and provide enough space for a human driver to sit in the go-kart. In the previous configuration the actuator was sitting on an acrylic bracket mounted to the original brake mount just in front of the driver seat on the left side. This brought the actuator high into the thigh area of the driver and made sitting in the kart, especially under accelerative loading, quite uncomfortable.

Description of brake mount

In the final design the mount for the linear actuator was relocated out of the way of the seat. The design considered the location of the seat as not fixed and involved redesigning the mounting of the seat around the relocated braking mounting solution. The mount moved the master cylinder, which is responsible for supplying pressure in the brake lines to the brake caliper, lower by moving it forward past the tubing in the chassis allowing it to sit in a better position for actuation by the linear actuator. The linear actuator was placed atop the master cylinder and the actuation rod was aligned to the arm on the master cylinder for smooth activation. This relocation allows for the drivers leg to sit comfortably.

The linear actuator that was chosen for this design is the Kar-Tech Linear Actuator. It runs on a 12V supply of power and uses the CAN bus for communication. The CAN bus allows the actuator to maintain a steady signal stream and provides a reliable feedback control loop, making it perfect for the brake application. CAN also allows it to work in tandem from one stream of information with other systems on the kart. The design utilizes the actuator primarily for its superior performance in providing a linear force of 400N (90 lbf) which exceeds our design requirements of 311 N (70 lbf) as established by the theoretical brake system design and the practical testing conducted.