Final Design

CAD showing components of steering system assembly

360-degree view of steering system assembly

Photo of steering assembly mounted onto the evGoKart

Description of Design

The final design of the electric autonomous go-kart consists of an EPAS (electric power assisted steering) column assembly from a 2017 Toyota Corolla and an external encoder. The Toyota EPAS column assembly is composed of a torque sensor and a DC motor which is connected to the steering output shaft by a worm gear. The Toyota EPAS unit is mounted onto the go-kart with custom-designed parts that were machined. The mounts consist of 3 main parts: the upper mount, lower mount, and steering shaft coupler. The motor output and steering output are all on a single shaft making this assembly highly space efficient and eliminates discrepancy between the angles of the motor output and steering.

2017 Toyota Corolla Electric Power Assisted Steering Column

2017 Toyota Corolla EPAS System

The 2017 Toyota Corolla's Electric Power-Assisted Steering (EPAS) system was decided to be our final design out of all the motors we tested. It has a single shaft for motor input and steering output due to its worm drive gear design. Currently, the motor is being actuated and controlled using a VESC controller. This steering system was chosen because of its high torque (70Nm measured) and response which is adequate to steer the go-kart with a human driver. The unit is also affordable and accessible and can be purchased through eBay or junkyards for $80-150. It also features an integrated torque sensor enabling the future development of a human interface between autonomous and human driving modes.

REV Robotics Through Bore Encoder

External Encoder & Mount

The REV Robotics Through Bore Encoder is used as a rotary encoder to track the angle of the steering shaft as the Toyota Corolla's EPAS System does not have an integrated angle position sensor. Its mount is 3D printed using PLA and designed to position the encoder at the end of the steering shaft mounted onto the go-kart chassis.

CAD of Encoder Mount (upright view)

VESC Controller

VESC - Vedder electric speed controller

Feedback control between the motor and encoder is created through the VESC. Plugging both devices directly into the VESC allows for precise controll of the steering output while eliminating the clutter of excessive wiring. The VESC also allows for future implementation of limit switches connected directly to the unit.

CAD of Steering Shaft Coupler

Steering shaft Coupler

In order to utilize the Toyota EPAS assembly to steer the go-kart, a coupler was designed to couple the motor output shaft coming from the EPAS to the go-kart's existing steering shaft. The design consists of a splined side to attach to the motor's 17mm x36-spline output on one side and a pocketed hole on the other side which allows the existing steering shaft to slide into and secured with a 1/4" hex bolt. The yield stress safety factor determined from the Von Mises stress is 2.22 determined using a static FEA simulation analysis at 50 Nm. The coupler is manufactured out of carbon steel with a wire EDM machine.

Upper Mount

The steering unit's top mount was designed in order to attach the Toyota Corolla's steering column to the evGo-Kart's existing mounting point on the chassis and constrain radial movement of the steering unit. It features easy adjustability of the steering wheel position by loosening or tightening the clamping screw on top to allow or restrain axial movement of the sleeve for the driver's comfort. It is made with aluminum to be lightweight and easily machined. Manufactured using a wire EDM (electrical discharge machine) and Tormach PCNC 440. Fastened with size 5/16" stainless steel bolts and nuts.

Lower Mount

The steering unit's bottom mount is a major load-bearing component and must withstand 70 Nm peak motor torque and resist fatigue over multiple steering cycles. Its aluminum construction makes it lightweight and easy to machine. It features slotted mounting holes which allows for horizontal position adjustability and accounts for future extrusion frame changes. The structural gussets and fillets reduce stress concentrations, transfer load to the extrusion frame, and prevent the deformation of mounting tabs. Manufactured with Haas VF-2 and Tormach PCNC 440 Machines. The top hole is used to attach the 2017 Toyota Corolla EPAS unit with a size M10 bolt and nut and the bottom slots use size M5 screws to attach onto the aluminum extrusions mounted on the chassis.

Page updated

Report abuse