Current TRL: 4 (3/9/22)

“Steering system fully assembled on the car. Currently undergoing rolling chassis test.”

Steering Subsystem

The steering system is mounted on the chassis using two pillow blocks which allow the system to slide back and forth. The two arms on either side are connected to a metal rod which is then attached to the side of the wheel. The system is controlled by a rack and pinion gearbox which is further controlled by the drivers steering wheel. The picture above shows the steering arms, rack/pinion box, and how they attach to the steering wheel.

Goal

The main goal for this year’s steering team is to construct a steering system that can safely navigate the FSAE EV track. This means that the system must be able to comfortably corner the tightest turns as well as to minimize bump steering on rough surfaces.

Main Documents

  • Endurance Track Analysis and Steering Calculations (HTML) (Last Updated: 11/1/21)
  • Test Plan (Google Drive) (Last Updated: 10/4/21)
  • Full Model (PNG) (Last Updated: 10/4/21)
  • Senior Design Expo Poster (PNG) (Last Updated 12/17/21)

Literature Review

The chassis, suspension, and steering on a racecar need to be integrated with perfect accuracy to get the intended results. While the chassis of our electric vehicle must be designed to provide strength in the face of impact and other ride stresses, the suspension attachment points integrated into the chassis largely affect the dynamics of the system. Additionally, our front suspension must be designed to create safe steering conditions as shock deflection can change wheel steer angle, camber, caster, etc. These same angle effects of the rear suspension deflections can cause instability in steering as well. While each subsystem has an individual function, we see that they are very interconnected, making cross subsystem study and integration of vital importance

Full Literature Review

Metrics and Constraints

Metrics:

  • Maximum steering angle of 28 degrees
  • Ackermann percentage of 0%
  • Tie Rod lengths must be adjustable
  • Hand wheel must not exceed 180 degrees from center

Constraints:

  • Steering system must be entirely mechanical.
  • Free play in the system can be no more than 7 degrees on the steering wheel.
  • System must not interfere with neighboring systems such as suspension and pedal tray

Design Space:

We devised our metrics primarily from an analysis of the race track as well as prior racing experience from teammates. The racetrack analysis allowed us to find the turning radius of the tightest turn on the track and furthermore the steer angle required (14 degrees) to make the turn. Due to our knowledge of racing, we decided that this angle should occur at 90 degrees of hand steer because any further and the drivers arms would become crossed. Because steer vs hand steer is linear at small angles, we decided that our maximum steer would be double this angle(28 degrees steer at 180 degrees hand steer). We chose an Ackermann percentage of 0% because it is common on race cars. Cars with 0% Ackermann or parallel steering are better than positive Ackermann steering systems because the outer wheel turns inwards more. The orientation of the outer wheel has a large impact on turning performance because it is the wheel that feels the weight of the car and therefore has the most traction.

Our constraints primarily come from the Formula Hybrid rules. These constraints must be met for the car to pass inspection and be able to compete.

Components:

Actuator Assembly

This piece allows the gear rack to slide back and forth smoothly. The arm slides through the shown pillow block to control the angle of the wheels using a tie rod. This piece also limits how much the rack can slide back and forth which is a major consideration with our design. We will need to manufacture or buy these parts.

Documents 

  • Clevis Rod End (McMaster-Carr) (Last Updated: 10/4/21)
  • Actuator Coupling (PNG) (Last Updated: 10/4/21)

Rack and Pinion

The main gear system of a steering system. This converts the rotational movement of the steering wheel into translational movement in the actuator arms. We have a prebuilt rack and pinion system. In last year’s setup, the rack and pinion do not allow the wheels to steer more than 14 degrees which is very low for a race car.

Tie Rod Mount Plate

The plate that connects the wheel chassis to the steering system. This was the main focus of our steering redesign because its dimensions are the biggest factor in steering angle and Ackermann percentage.

Documents 

  • Professor Brown’s Suspension and Steering Simulation (MOV) (Last Updated: 12/17/21)
  • Steer vs Hand steer for our mount plate setup (PNG) (Last Updated 12/17/21)

First Semester Accomplishments

  • Created working simulation of the front suspension and steering
  • 3D printed steering prototype made
  • FSAE EV Endurance track analysis created in Octave.
  • CAD assembly of steering system created

Subsystem TRL Chart

TRL What does this look like? Expected Completion Date
9 Steering performs successfully in competition May 2022
8 High-speed turning test April 2022
7 High-speed straight-line tracking test March 2022
6 Low-speed test with power from the drivetrain March 2022
5 Rolling chassis test in the parking lot for steering model validation Current
4 Fully manufactured steering system tested in the lab Completed
3 Model tested dynamically in simulation Completed
2 Steering model created using CAD Completed
1 Steering model type chosen Completed

The Team

Grant Hartman (Lead Steering Engineer)