Steering 101

WIP

Introduction

The car needs to be able to steer to control where it is going. This is usually accomplished by turning the front wheels of the car to change where it is pointing. Before we continue, there are a couple things to keep in mind:

Design Goals

The steering system is driven by 4 primary goals (Essentially in this order):

Be able to make the minimum possible turn radius
Be comfortable/useable for the driver
Reduce slop in the system
Reduce losses from induced tire slip

Be able to make the minimum possible turn radius

The steering system needs to be able to make the minimum possible turn radius given the requriements of the competition, FSGP and ASC.

Potential Constraint	Source	Outer Turn Radius Requirement (m)	Note

Potential Constraint	Source	Outer Turn Radius Requirement (m)	Note
U turn Test	FSGP/ASC Regulations 10.7.C	8m
Figure 8 test	FSGP/ASC Regulations 10.9.A	11m	This is the outer limit, we typically want the car to be able to fit into the lower limit of 6m to be safe
Slalom Test	FSGP/ASC Regulations 10.9.C	~41m	With perfect driving, the minimum needed radius becomes arbitrarily large
FSGP track	FSGP	Unknown	Sometimes, the smallest radius turn on the track is the smallest radius. We have found this in the past by measuring on google maps
Public Roads	ASC	12.802	Assumes we are driving on highways/country roads. Referenced from the TX DOT highway design manual

From the results above, we typically try to keep a minimum steering radius that can keep our car inside a 6m turning radius (including the width of the car). Keep in mind that regulations and track layouts change year to year so it is reccomended to check the new releases/revisions of regulations and update these numbers accordingly

Steering is not ideal:

In reality, tires to not roll entirely in their radial direction. The direction is actually related by a relationship called slip angle where, if you place more lateral force on the tire, the angle at which it rolls with respect to its radial direction (called the slip angle) increases as shown in the graph below:

We currently do not model the slip angle of our tires as there is no published data for our current model and from hand calculations, we estimate the maximum possible slip angle to be in the range of ~1 degree. However, this is defeinitely an area of potential improvement.