Baja Steering System DesignBy: Adam M Conrad

IntroductionCurrent State

•No Steering System in Place•Original Mount is Present•Steering wheel mount is present•No suspension in place

Goals for Project

•Design a steering system that utilizes as much of the current frame

•System must be able to withstand SAE racing conditions

•System should provide a competitive advantage

Customer RequirementRequirement Description Importance Rating

Reliability

The design must be able to perform under racing conditions. 30%

Cost

The cost needs to be low and fall within the customers budget 25%

simplicity

The design should be simple enough to build given the resources and materials that the design team has access to.

20%

Weight

The weight needs to be low in order to provide a favorable power to weight ratio 15%

Size

The size of the assembly must be small enough to accomadate the driver given the materials at hand

10%

Circulating Ball Worm-gear

Strengths• High Reliability• Low Friction

Weaknesses• Low simplicity• Heavier

Rack and Pinion Concept

Strengths• High Reliability• High Simplicity• Low Weight

Weaknesses• Fast-Ratio rack

and pinions are more expensive

Pitman Arm Linkage

Strengths• Low Cost• Low Weight• High Reliability

Weaknesses• Low Simplicity• Unfavorable size

Steer-By-Wire

Strengths• none

Weaknesses• Low Simplicity• Low Reliability• Expensive• Takes up a lot of

space• Heavy

Double Crank Rocker

Strengths• Low Cost• High Simplicity• Low weight• Takes up little

space

Weaknesses• Questionable

reliability

Concept Selection

CriteriaWeight

(%)rating

weighted rating

ratingweighted

ratingrating

weighted rating

ratingweighted

ratingrating

weighted rating

Cost 25 2 0.5 3 0.75 4 1 0 0 4 1Simplicity 20 2 0.4 4 0.8 2 0.4 2 0.4 4 0.8Reliability 30 4 1.2 4 1.2 4 1.2 2 0.6 3 0.9Size 10 2 0.2 4 0.4 2 0.2 2 0.2 4 0.4Weight 15 3 0.45 4 0.6 3 0.45 2 0.3 4 0.6

100 na 2.75 na 3.75 na 3.25 na 1.5 na 3.7Unsatisfactory 0Just Tolerable 1Adequate 2Good 3Very Good 4

Crank RockerAlternative Concepts / Embodiments

Concept Evaluation Using Weighted Rating Method (Pahl & Beitz Method)

Ball and Nut Rack and Pinion Linkage and Pitarm Steer by Wire

Criteria for Rack Location• Low Transmission Angle

– 30 degrees or below– reduce bending moments– reduce needed effort for turning

• Small Tie Rod Length– 14 inches or below– Low Material Costs– Reduce buckling

• Low Turn Radius– 8 feet or below

Location Concept 1

• 12 Inch Tie Rods

• Dismissed because of tie rods exposure

• Dismissed because steering shaft exposure

• Wheels pushed forward• Rack Mounted on the front of vehicle• 14 Inch Rack (12 to 1 Steering Ratio)

Location Concept 2• Wheels pushed forward• Rack Mounted in original mounting Location• 14 inch rack (12 to 1 Steering Ratio)

• 50 degree horizontal transmission angle

• 4 degree vertical transmission angle

• 21 inch tie rods

• 17.3 foot turn radius

Location Concept 3• New Control Arms • Rack Mounted in original mounting Location• 14 inch rack (12 to 1 Steering Ratio)

• 30 degree horizontal transmission angle

• 5 degree vertical transmission angle

• 15 inch tie rods

• 11.17 foot turn radius

Location Concept 4• New Control Arms • Rack Mounted 5 inches forward from original mounting Location• 16.25 inch rack (12 to 1 Steering Ratio)

• 12 degree Horizontal transmission angle

• 7 degree Vertical transmission angle

• 12 inch tie rods

• 8.75 foot turn radius

• 15.08 foot radius with half turn

Location Concept 5• New Control Arms • Rack Mounted 7 inches forward from original mounting Location• 16.25 inch rack (12 to 1 steering ratio)

• 0 degree Horizontal transmission angle

• 10 degree Vertical transmission angle

• 12 inch tie rods

• 6.978 foot turn radius

• 13.08 foot radius with half turn

Location Concept 6• New Control Arms • Rack Mounted 7 inches forward from original mounting Location• 11.25 inch Rack (6.4 to 1 steering ratio)

• 0 degree Horizontal transmission angle

• 9 degree Vertical transmission angle

• 13 inch tie rods

• 5.33 foot turn radius

Position Selection SummaryDescription

Rack Length "Inches"

Approximate Tie Rod Length

"Inches"

Lock-Lock Turn Radius

"feet"

Half Turn, Turn radius

"feet"

Horizontal Transmission

Angle "degrees"

Vertical Transmission

angle "degrees"

Concept 1Wheels forward, Rack in front 14 12 na na na na

Concept 2Wheels forward, rack in original mount 14 21 17.294 na 50 4

Concept 3New Control Arms, Original Mount

14 15 11.17 na 30 5

Concept 4New Control Arms, Moved forward

16.25 12 8.75 15.08 12 7

Concept 5New Control Arms, Moved forward and horizontal

16.25 11 6.978 13.08 0 10

Concept 6New Control Arms, Concept 5 with fast ratio rack 11.25 13 5.3324 5.3324 0 9

Final Selection

Final Selection

Bump Steering Check

• Approximately Halfway between control arms

• 2 inch clearance

Tie Rod Material Selection• Length: 13 inches

• Diameter: 3/4 inches

• Hole Diameter: 5/16 inches

• Threading: UNC 24

• Material: 6351 aluminum

(Yield at 40,000 PSI)

• Cost:

Tie Rod Stress Calculations

114 Lbs10.5’’

4’’

300 Lbs

Tie Rod Stress Calculations

300 Lbs

9 degrees

304 Lbs

Steering Shaft Material Selection

• Length: 25 Inches

• Diameter: 5/8 Inches

• Material: Mild Carbon Steel

Component List

• Heim Joints (2)• Clevis Rod End (2)• Tie Rod Ends (2)• 13’’ Aluminum Threaded Tie Rods• 25’’ Mild Steel Steering Shaft• Steering Wheel• Fasteners

Questions?