For senior capstone, my group and I designed and manufactured an off-roading steering system to be incorporated in the GWU BAJA team’s car. This project was initiated to provide insight into many integrations and components that come with the design of a steering system for an off-roading vehicle. Specifically, we designed and manufactured a steering system consisting of a steering rack, pinion, column, and wheel using GW BAJA 2024 off-roading vehicle geometry but the principles for the design process can be used by other BAJA teams.
Design Requirements
The following requirements were decided upon in conjunction with the GWU BAJA team due to geometric restrictions, necessary turning radius, and dynamic forces that would be transferred from the wheelbase to the system or from the driver.
- Steering Rack and Pinion
- 1.1. – Shall fit in the front packaging of the vehicle, the rack length ≤ 11.5 inches.
- 1.2. – Shall have rack and pinion displacement of 1.5 inches with +/- 10% tolerance.
- 1.3. – Must withstand static and dynamic loads from driving.
- 1.4. – Accomplish turning radius of 1.6m.
- Steering Column
- 2.1. – Must have a length of 20 in.
- 2.2. – Must withstand normal shear forces.
- 2.3. – Must withstand normal axial forces.
- Steering Wheel
- 3.1. – Shall have a diameter of less than 12 inches.
- 3.2. – Shall withstand axial full-body force.
- 3.3. – Shall withstand typical shear forces.
Steering Rack
Design Cycle:
- Utilizing the geometric relations in the car to determine steering ratio and Ackerman angles.
- Utilized the Lewis Bending Equations (static stresses), AGMA Bending Equations (dynamic stresses), and Fatigue Limit equations to determine material and sizing of gears.
- Frictional force between tires and the ground was calculated to be 741N.
- Total lateral forces generated by wheels determined to be 445N, rounded to 450 N.
- Using 1 and 2, determined size of gears.
- Factor of Safety determined to be 85 (>1). Although overkill, aluminum gears would be far less safe and more likely to break in high stress situations, when the force needed to steer may sometimes be higher.
- Original design we had forgotten to fillet in the inside of the gear teeth, causing stress concentration build ups.
Steering Column and Wheel
Both components were designed for modularity in the case that something went wrong with the vehicle and it needed to taken apart. It previous vehicles, the steering system could not come out of the car without considerable time taken. Additionally, removal of the middle section of the steering column allows for easier access to the differential, a component of the vehicle the team had been having difficulties with often.
BOM
| Subsystem | Item | Item # | Vendor | Cost |
| Steering Rack | High-Strength Steel Hex Nut Grade 8, Zinc Yellow-Chromate Plated, 1/4″-20 Thread Size | 94895A029 | McMaster-Carr | 29.13 |
| Steering Rack | Zinc Yellow-Chromate Plated Hex Head Screw Grade 8 Steel, 1/4″-20 Thread Size, 1-1/4″ Long, Fully Threaded | 92620A544 | McMaster-Carr | 12.66 |
| Steering Wheel | Low-Carbon Steel Bar, 1/4″ Thick, 8″ Wide | 9143K724 | McMaster-Carr | 112.23 |
| Steering Rack | Multipurpose 6061 Aluminum 1/4″ Thick x 6″ Wide | 8975K437 | McMaster-Carr | 110.64 |
| Steering Column | Easy-to-Weld 4130 Alloy Steel Rod 5/8″ Diameter | 6673T22 | McMaster-Carr | 25.71 |
| Steering Column | Easy-To-Weld 4130 Alloy Steel Round Tubes (1/4″ Wall Thickness, 1.0″ OD, 1.0′ Long) | 89955K801 | McMaster-Carr | 42.18 |
| Steering Column | Oversized Multipurpose 4140 Alloy Steel Sheet (0.5″ Thick, 6″ x 6″) | 4473T33 | McMaster-Carr | 102.58 |
| Steering Column | 1/4″-28 x 1-1/2″ Hex Bolts Zinc Yellow-Chromate Plated Steel Grade 8 Partial Thread (Quantity 25) | 4157043960 | Fastenere | 9.80 |
| Steering Column | 1/4″-28 Finished Hex Nuts Grade 8 Yellow Zinc Plated Steel Qty 100 | 842176192987 | Fastenere | 12.41 |
| Steering Rack | Ball Bearing | 60355K178 | Bearing | 11.30 |
| Steering Rack | Multipurpose 6061 Aluminum 1/2″ Thick x 6″ Wide | 8975K219 | McMaster-Carr | 37.40 |
| Steering Rack | Multipurpose 6061 Aluminum 1-1/2″ Thick x 6″ Wide | 8975K259 | McMaster-Carr | 82.41 |
| Steering Wheel | Digital Tachometer | B0C9TGTGNL | Amazon | 13.99 |
| Steering Wheel | Rust-Oleum Imagine Craft & Hobby Color Shift Spray Paint Turquoise Waters 11 oz. | 353336 | Amazon | 20.87 |
| Steering Rack | Self-Aligning Linear Sleeve Bearing for 3/4″ Shaft Diameter | 9533T5 | McMaster-Carr | 47.20 |
| Steering Rack | External Retaining Ring for 1-1/4″ OD | 9968K26 | McMaster-Carr | 21.43 |
| Steering Column | JOES Weld-On Pro Steering Wheel Quick Release Coupler | 13419-750 | JOES Racing | 59.36 |
| Steering Wheel | Tooling Leather Square 2.0-2.2MM Thick Genuine Full Grain Blue Litchee Cowhide Leather Sheets for Crafts Tooling Sewing Wallet Earring Hobby Workshop (Blue Litchee, 12″x24″) | B0C46Z242S | Amazon | 14.99 |
| Steering Wheel | Leather Sewing Kit, Leather Working Tools and Supplies | B0894S496F | Amazon | 9.98 |
| Steering Wheel | Rust-Oleum 267736 Specialty Glitter Spray, 10.25 Ounce | 267736 | Amazon | 8.90 |
| Steering Wheel | Red and Tacky Lithium Grease 1 LB Tub | HVDY-200-00016 | Amazon | 15.99 |