Programs and Codes

The mathematical program allows for a series of variables to be adjusted independently, and provides an instant visualization of how the suspension geometry will behave.

Parameters

There are 6 adjustable parameters, each with its own slider. Angles are measured in degrees. Length is measured in inches. Each of the parameters sliders are described below:

Left side

• Ang_chassis: The angle which the Chassis is inclined by. This value was based off of the Triton Solar Car Chassis.

• h_chassis: The vertical separation between the Upper A-Arm and Lower A-Arm connection points on the Chassis.

Right side

• h_kingpin: The vertical separation between the Upper A-Arm and Lower A-Arm connection points on the Kingpin.

• Ang_kingpin: The angle which the Kingpin is inclined by. This value was based off of scrub radius minimization.

• L_Upper: The length of the Upper A-Arm, measured from eyebolt to eyebolt.

• L_Lower: The length of the Lower A-Arm, measured from eyebolt to eyebolt.

The neutral position is defined when the Lower A-Arm is parallel to the ground. The above parameters are adjusted until the Camber Angle is zero.

Simulating Suspension Travel

The wheel is moved up and down, to simulate a bump (hitting an obstacle), or a droop (hitting a pothole). This is done by adjusting the following sliders:

• Roll

• Bump

The expected wheel travel is +/- 2 inches.

Measuring Performance

The Double Wishbone Suspension allows greater control over suspension geometry. As such, the camber change can be reduced during a bump and a steer, giving greater stability when the wheel is displaced.

The circle on the right side indicates the camber angle.

• Camber_pos indicates a positive camber angle (inclined outward) if the value is small.

• Camber_neg indicates a negative camber angle (inclined inward) if the value is small.

For example, at neutral position, there is a negative camber of 0.005 degrees.

At maximum bump (+10 degrees), there is a negative camber of 1.972 degrees.

The following parameters were set, based on predetermined factors:

• The inclination angle of the chassis (Ang_Chassis), which is around 20.34 degrees, is unlikely to change, given the fact that the chassis has already been fabricated by the Triton Solar Car team. This pre-determines one link of the four-bar linkage of the suspension geometry.

• The length of the lower A-arm (L_Lower), of 304.8mm (12 inches), is determined by the target track width of the car, 1397mm (55 inches). It is desirable to maximize the length, to increase the swing radius, which results in a smaller camber change during wheel travel. The chassis attachment is at the bottom of the chassis to increase the A-Arm’s length, and the kingpin attachment is designed to be as close as possible to the centerline of the wheel.

• The kingpin inclination angle (Ang_Kingpin), of 22.89 degrees. This is a result of the zero scrub radius design objective, which reduces the tire wear during turning.

As a result, there are a few parameters that are free to change. This includes the following:

• The vertical height (h_chassis) of the chassis’s Upper A-Arm’s attachment point. Parallel A-Arms will result in less camber change during wheel travel, but will result in the roll center being all the way at infinity, being hard to control and design around.

• The length of the upper A-arm (L_Upper).

• The vertical height of the kingpin (h_kingpin).

The parameters above are interrelated, and the graphing program allows quick adjustment and visualization of the result. To measure the performance of the chosen suspension geometry, the following variables are measured:

• Camber Change during maximum wheel travel (65mm, or ~2.5 inches). When the wheel is displaced by 65mm (2.5 inches) up due to a bump, or down due to a hole, the camber change was measured at the maximum points. A minimal camber change is desired.

• Camber Change during a roll (Chassis turning about the forward axis). When the chassis negotiates a turn, the weight may shift due to a centrifugal force, and cause a roll. A minimal camber change is desired.

After a series of iterations and adjustments, a suspension geometry was chosen, which is displayed below:

The resulting suspension had A-Arms that are non-parallel and have unequal lengths, which reduced camber change during a roll. Since the roll center of the car is located closer to the car, allowing for more adjustability in vehicle dynamics in the future. The final design parameters are shown in the table below:

Variable Design Parameter

Value (Metric)

Value (US Customary)

Vertical height of chassis (h_chassis)

142.2mm

5.6 inches

Length of Lower A-Arm (L_Lower)

304.8mm

12 inches

Length of Upper A-Arm (Upper)

188.0mm

7.4 inches

Vertical height of kingpin (h_Kingpin)

152.4mm

6 inches

With the suspension geometry finalized, the components were designed to fit the criteria. The A-Arms were made of steel tubes with rod ends at the end. The kingpin was created by welding a few rectangular tubes together. The other components, such as the spindle, hub, brake rotor, brake caliper, and wheel, are connected to the kingpin but are independent of the suspension geometry. They were nonetheless optimized for strength and weight.