Table of Contents
Frame / Chassis
Types of Solar Car Frames
There are three main options when it comes to selecting how to give a solar car structure: space frame, unibody or monocoque. To date, all of Midnight Sun's solar cars have used a space frame chassis except for MSXI which used a monocoque. Related information about frame design can be found on MSUN 101: Overview of Solar Car Design.
MSXII will use a steel space frame.
Metal Space Frame
A space frame uses lengths of round or square tubing, or other structural metal shapes to form the chassis structure. Although many solar car teams are trying to use more composites in their cars, many teams such as Principia, Appalachian, Iowa State and ETS Quebec still build space frame type vehicles. The aforementioned teams all competed successfully at FSGP and ASC 2016. Space frames are also commonly used by other design teams such as FSAE and Baja.
|
|
|---|---|
| GTM supercar space frame | A look at Principia's space frame |
Unibody
Increasingly, solar car teams are choosing to use a unibody frame where joined composite panels form the chassis structure. In general, an equivalent space frame requires more material and thus more weight relative to a composite unibody. However, composite frames are generally more difficult to produce and service. It is also more difficult to recognize damages/defects on them.
|  |
|---|---|
| A production car's unibody. | A look at Stanford's unibody. |
Monocoque
A monocoque is a structural system where loads are supported through an object's external skin, similar to an egg shell. MSXI used a monocoque as its frame which presented numerous challenges with regards to structure, manufacturing and serviceability. Due to these challenges, most solar car teams do not elect to use a monocoque.
|
|
|---|---|
| A Lamborghini Aventador has a carbon fibre central monocoque, with front and rear steel subframes. | MSXI's monocoque prior to vinyl wrapping. |
System Design Considerations
Impact on Suspension
Centre of Gravity and Handling
Material Considerations for Space Frames
4130 Chromoly
4130 is often seen as superior to mild steels like 1018 and 1020 for the use of space frames (ex. FSAE).
- Both chromoly and mild steels have the same elastic modulus
- Ultimate tensile strength of 4130 is higher
- Density is approximately the same
- Since UTS is higher, you can use thinner walled members in the space frame and save weight
- Chromoly could be around 50% more expensive (estimate)
- A chromoly frame could b around 80% of the weight of a mild steel frame (estimate)
- If stiffness if the limiting factor, chromoly will not help since elastic modulus is the same
Strength
Torsional Rigidity
Torsional rigidity is a measure of a vehicles resistance to twisting from a moment applied along it's longitudinal axis. It is often expressed in Nm/degree (torque required to create one degree of twist). Torsional rigidity is very important to vehicle handling, especially with regards to cornering at speed.
Modelling and Analysis
FEA
SimCafe
SimCafe is a wiki created by Cornell University that has some great resources for learning about FEA.
ANSYS
Scale Models
While designing a space frame, it may be useful to make a scale model of the truss structure (perhaps either 3D printed or laser cut from balsa wood). This will allow team members to better understand the shape of the car and how it will be constructed, especially those not on the mech team. A scale model can also allow you to "feel" the strength and stiffness of the vehicle. Although a model's strength can depend heavily on it's material (balsa wood for example is highly orthotropic), the ability to feel the structure in your had can still be useful.
Manufacturing
Tube Cutting and Notching
Welding
Suspension
Components
| Picture | Description | |
|---|---|---|
Tires |
| Tires form the only point of contact between the vehicle and the road. The grip provided by the tires help propel the car forward, maneuver it a round a corner or bring it to a stop. Excessive wear on a particular area of a tire can be an indiction of misalignment in the suspension. |
| Rims |
| Tires are mounted to rims which then join to the hubs. position of the point of contact between the hub and the rim is called the wheel "offset". |
| Hub / Knuckle / Uprights |
| A hub is the central part of a wheel that connects the control arms and axle or spindle to rim. A hubs contains bearings which allow the wheel to spin. |
| Spindle |
| On a non-drivewheel, the spindle is the axel that connects the hub to the upright or knuckle. |
| Control Arm |
| S hinged suspension link between the chassis and the suspension upright or hub that carries the wheel. |
| Tire-rod |
| The linkage between the steering system and hubs. |
| Shock |  | The spring damper system that helps to eliminate vibrations and give the passages a smoother ride. |
Geometry and Terminology
Offset
Offset is the distance between the central axis of the wheel and the mounting plane between the hub and the rim.
Camber
Camber is the angle between the vertical axis of the wheels used for steering and the vertical axis of the vehicle when viewed from the front or rear.
Toe
Toe-In or Toe-out is a slight angle of a wheel/tire measured from a line running longitudinally (along the length of the vehicle).
Caster
Caster is the angle, measured from vertical (90° perpendicular to a flat road surface), of a line that runs through the mounting points of the upright/knuckle, when viewing the wheel/tire from the side. Positive caster is usually used on vehicles to help the wheels move back to steering straight when the steering wheel is released.
Steering Axis Inclination
Steering axis inclination is the measurement in degrees of the steering pivot line when viewed from the front of the vehicle. Steering axis inclination is used to change the scrub radius and can help the wheels move back to steering straight when the steering wheel is released.
