Vocabulary

Longitudinal – front and back

Lateral – side to side (think seatbelt)

Beam Element – Consider a part with uniform material density as one “beam” (helps run the FEA faster)

Centroid – The dead center of mass of a uniform obj.

Ex for triangle the middle of each line’s intersection

Node – Vertices of triangle/tetrahedron, used in context of chassis design.

The Winning Solar Car: 10.D Chassis Structure Notes

Introduction

Driver, battery, and body are heavy stuff. Suggest that 60-70% Center of Gravity (CoG) be on the front tires.

Make sure that space for the driver and their controls (steering, braking, control panel) is considered in design.

All battery in one box at same temp. (optimal)

MAKE SURE canopy, roll cage, and driver head are all aligned (apparently this is overlooked)

Determine dist b/w front and rear axle (wheelbase) and width b/w F and R wheels. (For balanced weight + adequate clearance for wheels)

First Stage of Design: Establishing the Foundation

Identify where each of the systems will “fit” onto the frame.

Do CoG calcs to make sure the car doesn’t tip like a reliant robin.

Chassis should have points on which the suspension will hook onto.

Second Stage: Roll Cage, Bracing, and Analysis

(Potential) Materials to make this stuff: Composites, Steel, Aluminum, Titanium

Composites: Hard to optimize design, but can have the lightest weight (in theory)

Strength of composites directly related to what u use to make it.
- So, know what’s used so u can accurately FEA.
Apparently, it’s easy to build these. Make composite panels, cut them up and glue together to make a box looking thing. Suspension mounting made of steel/Al/Ti.
Disadvantage: Least stiff design. This inc rolling resistance (energy our car needs to send to the tires so it can have consistent speed)

Titanium: Tube truss frame type stuff has had a lotta success (seems like the standard ngl)(fig 10.18 visual)

Expensive and hard to weld but if u got the bands and machines this is a really good option.
Lightest weight METAL chassis
Super hard to repair/modify cuz welding titanium is hard bro.

Aluminum: A solid Al alloy is 6061-T6. Also a tube truss frame type. (fig 10.18 visual)

Less expensive than Ti and easier to weld (you still need to TIG weld tho)
Apparently Al can crack while “in service” Need to inspect it often for this reason.
6061-t6 is strong b/c of heat treatment, and welding removes some of this to a T-4 level (no significant change tho)

Steel: Widely used. Most people end up using 4130, which is also the stuff for race cars. (fig 10.18 visual)

Heavier than Al chassis but easier to weld, cracks less.
Steel can rust tho so aesthetics will be sad and maybe structural integrity will also decrease.

Structural Analysis

Ideally you want to satisfy the following 8 load cases:

3g bump – Assume a up force of 3*(weight on tire), then fig out what load goes to the chassis.
1g corner – Force = weight on tire acting laterally (across width of tire) at the tire patch (part that contacts ground?) and the weight on wheel. Take all this and fig out what happen to chassis.
1g brake – Brake force = ½ weight of car on each FRONT tire patch
5g front impact – 5*weight of car force applied to front, restraining back.
5g rear impact – Same stuff as above just reverse.
3g rollover – 3*weight of car press down on roll cage
5g side impact – 5*weight on one side, restrain other.
3g angular impact – 30 and 60 degree angular impact in relation to axis.

~ I don’t know how relevant the above info is, this book written a while ago (2003 copyright) ~

ASC/FSGP 2025 Regulations – Pg 39

https://www.americansolarchallenge.org/ASC/wp-content/uploads/2024/10/FSGP2025-Regs-RevA.pdf

10.3.A: Occupant Cell

Stuff above shoulder height is defined as “roll cage” (RC).

This NEEDS to be made of metal, NOT composites.

The thing that holds the driver’s body and to which the suspension sys connects is defined as structural chassis.

Stuff below the roll cage is the lower occupant cell (LOC)

Need to provide documentation that lists what parts make up the Occupant Cell (= LOC + RC)

When driver is seated – as if completely ready to drive – no part of them can go through any of the frame pipes (including any of their head movement).

You need to be able to have docs that say that any part of OC will not deform by >25mm and will not exceed ult strength (fail).

Front of RC should be designed in such a way that it can deflect oncoming debris (by angling RC back).

Wherever the OC can hit the driver’s HELMETED head, OC has to have SFI-45.1 or FIA 8857-2001 Type A or B, or better material on it to absorb the impact. Padding has to wrap around at min 50% of the part.

Need to have a 19mm thick resistant material headrest/restraint.

Must be 50mm dist b/w driver helmet and any part of OC. 30mm dist b/w driver helmet and the padding stuff.

Carbon fiber panels <500mm away from driver need to have shatter resistant fabric (Kevlar/Dynama) on the side facing driver, totaling 5oz/(yd^2) weight.

Modeling an FSAE Frame SW video(s)

Important to enter suspension geom first (dictate rest of car design)

Build off that by making some skeleton frame sketches (in plane and 3d depending on needs)

The way dude in video does it:

Suspension geometry hardpoints
Front sus box + rear box (3D and 2D)
Roll hoops (2D)
Seat belt, engine compartment, driver compartment.
Front structure (maybe crumple zone?)

Weldements

To create custom tubes:

Open a part, create cross section (sketch).
Save as library feature part
Save with rest of weldement parts
Program files --> SW --> data --> weldement profiles.
Select sketch lines to create a tube.
Do trims on tubes when they intersect cuz stuff starts tweaking out. (Trim/Extend Command)
Reference tabs to suspension hardpoints rather than frame.

Creating tab feature:

Know size of bearing/spherical u need to use (offset)
Know thickness of tab (direc 1)

To have place for all ur suspension tabs:

Create a block from a tab
Select tab --> save sketch as block, then you can create a drawing from that of all frame tabs (idk how useful this is)

SW has built in design documentation.

Right click top of feature tree (part) --> hidden tree items
Design binder --> Design journal --> open.
Need to add stuff yourself, but it’s still good to have as it’s receipts of the stuff u done.

Intro to Racecar Engineering: 04 Chassis Design Notes

https://youtu.be/G-p4GFL-F4E?si=IjZwpPpCEmTXfnvn

Space Frame = all structural loads are in tension and compression: NOT BENDING (BENDING = BAD)

Testing torsional Rigidity:

Frame supported on 3 corners, 4th corner unsupported.
Use dial indicator

Space frames have amazing structural rigidity

Structural Rigidity comes primarily from GEOMETRY of materials – that’s why it’s so important to simulate.

Race Car Design by Derek Seward - Chapter 2: Chassis Structure

2.1: Introduction

A chassis is like a human skeleton - a place for essential systems to be secured in order to ensure maximum efficiency.

Basic requirements of a chassis:

Make sure it follows regs
Be a location for stuff like battery to be housed, attached, secured
Be stiff and tough enough to resist forces from suspension, steering, acceleration, braking, and cornering.
House the driver safely, securely, and comfortably (this one more ergo)
Support the bodywork (aeroshell in our case)

The two major chassis structures:

Space Frame - Made with a bunch of metal tubes to which the aeroshell then goes on top of. Resembles a human skeleton pretty much.
Monocoque - Plates + shells that make a box type thing. Because things are more enclosed, the aeroshell can be partly integrated with this.

2.2: The Importance of Torsional Stiffness

Torsional deformation is when a chassis deforms because of a “twisting” force (see Noah’s Frame 101 guide to learn more about torsion and other stresses). This happens when cornering, or one wheel is above or below the other three wheels (suspension important to reduce this too).

Why does a car need to be torsionally stiff?

Your car can be tuned to maximize cornering efficiency (cornering causes twisting in chassis, see below pics). This is important for us, but not as much as it does for IC and Electric since we aren’t autocrossing.
1. Stiffer is ALWAYS better
2. Book recommends 1000 Nm/degree roll stiffness

The more stiff a chassis, the less strain energy it stores (good b/c more strain energy means more stress on chassis means more chance for deformation)

2.3: The Space-Frame Chassis Structure (2022-2024 car uses this) - Pg 36

So… how’s it made up?

T R I A N G L E S. T E T R A H E D R O N S.

Make sure that all major loads are applied at nodes so they can disperse nicely.

The cool thing about space frames is that if they’re done right, all the tubes only got axial forces: tension and compression. This makes the frame stiff and minimizes bending which is always a very good thing.

Page 37

But there’s one problem, it’s hard to make tetrahedrons in a box-esque structure like a frame. So, to optimize this as much as we can, we wanna make trapezoidal prisms or rectangular prisms, and triangulate their faces.

Page 38

If you notice the above chassis, it is more susceptible to torsion and bending because of the lack of diagonal members within the frame, they’re mostly only on the faces.

To help, one could consider the following:

“Sidepod” like diagonal members.
Straight up add additional diagonal members in areas of high vulnerability (like the sidepod).
Shorten some of the diagonal members by adding vertical/horizontal members.
Adding bulkheads (usually located towards the front of chassis, near driver feet)

When designing a space-frame, always keep in mind:

Regs…
Driver measurements
High load areas (h a r d p o i n t s, seat belt holders, and battery mounts)

Materials

2.4: Stretched-skin chassis structure - Pg 41

Pretty much wrapping the frame with a sheet/plate. It’s hard to attach such a sheet/plate to a circular frame member, so it’s prob easier to space frame than do this.

2.5: Monocoque chassis structure

Based on plates and shells that are under shear forces rather than tens/compres.

Very good at handling torsion.

Usually you want some metal inserts or ribbing of some kind because high-force point loads can make a thin plate die. - left off at page 54

Longhorn Racing Solar

Devansh's Documentation