...
- Fergo ASC and VR3 Documentation Break Down → This is an a non-negotiable must read for all members, as it specifically lays out the guidelines and regulations we must follow to ensure we meet ASC and FSGP standards.
- Calvin Guo - 2021 Exit Summary → This is an exit summary of a formal Solar Frame lead. This contains some good information when starting out on the frame subsystem. (Disclaimer: I touch on many of the same topics, but Calvin gives a different perspective on some things, so it's worth a read)
- General Roll Cage and Automotive Structure Guides → These articles range anywhere from FSAE to professional racing sectors, in which describe the purpose of a roll cage, building strategies, and tips on what to avoid and how to make structures more efficient.
- TIG Welding Topics - Miller Welds → Just trust me on this one, welding is fun and fairly simple to learn, but not so simple to master and get good at. Use the resources available here and any mentors around, you WILL need it.
- The entire “To Win” series by Carroll Smith is a great series written on motorsport racing and race car development as a whole. These are great reads as a whole if you like cars, motorsport, and automotive engineering in general.
...
Firstly, tubes in a frame will experience various forces and moments when analyzing the load case requirements. (see the ASC regulations)
- Force → load applied at a point, causes pressure and by extension stress (over an area), displacement, work, etc.
- Moment → measure of a force times a perpendicular distance from a point (I.e. tendency of a force to rotate around an axis of an arbitrary point)
...
- Bending moments (forces that cause a rotation around a fixed point, causing bending) can cause bending stress (this is the root of most all problems in frame design)
- Bending moments have a lot to do with load pathing (i.e. if your tubing and therefore your load path is a straight line, no bending moment is caused (forces are only axial), but as soon as you introduce an angled path, bending moments are caused)
Torsional Forces
- Torsional (or twisting) forces occur when torque is applied about the longitudinal axis of a part
- A good way to visualize this would be when the driver takes a turn, where one wheel must travel a farther distance than the other, meaning there is a differential in the forces on either side, causing a torque
Supports will come in later when you take Statics/are introduced to Ansys (FEA).
- Supports assume infinite stiffness in specific degrees of freedom. Some supports (like fixed) have reactionary forces and moments in all DOF, some like (roller and pinned) have reactionary forces and moments in only specific DOF
- All that matters is that different types of supports resist different types of forces/moments, which you can use to solve/isolate forces and understand the reactions happening in a system
Two Force Members
- A two force Supports are integral to setting up a simulation right. If you have too many constraints, your sim will be too stiff and you will have inaccurate results. Too little constraints, same problem, inaccurate results, that can cause you to falsely presume your part is safe/effective.
Two Force Members
- A two force member in our case would be a tube with forces only acting in two locations, with the forces being equal opposite and colinear. Two forces are
Truss Structures
- In our case, a truss structure is structure made to take high loads while utilizing 2 force members, thus taking high axial loads, while minimizing bending loads.
...
- As mentioned before, VR3 is our place for mitering and acquiring all tubing. That being said, I won’t go into much detail, as they have everything documented themselves. Follow their guides and you will be fine, they are very accommodating and friendly.
...
Frame Jigging
- In short, a frame jig is essentially an assembly of parts that properly support the tubing/suspension tabs/any welded part during the welding process.
- A lot of the writing composed in this section is from some of the lovely Combustion and Election Electric members who have helped guide and educate me and my members on the jigging process.
How to design a frame jig
“Table flush jigs" or “frame hockey pucks” are cylindrical stock that we turn down and then have a hole in the middle to go into the optical table.
...
Making your frame is fundamentally an exercise in precision locating and weldment construction, your main considerations should be datums (a fixed starting point) and stiffness. The optical table is your only reference for both geometric and positional tolerances, ergo, every critical jig you make should reference something about the optical table or something about a tube that is located off of the optical table. There are three main frame categories, critical external, critical internal, and non-critical.
After we fully weld the frame, we do the hardpoints (suspension tabs, ergo tabs, etc.) to mitigate warping from the welding. When welding/jigging, you need to have a planned order -> table flush (bottom layer) to the 2nd and potentially 3rd level, roll hoops, everything else (cross-braces) building upMaking your frame is fundamentally an exercise in precision locating and weldment construction, your main considerations should be datums (a fixed starting point) and stiffness. The optical table is your only reference for both geometric and positional tolerances, ergo, every critical jig you make should reference something about the optical table or something about a tube that is located off of the optical table. There are three main frame categories, critical external, critical internal, and non-critical..
How to design a frame jig
“Table flush jigs" or “frame hockey pucks” are cylindrical stock that we turn down and then have a hole in the middle to go into the optical table.
- These support the entire bottom level of the frame, which is the most critical part in welding the frame (i.e. if you start badly from the base, the entire frame will be bad, so support the bottom well and you will have better results overall)
After we fully weld the frame, we do the hardpoints (suspension tabs, ergo tabs, etc.) to mitigate warping from the welding. When welding/jigging, you need to have a planned order -> table flush (bottom layer) to the 2nd and potentially 3rd level, roll hoops, everything else (cross-braces) building up
- Critical external features are parts of your frame that drive car parameters decoupled from the rest of the frame (hardpoints, roll hoops, headrest supports, etc.
- Critical internal features are parts of your frame that only rely on internal geometry (steering column, rear box, etc.) These features of course will matter externally, but it’s more important to locate them to critical mating components, which if done correctly will satisfy external constraints.
- Non-critical features are tubes that don’t matter and are only there to provide structure to your frame, these are your buffers that take up tolerance stacks as they propagate through your frame and are there to support your critical features when the jigs are gone. These are the only tubes in your frame where you should be filling gaps, in an ideal world.
...