My name is Simon and this is how to build a racing car. The chassis is arguably one of the most important parts of most racing cars. Almost every single part of the car is attached to the chassis. Its design affects the handling of the vehicle, it affects the ergonomics for the driver, it affects the manufacturability and maintainability of the final car, it affects almost everything.
For this reason, I'd say the majority of my design time went into this critical component. In this episode, I'll show you a little bit about the design and construction of the chassis space frame. Designing the chassis was a hugely involved and iterative process. The first step I took was running through the Formula V rules to get an idea of what was and what wasn't allowed.
Things like the material, dimensions, safety considerations, envelope for the driver, attachment of components, all of that is written into the rules. In order to make sure I fit in my car, I got a tape measure and measured up all my limbs to create a simple dummy in SOLIDWORKS. I did most of the design making sure that this dummy would fit in the program, but ultimately it's important to double check things in reality.
You might technically fit, but be so uncomfortable that the car is close to undriveable. For this reason we built the ergonomics jig just out of wood. It's dimensions were the same as the chassis I had designed, and we mounted the driver controls in the same location as well.
I found I had to extend the car's legroom by about 100mm, but apart from that it fit really nicely. Making sure all of the parts fit was really just a case of having all of the various car parts drawn in SolidWorks and included in the assembly. Each needed to be mounted to the chassis. It really takes some patience to draw all of the little brackets and mounts, but it's necessary to make sure that there won't be any clearance issues once it's built. Also critical was making sure the chassis itself was strong enough, even in the event of an impact.
I used a finite element analysis model I had written in Microsoft Excel to do this. It was simple but gave me some guidance on where the chassis was weak and where it was strong. The car ended up being very strong, mostly thanks to the rules specified, member sizes and positions around the cockpit.
In reality, the side impact protection plates that are required by the rules but not included in the analysis will add significantly to the stiffness. Part of the design process was figuring out how I would actually build the chassis. A drawing showing every single tube in the car was produced. This would be useful after I had cut the tubes and needed to know where each one went. Round tube can be difficult to build a frame from as you need to cut the ends of each tube to accommodate the attaching sections.
Solidworks was invaluable here, I was able to unwrap and flatten the round tubes, then put markings on drawings which would then be printed on sticky paper and used to cut the tubes. The other critical consideration during design was the order in which the tubes would be inserted. If multiple tubes met at a single point, the cuts in the tubes would need to be done in the same order.
Otherwise, one tube might end up covering where another needed to be welded, which would mean that not all of the circumference could be welded. Additionally, parts like cross-bracings may not physically fit if I inserted the components after the surrounding parts were in. Finally, before I could start the chassis, one final thing was needed.
A stable and dimensionally accurate base to build from. For that, we built the chassis jig. My father had the idea to attach pivots to the end so that it could be rotated like a rotisserie. Very useful for welding.
The first step in building the chassis was simply cutting the tubes to the correct overall length and sticking the cutting drawings on each end. Each cutting drawing included a split distance that I would measure out between each drawing. This way I didn't need to print off the entire tube. Next was cutting the ends of the tube. I used a tube notcher and a bench press for this with metal cutting hole saws.
The drawing contained the hole size, offset angle, and distance of the hole centre from the edge. Where tubes met each other end on end, all that was needed was an angle between them. The process of cutting the tubes took a very long time. I cut some on the weekends, some in the evenings in my garage after work.
I didn't do them all at once, I did them in batches so that I could start getting the chassis together. Any tube with a very shallow angle had to be cut by hand. I found a combination of hand grinder, bench grinder and deburring tool achieved the best results here. As an aside, this is a job which can actually be done by some specialist laser cutting companies. I got a number of quotes for this, all of them came back at a few thousand dollars to do my chassis, which was just a little bit too expensive for me but it's not actually that unreasonable if you're short on time plus the accuracy would be much better.
I did have the roll hoop bent by a tube bending specialist we just didn't have the tools or the skills to do that ourselves plus the price was very good only a couple of hundred dollars. I provided this drawing which included the wording from the rules on bending the roll hoop which I would also use to check the quality of the work afterwards. The results were fantastic it was within one or two millimeters of being perfect. The first members to go in were the ones between the legs of the roll hoop. We began by tacking them in place.
After double checking everything fit correctly, the welds were completed. We built some of the side members separately since this was a lot easier than doing it on the roll hoop assembly in place. These were then welded on one side at a time to complete the car's main bulkhead.
The roll hoop had to be positioned at the correct angle. Its base was positioned directly onto the chassis jig in a pivoting mount while a temporary brace was attached to the top, holding it in position. If I were to do this again, I'd weld the bottom pivoting mounts directly to the chassis jig.
We spent just far too much time in the end double checking and repositioning the chassis on the jig as it would move around slightly as it was worked on or rotated. The lower members get welded on, extending the chassis forward. I tried to add the bracing wherever long unsupported members were added, that way I could ensure that the dimension or position of the member wouldn't change. The front lower members go on, showing the overall length of the cockpit.
The car is built upwards and forwards from here, starting with the middle rails. The order that this got welded together required some thought. I ended up welding most of the members together as a sub-assembly and allowing them to pivot upwards on the tacks at the main bulkhead, allowing the little riser to be inserted. My father built these little clips from pipe support brackets that allowed bracing to be added temporarily to the chassis as it was built. These were really useful for holding things in position before welding.
The main four longitudinal rails were in long before most of the cross bracing. At the front end of the car, multiple inclined braces were used, mainly due to the requirement to provide support to the damper, bell crank and H-beam support bulkheads. These all attached to the same longitudinal members which meant they had to go in very early. The final members get inserted between the primary and secondary bulkheads.
Until this point, I had only been tacking the cross bracing unless it was totally necessary to the final members. fully weld to insert another part. I stopped here and completed all the welds between the primary and secondary bulkheads to improve the overall stiffness of the frame.
The main cockpit area was now done and I must admit I couldn't resist jumping in to see what it felt like. If the front lower bracing stopped short of the pedal area, a flat plate would eventually go in at the base of the pedals. This way I was able to sit my feet as low as possible in the car without having any chassis members getting away. The plate would be riveted all the way around its edge forming a stressed skin.
The stiffness of the chassis shouldn't be significantly affected by this. From here the bracing went in pretty quickly. I changed from 1 inch to 1 inch cross bracing which meant that the tubes intersected a lot less.
This made fitting and welding the tubes so much easier. Final members, the front left and right verticals, contained holes which would later be used to mount the H-beam suspension to the car. For this reason I had to spend a lot of time double checking dimensions to make sure that it was correct. A small misalignment would result in a large effective twist in the chassis or offset in the car's track.
Let's see it anyway for the front of the chassis. Next we need to attach the rear members which connect the engine and gearbox to the car. I hope you've enjoyed this episode. Let me know what you think of the car so far in the comments and feel free to subscribe to get notifications when more videos go up and I'll see you next time.