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Sheena Is a Punk Rocker

Front upright design and tweaking has finally come to an end. With that under wraps I’m currently perfecting the rear suspension design and focusing on the physical build of the chassis.

A build of this magnitude should not be attempted without a chassis jig and a whole bunch other jigs, either universal and adjustable or completely custom made to the task at hand. I’m using a mix of both. I’ve got some off the shelf parts and pieces that I can use to lock chassis parts into position. With a build like this it is inevitable that you’ll be using a lot of home built one off jigs that position and hold pieces that are solely specific to your current chassis. I can honestly say that I’ve got almost as much time and material in jigging tools as I do in actual chassis parts.

That being said, your chassis jig can be as simple as some 4×4 wood pieces bolted together to some kind of exotic space frame and i-beam monster. As long as its square and level, and large enough to tackle the job it will work. I find myself adding new attachment points for locators, holders, and position markers all the time. The key is true, level, and adaptable. That’s all discussed in previous blog post.

Version 4.2 of the uprights have been the final form for a few weeks now. The left front pieces are all 3D printed and post processed. With the exception to some minor tweaks visually and structurally they are dimensionally perfect and therefore the left front is assembled for mock up.

Technical drawing of upright body

Without giving my specs away the roll center moves in 98% congruence with static ride height changes. Even in the most extreme dive and roll is maintains a stable lateral movement. Read that as it shifts only a few thousandths to either side at even the most extreme roll. So with that I’m pleased. Throughout the design process I’ve managed to maintain strict coherence to the numbers set forth in Suspension Analyzer. The physical iteration of this design should carry the same physics as the virtual unit.

So let’s talk about about the physical construction of the vehicle. I’m happy with keeping my tolerances with .001″ of design dimensions. And you may ask yourself, “how can this be done without million dollar equipment?” Patience, logical thought processes and procedures, and common sense. Of course it all takes longer without having all the crazy high end equipment. A good tape measure, some digital tools, paper, a calculator, and a lot of time can get the job done. And it will.

TurboCad rendering

I spent some time drafting out on paper the way the front “clip” will work in relation to the front suspension. Why? Well if you’ve been reading through my bullshit you may have taken away that we build from the tires inward. Tire size was determined, track width, wheel size and offset, and so on. Every single piece of this suspension was designed around a specific tire and track width. Minute measurements like rotor hat thickness, wheel hub flange thickness and width, rotor location, caliper location all located specific parts in distance relationships with the tire center and the center of the chassis. The planning and design stages have been tedious, and so shall the build stages. Mistakes cannot be made and will not be tolerated. If a piece is made out of spec and cannot be pulled, pushed, or melted into spec, then to the shitpile it goes.

Designing in BendTech Pro

Back to the front “clip”. A few things had to be taken into account when designing the front. Most notable and most important was the lower control arm location. Distance from the lower ball joint, center of chassis, above ground, and fore and aft of axle centerline were the contributing factors in determining frame rail width and frame rail height (not heighth…it has no place in proper common modern English). I also had to consider what would be in the forward compartment. Fuel cell, battery, radiator, possible a swirl pot, fuel accumulator and a tank for the dry sump oil system all came to mind. Measurements were double checked and I drafted a layout before transferring it into BendTech Pro then to Turbocad.

As you can see from the design and sketches I’ve constructed a forward “bulkhead” from which I will hang the main forward frame structure and later the firewall. The bulkhead was laid out on my Certiflat weld table and the neccessary jigging was constructed to hold it all in place. Fitting it to the chassis was easily accomplished by laying out the specs directly on the forward frame 3 x 3, marking distances and constructing a small locator made of angle iron and a 4″ clamp.

I’ve gone through several design considerations for the rear section of the frame. If I haven’t already made clear the powerplant will be a Gen 3 Ford Coyoted mated to a heavily modified Subaru 5MT in a mid engine configuration. This added a slight complication to the rear chassis design. I optioned designing and implementing a drop out frame that the engine, trans, and lower half of the rear suspension all attached to. It would have provisions for lowering the drivetrain out of the chassis from the bottom. I have several designs in the drafting stage for this, but chassis rigidity considerations are leaning me away from it. I believe service would be greatly eased in such a configuration, but at the expense of weight and structural integrity. As far as I can calculate designing a rear structure to support chassis loads and drivetrain loads while acting as a support structure for another support structure is negated by the weight gains when designing structural rigidity into the asset. Basically picture a stout structure with another stout structure bolted to it.

Next I looked into making a large fiberglass mold of the rear body of the car incorporating the rear screen, deck lid, rear quarters, and aft body structure. A complete carbon fiber piece that removes as a single “clamshell” unit. Having a removable rear clamshell would allow all rear structural components to be welded in and would remove the necessity for a detachable extra member solely for engine/tranny removal. All suspension hard points and engine/tranny mountings would be integral to the chassis design. I believe this will save weight and rigidity. However the complication of a large single one piece rear body half adds labor and further strain to the rear body’s construction.

My third option would be similar to the second, except I’d have 2 separate carbon bodies in place of a single. The first would comprise of the back section of the body and provide mounting for the tail lights, rear bumper, and some of the aero. The second would be made up by a rear lexan screen with approximately 1″ removed from the edges inset in a carbon frame flowing as a single piece including the deck lid and mounting points.

Both of the later designs are hinged on be ankento build the rear cage laterals in congruence with structural engineering while provide just enough room for serving and removing the drivetrain through the rear of the vehicle.

That’s where I’m currently at. As of this writing I’ve made the trip to S&W Race Cars to pick up the longer lengths of tubing needed for the main hoop and forward laterals. Expect a full cage review in the next writing.

Sorry for the lack of comedy. Enjoy the pics. Until next time fire up the Punk Rock and get to it.

theDoc View All

Chassis builder, engine builder, cynic

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