I just uploaded Video Update 5 to Youtube for those who like their pictures to move. This video shows the mounted differential, engine, shifter, fire extinguisher, dashboard, steering column, master cylinder reservoirs, “floor”, pedal cluster, steering rack, suspension rocker arms, front springs & shocks, fuel pump (moved later), and shoulder harness mounts.
Engine installed, along with lots of other pieces. Click to watch the video.
Almost finished mounting the body
Not much to say about this one… Just lots more piddly little brackets. The large bracket at the tail is necessary as that will be where the rear impact absorber will mount. Had to make some changes just behind the driver’s left shoulder to allow access to the fuel filler.
Time for a photo update showing how I built the cockpit, tube by tube.
A couple of videos posted to YouTube. #1 gives an overview of the chassis as it stands, and #2 talks about the chassis jig table.
YouTube Update 1
YouTube Update 2
A mysterious form begins to take shape on the slab
Now it’s time to test one of the big unknowns of this project: can the top rails be formed in the shape of a complex 3D spline, and can the left and right sides be made to match? The CAD software won’t even allow a structural member in the shape of a spline, requiring them to be composed of straight sections and arc sections. Other exoskeleton cars have been built, but as far as I know always with a single curve in the main frame members. And of course a tubing bender is designed with the assumption that it will be used to form constant-radius segments. I believe this is the first car to be done this way, so I’ve put a lot of effort into the chassis jigs to get it right. The top rail spline is a key to the beauty of this design. To make a long story short, it is in fact possible to bend a 3D spline on a tubing bender. It just takes a lot of trial and error, patience, and about a day of work per rail. And luckily, overbending can be corrected by running the tube back through the bender, clocked 180 degrees.
“The pricking of my thumbs” is not entirely rhetorical. In fact I almost cut off my left thumb while building the top rails, so a word about safety. A tubing bender is a SERIOUS PIECE OF EQUIPMENT. It won’t even notice bones and flesh being fed into its’ rollers. I had already turned off the bender and reached to grab the tube as it was twisting on the way into the bender. The bender caught my glove and started pulling my thumb in, stopping at the last possible millisecond before inflicting permanent damage. It hurt and left a mark, but I was insanely lucky. So, 1.) Never wear gloves while using a tube bender. They protect you about as much as Saran Wrap, and it’s better to have your fleshy appendages dangling about unprotected to remind you of the danger. 2.) NEVER, NEVER touch the tube on the side being fed into the bender. Always handle the side being fed out. and 3.) Before pushing the “on” switch, stop, think, and say to yourself “I’m not going to become an amputee on this bend.”
So here's the problem: how do we make this straight tube fit all those notches located in 3D?
Left top frame rail about half done
Top left frame tube fitted to chassis jigs
Both top frame tubes bent to shape and matched to each other, in place on the chassis jigs. Now it's possible to get a feel for the size and shape of the car. It's really going to be beautiful!
The main frame rail, running from the front to the back of the car, is so light I can lift it with a single finger.
Sitting inside the chassis for the first time. Time to make vroom vroom noises.
To get optimal suspension geometry and aerodynamics I’ve designed the car with a front keel under a raised nose. This gives the longest possible lower front A-arms, minimizing the angle changes of the front suspension as it goes through bump and jounce motions. The raised nose clear airflow around the front wing. My computational fluid dynamics (CFD) studies show airflow around the front wing is extremely important as the wing operates in ground effect and generates downforce all out of proportion to its size. I spent a considerable amount of time trying to increase the downforce generated by the underbody and rear wing to match that of the front wing, even though those elements are far larger.
The front keel will use a stressed skin of aluminum formed to shape and riveted to tabs welded onto the frame tubes. This is the highest-stress area of the entire chassis, as under braking something like 2800 pounds of force will be transmitted through these members. You can visualize the car supported vertically on the front keel, with two more cars stacked on top of it, so this needs to be really strong.
Front keel tube is drilled on the milling machine for front lower A-arm attachment points. This will give perfect mounting locations.
Lower front A-arm attachment points were cut and drilled on the lathe, then tapped.
Chassis table comes in handy again for welding the lower front A-arm attachment points into the front keel tube.
Completed front keel tube assembly. Front lower A-arm attachment points welded in place, ends of keel tube capped for strength.
Front keel tube assembly rigidly located in place on chassis table.
The 3-roller tube bender generates about 65 cm of scrap at each end on small-radius bends before it starts generating the correct constant -radius bend.
First front keel down-tube in place. The surface of the keel will be concave to let air flow better across the upper surface of the front wing, necessitating curved tubes to hold the keel.
More front keel down-tubes. The two rear tubes are a recent addition to the design as this area needs to be phenomenally strong and the tubes weigh almost nothing.
Finished front keel and front subframe
After more than a year and a half of design and several months of tool preparation, that long-awaited day has finally arrived: the day I touch saw to metal on an actual car part. The first step is to build the front subframe that sell sit horizontally at the bottom of the nose of the car. The chassis table already has holes drilled and tapped for 3/8″ bolts locating the subframe members precisely. Here’s the first tube in place among the pins on the chassis table.
First tube in place on the chassis table, bent to fit pins
Lower front frame member cut to fit and tack welded in place
Finished front subframe, fully welded. Since it's laterally symmetrical, it's flipped over to weld the bottom.
Front subframe raised to final position, supported by chassis jigs. Note Natural-Polymer Swing Press at right. A useful tool.
LudemannEngineering 