Progress at last!

With a lot of help from Dorri over at Ifitsgotanengine.com today we made some serious headway on my chassis. Previously I've lamented about not being able to digitally post the frame dimensions, but in this case a pic will do for now.

We're actually planning on building 3 complete chassis, since I have the axles and spindles and such for that many. All of them are over-sized as discussed, and break down as follows:

-Chassis 1 (mine): Opel Manta front spindles, hubs, and brakes, fabricated A-arms, and a Miata rear suspension with an RX7 rear differential. Engine and transmission unsure, but might end up test mule for my 280hp Opel project motor.

-Chassis 2 (Dorri's): C-4 Corvette front spindles, hubs, and brakes, Mid-90's Camaro rear axle with disc brakes and Posi, Chevy 350 with a NV3500 5-speed.

-Chassis 3 (spare): Early 80's Toyota pickup front spindles, hubs, and brakes, late model Crown Vic rear end, with disc brakes, probably a Toyota 5MGE, and 5-speed, since I have it sitting around, but with 6 motorcycle carbs instead of the fuel injection.

So far we have the floor of the first chassis built, and though not quite fully welded it's already amazingly strong. For the lay-out we employed no measuring devices when we cut the metal, and pretty much all the angles came out perfect. How? Quite simple, actually! Last night I got out my drafting supplies and drew out the entire chassis on to a couple sheets of MDF, making sure to make the lines all spaced apart appropriately as for the metal tubing we would be using. Today we got out a roll of 1" masking tape and over-lay-ed all the places a tube would be on the full-sized drawing. Since the tape was pretty much the same width as the steel, where the tape pieces met we decided how we wanted the joint to fit and cut across the tape with an x-acto knife. This gave us strips of tape the exact right length as well as all the angles required already on the ends. A little careful peeling and the strips were then stuck to the side of the raw steel, which was then cut to shape with a chop saw.

All the cuts so far were pretty much done in 3 sessions, each not much more than 10 minutes long, so under half an hour for all the cutting, and only a couple required any re-work to clean up ends being slightly too long. I'm well pleased with the result, and the tape did double duty in keeping each piece marked with where it goes until we had it in place on the lay-out board.

Chassis design finished

So, after countless revisions, I've finally got the chassis layed out on graph paper acurately enough to start cutting metal. What I've come up with so far:
-Chassis width: 46"
-Chassis height: 15"
-Overall length:140"
-Wheelbase: 109"
-Designed ground clearance 5" front to rear
-Engine bay length: 28"
-Passenger compartment length: 64"
-Toe width: 13.5"
-Tunnel width: 10" front, 8" rear

These dimensions reflect the latest round of tape measure action and the intended purpose for this car. I plan on using this chassis as a test mule for various engine and transmission options, to dial them in with easy access prior to installing them into their final destinations. As a result, the engine bay and tranny tunnel need to be big enough to swallow the biggest motors I intend to test, which in this case dictate a minimum length of 28" front to back for a Supra inline-6 and a width at the valve covers of 22" for a small block Chevy or Ford. Also equally important is the toe width, as my big ole' clod hoppers are 5.5" wide, which means 13.5" is absolute minimum, and that only works with a 1" wide gas pedal 1" off the tunnel. The book chassis would never allow for that kind of foot room.

Currently I'm trying to decide if I want to tackle digitization of the chassis drawings. I've got a couple of CAD programs, but I could fire up the T-square and have the tri-view and isometrics done in 1/10th of the time, then just scan in the results. Perhaps I'll get the hang of one of these programs yet. After I get back to the real computer and scanner, I'll post the graph paper sketches for perusal. Real drawings perhaps to follow later on.

I think, based on a rough tally of the weights of the metal tubing and some guestimation as to how much filler I'm going to use that the bare tube chassis will probably be in the 175-200# range. This seems a bit on the high side for a Locost, but there will be some weight savings with the IRS, and I never really believed the 35# claim in the book anyway; I think he meant 35kg. Square 14ga 1" tubing is nearly 1lb/ft, and there is clearly more than 35' in the basic book chasis.

I did stumble into one feature falling out of my chassis changes: The top and bottom rails will be parallel and directly above each other almost the entire length of the vehicle This means no curved wrap-around on the bottom of the front, which I think should make assembly quicker and cleaner. This only really works because the increased track width in the front will require longer control arms. That also means as long as I keep the tire diameter in the front under 23" I can actually improve on the turning radious over the book chassis by being able to turn the wheels quite a bit further before they hit the body. Even with the overall increase in length, assuming similar slip angles and Opel Ackerman angles I should be able to park this thing more easily than a book chassis. I'd call that improvement all-around.

constraints

So, everyone starting out on the Locost trek starts out with "the book." In addition, I have been referancing the Tiger Avon build book, the (nearly useless if you know much about cars) "how to build a cheap sports car" book, the "locost build manual" available on CD-ROM, Chassis Engineering by Adams and how to make your car handle by Puhl. All good stuff, and my research has lead me to a few modifications on the book chassis:

-Taller sidewalls. The book scuttle is <12" from the floor, and my feet are closer to 13" long.
-Wider chassis. I'm big, what can I say?
-IRS. I like the Avon chassis for this, though I have Miata stuff so I'll use it instead of the Merkur.
-Front of the chassis re-design. Yuck. The Avon lower arms mount so much better to the chassis, I'm going to use something more like that, but with Opel Manta spindles.
-Cabin floor and firewall. The book chassis ends the floor where the back of the bell-housing is, I plan on running it all the way to the front of the bell-housing.
-Mid-plate motor-mount. I'll never be able to hear anything anyway, so I'm going to use a mid-plate, like race cars, but have it bolted to the front of the firewall down each side. This should, depending on how the top "shelf" over the foot wells end-up allow the tranny tunnel to be completely closed off from the engine bay. I might then use it for heater ducting, haven't decided yet.
-Better triangulation. There's a lot of chassis bars meeting off-set from true triangulation for no apparant reason. G1 and G2, for example, run along the oil pan, below the block and starter, so there is no reason they can't connect directly to where the tranny tunel lower bars meet C. Same with where M2 and N2 meet on K2, they should all be in the same place.
-Wierd round bars- What's with the mystery changes in materials? Keep it all the same, then upholster and pad so no sharp corners to hit against. I'm OK with a few pounds of vinyl and carpet underlayment.
-Coilovers. Too darn expensive. Going to use either Miata or Civic rear struts, used and cheap of course, or transverse leaf springs if I can make room. An Opel Kadett or GT front spring should be just about ideal on either end, and would transmit load to the chassis better than the book upper strut locations.

Starting the project(s)

This is going to be the site where I document the build up of my own Lotus Super 7 clone based.