Making Chips… Finally!

Posted by jjludemann on May 10, 2012

Lower suspension attachment clevis assembly drawing

It seems that other people who’ve built cars from scratch attempt to get their cars rolling on the ground as soon as possible, so I figure I’ll do it that way too. With that in mind, it’s time to start fabricating the suspension. First up: lower suspension attachment clevises. I ordered 7075 aircraft aluminum from the United States as part of my big shipment. It’s amazing stuff– stronger than steel but light as aluminum. These assemblies have to be extremely strong, as I calculate that under braking the front one takes a load of over 4400 pounds.

: Start with a solid chunk of 7075 aircraft aluminum, here scribed for cutting slightly oversize

: Blanks are cut to size with thinnest abrasive cutting blade in high-speed angle grinder. I tried using a 12″ cutoff saw, but it couldn’t cut this high-strength aluminum.

: Finished raw blank

: Facing both sides of the blank with carbide-insert face cutter end mill

: Milling holes for bolts to attach to chassis. PDF drawing printed on sticky paper at 1:1 eases the layout and provides a useful double-check against errors.

: Milling the first outside radius on the rotary table.

: Milling the second outside radius

: 45-degree faces are rough cut with the angle grinder, then clevises are supported on V-blocks clamped to the milling machine.

: 45-degree faces milled smooth with face cutter

: Repeat eight times. Ready for slot milling.

: Milling the slots for the rod ends using a ball-end mill.

: Milling holes for the rod-end retaining bolts

: Milling an additional relief for the rod ends. Test assembly showed interference, so I went back to the computer model and, sure enough, there it was. Now I know to use the interference and clearance detection tools.

: Finished lower A-arm clevises. Outside radius on front was also cut on the rotary table / milling machine.

: Lower suspension attachment clevis assembly drawing

Contents: 1 Race Car Kit, some assy. req’d

Posted by jjludemann on May 2, 2012

I’ve been accumulating parts for almost the past two years in a warehouse in Los Angeles as it’s easier to buy things in the US and ship them all the way to Thailand than it is to just buy them in Thailand. Also, I only wanted to navigate Thai customs one time. Finally gave them the go-ahead to ship, and a few weeks later everything arrived at my door. Includes just about everything that I can’t make myself or buy in Thailand: wheels, brake calipers, brake discs, brake pads, master cylinders, Aeroquip tubing and fittings, torsen differential, rear axles, spherical bearings, bearings, rod ends, 2007 Suzuki GSX-R1000 engine, crash padding, radiator, oil cooler, kevlar, vacuum-bagging materials, vacuum pump, Halon fire system, and more. Also, everything I need to fully fit out my machine shop, like a rotary table, angle table, and cutting tools. Better than Christmas!

Some assembly required. May require common household items such as tape, scissors, stapler, lathe, milling machine, and TIG welder.

: Race car kit, somewhat the worse for wear after storage of up to two years and trans-Pacific shipping.

: Some of the parts: centerlock OZ Racing wheels, 13×8″ and 13×10″

: Truck carrying goodies

Redesigning Suspension Components

Posted by jjludemann on April 14, 2012

So I was ready to build the suspension attachment points and decided I’d better do a finite -element analysis. It turns out they needed a lot of tweaking, and in a shin-bone’s-connected-to-the-thigh-bone kind of way, I ended up redesigning just about every suspension part all the way to the lug nuts. Part of this came when the quote on building the upper suspension attachment clevises came in way higher than expected, so I redesigned them so they could be laser-cut, hopefully much cheaper than CNC machining. Don’t have the new quote yet.

Also, I received the huge shipment of parts, supplies, and tools that I’ve been aggregating in LA for almost the past two years, and some idiot in purchasing (me) managed to order the wrong brake calipers. Everything was right except for the mounts, which are the lug style instead of the radial style. At least now I really know the tradeoffs between the two approaches. The upright for lug mount brake calipers is only about 35 grams heavier than the one for radials, and the calipers are $80 cheaper each. Over $1000/pound for that weight savings… Actually, that’s not quite fair as I don’t know the relative weights of the two caliper styles.

Anyway, we have lots of pictures of FEA meshes and results:

: FEA mesh for lower suspension clevis, attachment point for all four lower control arms

: Finite-element analysis results for lower suspension clevis

: FEA plot for front upper suspension attachment bracket that will be welded to the chassis.

: FEA plot for one half of the laser-cut upper front suspension attachment clevis

: FEA plot of one half of the upper rear suspension attachment bracket

: Detail of the FEA mesh for buckling analysis of left front lower A-Arm

: FEA buckling plot for left front lower A-Arm under braking load

: Detail of the FEA mesh for static analysis of left front lower A-Arm

: FEA plot of left front lower control arm under 1600 pounds braking force

: FEA plot for left front lower control arm under 1600 pound right-hand cornering load

: FEA plot of left front lower control arm under 1280-pound left-hand cornering load

: FEA mesh for front axle static cornering analysis

: FEA plot of front axle under cornering load

: FEA mesh for front axle static braking analysis

: FEA plot of front axle under braking load

: FEA mesh for front/rear steering arm

: FEA plot for front/rear steering arm under maximum cornering load

: FEA mesh for front upper control arm attachment bracket, to be welded to chassis

: FEA plot of front upper suspension attachment bracket

: FEA mesh for left front suspension upright static braking analysis

: FEA plot of left front suspension upright under braking load

: FEA mesh for left front suspension upright static cornering analysis

: FEA plot of left front suspension upright under maximum cornering load

: FEA mesh detail of left front suspension upright for snap-ring analysis

: FEA plot of left front suspension upright snap ring slot under cornering load

Building the Frame: Roll Hoop to Tail

Posted by jjludemann on March 8, 2012

: Removed the chassis from the jigs for the first time. Welded the bottoms of all the joints, which brought the chassis back to true & flat

: It’s a commuter car! You can carry it like a briefcase.

: Test fitting the rear beltline tubes. Chassis table has pins to locate these tubes, too.

: Rear subframe beltline welded…

: And into place.

: First parts back from the machinists’. Rear keel jig and the keel itself. Beautiful and accurate! Thanks, Somkuan!

: Rear keel, ready for welding.

: …and welded.

: Welded rear keel jig. Really starting to get the hang of this welding stuff. Yay!

: Bottom perimeter of the engine compartment fabbed and welded.

: Finished rear keel and rear keel jig.

: Engine compartment left side lower tubes

: Engine compartment right lower diagonal

: Bulkhead H right vertical lower tube

: Another example of how my Solidworks fishmouthed tubes fit, this one at the front end of the rear keel.

: Lower diagonal tubes holding the front of the rear keel.

: H-J inner upper diagonal tubes securing the front of the rear keel.

: H-J bottom perimeter tubes in place. These 3 tubes were welded flat on the table then lifted into place. Here you see the bottom of the car start to curve upward to clear the diffuser.

: H-J side diagonals. Here we work our way from front to back to avoid cutting off the ends of the tubes to fit them in from the side.

: J left and right lower verticals

: J to L left and right lower diagonals

: Released from the chassis table again to weld the bottom of all the joints. It’s so much easier this way I don’t even try to weld upside-down anymore.

: J-K inner bottom diagonals hold the rear of the rear keel

: K-L diagonals secure the rear of the rear keel to the beltline. This is the back end of the frame.

: Top frame rails from the main roll hoop to the back of the car are finally in place. Now we can see the complete outline of the frame.

: G-H upper diagonals are curved outwards to allow us to remove the engine from the top. The curve must be in the correct plane.

: From this angle you can see the curve. Removing the engine from the top is a design change based on feedback from the ApexSpeed.com forum. Top rail will be made removable later.

: H bulkhead, upper left vertical. Note that it’s not really vertical, but leans forward and inward.

: Test fitting the G-J upper diagonals. Sometimes it’s necessary to fit a bunch of tubes before welding any in place.

: Now we start welding them in place from front to rear. These are the G-H upper diagonals.

: H, H-J, J upper tubes (6). Skipped a couple of photos…

: It’s almost done. Just a few inner diagonals left.

: J bulkhead, inner diagonal UL-LR. This area of the frame is extremely strong as it has to support the suspension rockers and engine mounts.

: J bulkhead inner diagonals, LL-UR, 2 pieces

: H-J inner diagonals support the rear engine mounts.

YouTube Video Update 1

Posted by jjludemann on January 29, 2012

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

How to Fishmouth Tubes in Solidworks

Posted by jjludemann on December 27, 2011

After playing around with various kinds of hole cutters, mills, angle vises, and so on, I’ve settled on the best method for cutting fishmouths in tube ends so they fit together properly when building a tube frame with round tubing. Since the tubes will be welded they don’t have to be perfect as you would get by using a milling machine. Also, the typical joint has several tubes meeting which need to accomodate each other, and on a milling machine this would take a separate setup for each tube at each joint, taking an inordinate amount of time. Forcing Solidworks to show the correct shape of the ends of each tube requires some real work, an explanation of which I found over on the LoCost website. I’m going to provide a modified and updated tutorial here.

The first thing to understand is that each tube must be fully welded before adding the next tube. This makes the finished structure much stronger than if you tacked all the tubes in place and simply welded around the remaining visible joints. Here’s an example:

In a multi-tube intersection, the first two tubes are fully welded before adding the next tube

Third tube in place before welding

Third tube fully welded

Solidworks Tutorial

Although the following tutorial may look long and complicated, once you understand what’s going on each step will only take seconds. And believe me, it’s much faster than grinding a tube to fit using trial and error. More accurate, too.

First, create a weldment profile with the correct outside diameter, a thickness of 0.1mm, and a gap of 0.1mm as shown.

Original weldment use a profile of 25.4 x 1.0 mm round tube

Replace this with the new, slitted profile

Each tube will need to be trimmed to the tubes around it, reflecting the order in which they will be assembled. Insert > Weldment > Trim/Extend. Check your trims.

Select the tube, right click and choose "Insert into new part".

Save the part with a descriptive name. I keep a separate directory of tubes.

Select an INSIDE EDGE and click Insert>Sheet Metal>Bends.

Just click the green check mark. No need to fiddle with any options.

Right click on "Process Bends" and choose "Suppress".

And you get a flat sheet.

Select he surface and choose a normal view

With a Normal View, dimensions and shapes will be correct.

Open a new drawing and insert the current model view.

Set drawing scale to 1:1, full scale

Right click on the drawing view and choose Drawing Views > Rotate View.

Through trial and error, figure out how much to rotate the view so that it is horizontal.

Now we have a horizontal drawing view.

Insert another drawing view...

Also of the current model view.

Rotate the view as before to get another horizontal view.

Two views on one drawing.

Align the views horizontally by right clicking on one view and choosing Drawing Views > Align Horizontally by Origin.

Crop each view by first drawing a rectangle with 4 lines. The automatic draw rectangle won't work because it uses the unrotated axes.

Crop the view by selecting the four lines of the rectangle, right click and choose Drawing Views > Crop View

Now we have both tube ends with the middle removed, fitting on a single A4 sheet.

Now we need a reference for how far the ends of the tube are from each other. Go back to the tube part and create a sketch like this.

Using the sketch, extrude a cut through the part and keep all bodies.

The part now looks like this.

Go back to the drawing and add annotations as necessary for use in the shop.

Save the file as a PDF and print it out on sticker paper. Cut out the 2 ends and stick them on the tube at the indicated distance. Use an angle grinder to grind to the lines.

By the Pricking of My Thumbs, Something Wicked This Way Comes

Posted by jjludemann on December 4, 2011

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.

Building the Chassis Jigs

Posted by jjludemann on November 25, 2011

First "professional" jigs

Because this looked like a lot of busy work, my first thought was to have the chassis jigs built by a local machine shop. So I bought the metal and had it sent directly to the machine shop and went over the drawings with them. They kept asking me how big various things were, when the dimensions were clearly right there on the drawing. Then it became clear they didn’t know how to deal with dimensions in meters. They asked me how to convert a dimension from meters to centimeters. “You mean like move the decimal point two places to the right?”, I’m thinking… This was not looking promising. Eventually I went home and tried to come up with a set of orthographic-projection drawings, with hidden lines removed, that they couldn’t possibly misinterpret. I soon gave up. When I went to pick up the first two jigs the next day, the list of errors was long and creative. Mounting footprint on one reversed, vertical tube holders cut too shallow and not in line, overall height incorrect, horizontal alignment out of spec, etc., etc.

Sigh. I called a local aerospace-engineer type that I know and asked him if he knew a good machinist, and he directed me to a local guy who I visited the next day. We met a couple of times and he is indeed capable of handling the project; in fact, I decided it’s really below his capabilities and ended up building the jigs myself, saving him for building actual car parts.