13 Dec 2008

Worked on CAD most of the day cleaning up the chassis, still not done. After getting tired of that went out and layed out the bottom chassis tubes on the table; if you look closely you can just see the lines. With it actually taking shape it’s another vote for a large table. The difuser behind the engine and the radiator support at the front will both make the frame about two feet longer. Looks like cutting steel will start tomorrow…

Earlier Cooper came in to check why I spend so much time staring at the dumb computer. He’s perfectly happy walking around the house with a towel like this, looking like the Emperor in Star Wars. With his short hair he likes the warmth on cold days.

11 Dec 2008

Phil pointed out a couple things about tube chassis construction that I was aware of but hadn’t really thought through. He stressed trying not to have a bunch of tubes coming together into one node. Technically it’s the right way to do it but causes a number of fabrication problems. The cuts on each tube can end up being very hard to fabricate, including being impossible to install without cutting off one fishmouthed end. Many tubes in one spot results in such a large mass of metal that a lot of heat must be pumped in to weld all the tubes which leads to heat warpage. Also, it can be near impossible to reach in between all the tubes and weld every inch of every joint. It’s easy to skip the hard-to-reach ones, which start corroding from the inside out since it’s open to oxygen and moisture (never mind rain water wicking inside.) Seems like good advice so I’ll see what I can do, space the tubes slightly to allow getting the torch in between and to simplify the tubing cuts. In many cases it doesn’t take much to greatly simplify the end-cut, sometimes just moving the end of the tube 1/4″ is enough to change a 3D cut to a single-plane cut.

Ordered some Christmas presents for myself. Google Sketchup works pretty well for creating the chassis but Google knows what they’re doing. Their free version only exports JPEG drawings which is very limiting. No .EPS format for the book, no .DXF for sending to metal fabricators, or .PDFs, or .TIFFs. Fine, they win; Sketchup Pro was purchased which has all the export formats.

Back when building Kimini, there were times it was nearly impossible to use the TIG welder foot pedal when welding in awkward positions. A finger-operated current controller fixes that. Since moving a finger to change current will likely move the torch head slightly it’s not a perfect solution, but better than the antics of struggling with the foot pedal.

Replaced the leather cover for the TIG torch hoses; it was worn through and contrary to my cheapskate nature it was replaced rather than waiting for a hose to spring a leak. Also ordered bandsaw blades for the weenie-but-faithful Harbor Freight bandsaw; we’ll see if it lasts another build. They have a larger $600 saw but as long as this one keeps running there’s no reason to consider it, plus it would consume sacred floor space.

10 Dec 2008

Added a tubing rack under the build table. Keeps everything clean and visible, off the floor, easy to check stock, and saves floor space. After that, dismantled the wood mockup(!) and cleaned off the table in anticipation of starting for real. To be honest, things are moving a lot faster than expected. With the Mini it was nearly five years before the steel chassis was started.

Coming up in three weeks is the appointment with the DMV, to see if a coveted SB100 exemption number is in my future. It’s kind of a big deal; if I get one it’s a huge relief as it means there’s no concern about getting the car registered, smogged, and provides incentive to have it rolling in 2009. If it doesn’t happen it’s not terrible, but it does drag out the fear of the unknown another year and there would be no chance of driving it in 2009. It would give time to concentrate on the construction chapters of the book though it would be nice to know how it handles before that. If there’s anything dire that needs changing it would be nice to have the right stuff in the book the first time rather than reworking chapters.

I’m just holding my breath until then. The real fear is that this law is too good to last; at any time they might pull the plug which would make getting the car on the road much more difficult. Of course, with California’s $15 billion deficit, maybe the DMV will continue taking our money for this service. Have to keep a positive mental attitude.

9 Dec 2008

The tubing is here, bent tubes, too! A big thanks goes out to Phil Burke and everyone at BurkeBuilt Fabricators for helping me get the tubes bent. Lots of places can bend 0.125″ wall tubing but not many can do 1.5″ x 0.095″ wall. Unfortunately I had the wrong bend radius on my drawing but they fixed it, which means some tube drawings have to change… which is another reason the tubing drawing issue bugs me. Anyhow, different businesses use different bend radii in their benders, making the main hoop and windscreen slightly different shapes and affecting tubes mating to them.

Received some good comments on what information to provide for tube fabrication. Of course the suggestions range from, “they don’t need anything”, to, “give them everything and let them pick what they need.” The answer’s somewhere in the middle; the trick being to not spend a lot of time providing info builders don’t need or can’t use.

Since Burke deals with this stuff all the time I asked his opinion on how much information to include, noting that a builder is typically one guy in a garage using a grinder or tubing notcher to do the ends. He had a good example: a simple angle cut on the end of a round tube. At shallow angles, the tip of the tube on the drawing will be quite long and sharp. However, in the real world it won’t be nearly that long because it’s not possible to weld such thin metal; it’ll either melt back or get ground off during deburring. His point is that measuring to the tip is only useful as a guide of how long to cut the tube before notching it. Another example for this same tube: the open end of the tube is an ellipse, so the centerline length of the tube is measured to the center of the ellipse. But how is a builder going to do that? It’s very difficult if not impossible before it’s cut and dang hard to do even after.

I know I keep beating this topic to death but when people who know this stuff say don’t bother with detailed drawings it makes an impression. Maybe it’s my excuse why tubing detail will be minimal on unimportant diagonal tubes but more detailed on important corner tubes. As was pointed out, probably the most important drawing is the one showing where the suspension pickup points go; everything else is just a big bracket to keep them in place.

A shelf will be added under the build table to store the tubing up off the floor. Learned that lesson the hard way last time; the tubing rusted quickly from the moisture coming up through the concrete.

7 Dec 2008

The final chassis is progressing though the round tube drawings bother me. As mentioned before, it’s not clear the best way to convey how to cut the ends – or even how much to try and make the drawings precise. The overall length is good, and the angles of the end cuts, but I’m not so sure about index angles, which I think will be rather useless to a typical garage builder. If a drawing specifies that the miters are offset at each end by, say, 27.3 degrees, how is a typical builder going to make use of that information, really?

Curious about build accuracy, I asked FSAE teams how they make use of laser-cut tubes – just what does someone do once they have perfectly cut tubes? The theory is that with them accurately cut, the chassis becomes “self-jigging.” Teams confirmed that while having the tubes pre-cut is a tremendous time-saver, that’s all it saves. They said a builder cannot just weld laser-cut tubes together and expect the chassis to be square; it’s just not going to happen without a big heavy fixture to combat weld distortion. The reason I mention this is that just because tubes are accurately cut has little to do with them fitting due to tolerances. What good are tube drawings with 0.01″ resolution when the tubes are cut and installed into a chassis with a realistic accuracy of >0.125″?

If someone hands me accurate chassis drawings, what would I do with them? I’d make sure a few major tubes are accurately placed and not sweat the rest. About 90% of chassis tube placement just don’t matter much; the various minor tubes just keep the big ones in place and the inboard suspension points where they’re supposed to be. All the tubes in between, eh. That’s how I intend on building the chassis myself, using the drawings to double-check overall dimensions, but other than gross lengths and angles, they’re a guide only. That’s all they can ever be due to weld distortion making accurate drawings fairly pointless.

This isn’t anything new. The Gibb’s book (“Build your own sports car”) supplies complete drawings of the chassis accurate to 1mm (0.040″). Yet right up front he warns: ” Precise dimensions are provided for all components, but in practice allowance must be made for welded joints and distortion. It is advisable to cut tubes – and check and trim as necessary – as the chassis is built up, rather than cutting all tubes before work starts.” So there it is from another source, having drawings with high resolution aren’t of much use other than a reference.

6 Dec 2008

The final chassis is taking shape, right side. It’s accurate as opposed to the “pretty good” original, at left, ensuring the final drawings are right – and the chassis symmetrical. The bottom tubes and bent tubes each have a dimensioned drawing which is why tubing is being purchased. The drawings will be kept ahead of fabrication to make sure each tube has a drawing to keep the chassis honest. This way when the chassis is done there is no doubt that it’s a faithful copy and nothing will have to be remeasured, edited, or rebuilt. Of course, only after the first trackday event will it be known whether the chassis needs any final tweaks. I’m trying hard to do all the work up front so that it “just works.” Kimini was pretty good right out of the box so we’ll see if it can be done again.

A lot of progress is expected over the next four weeks ­čÖé

Speaking of Kimini, at the last second the buyer asked that a color copy of the Kimini book and spare windshields be included. Since he’d already paid for the car I wasn’t concerned. However, after a couple months and a few polite reminders, well, so be it. Someday he’s going to need to know something about the car and I’ll be happy to explain, right after he pays the bill.

2 Dec 2008

With tube drawings starting an incentive seems in order. All the tube lengths are known – though not yet formally drawn up – so the numbers were totaled and tubing has been ordered! Since the main hoop and windscreen tube drawings are done they’ll get bent at the same time the tubing is picked up. All this happens next week, so between continuing with tube drawings and having the tubing on-hand, there’ll be plenty to do over the holiday break. First thing will be cleaning off the build table! Happy now?

28 Nov 2008

I’ve received comments questioning several aspects of the car and thought I’d give an explanation of my mind set:

Roll cage lacking tubes:
I anticipate builders configuring their car for what they want it to be. I have no interest in SCCA or NASA events and want the ease of getting in and out, so, I’m not adding any additional tubes to the rollcage. For hardcore racers, they can install longitudinal tubes to brace the two hoops together to make sure the cage meets the rules but most builders won’t want them. Builders building a car for cruising or going to weekend lunches probably aren’t interested in a fully-triangulated SCCA-approved roll cage. The way I look at it is that the car will be much safer than a Locost, and besides, competition rules vary around the world and are always changing so there’s no way to present a be-all-end-all solution. It’s up to each builder to double-check their local competition rules to make sure there isn’t a problem.

(Example: It was pointed out that the diagonal in the main roll hoop does not meet NASA’s rules because it’s installed to the opposite corner (though it does meet SCCA regs.) The reason it’s that way is it gets the diagonal away from the driver’s seat for better clearance. If a builder is going to participate in NASA events they’ll have to change things around which is fine. For all other builders it’s that way to keep the tubes away from the driver’s head. This is just one example of how everything’s interconnected and how each builder will be responsible for their own car – as it should be.)

The car is too tall, lay the seats back further to lower vehicle height:
This is a double-edged sword by possibly making it too low for a street car, becoming invisible within 50′ of SUVs. Right now it’s 45″ to the top of the main hoop. How low can it go before it’s unsafe in traffic? Laying the seats back means lengthening the wheelbase, slowing slew response, something important to autocrossers. Lean the windscreen back too far and the driver’s line of sight will become distorted by the glass or Lexan windscreen, or the headlights may start blocking the field of vision, never mind being too low to meet local laws. Being too low can actually be a detriment at an autocross event due to the “forest of cones” issue but it does lower the CG. Builders will have to decide what’s most important to them.

How about side-pods?
Other than the yet-to-be-rendered side inlets, I don’t think Midlana will have them. Not because they’re a bad idea; they provide several benefits such as under-chassis diffusers, space for radiators and better side-impact protection. However they also make the car heavier, more complicated, and expensive. Not by a lot, it’s just more “stuff.”

I appreciate all the input, really, but there’s a growing sense of needing to move on. The car’s a compromise and at some point I have to draw the line somewhere – figuratively and literally – but draw it I must or I’ll be forever stuck in the design phase of trying to make everyone happy. The book will note areas where builders must make decisions – which I encourage – based upon their own goals and preferences. It’s okay to be different. I’ll try to include renderings of side-pod ideas so that individual builders can pick and choose what they like, or they can do their own unique modifications.

I’m far from any sort of design and styling expert; I want people to customize their car. I’m 6′ tall, so if you’re taller or shorter, the roll cage can be changed to suit. Or, maybe you’re heavier or more slim. Widen the car, narrow it, move the seat forward or back, or tilt it and bring the cage down. Want to add tubes to the cage, great. Want to change the engine cover look? Great. Variations are a good thing, really. It’s like the book is offering a recipe for, say, a cake. If builders/chefs want to add a little more or less sugar or butter, great! The point is, it’s a starting point, a known-good solution (or, it will be) to provide a fun safe competitive car that works, but individual variation is a great thing and can result in some pretty cool cars. As long as the suspension geometry isn’t changed, where the tubes go isn’t a big deal, really. But as some point… like about now, I have to stop experimenting with different chassis designs or the car will never happen. I want to move on, keep things simple, and let builders handle the individual variations. I hope this doesn’t come across as harsh; being a one-man show means doing everything myself but has the advantage of being able to decide when to push forward in spite of not achieving perfection on all fronts.

23 Nov 2008

This explains the thinking behind how the tubing drawings are evolving.

Since the basic chassis is complete it’s time to start a redraw to: eliminate inaccurate nodes, remove overlapping tubes, double-check that nodes are symmetrical, create individual tube assemblies, and start dimensioning everything. The overall drawing of the bottom tubes is complete though not the individual tube drawings, which brings up an issue that’s been nagging me for a while – how to draw the tube ends.

It would be great to have an exact drawing of each tube showing the precise shape of each end; cut them per the drawing and it all “just fits.” However, cut tolerances and welding distortion change the shape of the chassis, unless of course the chassis is assembled on a 10,000 lb welding jig. Since we don’t have that we tack-weld the chassis, clamp it together the best we can, and weld it up. This often results in hearing a loud “bong!” as the tube that’s being welded causes a tack-welded tube elsewhere in the chassis to let go due to the tremendous heat distortion. Once that happens it means the chassis has changed shape and exact-sized tubes aren’t going to fit. Kimini was welded on a fairly heavy jig which included 4″ I-beams (H-beams to you Brits!) Even then the chassis accumulated about 1/4″ of heat distortion, bent up at the ends like a banana. Part of the trouble is that after the lower chassis tubes are welded on the top sides, the chassis has to be unclamped from the table and turned over to weld the bottom. Having precise drawings does little good if a tube that’s┬á exactly 10.000″ long in reality having to fit into a space that might be 9.912″ long. This is one problem.

Then there’s how to convey to builders the shape of each tube ends; square tubes are easy to show on drawings but round tubes are much harder. Some chassis plans deal with this by showing tubes with the ends “unwrapped”. The idea is that a full-size paper template is cut out, wrapped around the tube, marked, then the tube cut along the line, and presto, perfection. However, I’m skeptical; there’s always some cutting error, which if the chassis is started at one end and built toward the other, can accumulate into a surprising amount, and then there’s material thickness. Wrapping a paper guide around a tube gives the correct line to cut, if the wall thickness is infinitely thin, which it isn’t, or if the tube junction will be 90 degrees, which it seldom is. What happens is that facing inside surfaces of tube junctions don’t fit up because the ID of the tube prevents the edges from properly mating up, and the problem becomes worse the more acute the angle.

Because of the above, tubes will be dimensioned but not unwrapped. Square tubes will have basic dimensions while round tubes, thought they’re very hard to show numerically, are trivial to fabricate if a tubing notcher is used. Since inexpensive┬átubing notchers are now on the market it’s reasonable to require one. With a notcher, only the length of the tube and angle of the cuts are needed; the exact path of the cut on the ends of the tube becomes moot <em>and</em> the notcher deals with the wall thickness issue.

Somewhat related is the issue of customized tubes; no two Midlana cars are going to be the same due to different drivetrains, seat choice, pedal placement, engine cover design, etc. This will be dealt with on the drawings by colored tubes where placement depends on the parts or style the builder uses. For example, on the drawing of the bottom tubes, there are two diagonals stiffening the bottom of the engine bay. While they will be dimensioned they will only correctly fit a Honda K24 drivetrain. For other drivetrains they’ll have to be different in order to miss the oil pan and transmission bell-housing.

Brackets are missing from the drawings for now since it’s too early to know where exactly they go. They’ll be added in due time though for the most part, it’s pretty obvious when a bracket is needed when the time comes.

22 Nov 2008

My brother took his Super Stalker to its first trackday event at California Speedway in Fontana, CA. He had a great time (other than being sore the next day.) The car did well other than a miss in 5th gear that may be hard to diagnose, and the right front tire seems to have too much camber which is odd. He did just under a 2-minute lap and was barely outpaced by a 300 hp Arial Atom. Given that the Atom is supposed to have 25% more power (versus the Stalker’s 240 hp) and had stickier tires it should have walked away from him but didn’t. Than again much of driving is mental. My brother – and other drivers – admit that while their cars could go faster, driving on a superspeedway is mighty intimidating, having a wall to the right that’ll stop you like a bug on a windshield. Just how far out do you hang the back end at 135 mph when there’s no national championship on the line, never mind being older and more aware of one’s mortality? Anyhow, he had a good time and the car did well.