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  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 tubing 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.

21 Nov 2008

Turns out that a set of good brand-name gauges approaches the price of some flat dashes. One big perk of some flat dashes is that they connect to the ECU, displaying the same values that the ECU is actually using versus only reading their own sensors. The advantage is that what the dash displays is what’s being used by the ECU rather than a copy. If there’s wiring or sensor problems it’s readily apparent instead of reading fine from the gauge’s sensor while the ECU sensor has a loose connection. Then there are the configurable alarms which is real nice because if any parameter has a problem it flags it Right Now rather than driving a couple more laps before noticing.

I’m not sold on this one way or the other but am surprised that flat dashes are getting close to being cost effective. On the other hand I read about unhappy flat dash users discussing flaky software (with some dash brands.) There is something to be said for the simplicity of traditional gauges though there’s plenty of time to think about which way to go.

20 Nov 2008

Here is Midlana with a traditional Seven rear end which looks pretty good. It has a convenient area on top to vent engine compartment heat yet not be visually cluttered when viewed from behind, and gives room to fully hide the muffler. However, the engine cover that builders chose will be entirely up to them due to strong and very differing opinions of what looks best. The book will provide suggestions but not dictate a solution since it’s clear everyone wants to do their own thing, which is great! The only question is if hot engine compartment air might swirl forward due to the low pressure behind the windscreen. Or, will air pressure be lower behind the car so it isn’t an issue? Guess we’ll find out.

What’s not yet decided is how much of the bodywork will be removable around the engine. It would be nice if the entire rear area could be removed: fenders, rear panel, and top cover, to ease access, something I didn’t do so well on Kimini.

19 Nov 2008

Odds and ends.

I’ve been thinking ahead about what gauges to use. I’d decided upon the combination flat dash and datalogger from www.race-technology.com. With Kimini sold and cash in hand it’s all too easy to go nuts and buy really cool stuff, and cool it is. A flat dash, all instruments nicely integrated into one package. Alarms on all the important parameters, a datalogger and GPS, what’s not to like – and then a funny thing happened…

First off, Midlana is an open car. The thought of having $1600 of dash and logger sitting there begging to be stolen bothers me. Then there’s thinking of it getting beat on by sun and no doubt someday rain. Then there’s something else – the economy. I’m surprised to admit it but what’s going on is affecting me, like millions of other consumers. “Do I really need this?” No. I’m becoming turtle-like, slowly pulling arms and legs into a shell in anticipation of an economic storm of unknown size. I guess I’m getting older and a little wiser, no longer as quick to spend money. Who knows what’s coming next year, the year after, or even the year after that. I think we’re watching history in the making – what’s that Chinese proverb/curse, “May you live in interesting times”? I digress.

So the current thinking is that there’s nothing wrong with old fashioned gauges. Looking through all the various tachometers it’s a bit surprising to end up right back with the Spa Techniques tach/speedometer that was used in Kimini. It has an odometer which is nice for road use (and just for curiosity.) A nice tach, shift lights, 0 – 60 timer, electronically calibrated, it works well. Stack has a similar “all in one tach” that also has two sensor inputs. However, at around $750 versus $350 for the Spa unit, it’s a no-go. For the $400 difference a couple extra gauges will work just fine.

Regarding the engine cover, there are a lot of very differing opinions about what looks best. This part of the build will definitely be left open for each builder to do as they please. I’ll provide suggestions but there isn’t much point in saying “do it this way” when everyone wants something different. I think it’s great that each builder will create a different car; why build a car with plans that dictate ideas you don’t like; I think variations are great.

The side inlets are proving difficult to model but there’s no much pressure to dump a lot of time into them. At this point it’s not so important to produce nice renderings; the ones already posted give a decent idea of where it’s headed. Seeing an actual car is more important that a CAD rendering. Time is best spent pushing forward with finalizing the chassis, dimensioning it, and moving toward cutting steel.

Headlights, wipers, taillights. Headlights, tradition dictates the typical chrome bolt-on units but there are some interesting alternatives now such as 2″ projector units, though they don’t include housings as far as I know. Today I saw some 4″ LED(!) “work lights” that might work as headlights but are probably not bright enough. Wipers, ugh, haven’t given them any thought; how much does someone drive an open car in the rain? However I realize most areas require them by law and it’s tempting to just specify hand-operated ones sold by hot-rod shops. We’ll see. Taillights will wait until later, too. While they aren’t a big deal they certainly change the appearance of the car. If they go on the fenders it pretty much dictates an external-mount style like the original Seven to stay clear of the tires. OTOH if they go on the body then just about anything can be used. However, they seem so far off I haven’t given them much thought.

And finally, I just got another e-mail requesting to be added to the pre-order list and thought I’d yet you know there is one… now. If you want to be on the list let me know. No, there’s no free gift for doing so, just the knowledge knowing that you’ll be the first to know the moment the book and plans are available.

17 Nov 2008

Using Sketchup components of a Caterham 7 posted to the internet by “terradog”, the nose and fenders were borrowed and rescaled to quickly create (very) rough renders of what Midlana will look like. And yes, I am partial to the burnt-orange color that’s been appearing on new cars.

There is some discussion about how to style the curved back panel. Thoughts are: nothing (no cover), painted aluminum mesh, aero shaped louvers, an aluminum panel with many punched louvers, or a more traditional Locost back end (thanks to Dean again for bouncing these ideas around.) Regardless what is used, good air flow is key. If there’s no clear styling winner then all will be presented in the book and builders pick their favorite – variations are encouraged!

The CAD chassis has been sent to a generous reader to run it through an FEA analysis. The results will only be approximate since stiffening by the attached panels isn’t being taken into account, but it should give a good idea if additional triangulation’s needed. It also has the benefit of not counting on the panels to be structural. One feature not dealt with yet are the side air inlets just forward of the rear fenders.

9 Nov 2008

Slow work churning through the rear suspension redesign, coupled with long hectic weeks at work.

Adding colors makes an enormous difference for clarity, so much easier to see things. With a rough model of the drivetrain in place it’s apparent why tubes are being run the way they are. Note how the transaxle differential housing extends rearward, preventing simpler triangulation. Hopefully – for the last time – the rear suspension is settling down; current total bumpsteer is less than 0.020 degrees over full suspension travel. A few tubes will change and a few are missing but the difficult ones are placed.  The diffuser has been enlarged, using otherwise wasted space, currently at 12 degrees. The turbo is approximately where it’ll go, though it’s unclear if it’ll be top or bottom mount.

The large radius rear curvature of the chassis is slighly larger than the rear fenders, visually integrating the rear curved deck and fenders, or that’s the plan. The rear wheels and fenders will be rendered to see if it looks dumb or brilliant.

3 Nov 2008

Due to drivetrain placement and the overall shape of the car, there’s really only one place the shocks “want” to go, just ahead of the axles. The bottom of the shocks attach to the lower trailing link, but the proposed upper trailing links run right through where the shock body wants to be. While the shocks <em>can</em> go there they would have to lean inboard to miss the upper arms, getting too close to the drivetrain. Since it’s unknown what drivetrains will be used it’s best to provide as much room as possible. So, the upper links are returning to A-arms…

Mitchell’s uber-cool BumpSteer program made short work of determining the toe-links locations, resulting in 0.016 degrees of bumpsteer from 1″ of droop to 3″ of compression, or about 0.008″ toe-change measured across the face of the tire. (A big thanks to my suspension advisor buddy – it’s great to have someone to bounce numbers off of who’s been through this before!)

I hope this stuff is helpful, though perhaps a bit dull and boring; weeks of going round and round to get everything to work together. Sometimes this means violating engineering practices, such as the lower rear suspension arm having the trailing link intersect the lateral link part way along its span. The shocks will attach near the intersection, feeding a large bending load into the assembly. As mentioned, it’ll be dealt with by using large OD tubing and overlapping plates, not a perfect solution but a reasonable compromise. The realities of using existing suspension uprights and clearances with the drivetrain and body sometimes dictate a less than perfect solution. It’s all about compromise, which are all over cars, one-offs, and even production vehicles. As long as the reasons are understood and a safe solution arrived at, it’s okay, and allows moving on with the rest of the design. This reminds me of what someone said during the Kimini build, about “walking a fine line between doing it right and getting it done.”

FWIW, the long lateral links provide near-zero vertical roll-center migration in roll – within 0.001″ over +/-2 degrees.