Tag Archives: technical stuff about building cars

My biggest impediment is my sense of esthetics

My main guide to engineering is the math, but after that is my sense of engineering esthetics. And sometimes that gets in the way of finishing a design. Seriously, the single 3″ tube would have worked fine for the de Dion suspension, but a truss would weigh less and be stiffer, by a small amount on both counts. And the new truss is much simpler both to build and to mount than the previous truss of 0.5″ thinwall tubing with a plethora of tiny triangles in two planes as it is just 7, 1.5″ X 0.120 wall round tubes in a single plane. The tube diameter and wall thickness are enough to hold the toe and camber alignment while the truss is strong enough to take all the vertical and horizontal forces with a huge safety margin. The truss weighs 20 pounds with brackets, not including the filler wire from the welds. This compares to the 3″ tube which comes to exactly the same weight but not as stiff vertically. Or as pretty to look at, which as I wrote earlier is an equal criteria after weight.

I mean face it, the 3″ tube would work just fine and probably less than 3 people out of 100 would be able to feel the difference in stiffness compared to the truss. Even fewer than that would care about the looks of the truss compared to the single tube. TBH even I am just the slightest bit ambivalent about the difference in appearance between the truss and the single tube. There is the simplicity of the single tube across the back of the car, but on the other hand there is the zen-ness of the collection of triangles running across the back of the car, even if it is hidden by the bodywork for aerodynamic reasons. There is also the fact that I can lower the roll center by almost 2″ in the rear to reduce oversteer slightly with the truss. And finally there is the cost issue, a single 58″ 3″ X 0.120 wall tube is less than half the price of the 132″ of 1″ X 0.120 I would need for the truss.

And even while I’m thinking about the rear suspension I’m still thinking about the cockpit and a possible roof and side windows. Mrs. the Poet is still saying there is no way I’m going to be able to get in and out going through the top of the roll cage after climbing the side of the frame. I have zero doubts about getting in and out of my own car, if for no other reason than I will have lots of time to use the frame as exercise gear to get my upper body strength up. Or I could screw together some black pipe for a dipping rig and chinup bar and continuously build my upper body every day. 😀

And I think I need to go to bed now, and so become the Nighty Knight.

Apologies for the radio silence

This has been A Week. Excuse me this has been A Week. I spent all day Monday on DART or DCTA buses or trains to do that echocardiogram thing. But I did see an interesting car.
I think this was a NASA (other NASA) event car

I got to watch my heart beating again while they did the echo, which was cool.

Tuesday was go to the lab rat and get the 24 hour BP monitor and the jug to collect my urine for the next 24 hours, and also I got hit by a huge blast of grass pollen, so bad that when my allergy pill took effect I fell out of my chair trying to do a post which I discarded because it made even less sense than that post I did while dehydrated and tipsy. And how can I tell you how much fun it is to tote a jug of your own urine around? Next paragraph. Anyway I didn’t hit anything valuable or breakable on the way down out of the chair, so I counted my lucky stars and decided to sleep it off in bed for the next 2 hours, which didn’t prevent me from falling asleep early that night

Wednesday was get rid of the half-full gallon jug of urine, and the damnable blood pressure monitor that was squeezing my arm to death. The jug got a lot of stares on the bus with the biohazard sticker and the “Danger Acid” sticker. Then it took 2 tries to draw blood. I think the needle went through the vein because no blood would come out with the needle in and when they took the needle out it wouldn’t stop bleeding. Then I got stabbed in the other arm. After lunch I went to a place that does a 45 minute leg and foot massage with a 15 minute back massage for $30. I felt much better after that than I usually do after the full hour on a full body massage. Then I was going to get a haircut, but there was a wreck on the Tollway that made a normal 20 minute bus ride almost twice as long, which made me miss my connecting bus which got me to the stylist after my stylist already left for home. So my head is still shaggy. “How shaggy?” you ask. Well my back hairs go all the way up my neck and the only way to tell head and back hair apart is the back hair is going white already, and slightly more wavy than my head hair. And my character in Shadowrun just integrates the back hair into his regular hair style, flattop all the way back and down like a horse’s mane.

And during down time I did some more research and changed the race tires again, for a set of Formula Atlantic tires. Good grip for a car about the same size and weight as the Mid-Bucket and I can find wheels that fit the tires and the bolt circle of my car. Amazingly it is way easier to find 15 X 14 wheels with a 5 X 4.5 bolt circle than 16 X 12 wheels. So the front wheels will be 15 X 10, the rears 15 X 14 and I may be able to get the car balanced without adding an antiroll bar.

And it is almost dinner time and I need to get cleaned up.

Late Night thoughts

I’m awake at 0424 and thinking again, about enclosing the cockpit to protect the instrument cluster &tc. I was also thinking I could use the HDPE to make a fake rag top. Using the white HDPE to make the roof hatch look like a “regular” Bucket top until I use it to get in the car, with the side windows to make it look like a “normal” car.

I’m also trying to figure out how and where to mount the mirrors for street driving, and I’m leaning to a pair just inside the windshield posts for my side view mirrors and another pair on either side of the seat for directly behind me.

I’m going to go to bed now and let this ferment a while, then come back and complete it.

OK I’m back it’s right at 1800 and the ideas about the top and windows have been rolling around since I got up and started sipping coffee. Part of the problem is ventilation. Gluing the side windows in would be easier and better looking, but leaving the windows shut in the summer while waiting to make a race run would make for a very uncomfortable car. Somehow I have to keep air moving through the car even when it is not running. Maybe a solar powered fan of some kind? And definitely hook up the AC for summer driving. Fixed windows and top with no AC would be looking for heat illness issues especially here in TX during the day. And with the Goodguys event just down the road in Ft. Worth I will definitely be driving during the heat of a TX spring and summer.

Mirrors are another issue, but I think 4 small ones should do the job. Put 1 each at the lower corners of the windshield for side views and blind spots and 2 more on either side of the seat at the top of the windshield for direct behind views and I think we’re covered for that. Just make sure the field of view is not obstructed and I can adjust the mirrors to work as long as they are not obstructed.

Now how to construct this top, well I’m still figuring that part out. The back part was easy to figure out. Most of the back will be a flat window except the part that wraps around the corners of the body, which will be molded to the radius of the corner all the way up to the top surface just like it was a rag top, and the side part will be on a diagonal like a traditional rag top.
Notice the way the side of the top goes up and to the back?

And this in white.
Famous T-Bucket from the '60s

The top on mine will more closely follow the top picture in that the top will be level front to back, but much lower because I won’t be sitting as high in the body as the seats in that car.

And now I want to go for a walk, so Bye!

Still thinking (know where your local fallout shelter is located just in case)

One thing I have been thinking about is the rear suspension. Well two things actually. The first thing was it saves less than $40 for me to use the steel swingarm/spring mount in the Mid-Bucket suspension, and it seriously complicates the rear frame. The second thing was that putting the rear spring that far out on the suspension complicates the roll stiffness bias. Putting enough spring to give the right rate for a 2 wheel bump over the end of the axle just makes the roll rate too high for the light front end even with the front springs almost on the kingpins. Seriously I’m going to mount a spindle with the steering arm on the axle and put the side of a pencil against the steering arm with the point against the axle and turn the spindle back and forth and watch the mark on the axle. The point that is furthest away from the kingpin boss is the closest point of the lower spring mount on the axle. That will give me the most front roll stiffness I can get with just the springs. It still won’t be enough to balance the car with the springs mounted on the trailing arm or to the rear upright. So I either have to use a front anti-roll bar, or I have to mount the rear springs closer to the centerline.

Mounting the rear springs closer to the centerline means making the de Dion truss strong enough to handle vertical forces. I have been thinking about that, and if my sums are right putting a truss of 1″ square tubing with 0.5″ round verticals and diagonals on top of the 0.5″ round tube truss would support the rear of the car with adequate safety margin. “Adequate” in this context means no damage if I hit a few pot holes or slide off the track during a time attack run, it doesn’t mean taking the car off-roading in the desert.

The other thing I have been thinking about is how light I could get a front-engine bucket like the Sprint-T. By adapting an A-904 Torqueflight to a Pentastar V6 with a steel 9″ Ford rear axle I could get 1450 pounds without even trying hard. Start swapping out an all-steel 9″ for an aluminum and magnesium quick change in the rear axle and carbon fiber in the driveshaft and we are looking at a 1400 pound bucket with 305 HP on 87 octane regular without changing anything in the engine or calibration. Get serious about making the frame lighter with aluminum instead of steel and a space frame instead of a ladder and maybe 1375 pounds. About 4.5 pounds per HP. That’s like a 750 HP Corvette or Viper running on Regular gas. As in car*√-1, imaginary. Even with the frame from the Speedway kit we are talking a hot rod that could give anything short of a Hellcat or Z06 a run for its money 0-60 MPH, on 87 octane regular gas. There are 2 ways to make a fast car, 1) lots of power and 2) no weight. 1) is fast in a straight line, 2) is fast everywhere. I think I like 2) better.

Incidentally, did I ever say how I figured out that I needed to use different size tires and how different they had to be? The book Chassis Engineering has a graph of grip over load for a typical race or passenger car tire. The problem here is it’s a graph for just one size of tire, and has to be scaled for a different size of tire. The way I did it was to leave the shape of the graph pretty much alone for the big tire and then scale the grip by dividing the load and grip by the ratio of the squares of the widths between the tires. F’rinstance the street and street tire autocross will use 195/50 fronts and 245/40 rear tires so the graph was scaled down by a factor of 1.58. This is not perfect, but it is close enough that I can come close to getting the balance right with just the springs and a light anti-roll bar to make up the difference of not having the perfect spring rate. For street and highway driving I will need slight understeer for stability, but for the autocross I need a slight oversteer for better turn-in and rotation through the middle of the corner. I’ll be able to do this with just a swap of shocks and springs which I have to do anyway because I need a lower ride height for autocross than for the street. Theoretically I could do that without changing springs and shocks but that would require carrying around a slew of scales and platforms and adjusting before and after the competition, or I could just do that once and pull those shocks off and put them in a case with labels as to which one goes on which spot on the car. Instead of spending time adjusting and re-adjusting the spring seats to lower or raise the ride height and move the weight around to balance the car in turns, I do it once at a test track and then just swap the coilover shock/spring units at the race from street to race and back to street in just a few minutes instead of the hour or so (if I get lucky) each way adjusting the spring perches.

And I have wandered around the verbal landscape long enough, time to wrap it up and do something else.

Opus the Unkillable

Design is getting down to brass tacks

That is a very archaic turn of phrase in the headline, it means discussing the ornamentation on a custom saddle and dates from at least as far back as the 17th century. Today it means getting to the fine details of a deal or design. As of this point the front end is approaching brass tack territory.

I went back to earlier drawings of the front end and found a couple that placed the crossmember above the front axle, but not as high as the one I discussed yesterday. So I went back to that and moved it higher, and also added the radiator mounts and body supports in front and hung the rack off the backside. I dropped the MD3 nose from the design in favor of making less drag and downforce with a nose made from the same HDPE panels the rest of the body is going to be made from. The right side of the rack might protrude from the body at full left lock but I don’t care at this point. That is a minor aesthetic point that is overridden by making the damned thing work right. There is nothing for it to interfere with on that side.

At this point I have started thinking about the cockpit design, specifically protecting the instrument cluster from the environment while parked outside, and making the cockpit tolerable at highway speed. Putting a roof on took care of most of protecting the instruments from condensation, rain, and bird poop. Further enclosing the environment with some kind of side windows will do a better job of preventing condensation and blown rain from getting to the instruments. I don’t know if that would be enough to allow driving in the rain, but it will probably do a lot for making the interior livable at highway speeds by reducing cockpit wind and turbulence. The original cockpit had no windshield or side windows with the driver wearing a helmet with a face shield all the time, even on the street. That was back when the car had a V8 in the front and the driver sitting on the left side of the cockpit. Now I’m even thinking about heat and AC 😇. There are races in FL during the winter that might be fun to run in, which means driving in winter, which means a heater. Driving in the rain means a fogged windshield which means a defogger which means AC of some kind.

I even looked up what sender to use on the gas tank so the gas gauge works right (10-90 ohm). Really this started when I discovered the entire instrument cluster came out as a unit. And that the engine and transmission controllers expected to find the instrument cluster before they would let the car run. Since I need a tach and speedometer and the computers know how to use the ones in the cluster and everything will need to be “unconfused” L8r, why not use the OE cluster? It saves having to buy those instruments later and figuring out how to make everything work together which is even a bigger hassle than telling the computer it isn’t in a minivan any more.

And now it is about time for my walk, so more thinking about random things.

Opus the Unkillable

I have Moose Trax on my shirt

Just opened a container of ice cream and within a few spoonsful I managed to drip it on my shirt. What, you think I would let a moose walk on me? Where would I find one? Anyway, the ice cream was very chocolate I mean good.

I’m still refining the design for the Mid-Bucket. Now that I have decided to use the rack out of the minivan I need a place to mount it where it won’t interfere with the suspension but still line up with the steering wheel, and if the mount could do a couple more things like hold the radiator, hold the shocks and springs, and keep the body panels straight… that would be one busy steering rack bracket. Well mission accomplished. The crossmember that holds the steering rack will be integrated into the spring mount and body mounts, for a more rigid structure and better handling. And less weight.

The crossmember sits in front of the front axle leaving enough room for the axle to move up and down with the steering rack suspended above the axle and the drag link going between the axle and the tie rod. A nice compact arrangement, that gets as much of the moving parts of the suspension away from things like gas tanks and body panels and leaves as much room as possible. The radiator mounts to the front of the crossmember and the cooling fans behind the radiator will be protected by the crossmember from the axle. The bellypan will go all the way forward to a splitter, with air going above the splitter ducted to the radiator and what goes below to the rear diffuser to make rear downforce. The splitter will be as wide as the wheel angle at full lock will clear with the side strakes from the splitter blending into the running boards and rear fenders for more downforce over the whole car. This will also clean up the airflow down the sides of the body and give highway gas mileage a tiny boost.

I think I mentioned how finding a 16 X 12 wheel in a 5 X 4.5″ bolt circle was driving me slightly crazy? I’m giving up on maximum grip in favor of sanity. The one (1) wheel I have found in that size and bolt circle is a heavy steel wheel meant for modern-day lead sleds. That leaves me with the 15 X 4 front and 15 X 10 rear option with a rear anti-roll bar for balance between the skinny front and massively wide rears.

And other things are calling me away from the keyboard, so it’s time for Nighty-Knight the dream warrior to take the stage. And if you get that reference you are really weird, and you should give yourself a pat on the back.

Opus the Unkillable

It’s ‘Dega baby!

Just finished watching the Xfinity race from Talladega. There were lots of wrecks but not while I was watching. I kept coming back to the aftermaths instead of the actual wrecks. I don’t like wrecks, I hate seeing good race cars torn up, I’m also not very happy about seeing crappy race cars torn up. I mean sure I am less unhappy about crappy cars getting torn up, but at the Xfinity and Monster Energy Cup levels there really are no “crappy” cars, just “less perfect” cars that could run just as fast with a few adjustments. Part of that is rules, part is the teams are just that good.

Watching the Xfinity and Cup Series is part of my inspiration for both the Sprint-T and the Mid-Bucket. Also I watch YouTube videos of Goodguys Autocrosses from recent years and SCCA Solo events that have Modified category cars for when I run slicks. Speaking of slicks, I just can’t find 16 X 12 wheels in my bolt circle at a reasonable price, so that means the 6″ Formula Vee rears on the front on the 4″ wide wheels, and the 12″ wide tires on 10″ wheels on the back.

And now the ARCA cars are about to run (on the tube at least, I don’t know if this is live or tape-delayed) and in about an hour is the IMSA race from COTA outside Austin. So then I start flipping back and forth. And I won’t have the split attention that will let me write and watch 2 races at the same time so I’ll go ahead and end this post.

Dangit, that won’t work!

Remember when I was writing about lightening the power steering rack and pinion out of the minivan to take more weight out of the car? Well it turns out if I do that I won’t have power steering any more. Allow me to present a couple of images I found when trying to find dimensions of the rack.

The power servo is part of the rack instead of on the input shaft like on a PS box.

And this one off an actual 1996 Chrysler minivan.

Not much room to be cutting stuff off on that one!

So, minor change of plans. Since the hydraulic servo is part of the rack and there isn’t enough room to remove anything without destroying the servo, I’ll just be removing whatever still sticks out of the right side of the rack at full right lock (rack all the way to the left, turning the wheels to the right) and then sealing the end of the rack like before. The drag link will go on the left side of the rack so the axle will have less side-to-side motion as it travels. I mean sure I could run the drag link off the right side but that would require a very short drag link, which in turn would require a very short panhard rod to prevent bump steer from the steering. But this would then cause another form of bump steer as the short panhard rod moved the axle side to side on the 4 bar links. There are just so many sources of bump steer that the best you can do is eliminate the worst and minimize the rest of them as best you can. And in this case the biggest can be eliminated by making the panhard rod the same length and angle to the axle as the drag link, with most of the rest minimized by making the panhard rod (and thereby the drag link) as long as possible and as close to level as possible. And yes after considering the clearances involved the drag link is going top of the stack on the steering arm. That way I don’t need to worry about the tie-rod hitting anything like the gas tank or the steering rack.

And that cerveza? Bien. Even without the lime.

Opus the Unkillable

I did some more mocking up

One of the nice things about having parts on hand is the ability to use them to mock up the car and get a better handle on what goes where.

I really should take pictures when I’m thinking like this, but that thought didn’t hit my brain until after everything had been put away again. Anyways I marked the front axle for the centerline, measured out the distance from the firewall to the front axle on the floor and set the axle up on stands in front of the body and plunked my butt about where I should sit and checked out the view. The view was nothing short of spectacular. Setting the front axle the same distance from the rear axle and firewall as on the original Model T and using center seating will make this a good Solo Racing and autocross car. I can see both front tires and what is in front of them pretty good, better than any street car I have driven and almost as good as the autocross-spec Formula Vee I drove back in the ’80s. Now talk about a car built to dodge cones in a parking lot, that’s exactly what that car was built for. And it looks like my Mid-Bucket will be close to that good.

And now that I have the street and street tire autocross tires and wheels picked out I still need to determine the race slicks tire and wheel combination. I think I have the tire combinations narrowed down to three from two brands, two from Hoosier and the other from American Racer (formerly McCreary). Where it gets fun is finding wheels for the tires. Two of the combinations will work with pretty close to the same wheels because they use the same front tire by different manufacturers, the Formula Vee rear tire on a 4″ wide wheel with either a 15 X 7 or 10 on the back depending on which manufacturer I use. The other one uses a 15 X 7 in the front and a 16 X 12 in the back. This one has a much higher potential grip but is a cast-iron one to find rear wheels for. And unless I get the tune on the suspension right it will be slower than the other two. Such is the life of a hot rod builder…

Signing off for now

I found bigs and littles I can race and run on the street

At least until it rains, then all bets are off.

The tires (by Hankook) are not that bad in the wet, but put them on a 1600 pound car with brakes that can stop a much heavier car even without power assist and then add water in typical TX thunderstorm amounts and with a car that is naturally tail-happy… Wet weather driving will be done quite cautiously.

The main problem I’m having now is getting the right size wheels for the tires I chose, especially the front ones. You wouldn’t think 15 X 6 wheels would be so hard to find at a reasonable price, but they are. The rear wheels are comparatively easy, but where it really gets hard is getting both wheels in the same style and in compatible offset. In fact I’m having so much trouble finding the compatible offset I’m strongly considering using wheel spacers up front to make the mounted offset compatible.

That’s just for the street, for racing I don’t give a flying fig if the fronts match the rears as long as the widths and offsets are right and the wheels are light enough. And it is looking like the race slick wheels are not going to match styles at all, the front tires are 22/6.0-15S while the rears are 23.5/10-15S in a softer, more grippy compound. I’m definitely swapping at least the rear springs and shocks when I race SCCA so that I get a better balanced car. That and I’ll need to lower the car anyway as the race slicks are about an inch taller than the street tires which would totally screw up the undercar aerodynamics unless I dropped the rear back down to match the front. And since I’m swapping one set of shocks and springs anyway it won’t take but a few minutes longer to swap both sets. The time consuming part would get done beforehand as I adjust the ride height and set the damping on the shocks before labeling which corner they go on and putting them in some kind of carrying case.

And I have good company in having issues with controlling which way the car is going. Even the best hike the inside front wheel .

And on that note I close this post and bid you farewell.