Tag Archives: Sprint-T

Never stop thinking

I can’t, it’s part of my condition. I have the frame almost complete in design phase, so what do I do? That’s right, I change everything forward of the firewall.

I’m trying to get unsprung weight down so the tires will be easier to keep on the road over bumps. This means making everything between the frame and the road lighter, and one way to do that is indirect springing AKA push/pullrod suspension. The thinking is that the connecting bits between where the push or pull rod attach to the moving part of the suspension are : a. lighter than the spring/shock unit, and : b. more sprung than unsprung weight. The coilovers on a rod-activated suspension are believed to be 75% sprung weight with the same said for the rocker. The rod is 100% unsprung, but the total of the rod, unsprung weight of the rocker and unsprung weight of the coilover is (hopefully) less than the unsprung weight of the direct-acting coilover. Another thing is the motion ratio, or the ratio between how much the wheel moves to how much the end of the shock that moves the spring moves. With the rocker arms the effective wheel rate can be anything just by drilling the hole where the shock bolts to the rocker a different distance from the pivot, and a long travel softly sprung shock can be used on a very stiffly suspended car.

Now what this does is change everything that connects the front axle to the frame. There are no spring mounts hanging out in the breeze and everything is tucked up tight. Google a shot of a modern F1 front end as an example. This means the parts of the frame that would have interfered with the tires when they were steered aren’t there any more, but it also means that I don’t have the same radius of gyration to work with as I would with direct springing. And since torsional stiffness is proportional to the 4th power of the radius of gyration that’s kinda important. Like this is going to make the front a whole lot less stiff unless I add a lot of bracing to reduce the average length between pivots or whatever the technical term is for bracing the heck out of the structure. It has been more than 40 years since my last structures class, the one where we built a scale model bridge with 1/16” square balsa and a piece of Bristol board for the road deck, so my terminology is a little fuzzy. Anyway, major loads would be carried by the .060″ wall tubes, and also the braces since I could use the cut-offs from making the major pieces of the frame.

Another thing on my mind has been replacing the heavy steel tube axle and steel spindles with a carbon fiber axle and aluminum spindles. I have even been heavy thinking about how to construct said CF axle. What brought this on is I have had to move the steel axle I bought back when I thought I was going to be using the minivan engine and drivetrain, every time I needed to go in or out of the office, because Mrs the Poet didn’t like where she put something and insisted it belonged in my office. So because leaving the axle on the floor was a tripping hazard and because it blocks access to the door when leaning against the wall, the axle has to be moved every time I go in or out of the office. And I have come to realize that it is freaking heavy and detrimental to handling because it is 100% unsprung weight, and will work to get the car built but needs to be replaced at the earliest opportunity. Between the axle and the forged steel spindles we are talking about 80 pounds (+/-) of unsprung weight on a 1450 pound car. And replacing it with a 16 pound axle carrying 2 7 pound spindles. So replace 80 pounds of unsprung with 30 and the hubs that fit those spindles are lighter than the ones that fit the spindles I have now, by about a pound.

And final note, I screwed up again in my last correction. I used an old value for the rollover hoops of 16 feet back from when I didn’t have a good idea as to how far the rollover structure had to be over my head. The actual value is about 11 feet which takes a metric buttload of weight off the frame. Well a little bit because 5 feet times 1.75 pounds per foot isn’t much, about 9 pounds per hoop, or 17.5 pounds total. But every pound, every gram, adds up, and the fewer there are to add the lower the total will be at the end of the project. Also the less metal I have to buy, the less money I need to spend. Also important.

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Ooops.

I made a statement two posts ago about revamping the frame design adding 30 pounds to the car. That was an error based on the fact that I added or relocated 8 frame braces during the redesign so I figured the weight for all 8 changes. Then last post I stated the empty car weight was 1450 pounds which was accurate based on calculating the length of every frame member and multiplying that by the weight per foot of tubing for that size tube.

There are 2 different tubes used in the Sprint-T. Most of the frame is made from 1.5″ X 0.060″ wall round DOM tubing, except the rollover structure which is 1.5″ X 0.120″ for rules compliance. Now because of the design there is room for interpretation as to where the frame ends and the rollover structure begins, but I’m taking the interpretation that any diagonal braces that touch the rear hoop inclusive are rollover, and everything else is frame. There are a lot of tubes in the frame, the front and rear hoops are the longest at roughly 16 feet apiece as they wrap around the body, and then the upper and lower frame rails at roughly 100″ each for a total of 400″ or just under 34 feet total. Then there are the front suspension mount, the internal diagonals for the rear hoop, the bracing inside the top halo, and the rest of the diagonals that connect everything together to make one solid structure. That comes to another 40 or so feet in mixed sizes.

So, all told the Sprint-T frame carries a few more pounds than the Speedway kit frame, but is orders of magnitude more stiff, both in bending and especially in torsion. The Speedway frame is 2 hunks of 1.5″ X 3″ X 0.120″ wall rectangular tubing with round tube crossmembers to hang the engine and transmission from. Adequate in bending loads under all circumstances, but lacking in torsion to be charitable. It is an upgrade from the Model T frame or any OE Ford frame used back in the day, but that is damning with faint praise. It was designed as a cruising or freeway frame, not for racing and especially not for racing around cones set up in a parking lot. It was not made for installing a rear roll hoop that meets SCCA safety rules for one thing and as an open car (no roof structure) it would be required to have a full cage, and there is no place to mount the front hoop either. Now there is a place to mount a drag race style cage, but not an autocross legal cage. This is annoying because using the kit frame would make the build so much easier. And probably cheaper, too. There would be work involved with relocating the suspension pickups to prevent the tire-lifting behavior of the stock rear axle and the resulting power oversteer in tight corners even with radical bigs-‘n’-littles tire sizes (I saw a YouTube video of a bucket getting sideways off a corner with 14″ wide rear tires and 3″ wide fronts).

Not feeling good today

I did several days in a row with 2-3 miles walked with allergies and now my back is complaining, not loudly, but making its presence known. This is my notice to take a break and not overdo things. Also after several days of good behavior the “m” key on the keyboard is acting cranky again, and Google keeps sending me notices that my OS is no longer supported.

Now this can be dealt with in many ways. I can buy a new computer (ha, ha), I can get the keyboard fixed and install Linux, I can install Linux on my Dad’s old computer after I drag it out of the box it has been stuck in since 2012. And one of my friends might have an old laptop they can give me. First I need to call and find out how much getting the keyboard fixed will cost, then work from there.

On the Sprint-T I have been contemplating a frame revision that would add maybe 40 pounds but provide a major increase in torsional stiffness. It isn’t as pretty now, but it will be much more tunable for handling. Basically what I did was make sure all the possible load paths were continuous and triangulated in all 3 dimensions and clear the body. It was that last requirement that has been the monkey wrench in the works, as the body is 34″ wide underneath and 45″ wide at the top and there has to be a structural member to meet the mounts underneath or the body would have not crashworthiness. That’s not the problem by itself, the problem is the diagonal from the top of the rear roll hoop to the bottom of the front roll hoop. Now I thought I had this solved a while back, but when I traced the load paths I found it went all wonky at the front roll hoop. The loads went from in line to bending around the front hoop because of having to have a member under the body and the diagonal snake around the bowed-out sides because there is no straight line from the top of the rear hoop to the bottom of the rear hoop. Interestingly enough, there is straight line access from the top of the rear hoop to the middle of the front hoop, and back to the bottom of the rear hoop, but that places bending loads on the front hoop unless there is a corresponding member from the front suspension support to the front hoop. And that is what increases the weight so much, about 8 additional members about 50″ long each weigh 30 pounds total plus the gussets at each intersection add about 8-9 ounces each end. If I could reduce the size of the structural members any more without worry about damage from people leaning or climbing on the car I could make it lighter, but I have to use the frame as a ladder to get in through the top of the cage.

While I have been writing about fixing the mistakes in my frame I had a show about engineering mistakes and fixing them on the Science Channel on the Tee Vee. Some of those mistakes cost hundreds of millions of dollars to fix, some couldn’t be fixed for any amount of money. I’m just glad I’m finding my mistakes before I spend money building unusable junk.

Happy Beltain!

Today is the arguably the second-biggest holiday in the Wiccan liturgical calendar, after Samhain (pronounced Sow-when (more or less, depending on your particular accent of English)). There’s a rude rhyme that goes with the holiday about how the usual weather on the British Isles is warm enough that sexual activity in the out-of-doors is unlikely to cause death by exposure after this date. If that’s what you’re into, enjoy. Here in TX we have been enjoying that particular activity for over a month now.

I’m not going to explain the holiday here, Witchvox used to have a nice explanation of our liturgical calendar and what the holidays meant to our ancestors, but that was then and this is now. It’s still a celebration of the Earth and its fertility and ability to give life, but we don’t have sex in the fields to show the plants how it’s done. My eyes and nose are ample evidence to plants already knowing how to have sex, and that they are unable to keep their sexual activity to their own species. They don’t need any training on this. I’m just going to say if that’s your thing then party on dudes.

I’m still thinking about the Sprint-T, and how to wrap the cage and frame around the body without any need to cut the body for clearance except the firewall and the bottom where the engine and drivetrain make that a requirement. I have also been looking real hard at the Winter’s catalog for lightweight alternatives with the required 5″ driveshaft offset to match the engine and reduce u-joint angularity. So far the best I have found is the 8″ with the aluminum billet locker as the best compromise between street manners and light weight and also able to handle the HP of the mighty Pentastar. The 7″ is lighter but might be marginal with a Pentastar for street driving and autocrossing. The setup for one or the other would work, but trying to do both requires changing too much going from one to the other. The harder ring gear that would work on the street is just too brittle for the shock loads of the autocross standing start. Think drag racing with 1st and 2nd gear left and right turns and you’ll have a good idea of the stresses of autocross, but the materials that work for that are too soft for street driving and will wear out quickly. The larger 8″ ring gear has enough inherent strength that the harder material will work for both applications.

Well I need to put this one to bed while it’s still Beltain.

Still thinking about the Sprint-T and Happy Earth Day

I was walking and thinking about the Sprint-T. The main thing I was thinking about was torque control of the rear axle and how to do it without spending any more money than I already have. The current plan and existing hardware for locating the rear axle and also mounting the springs and shocks uses a part called a “swing arm” that I have shown a picture of in the past.
These are MY swing arms
Well, I can slightly modify one piece to run a steel link with rod ends that runs from a bracket on the rear axle to a bracket on the nose of the swing arm. This would triangulate the swing arm and make it a rigid link that would prevent the axle from rotating under power and because it’s offset to the right also plant the wheel that lifts when power is applied. Basically what it amounts to is welding a pair of plates to the nose of the arm with a hole to run the mounting bolt through, then running the previously-mentioned link from a bracket under the axle to the nose of the swing arm. Now I couldn’t do this for the 3000 pound car this part is intended for, but for ~1500 pounds and 300 or so horsepower it should be adequate. And if it isn’t the part that would bend or break is not very expensive and is easy to replace, that being the rod end on the front. So I guess I would need to keep a pair of those rod ends and a pair of generic vice grip pliers to remove the broken bits from the swing arm for a roadside repair. But I should be good because the Speedway catalog torque arms for this size vehicle use the 5/8” rod end while this part uses the 3/4” rod end which is up to 30% stronger. And another benefit of controlling the rear axle rotation like this is the ability to almost instantly change the pinion angle from street to race and back again. It’s like a turnbuckle to control the pinion angle.

And with a torque arm this short I would need to run brake floaters to prevent wheel hop under heavy braking. The floater decouples the brake torque reaction from the rear axle and sends it directly to the frame via another radius link, making the rear frame area visually cluttered but dynamically simple. Because the Sprint-T has such limited wheel travel short links from the brake floater to the rear hoop of the roll bar will work in spite of there only being 5″ from the center of the axle to the roll hoop. Then instead of using spring rates and shock absorber settings to control the brake reaction at the possible detriment to handling and grip while turning I can leave those settings for hustling through the corners. And these links will be under very little load, because the torque reaction under braking would be forward from the axle, while the traction reaction from the axle would be backwards. So lightweight aluminum links would work fine between the floater and the frame.

And while I realize my little project isn’t as earth-friendly as riding a bicycle, it’s still an order of magnitude better than anything on this list . So, have a happy Earth Day anyway.

Another update for Sweatcoin app, and weather

OK I’m taking a walk tonight to see if this latest update fixes things, but the app is tracking steps again around the house. I think maybe I’ll take the opportunity to buy a lottery ticket, as I keep telling Mrs. the Poet, the odds of winning are almost zero if you buy a ticket, but absolutely zero if you don’t buy a ticket. And we are among the teeming throngs who could live a comfortable life if that chunk of income was shifted down a bit.

We had a dry line move through this morning but it didn’t wake me up, and another forecast for this evening, but not much rain near Casa de El Poeta. It was mostly wind and lightning according to Mrs. the Poet. The cats were not even bothered by this morning’s rain, and I can’t find any evidence of the rain outside.

And just for a few minutes yesterday I was considering centerline seating on the Sprint-T to see around the engine, since raising the driver’s seat enough to see over the engine would also raise my butt high enough to clear the transmission tailhousing. But that was quickly discarded because of the previously discussed raised Center of Gravity issue. Also the issue of running the steering from the center to the steering box on the left side of the chassis with the engine in the way.

But other than that I don’t have anything worthwhile to post today.

If it sticks out, it sticks out

I have made the decision. The engine will stick up, out, and sideways and I will look around or over as required because I put the bottom of the bucket body even with the bottom of the car. This will get the C of G as low as possible for best handling, and since handling is the #1 priority for this car inside the superset of [Win Goodguys Autocross], compromise will be made that prioritizes handling over things like seeing out of the car and gas mileage. The main reason the Sprint-T even exists as a concept is participating in autocross and solo racing and winning Goodguys. I’m not happy about not being able to see around or over the Pentastar leaving a big blind spot to the driver’s right front, which means the Sprint-T is not going to be a daily driver. And using it for trips between races is going to require some method of seeing what’s behind the engine. Maybe having two different seat inserts, one for racing and the other for just driving around? That would mean the shoulder belts wouldn’t work for the “just driving around” insert because they would put my shoulders too high to be safe. And the SCCA rules about roll bar heights above the driver’s helmet would mean that when my eyes were high enough to see over the engine just driving around the halo of the roll cage would be right next to my head. Not good, so the simple expedient of raising the driver’s seat is out. But the alternative is raising the body and everything above the body by roughly 7″ which in turn raises the Center of Gravity, which reduces speed at ultimate grip. And that runs counter to #1 priority in the superset of reasons to build the car. So, more thinking is required on this.

In other news my Sweatcoin app is completely screwed up and stuck at 100 Sweatcoins, not even counting the bonus coins for clicking on ads in the app. And I can’t buy anything in the shopping section of the app with 100 coins, except discounts for things I don’t want. This makes the app pretty much useless for me until I can start collecting more Sweatcoins.

On a tangent, I keep hearing a violin instrumental cover of the Twisted Sister song “I Wanna Rock” in a TV commercial, but I can’t see to find it to listen to minus the smarmy commercial voice-over. I really want to find it as a stand-alone. The concept sounds as crazy as AC-DC played on cellos and we all know how that turned out. So far all I can find is this duet with guitar which is good but not the music played during the commercial. Which I was able to find. Not as good as finding the music separately, but at least I know the name of the violinist. Damien Escobar. Now I need to find a clean track of the whole song minus the smarmy announcer and more than 60 seconds long.

Seriously!? Again?!?

I was out and about again today after seemingly getting the Sweatcoin app back up yesterday. Well it happened again, zero steps detected all day, in spite of a 1 mile stroll in the middle of my travels. The stroll was to get from my bank to the nearest Jack in the Box for the BOGO special on the Ultimate Cheeseburger, today only and only in TX (suck it OK!). But as nice as half-price half-pound cheeseburgers are it’s still annoying to not get my steps counted when I almost have enough Sweatcoins to cash some out.

The other reason to go out today was the reason I stopped at the bank, Mrs. the Poet had a check to deposit for getting the sink fixed. And if there’s enough left over after doing that I get to get a massage. I don’t know about there being enough money for a massage, but there should be enough to get some pork chops and ground beef (the person sending the check suggested buying some meat).

I mentioned last post about the Locost homebuilt Lotus 7 clone community, and shared some pictures of Locosts. Now I’m not abandoning the Bucket, but you have to admit the Locost would solve a lot of problems I’m having with packaging on the Sprint-T, like getting the body mounted, and trying to see over and around the Pentastar engine, keeping the CofG low and the whole nose thing. TBH the whole engine-offset thing has really messed with the nose of the Sprint-T, where hiding the mess under the Locost’s hood really cleans things up. The Sprint-T will have the engine hanging out the passenger side of the body because of the pinched firewall on the ’23 T is barely as wide as the engine. The 5″ offset for balance can’t help but hang the right 5″ of the engine out of the right side of the nose. I suppose the idea I had to “unpinch” the nose that I demonstrated with “Stick-aided design” would help with this (cue the picture re-run).

It's sticks taped to the body, what were you thinking it was?

Enormous amounts of bodywork aside the smooth cowl modification would have done the job at hiding the engine offset nicely, especially if accompanied with hood sides and top that keep the engine hidden but adequately ventilated. And “adequately ventilated” means just enough metal between the louvers that there is a strong semblance of structural integrity without blocking any airflow.

Here’s that side view with that measuring tape

I mentioned a while back I had a picture of a Pentastar with a tape measure in the picture for reference to scale the picture. Well here’s the picture for you to use.

the measuring tape is across the top of the bottom of the engine stand

Hmm, it doesn’t look as tall scaling from the side. If I measured right I might be able to get the engine inside the upper edge of the firewall without having to raise the body. The initial calculation was 22.5″ from the bottom of the bellhousing flange. I could make the hood top even with the windshield bottom and have like a cowl induction scoop.

put the top of the scoop even with the bottom of the windshield and just have the hood sides even with the scoop sides

I think there might be some image problems here, the side view scales to exactly 18″ from bellhousing flange to crank pulley, and published data has that at almost 20″. I think the camera is fitted with a wide-angle lens that distorts the image, which means the previous scaling on the rear view is also suspect since it was shot by the same camera. I’m going to have to see if I can contact the photographer and ask if he ever measured how tall the engine was before he installed it in the car.

That should do for tonight with this one note: There was a published one day only special at the local grocery, $0.99/gallon milk Sunday only, so we skipped buying milk at $1.99/gallon yesterday. I walked to the store a mile away to get the good price today, and after I walked a mile there and another mile back, I checked the register tape. I didn’t check before I left because I also bought half off discount Cadbury Creme Eggs and there was a change in the total on the display that matched the $1 off the milk. So I didn’t check until I walked the mile home. Now I need to take the tape and the ad back and get the $1.

Well I have been thinking about the Sprint-T

I have been thinking about cooling for the Sprint-T. I’m going with the assumption that the 22″ wide catalog radiator is going to be roughly equivalent to the OEM radiator, but for insurance against overheating I’m going to stuff as much oil cooler in the nose as will fit. The boxes still need to be moved around a bit but there is room and airflow to stick a cooler sideways so that the air comes in the front and flows out the driver’s side.

Other things I found out include the Pentastar engine is identical across a model year except for the intake manifold and oil pan for packaging under the hood. The only reason the FWD versions are rated at 245 instead of around 300 is the 62TE transmission can’t handle any more than that. If I grab an engine out of a minivan, swap the intake manifold to a RWD manifold and the ECU loaded with the RWD engine map it would make the same power as if I pulled it from the RWD car/truck. That really expands the available engine pool. And I’m still looking at printing up a new manifold with dual throttle bodies to get a lower profile and maybe eke out a few more ponies on the top end so that I can maybe not shift a time or two on course to save that odd thousandth of a second on the track.

And I’m spending the weekend with the cats because Mrs. the Poet is going to commune with Nature away from me. And Winter is making a comeback as we drop more than 40°F between yesterday’s high and tomorrow’s low, even worse if you factor in the “feels like” temperature forecast of 15°F. It’s going to be “fun” getting the cats back in so they don’t freeze.