Tag Archives: Mini Sprint-T

Thinking about the Sprint-T again

Not a big think, because it’s a small but important thing. What I was thinking about was what to do about the top of the frame?

Just in case you missed it, there will be a structural bellypan welded to everything on the bottom of the frame for aero and structural purposes. The problem is that leaves an open space to catch water and debris that will lead to rust spots as the frame ages. Possible solutions include moving the pan to the top of the bottom frame members which has the advantage of making the body mount easier, but which requires mounting the engine 1.5″(38.1mm) higher and also leaves a nasty lower area as far as aero is concerned. Plus that just moves the rust out area someplace harder to inspect.

Anywho, what I was thinking about was using some of the HDPE plastic I have for the fenders and hood to cover the exposed gaps in the frame. Then as I was thinking about the bellypan on top of the frame it occurred to me that it would be much easier to make access panels from HDPE than from steel or aluminum, and I wouldn’t need to paint it. And if I did the HDPE on the bottom I could just hotknife the hatches from the HDPE and be able to reuse the cut piece as the hatch because a hotknife has a very small kerf. For the Mini Sprint-T it wouldn’t make any difference because I would do the same thing for either one, glue a piece of 0.01″ styrene to the frame between the tubes. Visually it wouldn’t be any different on the model, a flat surface outside the body is a flat surface outside the body. Flat is flat, model or 1:1 scale. The main difference is if I put the solid bellypan above the rails I would paint it to match the body color of Omaha Orange aka Schoolbus Yellow, and the HDPE is a different kind of yellow. On the bottom the difference would be the steel pan would be black and the HDPE would be the same yellow as the top, because it’s cheaper that way. Or I could go with the black HDPE because it ain’t that much more expensive, and I’m really not quite that big a tightwad. Or getting back to cheaper, the flanges and bits to mount the HDPE plastic might be enough to make the part of the frame that goes under the body smooth might be enough to not need to weld the pan to the frame for stiffness, and I could just go with HDPE top and bottom and save a few ounces. Not to mention HDPE is cheaper than steel for the moment because of the tariffs. We make HDPE here in the US so no tariffs.

Well, this is the second post today, and there was a lot of stuff in the first post what with all the pictures, so I’m going to bliss out to my trance mix and get some meditation in.

My steering box is on indefinite backorder

AFAIK Speedway Motors is having similar problems with China as I am in that what used to be a Sure Thing is now Vaporware. My steering box can no longer be considered a viable option, and the people I used to work for no longer have a working web site. E-mails sent to them come back as undeliverable and there is no solid date on stocking my steering box either. Both of us are up the proverbial unsanitary tributary.

Which means I can stop sweating about my bank balance getting below the amount due for the steering box order because it won’t be due any time soon. The good news is Speedway will honor the price I placed the order at including discounts in effect at the time of the order. The bad news is they have to get a new supplier and won’t be able to ship my order until they get the parts from the new supplier.

In other good news (really good, not sarcastic “good”) I got in contact with the person I got the LS7 I’m using to make the Mini Sprint-T to purchase another and a scale Powerglide transmission to build the A/Mod SCCA Solo Racer. I think I might have mentioned the LS/Powerglide combo a few weeks back when I was thinking about how to balance my weight against the powertrain weight from side to side with my legs in a pretty narrow footwell next to the engine and letting my shoulders hang out over the transmission so the total polar moment was as low as possible. Anywho, I decided to build a model because I’ll never be able to build the full-scale version while I’m building the Sprint-T. The plan so far is to have the left side exhaust run over the driver’s legs like the right side of a supermodified. And also to have insulating blankets between the manifold and the driver’s legs, like in the supermodifieds. With the short runs in SCCA Solo Racing that’s probably overkill, but it doesn’t weigh much and it increases the safety margin over just wrapping the pipes with exhaust wrap which I was going to do anyway because of the performance benefit.

Last thing before I drop this on you, the remnants of the hurricane passed far enough to the east that we only got one brief shower here that was dried up before I finished. The walk was dry when I went to get the mail, that’s how brief the shower was. Also someone dropped this link on me and I liked it, so I think I will pass it along.

I hope you had a happy and safe 4th

I went grocery shopping and since we can’t go outside with Mrs. the Poet yet, we had a fried chicken picnic in the house. I bought actual real chicken from the Deli at Tom Thumb, some chicken tenders, and some potato salad for the feast which we had after the races were over at Indy. Then I watched the IMSA race from Daytona while I was eating.

I got some really good information on the steering box while I was doing the last post so I will know how big a box I need to make to simulate the steering box in the Mini Sprint-T. Basically it’s a 5″ wide including the mount by 8″ tall by 6″ long box that I need to remove the bits that don’t look like a steering box from. Simple as creating the statue of David from a misshapen block of marble, little Renaissance Art humor there. I’ll have to do that in scale from plastic for the Mini Sprint-T.

I’m going out tomorrow to pick up a copy of Gran Turismo 5 from the local Gamestop for a literal pittance, $3 plus tax. If I get a day pass the bus pass will cost as much as the game. The idea is to hack the game to get access to the Caterham in the game and also give it the same power and weight as the Sprint-T as it already has similar aerodynamics and grip, then figure out how to get something I can use as a practice course for an autocross, probably something from the licensing tests they use in the game to unlock tracks and cars… Also tomorrow I expect to get my Joyce Smile mask and to model it for you.

I’ll be back tomorrow night with a new post, I hope. Stay safe until then.

Still thinking about building the Sprint-T

And also its scale replica, but that’s pretty much a given. I think all the time, either building things in my mind or writing stories about things and people not in this world. It’s a good thing I’m not a billionaire, because if I had the money to build some of the things I think about… Well let’s just say the world would be very different. I like to think it would be better, but only from some points of view, for other people it would be Hell, so yeah, good thing I’m not a billionaire.

So, anyway, thinking about things, like how long the legs on the hoops for the cage should be, how to build the fenders, how if I made the front fenders from HDPE I could make them a bit shorter than if I used something like carbon fiber or any of the metals because I wouldn’t need to have any clearance to the top of the tire from the inside of the fender at full bump because HDPE flexes instead of breaking or cutting the tire. I was thinking that the structure needed for the headlights would basically work for the front part of the fender, because the headlights needed a rigid and vibration-free mount so the light only goes where it’s supposed to and I was already putting the light at the top front of the fender for aerodynamics and because it was out of the way, oh and because making one thing do the job of three or four without having to be any heavier is my jam (air guitar sounds). The kit version of a T-Bucket from Speedway uses the front shock mount as a headlight mount, so it’s not like my idea is unprecedented. It’s a little different but not completely out of left field.

And my YT Music app is playing “The Song That Must Be Played At Full Volume” aka “Won’t Be Fooled Again” by The Who. So excuse me while I Rock Out a bit here. (Full Throated Scream) Yeaaaaahhhhh!!!!!!

(8:31 later)Yeah, rear fenders, important bits, still trying to figure out what shape they need to be. There are many problems to be solved here: 1) keeping stuff from getting thrown on my car and other cars when it rains, 2) streamlining the rear tires, 3) fitting into the look of the rest of the car, 4) cooling the rear brakes. Of those parameters only 3) is optional-ish because if I get 2) and 4) right I basically cover 3). One option I’m considering is making the rear fenders a copy of the fronts minus the headlights, because that would be easy since all that requires is making 2 more fenders exactly like the fronts except without lights in the front. I guess I could use a repro ’59 Caddy tail light to finish the back of the fender. The downside of making the basic shape of the rear fenders identical to the front is while it ties the car together there is a bit of visual monotony in having what amounts to boxes over the tires with streamlined front and back bits on both ends of the car. But that’s what the Mini Sprint-T is for, trying out ideas to see what works and what doesn’t.

And my neck is sending scatalogical telegrams right now because I have been sitting at the computer for too long, so this is a good place to end today’s missive.

Planning a trip

I’m going to make a trip to Harbor Freight tomorrow to pick up some things. I need a new 12v power supply (battery charger) for electrical testing, and they have a sale on kitchen shears ($0.39). Also I need to get a cordless version of their take on a Sawzall . This will be necessary to cut the headlight buckets out of a car or truck in the junkyard so I’ll have a way to mount my headlights in the front fenders.

Along the way I’ll also pick up lottery tickets and some candy for Mrs. the Poet because she’s getting a little stir-crazy from not being able to leave the house. She’s been stuck here since she was released from the hospital back on 3/8. I need to get some stuff before I can do anything more on the Mini Sprint-T.

Speaking of which, I have maybe solved a problem with the Sprint-T. One of the things I want to do is use a Tri-Y exhaust manifold, which is expensive as Hell for LS architecture engines. The reason I want to use this is the Tri-Y configuration improves low and mid-range torque without restricting flow at higher RPM for peak power. Well what I want to do is use a dual inlet, single outlet muffler on both sides to act as a large-volume collector and massively boost low and high RPM power because that’s what theory says it will do. Another thing this will do is quiet down the engine a bunch without restricting it any. For the model there are muffler bodies without inlets or outlets available that can be customized exactly for this application. Unfortunately I can’t link to these because the web site they’re sold from doesn’t let me link to individual parts and when I try the links just go back to the products page. parts See?

So, after lunch I get to catch a bus, wait a while to catch another bus, ride for a while, shop, and wait again for the bus home, unless I time my shopping trip right, then wait some more to catch the bus home. [Yay!/s]

Many things have happened since last I posted

And one of those things is the store where I buy my Lotto and Powerball tickets is selling masks for $2 each. This is a good thing, since Dallas County has instituted a “can’t leave the house without a mask” policy. They are not enforcing that as a criminal offense yet, because 1) masks are nearly impossible to find or make and 2) police don’t want to get that close to people.

Other things, people are still ignoring the one-way arrows on the floor of the aisles in the grocery store, and wandering around without face coverings because “I don’t feel sick” and they don’t know or more likely don’t care that most people don’t show any symptoms until the second week after they are infected, and that they can spread the virus starting with as few as 2 days post-infection. I realize that with my immune system I probably won’t reach they symptomatic stage of COVID19, and I could be spreading the virus like a modern day Typhoid Mary and not be able to tell.

We had a protest against social distancing down in Austin because “Freedumbs”, complete with assault weapons on display, likewise because “Freedumbs”. I’m unsure if being stupid is a consequence of Conservatism or a prerequisite for it, but it certainly seems to be something that accompanies it.

I feel like I’m surrounded by idiots, but they were there all along. It just took a disaster to let people know they are idiots, and the bad thing was before they were “mostly harmless” idiots, now their idiocy could kill people I love, as well as people I don’t know.

I discovered my seat for the Sprint-T was still a bit snug through the chest, so I took my Orange Hammer to it again to widen it out at the top where it was still too small.

Setting up for a test fit

Checking the fit after beating on the chest restraint with the Orange Hammer

What I was originally looking at was if I needed to raise the shoulder harness passthrough so that I didn’t get spinal compression in a frontal collision or a sudden stop. That was what I was checking with the pictures, to see if I could see the holes for the shoulder harness from the front when I was in the seat. Spoiler Alert: I can’t. And the composition of the pictures was determined by where I could set up the seat to test sit, as the only place I could put the seat and still sit in it was the couch, and the only place where Mrs. the Poet could take a picture from was on the far side of the dining room table. I couldn’t take the picture myself because I needed to be in it, and the camera needed to be at a distance from the seat to reduce parallax. So the image is not as good as it could have been with a dedicated studio and a longer focal length lens than my phone had. The wide angle lens on my phone creates a lot of parallax and the longer focal length lens I bought for my previous phone won’t work for this phone. And so it goes.

All those words and I forgot to say what I came to say

Since this is a follow-on post I won’t use much space this time. What I originally came to say was that while I was trying to figure out how to build the Mini Sprint-T I figured out how to build a better frame for the 1:1 Sprint-T. Anyway, what I had decided for the Mini was front and rear hoops that went all the way down to the belly pan and had the frame rails glued to the front and back of the verticals of the hoops, instead of continuous frame rails and the hoops on top of the rails. What evolved from that was a lower rail with 0.120″ wall inside the roll cage area and 0.060″ wall in front and back of the cage so that in front or rear collisions the lower rails would collapse first and send large objects attached to the frame under the driver compartment and not into the driver or passenger.

So, when I build the frame I bend up the hoops and leave the legs 1.5″ longer (scale) than I would with the legs on top of the frame, and glue the lower rail between the legs. On the real 1:1 car that part would be the 0.120″ wall. Also the top rail would be one continuous piece from the front bulkhead to the rear bulkhead, which means I will need to figure out how far to bend it where it comes past the front and rear hoops. On the 1:1 car it will be 0.120″ wall and the biggest length of tubing on the car and run the full length of the frame and require careful gusseting where it passes the front and rear hoops. That’s also true on the Mini Sprint-T, but the mechanics are completely different because of the scale.

And since this is just what I should have posted yesterday instead of rambling, this is a good place to end.

Can’t stop thinking

And one of my favorite subjects is how to make the Sprint-T lighter and safer, which was not caused by seeing Ryan Newman’s Daytona crash. Actually it was brought on by wanting to make the frame fail in such a way that the engine didn’t try to join me in the driver’s compartment in a frontal collision. Second consideration was using as much 0.060″ wall tubing as possible. I say “as possible” because while some of the 0.120″ wall tubing is required by safety rules, some of it is required because of the stress risers created by the 0.120″ wall tubing.

And once again I wish I could show you what I see in my mind, when I’m thinking about the Sprint-T. The rest of the time I don’t want you to see what’s in my mind, that’s like being on the wrong side of the eyewall of a hurricane full of garbage. But seriously, I wish I could show and not tell about the frame for the Sprint-T.

OK basically The Rules require the hoops and diagonals and upper parts of the roll cage to be 0.120″ wall, but to balance things out so the cage holds together that means the bottom frame rail has to be 0.120″ as well at least between the rear and the front hoops. The fun(?) part is deciding how far back the 0.120″ wall has to go, at least to the rear hoop but behind that do I want 0.120″ all the way to the rear bulkhead/bumper, or do I want that to be a crumple zone up to the rear hoop? Going back to The Rules at least one of the diagonals must be a single length of 0.120″ wall tubing the same diameter as the hoops (1.5″), but do I want/need more than one diagonal, and if I want/need to have two diagonals do both of them need to be 0.120″ or can the lower stressed one be 0.060″? Add into the mix that I can also have a rear hoop and a left and right hoop, and run a diagonal from the front crossbar to the rear corners of the left and right hoops and get a much stiffer but slightly heavier frame.

But we were approaching the point of diminishing returns for frame stiffness given the suspension design of “stick” axles front and rear. I mean the main point of torsionally stiff frames is to keep the front and rear wheels at the best camber angles and also to balance the roll rates so the weight transfer between the front and rear outside tires can be tuned for desired handling behaviour. Well stick axles don’t change camber angles unless the inside tire is lifted out of the plane parallel to the ground which likewise limits the weight transfer ratio between the outside tires. And that one didn’t come out completely right, as the inside wheels can also go over a bump and remain in contact with the ground and not be lifted by trying to transfer more weight than exists on the inside tire by either excessive roll angles or by roll centers that are too high and transferring weight without compressing or extending the springs. This is the mechanism that allows changing the handling by raising and lowering the roll center on one end. The closer the roll center is to a line running through the center of gravity of the car the less control the springs and anti-roll bar exert over the weight transfer and also the less the car will roll over on the suspension in a turn. Get the roll center higher than the center of gravity and the car will try to roll opposite the cornering force and pick up the inside tire. This is why standard kit T-buckets are no good for autocross and Solo Racing because they have such high rear roll centers to compensate for the “normal” size difference between the front and rear tires on the street.

Anyway, back to the frame. Running left, right, and rear hoops will give me four uprights on the rear so lots of crush resistance where the majority of the driver sits, which is good. But also less tie-in at the top of the rear hoop which is ungood (not actually bad becauuuse there are other ways to tie-in and brace the top of the rear hoop). And running left, rear, and right hoops means an extra hoop of 0.120″ wall plus the crossover bar over the front of the cockpit and the verticals under the crossover and the diagonals from the verticals to the rear hoop have to be 0.120″ where front and rear is just the two hoops plus the crossover bars between the two hoops and whatever gussets they get attached with and the diagonals that are a single piece of tubing between the hoops. Like I said, compromises and where weight can be saved.

Also, while I’m trying to do this for the 1:1 car I’m also trying to figure out how to build the 1:25 Mini Sprint-T, which is where this mess got started because of the upper rail running from the front bulkhead spring mount to the front hoop.

A little late, but here it is

Sorry to take so long but I finally got a decent picture saved someplace I can use to post it to the blog.
See that teardrop opening?
There’s a wrinkle that doesn’t show well in the picture because of the angle, but is glaringly obvious IRL. So this part is Just Practice while I perfect my technique. Also I have been looking at pictures in catalogs and online of turnouts that used this method and they have egg-shaped openings, not teardrops. That means I have to work on my technique even more to get the opening right every time.

Since I spent so much time trying to get a good picture today after trying to get a good turnout yesterday I’m up past my bedtime and I really need to be awake when the stormdoor installation team shows up in the morning, I’m putting this to bed and then myself. Hasta la Friday. Which I know is ungrammatical Spanglish, but anyway, Mañana

I spent hours practicing

Last night I did the bender again and started trying to do the “sliced tangent to the inner radius” exhaust tip. Now while I was building my tool and practicing bending the raw stock I was listening to YT Music on my phone, which ran the battery down so I couldn’t take pictures after I was done. But I promise pictures for tomorrow after the phone gets charged.

The tricky part is the heating of the raw stock to make it soft enough to bend without causing the tube to collapse. I ruined many bends because I overheated the tube and collapsed it. I also discovered that heating the stainless steel bolt I’m using as a bending post doesn’t work for tubing at all, unlike solid rod. If the post is warm enough to soften the plastic, the wall of the tube next to the post collapses before the outer radius starts to bend. In retrospect I should have expected that, but I was thinking in metalworker mode not plastic model builder mode. The way to go for the plastic tube is to spin the tube on its long axis with the intended bend area in the heat source (butane torch flame) until it gets soft but not floppy, then put it in the bender and make the bend. This has to be done extremely fast because the temperature spread between floppy and rigid is very small and soft enough to bend and too cold to bend smoothly is even smaller.

Anyway I discovered another reason for using the sliced bend exhaust tip, it leaves a delightful teardrop shaped opening besides directing exhaust away from the car, similar, shorter, but not exactly like when the reverse technique is used for side-exit exhaust. But I wasn’t expecting this shape from the inside bend, I was expecting a more oval shape opening. Maybe when I get a better quality bend the shape of the opening will be more oval than this attempt. But better quality requires more practice and there is a limit on how much raw stock I can waste on practice. I really need to reserve one stick of tailpipe material for the final build so I have enough length. But I will get a picture of the pretty practice tailpipe for tomorrow’s post