Tag Archives: technical stuff about building cars

Feet still hurt and other things

Well I was supposed to go run errands in Carrollton today but I could barely walk to the mailbox in front of the house so no trip to Carrollton. I seriously did something bad to my feet, and I wish I knew what it was so I could not do it any more. I mean this is highly annoying not being able to leave the house except to get the mail.

Anyway I didn’t log on to post about my feet, I’m here to post about THINKING! > thunder, lightning, dogs and cats living together < No need to panic I’m just going to discuss on how my brain works > spooky music, portals to strange dimensions, screams of the damned <. NOW STOP THAT! I swear I will turn this blog around right now if this doesn’t stop > … <

OK now as I was saying I’m going to show I knew about how much to move the springs in on the front and rear axles so I could balance the car’s handling without resorting to heavy anti-roll bars. It has to do with single and double wheel rates and how they differ on a beam axle.

On double wheel rates or technically a “two wheel bump” the wheel rate is whatever the spring rate less whatever is lost if the springs are not vertical. Plus the motion ratio for springs not mounted directly to the axle which doesn’t apply here. What starts getting weird is when you get body roll or looking at it from a static body reference a “single wheel bump”. Then you start getting all kinds of motion ratios involved.

I should explain what a “motion ratio” is before I continue with this post. On a beam axle like both the ones on all of the iterations of the bucket from Sprint-T to TGS2 the motion ratio is the ratio of the tread (the distance between the center of the wheels looking from one end) to the distance from the center of the wheel to the point that the spring affects the axle, on the slant height. I guess you could use the distance on the horizontal plane because there is only a few % difference, but if you know the slant height between the contact point of the stationary tire and the spring closest to the affected wheel, why not use it?

On the front axle the springs are mounted as close to the ends of the axle as is physically possible, so the motion ratio for the spring closest to the bump is nearly 1:1 and the motion ratio on the other end is effectively 0, after taking the effect of applying the motion ratio into consideration. (The effect of a spring on the wheel rate is effective spring rate at the mounting point times the motion ratio squared.)

On the rear axle the spring away from the bumped wheel is actually close enough to be affected in a single wheel bump and contribute a significant amount to the spring rate at the wheel, so it has to be added in to find the wheel rate. To explain why I present a reductio ad absurdum where there is a single spring mounted on the center of the axle. The effective single wheel spring rate is ¼ the two wheel spring rate with zero resistance to rolling over in a turn, demonstrating the three spring rates for a beam axle: the two wheel rate, the single wheel rate, and the roll rate.

And I bored myself writing about it. I don’t get it, this is exciting to do, why can’t I convey that excitement when I write about it? Seriously this is giggly hand-rubbing exciting to do with the calculator and the graph paper, why can’t I make it sound as fun when I’m writing about it? I make it sound like homework instead of the nuts and bolts of deciding where the nuts and bolts go.

I guess I’m just tired and need to take a break from writing and go do something.

Happy Father’s Day, I’m changing the TGS2 design again

I woke up in the middle of the night thinking again, because I had to use the bathroom. While I was sitting I started thinking of how I was going to make the splitters, because they had to be somewhat thin and fairly strong because the aero loads would get rather high at highway speeds and faster, and because people would probably stand on them getting in and out of the car. Then I had a flash from the past back when I was building ultralights (lightweight single-seat airplanes that don’t require a pilot’s license under Civil Aviation Code Part 103) and I sat in on a composite construction clinic. During the clinic we watched a video on making a solid core wing with fiberglass skins using vacuum bagging after wet lay up. I realize that the preceding sentence read like Star Trek technobabble for most of you, so I will explain by describing how I’m going to make the splitters and how that changes the way the rest of the car will go together.

First of all, the core. I’m going to make the splitters and the floor of the car as a single piece, using blue styrofoam insulation board, from the nose to the start of the diffuser at the rear. This is our solid core. Now I could get all high-tech and use carbon fiber to remove every last gram possible, but that would be both expensive and overkill. I will make use of different layers of material for different purposes in the lamination, but the most exotic will be the Kevlar under my butt and the gas tank. Now the layers outside in from the ground up. First will be some light fiberglass mat that will basically be there as a sanding layer and to prevent “print through” from the woven layers. Next will be three layers of fiberglass cloth oriented in different directions to make the splitter stiff no matter how it’s loaded from people standing on it. Then the core of insulation board, then another three layers of ‘glass like on the bottom and the ‘glass mat. Then under the driver and gas tank compartments 9 layers of Kevlar oriented like the ‘glass cloth in the previous layers. The purpose of the Kevlar is to protect my butt and other parts from road debris like what broke the engine on my last car. It goes on top of the mat because the Kevlar is inside the car and it is easier to lay up that way and the mat is damned cheap so I can just run it all the way across without leaving any gaps.

Now the “wet lay up”. This means I mix up batches of very slow curing resin and completely saturate the various layers with the resin before laying them on the core using things like paintbrushes and rollers to make sure every fiber is covered in resin before it goes on the core. The reason slow curing resin is used for this process is applying the many layers is time consuming and exacting, because there can be no gaps or wrinkles in the lay up. Now why wet lay up is simply cost, buying cloth and resin separately is much cheaper than buying pre-preg which is the cloth and resin all-in-one but not yet cured, because it is made below the kick-off temperature of the resin and shipped frozen to prevent the resin from curing until the cloth is molded to the desired shape.

Now “vacuum bagging”. As the name implies there is a bag involved that has the air removed from it after the part is placed inside. Now between the bag and the part are 2 more layers of materials that just keep the bag from sticking to the part. First is what is called the “bleeder layer” that just exists as a path for the air to escape from around the part so atmospheric pressure can squeeze against the part and the layers and get everything really close together. Next is the “peel ply” that goes next to the part and gives the excess resin a place to go and is the real reason for vacuum bagging a wet lay up. The process squeezes excess resin out of the layers which then goes into the peel ply where it is wicked away from the part. Resin is the heaviest part of a composite part, my 47 pound bucket body probably has less than 20 pounds of glass fibers and the rest is resin, in fact from looking at the actual body I would say it is closer to 15 pounds of fibers and the rest resin. So leaving just enough resin to hold the fibers makes a major difference in weight. You can see graphically how much resin is squeezed out by weighing the peel ply and bleeder after unbagging the part. The outside of the bag is polyethylene sheet like what is used as a drop cloth for painting.

And there you have my major objection to vacuum bagging, the amount of waste left after the process. The bag, the bleeder, and the peel ply are all garbage after the part comes out of the bag. The only thing in the process that is reusable is the fitting between the bag and the vacuum pump, and that vacuum pump. In my case I will be using a shop vac so I will be getting sub-optimal results compared to using a real vacuum pump, but I will be getting a flatter, smoother surface by leaving the part to cure on the garage floor. And then throwing away a full garbage can worth of bag and bleeder and peel plies.

Now the real thunder, I can use this process to make an entire monocoque frame and only have the roll cage made from tubing. And in the process reduce the weight of the frame by half over welded tubing.

Moving the driver forward completely changes the frame design

Moving me forward of the original firewall really changes the frame design. And I’m not just talking about swapping the seat and gas tank around, either. The original frame could be considered an exoskeleton as almost every part was outside of the body to some degree in order to increase torsional stiffness. Well the new frame is much smaller, only 27″ wide to fit the firewall on the body, up to the point the engine and drive bits mount which will have to be wider because of the transverse mounting.

Basically the part of the frame forward of the firewall are going to be like a ’50s Indy roadster. This is still going to be hella stout and light, but the frame members are going to be different than the Sprint-T derived frame. This frame is going to be designed for a mid engine from the get-go instead of trying to cram a mid mounted engine in a front engine frame. The other major change is all of the frame is going to be round tube, most 1.5″ diameter and most 0.060″ wall thickness except for the bits around me that have to be 0.120 by SCCA rules. This will lighten the frame by a few pounds, but nothing spectacular. What will do the most to lighten the frame is tucking everything inside the body and doing the engine and transmission mounts first instead of making them fit what was already there. Also the Sprint-T was designed around a roll cage that won’t be there because the driver isn’t where the roll cage is designed to protect.

I can make this frame as stiff and light as the Sprint-T, it will just take a bit more brain work to do so. Instead of spreading the frame as far apart as possible I’ll have to concentrate on using internal structure for stiffness. It can be done, and I’m the guy who’s crazy enough to do it. Incidentally, the changes move the fuel tank right over the center of gravity of the car so the balance doesn’t change at all between full and no gas. The Princes of Serendip are victorious again! (Look it up)

On other fronts I need to get that brake hone this evening so my walk will be extended to the auto parts store. And tomorrow’s walk will be by the pharmacy to pick up more not-sad pills for my brain. Tonight I’ll be walking about 3 miles to get some bonus check-ins on my mobile game. I haven’t been able to walk as a workout for 2 days now and I need to stretch out a bit.

More later.

Can’t. Stop. Thinking.

I was on my walk, again, and thinking, again, about alternative layouts. I remembered a Bucket from “back in the day” that had the engine actually in the body, but Google Image Search can’t seem to find it. It did find this earlier car.Engine in the back, driver in the frontThat did much the same thing but wasn’t a street car.

So what I was thinking was move the body back so the engine was about the place the upper black line is in this picture.Reusing a picture here.
And have the sticky-outy thing on the right sticking out of the body.That's close to what it looks like now.This is cleaned up
And I know the “sticky-outy” thing is the final drive housing.

Doing this won’t change anything except where the driver goes and how he (I) fit.View from the back. Mrs. the Poet is obviously fascinated. Three-quarter rear viewThree-quarter front. Clint is obviously as interested in the car as Mrs. the Poet
You know you have a tiny car when you can mock it up in the living room and not have to move any furniture around. The back of the chair in the pictures is right where the radiator will be on the car. I saw the chance to get a visual reference in place and I took that chance. The gas tank will go about where the box is in the bottom view and the rear view.

Now obviously part of the back of the body will need to get cut away to clear the engine and transmission if I don’t change the wheelbase. Now if I wanted to be really sneaky I could shorten the wheelbase from the 100″ of a stock model T and move the entire engine and transaxle inside the body and just have the axle sticking through the side like on some tubs.Just keep sliding that body back...
And hide everything inside the body. Nothing of the engine would be visible except the exhaust tips. And this configuration has precedent in the original Thunderbolt Grease Slapper.See how far forward the rear tires are?
Move the body back until the back of the rear tire is even with the back of the body with a fake convertible top and just keep the same space in front of the original firewall. Or I could get really sneaky and keep adding that distance in front of the body while moving the engine and transaxle forward until the rear tires are even with the back of the body and keep the original 100″ wheelbase, and put a smooth hatch over the driver’s compartment so that when it’s parked you can’t tell where the engine is.

And looking at the original TGS had me wondering where Tom kept his legs when he was driving, because they obviously aren’t in the car with him. He would have to be an above-the-knee amputee to fit in the car, or drive with his feet sticking through the firewall next to the engine. Ah, well it’s only a cartoon, a fifty year old cartoon at that. They had their own logic and physics .

Also getting back to the car I’m building, if I shorten the wheelbase that moves the balance more neutral to make the handling better. Another reason to move the engine forward.

And I need to get ready for my walk.

Pushed my limits a bit today

I was out in the heat again today paying bills and I really cut it close this time. I had to pay the phone bill after getting to the office just after they closed yesterday, so I was out during the day in the sun and the heat. Well I didn’t get any water or hydrate before I left and I started getting nauseous walking around. I didn’t check what the temperature was, but it was over 90 and it felt muggy when I opened the door.

I think I might have saved enough money from various gigs to get that brake hone and install those spindles this week. I have 2 trips to the lab rat keeper and another trip to take movies of my heart beating. This time I’m getting driven to the echocardiogram so I don’t have to spend more than 7 hours on the roads to get a 20 minute procedure done. I have to wear that infernal Automatic Blood Pressure Monitor and carry a jug of my urine around again, but maybe by the end of the week I’ll have a mockup installation of the spindles on the axle.

And I was just taking a “think break” to let my mind put more words together and putting the kingpins in the axle bosses where they are supposed to go, and as the instructions warned they don’t fit. First installation in a new tubular axle and both bosses are out of round by a few thousandths, just enough to keep the pins from dropping in unhindered. Enough that I had to get a hammer and drift to get them back out. And the instructions also say that the only way to fix this is with the brake hone… Before anyone says anything, yes I had the grub screws all the way out before trying to install the pins.

I’m trying a different strategy on sleeping, going to bed early before I’m tired and just letting the brain do its thing until I fall asleep. I was up by 0800 today waking up all on my own. It really looks like the longer I wait to hit the bed the longer it takes to turn off my brain. I was asleep in under an hour last night and the night before and woke up before my alarm yesterday and this morning. It’s weird being up that early. My usual M.O. is to wait until I feel sleepy, then get in bed, and have the brain go crazy trying to solve all the problems I didn’t get to during the day. Then several hours later I finally fall asleep only to get awakened from REM sleep by my alarm. If I turn the alarm off and get back to sleep I drop immediately back into REM and either continue the dream I woke up from or move into another one. One recurring theme I have been having lately in my dreams is mountain freeways replaced by multilane fiberglass slides that go for miles. Everyone gets out of their cars and slides down the mountain to meet their car at the bottom of the slide. This says something, but I’m not sure what it is yet. It is loads of fun sliding down the mountain, especially at night. But anyway that doesn’t happen when I go to bed before I get sleepy.

And I was writing a paragraph about sleeping and guess what happened? Yep, faceplanted right into the keyboard. Can’t sleep when I want to but when I’m doing something and need to stay awake? ZONK!

And now I really need to leave and fill out my bag limit of check-ins on my mobile game so I can get what I can out of it before it goes belly up.

Comparing forward and conventional driver seating

Watching the Canadian GP on the idiot box while waiting to walk down to the phone store and pay the bill. Aside from Hamilton running away and hiding from the rest of the field it is a good race to watch with lots of close racing all up and down the order. And in a few minutes the Cup race from Pocono starts.

You have heard the saying about a picture being worth a thousand words, and my usual post is about half that. So instead of talking about the difference in the driving position I marked the body with the rear of the conventional driving position to go with the previously marked far forward driving position.You can easily see how far forward the driver gets moved
The forward mark is the same one I used before, same piece of tape even. The rear mark is what I get by putting my feet behind the original firewall. That tiny piece of tape was the inside edge of my butt marker from when this body was going to be a front engine bucket with two seats. Yes, my butt is that narrow, the outside edge is the edge of the floor where the body turns up. And moving my butt that far forward only changed the weight bias from 63% rear to 60% rear without the 0.25″ floor pan under said butt.

OK F1 race just ended and Hamilton finished like 20 seconds ahead. Except for the usual first lap/early race carnage most of the attrition was brake failure except for one engine vibration retirement to keep from scattering the engine on the track. So now I switched to the Cup race at Pocono which is still in Stage 1 and drivers are already complaining about brakes going away, which partly shows why I want to make sure I can get enough tire to make good use of the big brakes on the TGS2. I know with the rear weight bias the front brakes won’t get as much use as they would with the front engine, and the rear brakes will see much higher temperatures than with the front engine.

And Junior just missed a shift and damaged the engine. And now it has been a few laps and Jimmy Johnson and Jamie McMurray both just had brake failure in the same turn, same lap to crash within feet of each other with McMurray catching fire from the impact damage. Jimmy absolutely nailed the wall, almost knocking it down. He got out under his own power but had to catch his breath a bit before taking the mandatory ambulance ride, while McMurray was in such a hurry to get out of his burning car he didn’t disconnect the AC hose and was walking around after the wreck with part of it hanging off the back of his helmet. Race has been red flagged because of the mess in turn 1, when Jimmy hit a lot of parts and pieces fell off the car and fluids ran on the track.

And Ryan Blaney just beat Kevin Harvick to the checkered flag. Sorry I got hung up with watching the race and forgot to report on it, but if you were interested in the race you would watch it I guess. And to add fuel to the Ford v Chevy wars, Harvick did the 3-2 instead of 3-4 shift and his Ford was fine but the Chevys all blew up in the same situation. And a Ford won.

I just saw an interesting use for coal, a carved anthracite trophy at Pocono. I don’t know if the eagle is made from coal but what is under it is.

And it’s time for me to walk to the phone store and pay the bill.

Why I need to run cartoon tire sizes

I found the perfect video to explain why there needs to be such a large difference in tire width.

Tire Load Sensitivity – Why Wide Tires Add Grip

Most mid-engine cars don’t have the extreme rear weight bias the TGS2 is saddled with and they still run the very different tire sizes. Heck, the Corvette is almost 50/50 and still has to run wider rears than fronts because of the added tire load caused by the high horsepower.

And that’s all I have to say because This Hit Me while I was in bed and I had to post it before I forgot it. My memory still hasn’t gotten any better. And my neck still hurts, but I had to do this.

I want to take a walk but my foot hurts

Physical health first. Sometime during my last walk I rubbed a hole in my left foot. Don’t ask me how, I didn’t notice until I was getting ready for bed. Kinda like I didn’t notice all those torn ligaments in my knee. But now I notice, you betcha I notice. It hurts like a sonuvagun. As a certain “reality star” would say, bigly. Now if I could just remember what I did besides walk… Nothing comes to mind.

Mental health, Mrs. the Poet will be leaving to visit her mother and the rest of her NY relatives on the 29th. She won’t be back until the end of August. She’s worried about the house, and what the cats would do to it. And what I won’t do to it, like mop the floor twice a day. I’m worried about not having a human to exchange physical affection with. Seriously that kinda stuff makes me a bit off, or rather not having that kinda stuff. I’m sure somebody will come visit me or invite me to dinner or some such.

Moving on to car-building stuff, I decided to confront my fears and install the kingpins in my spindles by myself using a brake cylinder hone . Of the three choices for fitting the bushings the brake hone was the least tool-intensive and only barely the most labor-intensive over the reamer. The one that was the most out-of-pocket was taking the spindles to a machine shop to have them Sunnen honed. The setup charges alone for that one would buy 3 new brake hones. And after I install the spindles to the axle I can measure to find the tie rod I need instead of guessing at it.

And I promise to take lots of pictures while I hone out the bushings and fit the kingpins to the spindles, because it will probably be funny as heck (not Hades because he’s really a dour dude). There may even be some blood involved, applied to the parts in some manner. The Big Thing will be Parts Assembled (like Avengers Assemble only without superheroes and the parts only move when I move them, so almost completely unlike Avengers Assemble).

Now I desperately want to walk to the parts store and get that brake hone and some grease fittings for the spindles, but my foot still has a hole in it so I can’t.

Opus the Unkillable

Too hot to be walking around

But I did anyway. Bills had to be paid and there wasn’t enough time to get payment there in the mail. So I walked 3 miles in the heat, sweating profusely.

I’m getting frustrated trying to get the handling balanced on the TGS2. How frustrated you ask? Frustrated enough to look up RWD transmissions that bolt up to the 3.3/3.8l V6 that is in the free donor vehicle. Frustrated enough to look at tire combinations that look like they go on 2 different cars. I need enough tire to work with the 12.19″ front brake on my build list, and enough rear tire to keep the back following the front. And it has to be cheap and Not Ugly. Not demanding beauty just Cheap, Works, and Not Ugly. And until I get enough money to actually start building this car all these ideas are going to have the life expectancy of a drummer in Spinal Tap.

I gotta go, y’all keep cool.

More about that cascade effect, and do I miss the bike stories?

I got a PM from another web site asking me about the bike stories I used to cover, and do I miss them? Well, yes, kinda. I miss being helpful and telling people how they could avoid the same fate if it could be avoided, I miss vicariously yelling at people about crappy infrastructure, but I don’t miss the death and destruction involved. Having been through one myself I know how painful it can be to survive a major wreck, ditto not surviving it. Not surviving is painfully boring but aside from that not bad. I’m the kind of guy that has to be doing something or at least planning with the possibility of doing something, and where I was didn’t have any fab shops or building supplies. And TBH that was my biggest problem covering bike wrecks, there wasn’t a damned thing I could do to prevent another except make note of what infrastructure would have possibly prevented the wreck.

Moving on to the cascade effect on the TGS2 moving the driver’s seat, I marked the body with where the roll hoop behind the driver would be with my feet all the way against the front axle.That black line is where the rear roll hoop goes.

You can see that the rear roll hoop is right in the middle of the bucket. That is not the ideal location for the front center bulkhead if maximum torsional rigidity is high on your list of priorities. Now if the rear hoop is used to triangulate the center bay and driver entry is from the front instead of the top I might could make it work.

Or I could make the TGS2 a two-bay design using the rear hoop as a tower in a bridge structure. This is a design that I’m not familiar with, at least not as familiar as a multi-bay construction. Basically in this construction all the loads are passed through a central structure and everything is triangulated around that. The important thing in this type of design is to keep all the load paths balanced with structure to connect everything directly because there is no secondary structure to carry the load around design gaps. If I don’t provide a triangulated path to carry the load that load will cause the frame to flex. This style of construction is considerably lighter for the amount of rigidity it delivers than the multi-bay construction I had used on the first iteration of the design, but it makes hanging the engine and rear suspension more difficult. And as I’m trying to visualize the structure I notice there is no way to put the bucket on the frame without making a jigsaw puzzle out of the body, so that’s out.

So back to integrating the rear hoop in the center of the wheelbase, again. Or not, I mean it’s not like I don’t have a design already, it’s just not optimum. All this hair-pulling is just trying to find a better solution with better balance. Well guess what, as long as I have 620 pounds of engine and transmission sitting just 10″ forward of the rear axle in a 1600 pound car the car is not going to be balanced. I’m going to have to give up front grip to keep the back end following the front, or install ridiculous rear tires which is basically the same thing.

This combination has a long history in T-Buckets because the construction techniques raised the rear roll center several inches above the axle, which caused jacking, or lifting the inside rear wheel as cornering load increased. This combined with high power caused severe oversteer which got patched by stupid wide rear tires. If you watch videos of Goodguys autocrosses you can see this effect when someone tries to run a T-bucket. Any power applied before the car is pointed straight results in the back end trying to pass the front. This was also the problem with the pre-1965 Corvair, the swing axle rear suspension had a very high roll center combined with rear weight bias caused by hanging the engine behind the rear axle and 4 equal-sized tires and you have the perfect recipe for leaving the road back end first. This car was designed during a period before computers were used to test designs and also during a period when GM banned participation in motorsports so designs were not examined with that potential in mind, which would have caught this blunder before it entered production.

And after that historical note I think it is about time to take my walk.