Tag Archives: technical stuff about building cars

The heat is taking a break and Mrs. the Poet returns

The forecast high for today is was “only” 103 104°F getting down to 75° in the AM. And to welcome Mrs. the Poet back Tuesday the forecast high is just 99°. Mrs. the Poet is strongly considering staying in Upstate NY, except that her ticket is only transferable if her flight is cancelled. I know the cats will be glad to see her, they wander the house calling for her like they expect her to appear from the air or something. And I’m missing her, too.

On the Sprint-t project I have simplified the body mount somewhat. Instead of welding a box structure with a complex flange and dozens of holes in the top that would allow water intrusion, I moved the face between the floor and the filler over to the other side of the mounting nuts with a simple bend to carry the flange up close to the nuts through the cowl pinch which won’t affect the mount stiffness since there won’t be any bolts except next to the firewall. This would have almost the same effective stiffness as the more complex mount with all the fiddly out-of-position welds I would need to do standing on my head. Most of the welds I could do outside the car on a bench, but there would still be some yoga welding in the car, only about a third as much as the other design. This design leaves the nuts and bolts inside the body and exposed for maintenance. And there would literally be a line of bedliner caulking the bottom of the body outside in the joint between the body and the frame.

Like I posted earlier the design is getting to the fiddly bits like body mounts and making sure the floor doesn’t oilcan when I get in and out of the car, without disturbing the smoothness of the belly pan that is the other side of the floor. This excludes running beads on the floor because that also is either a bump or a depression on the belly pan. This leaves welding light angle sections or just vertical flanges on top of the floor like for the body mount. And I forgot to reiterate the floor/belly pan is a structural part of the center bay to prevent distortion of the roll cage in a wreck and also act as a transmission mount. I decided the trans/driveshaft tunnel will be removable from the inside of the car for installation and maintenance of the drivetrain. This solves a ton of issues with keeping water out of the interior and also keeping the belly pan smooth, and makes the floor a better structural component for the frame. Otherwise I would have to figure out how to route the shear loads around the hole in the floor to get the transmission in and out, and make a removable cover for the hole. This would be a weak point in the frame that would be a bear to fix without adding a bunch of extra weight.

And I have to get the clean sheets out of the dryer and put them on the bed. I had some bug bites that bled a little on the sheets, plus there was the matter of sweating making the bottom sheet dingy looking, so I got some bleach at the store and tried to whiten them. And it doesn’t matter if I succeeded or not, they go on the bed tonight so Mrs. the Poet has a clean place to sleep tomorrow night.

[$DEITY] it’s hot

The heat here in the Beautiful Suburbs of Hell has been, well like Hell. As I compose this the local dry bulb temperature is 108°F (42°C), but the air is so dry that the wet bulb is only 110F. The best the poor AC units can do is pull the inside of the house down to 90°F. Other good news, Clint finally made it home, safe and noisy. He has been elsewhere pretty much as long as the Internet was out. He wasn’t eating going by how hard he hit the food dish, but he found water someplace because he’s not exhibiting any signs of heat injury, and also not attacking his water. But he does like to sit in the direct blast from the AC unit so proving he’s no dummy.

One of the things I’m doing to beat the heat has reminded me of another way of removing water from alcohol called cryo distillation. How I was reminded is I bought store brand frozen pops, the kind that comes in the clear plastic tubes you put in the freezer until they freeze solid like the brand name Otter Pops. One of the methods of cryo distilling is to put the mixed liquid in long, thin tubes with a spigot at the bottom to drain off the desired fluid after freezing out most of the water, which is kinda what you get when you freeze the pops vertically. Most of the sugar syrup and flavor ends up at the bottom of the tube, but you get a nice air space at the top to cut open the tube without spilling anything. This was one of the ways they used to make an apple liqueur known as Apple Jack. And yes, that’s where they got the name for the cereal. Legend has it the first apple jack was made when a keg of hard cider was left on the porch during a hard freeze and split the keg, leaving a center of concentrated alcohol and flavor near the bottom of the keg. Apple cider had been heat distilled before to make apple brandy, but that’s a distinctly different beverage than apple jack which retains much more of the original fruit flavor than apple brandy, or so I’m told as I have never sampled either one. But if you wanna make your own now you know how, and PVC pipe and fixtures are not that expensive if you live on a place where extended periods of sub-freezing weather are common. If you don’t, you can dedicate an upright freezer to the cause and go small scale.

I mentioned I had determined a new way to mount the body for the version of the wide frame that did not have rails just for mounting the body, and it’s lighter (by a bit) than using the rails welded to the top of the floor. Basically it takes the filler between the main rails and the body intended to keep water out of the interior and makes it structural by replacing the tube with a shaped sheer web, and drilling the holes for the mounting bolts and welding nuts to the filler piece instead of the second frame rail. This eliminates 3 of the 4 walls of the rail to save weight at no loss in rigidity for the final structure, but it will be kinda floppy until all the edges are at least tack welded together. This cavity would be a prime place to get a dose of Boshield tube protectant to prevent rusting out. And the joint between the frame and the body will get a shot of bed liner spray to seal it from the inside and prevent road spray from collecting in the floor. Actually I’m thinking about masking off the part that goes outside the body before mounting the body and putting the body on while the spray is still wet to seal the bolts from allowing water inside.

And I’m starting to get hungry and dinner won’t cook itself like it does when Mrs. the Poet is here 😇.

I have internet back!

I am so glad to be back on a full-size (more or less) keyboard. The fix was so annoying, it wasn’t the interface board that was out, the µP controlling the interface board needed a hard reset, as in push a button on the board to send s signal to the µP to do a hardware reset. Now I’ve done some hardware back in the day, but I have never seen a µP that didn’t do a hardware reset when coming back from a power loss, but then again my last work with µP was back when the Zilog Z8 was cutting edge and I connected a TI speach processor to one for a prototype toy for the toy company I was a co-owner for. You could also use the speach processor for sound FX. But anyway for the online tech remote accessing the situation it was impossible to tell the µP stuck in the POST (Power On Self Test) loop from a fried interface board. The return signal is the same, nothing. Unfortunately the reset button is behind a cover fitted with tamper-resistant screws and they have to send a tech out to push the button or replace the fried board.

Anyway, this left me with lots of time to do the most dangerous thing I can do: think without interruptions. And what I thought about was the Sprint T frame, Subaru engine edition. I had previously dismissed using the square front hoop design as ugly but as I had nothing but time these last few days I used the actual body and some 2 by 4s I had lying around to do a mock up of sorts, combined with a little basic math and trig to calculate important stuff like will the tires hit the frame at full bump, full lock, or full droop or any combination of non-conflicting parameters. And it looks a little “off” to have the legs of the front hoop so far away from the body, but it’s something I could get used to because you would not believe how much that increases the torsional stiffness, and it also improves the beaming stiffness slightly.

Anyway, verbal description since I still haven’t figured out how to get the drawings out of my head and into the computer. The front and rear hoops are the same size and profile but have different bracketry hanging off them the diagonal from the top of the rear hoop is straight, but the opposite diagonal from the top of the front hoop to the bottom of the rear hoop isn’t. That diagonal makes a detour to collect the front mount for the swing arm that locates the rear axle and also connects the coilover to the rear suspension. That then continues forward until it intersects with the diagonal from the top of the rear hoop, and the diagonal from the top of the front hoop connects to the intersection of the rear hoop diagonal and the lower half of itself so that everything triangulates. The top of the coilover for the rear axle connects to the rear hoop below where the locating rod from the brake floaters connects, or maybe they are co-located, because I still don’t know how long the reaction arm is on the floater. It might be long enough that it sticks up higher than the coilover, but then again it might not. Moving on, there are two forward-running members from the front hoop per side, one from the top and one from the bottom, to the front spring mount, and another from the bottom to the front crossmember/diaphragm. Now I’m still trying to figure out which way I want the front diaphragm to connect to the rest of the frame. One way would to continue the body mount forward to pick up the engine mounts and steering box mount, which simplifies packaging, but adds weight because I would have basically two frames, one for the body and engine, and the other for carrying the suspension loads. The other way would be to have the front rails go from the lower corners of the front hoop to the center of the front diaphragm, and stretch the engine mounts sideways to meet the rails. Both methods have points that increase weight, in that the longer engine mounts will weigh more by sheer size and may need to be made from thicker material because of that, and extending the body mounts to meet the front diaphragm adds 2 extra chunks of metal that wouldn’t need to be there except to collect the engine and steering box mounts. And speaking of the steering box mount, either way it’s going to be a mess, less of a mess with the two parallel rails from the body mount, more of a mess with the rails that meet at the front, but either way a mess. Looking at it without getting into fine details the two rails that meet at the front diaphragm is lighter basic structure but may be heavier after the mounts and brackets are added in, compared to 4 rails with two parallel spaced the same as the body mounts and two running from the bottom outside corners of the front hoop, and a more complicated front diaphragm. all with more material.

And while I was sitting here thinking about how to describe this frame in words I came up with a simpler and lighter way to mount the body. But it’s getting late and I have a lot of e-mails to catch up on. Not as many as I would if I hadn’t been burning my cell phone data keeping up with it, but enough that I really don’t have the time to pound out another 500 or so words describing what I just came up with.

It was suggested I should keep the Subie transmission

And the AWD drivetrain that comes with it. And as with anything else with this car, this would solve a few problems while creating a bunch more.

The main problem solved would be getting a transmission on the back of the engine that connects to the rear axle. The first problem this creates is added weight, the Subie transmission is about 50 pounds more than the T5. Second is width, the Subie transmission has the FWD drive spuds hanging off the side behind the bellhousing that extend beyond the width of the bellhousing, which restricts how far the engine can be offset if I stay with the RWD. Or if I decide to use the full capabilities of the transmission I can’t offset at all because of using the FWD portion of the system requires centering the transmission between the front wheels. Basically if I do that everything that can be moved to the right side of the car gets moved to try to get the car balanced left to right.

Now the reason I was thinking about this is the starter for a Subie mounts to the bellhousing, not to the engine. This makes making a bellhousing to use a different transmission a problem as the starter is designed to mate to a machined surface of a casting or forging. This is outside my abilities as a fabricator, because making a casting requires making an oversize pattern first to make the mold, and everything has to be just slightly bigger than the actual part because of shrinkage when the metal cools from liquid to solid, and I lack the skills to do that. Make the pattern, that is, to the required degree of precision. I know where to find the shrinkage rate and how to calculate how much larger to make the pattern, that’s just brain work, but converting those measurements to wooden patterns, that’s woodworking, something I have only been so-so at. I did OK at birdhouses and whirligigs in middle school shop class, but anything more complex just turned to garbage. On the other hand I can pull a mold off the original bellhousing and use that to hydroform an adapter housing except for the stupid starter mount. Hydroforming is easy-peasy compared to doing a casting. I take the OE bellhousing and cut it off at the right depth for the input shaft to mate to the pilot bushing in the crank then weld or glue a plate or board to make it solid across the back, and then bolt the housing to a piece of flat plywood about 5 inches taller and wider than the housing and add more plywood to make a box with an open top and the housing as the bottom. The bottom board and housing is sprayed with a mold release agent called form oil. Then a single layer of hardware cloth gets formed loosely around the housing so that it surrounds but doesn’t touch the housing and sits evenly against the bottom board. After that a thin mix of cement and sand is poured in until the mold is filled completely and allowed to set. Now if I was doing a mass production run I would then carve the concrete mold out by the thickness of my production mold material, and use that to form the production mold which would then get stiffeners welded to it so it would hold shape while turning out countless production parts. But for this project I would just make one or two out of the concrete mold and toss the concrete mold.

But because the starter has to mount to a machined surface precisely aligned to the engine I can’t make my own housing that way. So at this point it looks like modifying the OE bellhousing is my best bet.

And I got wrapped up in answering e-mails instead of finishing this post before midnight, so I’m wrapping it here and going to bed.

A Meandering Post

This post has a lot of subjects to cover so it may seem like the literary equivalent of a one-man ping-pong match.

First things first, I had some kind of gunk in my eyebrows when I took my shower this morning. I don’t know what it was, but it was itchy and took several tries to get it out of the eyebrows. I’m blaming allergies because pollen was deadly high this morning and it wasn’t there when I washed my face before bed this morning. And that’s not a typo, I usually hit the hay between 0300 and 0500.

Sprint-T: The pullrod suspension will lower the C of G very slightly while it also improves shock cooling. It lowers the C of G by letting me lie the shocks down at the bottom of the car instead of standing them up on top of the axle, and it improves shock cooling by collecting a larger mass of air and forcing it around the shocks than they would get just up in the airstream. It seems paradoxical, but you can actually get more cooling by putting something inside a duct than by leaving it in free air. And I was looking at the available springs, I do believe there will be a problem in getting a soft enough spring if I let the motion ratio for the rocker get too large.

My employment situation has gotten worse again. The company I have been getting gigs through has been having problems getting customers to pay for completed projects after delivery, and the standard agreement with us working drones has been payment on delivery to the customer. This has left the company covering for the customers between delivery and payment, but the customers had been paying on time so everybody was good. But lately us drones have delivered on time while customers have been paying late or not at all. Because we drones are technically contractors, or even guns for hire for some of us, we don’t have much recourse when the customer doesn’t pay except to sue the company in the middle that also did not get paid. We can’t sue the customer directly, and the guy we can sue doesn’t have much money to sue for. How this directly affects me is I ordered an expensive comic book (a $20 trade edition) that I was expecting to pay for with my share of a completed project that as of the first of the month hasn’t been paid for, and had to ask Mrs. the Poet for the money so I could keep my account at the comic book store current so I could keep getting my pulls. I only get one pull but there are one-shots and trades I want to get and I have to keep my account out of the red to order them. And yes I do like this particular comic Unbeatable Squirrel Girl enough to actually buy it every month. But with income getting dicey again I’m going to have to change my pre-order to pre-pay when ordering to ensure I get my books.

And I need to pu this to bed and take care of e-mails.

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.

No NASCAR race, and trying to rain here

No race to watch on the flat screen, and the weather is threatening so I can’t go for a walk. That means I have to post something here or go crazy. Going crazy is no fun, and I think you have figured out by now what choice I made.

On really good thing about the Pentastar for the Sprint-T is its extremely short length. There’s 43″ between the firewall and the centerline of the front axle on the Sprint-T and allowing for movement the steering linkage is 7″ behind that so 36″ from the firewall to the effective limit on the space. There’s a 3.5″ thick radiator to leave room for and a 9″ long steering box with a steering shaft that has to snake around the radiator, that goes between the radiator and the axle. Measuring the space from the part where the Pitman arm bolts to the rearmost part of the box as installed on the car and adding the working length of the Pitman arm (7″) I get another 12.5″ between the steering linkage and the radiator leaving just 23.5″ unless I put the radiator over the steering box like they do on the Speedway T-Bucket kit. Putting the radiator in the space between the front of the box and the steering linkage solves a lot of steering issues at the cost of raising the CofG slightly, but the radiator is only 19″ tall and there is literally 27″ to put it in. Mounting the steering linkage below the axle leaves even more room for the radiator in front of the steering box because the radiator can go over the linkage and still leave room for the axle to travel up and down. At this point in the design the radiator is a box that is 26″ wide by 19″ tall and 3.5″ thick that can be moved back and forth and up and down until room has been found for everything else. Anyway, the engine is a 20″ box in front of the firewall that leaves 16″ for everything else. And here you are reading in real time my thought processes as I build the front end of the car.

Recentering my thoughts, there is 16″ between the steering linkage and the front of the engine, the problem is the steering box and the radiator are trying to be in the same bit behind the axle. I could put the radiator on the right and the steering box on the left and have room for both. The steering box is 4.5″ from the mounting face to the right side of the box, 5.2″ total width, and I have 34″ of width to play with behind the axle, 17″ on either side of center. That means I could stuff a 28″ radiator in the car and still not hang out past the frame rails/4-bar if I put the radiator next to the steering box. If I choose to slide the radiator between the steering box and the steering linkage then I have more room for radiator width, but only just, and the radiator outlet would have to be passenger side to prevent interference. The widest radiator I can get a passenger side outlet at the places I’m looking is 31″ which is the inside to inside width of the bottom frame rails when I build to a width of 34″, serendipitous isn’t it?

And it’s time to check e-mail and get ready for bed.