Tag Archives: technical stuff about building cars

Short months throw me off a bit

And by “short” I’m not just talking about February, I’m talking about all the “less than 31 days” months. I’m taking part in a 3-day challenge to not drink alcohol for the 29, 30, and 31 of February😆

The Shadowrun game is proceeding apace. We had a technical issue with my headset that prevented me from talking to the rest of the group which burned up an hour of game time, but my character grabbed one of the slower characters and carried her into the fight at her request so she could get within range in one initiative pass to save play time. I have one synthetic arm and the other arm is enhanced to the same strength so since she’s classified as a “small” character my strength could handle her weight no prob. I scored low on initiative this time, so I had to wait for the spellcasters to handle their mechanics first before I could fire my grenade launcher, since I couldn’t swing my katana with the munchkin over my shoulder. At some point we’re going to have her either get off of me or switch to riding my shoulders like Master Blaster so I can use both arms/hands. Anyway, I only got 3 shots off all game, 2 single and one 3 round burst to clear away a mob of shelves and cursed products in front of the party, that was very effective at providing a clear shot at the objective. Our short-term goal is the employee-only space at the rear of the store, which should be outside the building as the volume of the shopping area in the building is pretty much the same as the size of the building, so we’re assuming that is where the really weird shit is either hanging out or being stored. The spellcasters are taking care of living things and I’m blowing shit up, so that we have a clear path to the objective. My character is having a good time, but wants to have both arms free to fight so he can use his katana when things get too tight to use the grenade launcher and he has to go to melee range.

On the Sprint-T front I found a kit to fill the gap between the engine and a t-5 transmission yet another cost for building a manual transmission car avoided with an automatic transmission. And I’m still looking for a transmission that can be shifted with only a throttle lift without using the clutch, as there is only enough space for my feet side by side and a steering column between the bellhousing and the inside wall of the body with the engine moved as far to the right as it will fit (26″ inside to inside where the engine fits in the front of the body, and a 19″ wide bellhousing leaves 7″ for everything else), so I’m thinking hand clutch instead of a pedal. That means I need both hands to use the clutch and shift if I have to use the clutch to shift, thus the need for a transmission that can be shifted quickly without needing to de-clutch. This means I need a faceplated or dog box (same thing, different name) transmission. The lengths I go to, to remove a few pounds from the car.

And this feels like a good place to put this post to bed.

Still cold, hands still not working right

And we may not be going shopping if the roads refreeze tonight. The roads got better during the day because they were in mostly full sun until sundown, but the temperatures dropped like a rock in a still pond as soon as the sun set and as I compose this post it’s 25°F a full 10° colder than the high for the day. (For my SI readers that is -3.9°C and 5.5°C).

The window next to my desk where I compose these posts is leaking cold air over my feet and also my hands so I’m freezing now. The thermometer on my desk says it’s 63°F up there by the wall, but the softdrink under my desk says it’s significantly cooler than that. The soda is significantly cooler than my mouth and cooler than the room temp on top of my desk. In fact I’m thinking about putting socks on inside my slippers to keep my feet a little less cold. BRB. That’s better, not toasty, but less cold.

I’m still trying to find the right transmission for the Sprint-T. I have to keep my budget in mind, as well as the output of my most-likely engine, and also trying to maximize the result of M=f*a by reducing the value of “M” and increasing the value of “f” to get the largest possible value of “a”. And at the same time getting the highest possible final drive (lowest absolute value) for best fuel mileage on the highway, and a first gear ratio that tops out at 40 MPH in first gear. That’s a lot of conflicting values that have to be juggled. I’m still finding different transmissions that will bolt to an LS engine.

And I’m starting to get tired and ready for bed, because sleepy, so I think this is a good place to put this post to bed, then me.

Sorry for not posting

Because I don’t have anything to write about. Mostly what I have been doing is looking for an overdrive transmission that doesn’t weigh anything and has a torque capacity to handle large displacement LS engines and can be picked up for next to nothing at a junkyard. The difficulty is light weight and high torque capacity are pretty much mutually exclusive, or are hideously expensive. There is a T5 variant that weighs 80 pounds and has 550 ft-pounds capacity, but runs north from $4k when you can find it, which is slightly more often than “never”.

There’s a kit that makes a T5 handle 600 ft-pounds, but you have to have the T5 first, which I don’t. The good thing is the replacement gears in the kit are only a pound or so heavier than the stock gears so your finished transmission is 76 to 78 pounds plus a quart of ATF.

What I’m fighting against is the power to weight to cost champ is the LS-LT GM family of engines from the junkyard have more torque than the cheap transmissions can handle. The cheap champ OD transmission is the T5 at $500 and up for rebuildable cores locally, but only has a 300 ft-pound capacity and the 4.8 LS has 300-330 ft-pound output depending on tune which is the lowest of the engine families. If I wasn’t trying to build as light as possible because the classes I’m competing in have essentially no minimum weight, or a minimum weight so low that I will never get that low with the car I’m trying to build, I could go with the heavier transmissions. But I’m building light and cheap because F=m*a and reducing “m” increases “a” proportionally, and I’m a genetic tightwad. Or maybe a cultural tightwad because I don’t see any signs of it in my kids. But I’m building to a 900 pound with driver minimum weight for the class with a published minimum weight, or about 700 pounds empty, and the other classes have no minimum weight but do require equipment that kinda raise the weight the car has to be built to, like horn, headlights and fenders. And a pickup bed in one class. So we are looking at about 1500 pounds empty± in race trim (3 gallon gas tank).

And this is about where I’m putting this to bed, I’m running out of things to say.

Forcing myself to actually care about something

I think that’s something old people have a problem with, finding something to actually give a shit about as they get older. Also I’m dealing with something that’s making my damaged hip hurt, so there’s that, too.

What I have been thinking about for something to do is looking up stuff that might be useful for building the Sprint-T. The price of that upgraded T5 transmission is $3600, this week. But it only weighs 77 pounds, 2 pounds more than the stock T5. That’s pretty good for a 67% increase in rated torque capacity from 300-500 pound-feet. Most of the increase in capacity comes from upgraded materials, with the rest from slightly larger gears.

While I was it it I also looked up the weight difference between the straight axle and the independent front suspension. Actual weight on the tires is about the same, but the ratio of sprung to unsprung weight change is huge, mainly because each wheel only has half of the unsprung weight as opposed to both wheels having all the unsprung weight with the straight axle. If I got my sums right the independent suspension is 5 pounds more than the straight axle, with most of that in the frame where the suspension attaches, brackets and bracing not needed with the straight axle.

There’s also a bit more weight for the moving parts in my design because I like to have the lower arm almost a center pivot with pretty much no change in track with suspension movement. That means there will be some bump steer as the instant center moves during suspension travel and the tie rod can’t point at the point where a line drawn between the upper and lower control arms intersects so it has a different arc than the place where it attaches to the spindle. That also means the lower control arm goes halfway across the car, which makes it heavy. I’m still thinking I want to make the lower arm shorter than that just to reduce weight because it doesn’t make that much difference for the geometry of the front wheel travel. But I’ll have to buy some suspension CAD program to play around with the suspension arms to see where the crossover point between long and short control arms is for the Sprint-T.

And for everybody who reads the tags, the weather today has been wonderful, warm enough to not require heat, but cool enough to not require AC. We get about 2 to 3 weeks like this twice a year here, and we just bask in it. The electric bill is almost nothing as we only have to pay for keeping the water heater going for showers and dishes and washing hands.

Perpetually thinking about “things”

Yep, I’m still thinking because I can’t “do” because my money is getting spent on other things, like buying windows I can actually see through, and health care. Yes, we are replacing the opaque thermal windows that have degraded so bad that one corner is almost like the insides were painted over. Also paying for seeing a doctor who is not the Lab Rat Keeper.

But that’s not what I was thinking about today. I was thinking about the frame, about how I can make it easier if I make it in bolt-together sections with bolt-in braces that keep the sections rigid, and allow for different suspensions for real A-B-A testing. Like I could build one front clip with the straight axle, and another front clip with independent front suspension, and swap back and forth between the two to get a true comparison. Like swap in a few hours from straight to wobbly.

But the first part will be building the roll cage with the two hoops that are exactly the same size as the body and barely clear it as the body passes through the halo opening in the top of the cage with the bolt-in brace removed. The thing is to route the bracing so that as little needs to be removed as possible to get the body inside after everything gets painted but still braces everything against torsional flexing. What I have is a full cross brace all the way from the left to the right but split to unbolt and allow the body to get through. Then the diagonals run from the corners to the transverse brace in the middle to where the brace is removed for the body to get through. There is not that much vertical thickness to the body so most of the opening can be blocked by the diagonal bracing and still allow the body to get fed through sideways from the top. Just spin the body through the roll axis and let it fall through the halo by overlapping the diagonal bracing.

Don’t forget I have to get through that hole to get in and out of the car. I have been thinking about that and the motions required, where I have to grab and brace my body. From inside getting out is easier than from the outside getting in. Getting out is a matter of bracing my feet against the transmission crossmember on the floor, grabbing the cross brace of the cage and using my legs to push me up against my arms and sitting on the top of the cage and swinging my legs over the side and sliding down until I’m standing outside the car. Getting in requires climbing until I can sit on the side of the cage and swinging my legs over the side and into the car and using the bracing to lower my body into the seat. Anyway I have to get two 12 foot sticks of roll cage material (the 1.5″ diameter 0.120″ wall) and get two legs bent at right angles 46.5″ apart, centered on the stick so I have lots of material to work with to set the height of the cage. The top part of the upper frame rail and diagonal braces are also part of the cage, so they have to be made from the same material. But the front clip can be made from 0.060″ wall tubing which saves a few more pounds.

And I didn’t get good sleep last night, so I’m nodding off at the keyboard. I’ve basically spelled out the changes in the new design, so I’ll put this post and me to bed.

I want to stop thinking about stuff and start DOING stuff

The biggest problem I have now is I lack funds to buy tools and raw stock, or to buy the parts I can’t make. And this frustrates me no end. On the plus side I have time to think about how to do it better, like I recently did by going from a fabricated steel panhard rod to a straight piece of aluminum that weighs less than half as much by moving the frame out of the way.

“Think before doing” is a good maxim to live by, but I have reached the point of “Do something even if it’s wrong!” Or more accurately, “Do something before you can’t do anything!” as my infirmities multiply and grow worse.

At the rate things are going I won’t even be able to get in and out of the Sprint-T after I finish it because I won’t be able to bend at the hip far enough to get past the roll cage. And then I would have a true Greek Tragedy, all that planning and work but unable to harvest the fruits of my labors.

Moving on from self-pity, I’m still trying to find a transmission that will work for the mission of racing around in first gear and hitting redline at 40 MPH but getting good freeway mileage, but still not weighing anything or having to change gearing between racing and highway, and not coming up with any good answers. So far the best (lightest) solution was the 2.43 1st gear Super T-10 and swapping the gears in the quickchange rear to get stupid tall final drive in 4th from the 40 MPH in first ratio. The next best I have found is the Super Street 5 speed with OD that comes in at 35 pounds heavier but has a 3.33 first and a 0.77 5th. No need to swap spur gears to go from redline @40MPH in 1st to cruising at 2068 in 5th @70MPH.

[squirrel!]Excuse me a moment my music app just played The Song That Must Be Played As Loud As Possible (Won’t Get Fooled Again by The Who) and I had to crank my headphones up to 11. Now I have to stuff cotton in my ears to keep the blood from running out.[/squirrel!]

Getting back to the post, one has simplicity in its favor, and the other has lightness on its side. Neither has anything for cost, the cost of buying an extra spur set for the quickchange and the ongoing costs of buying rear end lube for changing the spurgears easily offsets the higher cost of the 5speed. And as I don’t have funds for either one at the moment it’s mox nix. (Or macht nichts in the original German). Also the torque limits on the Super T-10 are so low that even a stock tune L33 will stress the transmission to its limits, except the 2.43 ratio 1st gear model’s 375 foot-pound torque rating is comfortably inside the L33’s 335 foot-pound rated output.

Everything else is marginal to “ain’t no way”. 2.64 1st is 325 foot-pounds (iffy) and the 2.88’s 300 rating and the 3.42’s 266 rating are both “grenade city” except when you pull the pin on a grenade you have a pretty good idea of when it’s going to blow, about 2.5 to 3.5 seconds after you throw it. The 3.42 ratio might last until you floor it or a few seconds after, but the 2.64 is the real question mark. It might last for a season or 2 or blow up while you’re hundreds of miles from the shop and spares with no way to get there. No, if I go with the T-10 the only way to go is the 2.43 1st gear. But that 35 pound weight savings looks sooooo goooood. It’s the difference between 1490 pounds empty and 1525 which is 2.3% and all I have to do is crawl around under the back of the car a few minutes to half an hour before a race and the same amount of time after. It’s tempting as hell.

Still thinking alert, take cover immediately

J/K there’s no imminent danger. I was thinking of ways to improve the front of the Sprint-T. Also still thinking about the drivetrain with a possible manual transmission.

Starting with the front suspension and related things I decided it might work better if the panhard rod (AKA track bar) was straight. That requires redesigning to the front part of the frame so there is nothing that the panhard rod has to go around to get from the driver’s side of the frame to the passenger side of the front axle. I did this by moving the front diaphragm that carries the loads from the coilovers to the rest of the frame from in front of the axle to behind the axle. This requires moving the steering behind the axle as well as the steering box back to the kit location. This also means the radiator has to be moved back and up to clear the steering shaft from the steering box to the steering wheel. This is how designing a car goes, you can’t just change one thing, it cascades across most of the car. And I forgot to mention the complete redesign of the bumper support structure because the top and bottom frame rails stop at the front axle.

The other thing I was doing was trying to find a lightweight transmission with overdrive, and basically what I found was the Super T-10 couldn’t be made to have an OD without basically redesigning the transmission because the cluster was a solid hunk of steel. Now if it had followed the path of the sister/progeny transmission that used to be called the Nash 4+1 which uses a cluster with replaceable gears, then I could just have a replacement 3rd gearset machined and installed instead of a full replacement cluster. Anywho, the mentioned 4+1 is now the Super Street Five Speed with much higher torque capacity compared with the Super T-10, and extra weight from the structure to resist loads from the increased input.

The 5 speed handles 600 ft-lbs, compared to the 300 to 375 rating for the T-10, and also has a much lower 1st gear (actually several options that are as low or lower than the lowest 1st gear on the T-10). The price for gearing this low and higher torque handling is weight. The 5 speed comes in at 105 pounds compared with 70 for the T-10. Still lighter than any of the self-shifting transmissions with overdrive, by 60-80 pounds, plus it takes up less room inside the car, especially since on the Sprint-T the inside of the floor is also the top of the bellypan and nothing hangs lower than the bellypan, that’s another design paradigm for the Sprint-T.

The top of the bellypan is attached to the bottom of the bottom frame rail, and if there were no bellypan the bottom of the bottom frame rail would be the lowest part of the car except the wheels, because that lets the car be as low as possible without dragging the road if a tire goes flat. Theoretically all 4 tires could go down and the only thing touching the road would be the tires. This requires the road to be pool table flat, but even on normal pavement I can still get both tires on an axle going flat without anything touching anything except tires. I picked this one up from off-road trucks that need to be able to keep going with flat tires.

Anyway, going from a bent panhard rod to a straight one allows a smaller size rod and also allows changing from steel to aluminum, and the combination allows for the drastic reduction in weight of about 2/3, and as half of the panhard rod is unsprung a reduction in unsprung weight as well. This results in a slight increase in grip on bumpy roads and courses as less unsprung weight improves the ability of the tires to follow bumps without leaving the road. This is why I try to reduce unsprung weight every chance I get.

Couldn’t stop thinking last night

And it kept me awake until nearly dawn thinking about getting an overdrive for the T-10 by swapping in an OD for 3rd and changing the shifter to allow it to be the new 4th.

In doing my research for this I discovered that the OE 3rd gear is already a slight OD as the ratio between the input and cluster shafts is 1.28:1, while the output from 3rd is 1.23:1, which means the ratio of the gears on the 3rd position of the transmission is already an OD just not very much of an OD, 0.96, probably just a tooth larger on the cluster than the main shaft. It’s looking like I will have to order a custom cluster with a custom gear for the main shaft that is as small as will fit. This is not an inexpensive alternative.

And it’s not like I could amortize the costs by selling duplicates at a profit until the tooling costs are covered. This application is very niche, not many people are in the market for this combination of light weight and OD top gear, and can live with only 4 speeds. Also I have been looking at the ratios in use on the transmission and most of them are not actually useful in making 3rd OD. Swapping the gear for 2nd gives an OD that is not even enough to make the output OD, the gears are 1.25:1 as they are before swapping which is less than the 1.28:1 of the input gears. So basically I’m looking at finding the smallest gear that will fit the output shaft and designing a gear to machine into the 3rd position on the cluster and hoping the resulting ratio is enough to be more overdrive than the underdrive ratio of the input shaft to the cluster. Also most of the different ratios available are just from changing the ratio of the input to the cluster, the 2.43 S cluster, and the 2.64 W cluster are the same ratios except for the input/cluster gear. In fact checking the spares list shows that most of the ratios are shared with common 2nd ratios for the S, W, CC, and Z clusters, common 3rd for S and W, and common 3rd for X, CC, and Y. So yeah, I will have to order a special cluster and gear for the main shaft if I want to hang an OD 3rd on my transmission.

And I have been going back and forth between the PDF of the spares list, the calculator app, and this post for like 4 hours, it’s time to put this one to bed.

Been thinking again about suspensions

Basically what I was thinking about was tall front uprights for camber control. Basically the taller the upright the less the suspension arms change the camber of the wheel because the side to side motion induced by the arms rotates the upright in the camber plane in inverse proportion to the distance between the ball joints.

GLOSSARY

Camber – The angle between the tire and the road surface. Positive is the top of the tire tilted away from the center of the car, negative tilts toward the center of the car. This is backwards because positive camber is almost universally bad for tire grip and is therefore a negative, but the terms were defined prior to the invention of the pneumatic tire and now we are stuck with them.

Kingpin inclination – Another term that is archaic because kingpins are from solid axles except for a very tiny number of early independent front suspensions. It refers to the angle of the axis of steering rotation for front wheels between the upper and lower ball joints.

Scrub radius – The distance between the intersection of the steering axis with the ground and the center of the wheel. Basically this is the moment arm of the force generated by the brakes through the steering system. The greater the absolute value of this number the larger the force felt at the steering wheel under braking. The direction of this force depends on the positive or negative value of the radius. If positive the steering wheel will turn in the direction of the greatest braking force, and opposite if negative. Now there are schools of thought that if the system is designed to turn away from the stronger braking force it will be self-correcting in the case of brake failure. There are other schools of thought that drivers will instinctively turn away from forces trying to steer the car so positive scrub radius is better, with the debate coming down to do you want your driver to be an active part of the car.

Upright height – The distance between the upper and lower ball joints of an independent front suspension

This is a hypothetical discussion because the front suspension for the Sprint-T has been frozen as a straight axle, and because my fabrication tools are not up to building suspension uprights. So theory only. No labs for this lesson (shoutout to my teacher friends who “get” this joke). Theory for this starts with the statement from the opening paragraph camber change is inversely proportional to the distance between the ball joints. Second is that the position of the bottom joint is constrained by the dimensions of the wheel used, because kingpin inclination and reducing scrub radius dictate the location somewhere inside the wheel. Excessive positive scrub radius has been proven bad experimentally by excessively increasing the force required to steer under braking.

And it just dawned on me this post needs a glossary to keep track of all the technical terms. We already have camber, kingpin inclination, and scrub radius besides upright height. Basically I’m assuming my reader has a working knowledge of terms used in suspension design, which is probably not the case. So I’m inserting one following the first paragraph. It’s there now but wasn’t before I started this paragraph.

Anywho, the design parameters basically dictate the lower ball joint be as far inside the wheel as possible constricted by the brake disk because of scrub radius minimization. It doesn’t matter if you want positive or negative scrub radius, you still want it to be small or variations in braking force caused by changes in road surface can tear the steering wheel out of the driver’s hands which is bad no matter how you look at it.

Also, the amount of camber change caused by body roll is proportional to the ratio of the distance between pivot points on the frame and the distance between the pivot points on the upright. Desirable geometry of defining the instant center dictate this is going to be close to unity and usually less than 1:1. There are some old GM cars that had this greater than 1:1 and they understeered excessively with the outside front wheel riding on the sidewall of the tire. Look for images of the late ’60s Chevelles making hard turns and you can see this in action, but not many of those pictures made it to the internet and the only ones I have are in paper books on suspension and my cell phone camera did not get a good picture of the picture. One of the things about having the ratio between the distance of the suspension pivots greater than unity is the front roll center is underground, which causes the body to roll excessively and further causes the car to ride on the sidewall of the outside front tire. This meant that racers using this car as a base for stock cars had to crank in ridiculous amounts of static camber and excessive amounts of roll stiffness to keep the car driving on the tire treads instead of the sidewalls. They made it work but it would have been easier if the front suspension was designed right in the first place.

Getting back on track for this essay without any more digression (squirrel!), we want to basically define a height range for the front upright. Too tall and either we get “funny” geometry in the suspension or we get the pivots for the upper suspension arm somewhere in the boonies, which technically is “funny” geometry. Too short and we get poorly controlled camber as the car goes through bump and/or roll. My personal take is I design about the same as the inside diameter of the front wheel as my max, and about 8″ as my minimum except for suspension karts. No matter what you do those are “funny” because no room.

And I seem to have lost the point of this post except that I woke up in the middle of the night thinking about front suspension uprights. So since we hit over 1000 words this seems like a good place to stop and hope I get my train of thought back on the rails for a future post.

Still thinking, remain in cover until the all clear has been given

I’m still reading my new book about suspension geometry and contemplating the information, but it hasn’t resulted in any changes to the Sprint-T. The front is still a tube with fore and aft location by parallel 4-bar and laterally by a bent Panhard rod to clear frame members, rear is still fore and aft by dual trailing links and laterally by a Watt’s link and a torque arm for control of reaction torque from the engine. And torque reaction links for the brakes. All rotational reaction forces are isolated from the suspension to prevent locking up the suspension from either engine torque or brake torque, allowing the suspension to move freely at all times. The front springs are mounted as close to the ends of the axle as will clear moving parts, and the rear springs are mounted to the trailing links originally designed for swingarm suspensions of much heavier vehicles on rough tracks. This allows easier tuning of suspension stiffness by changing the motion ratio for the springs as there is quite a bit of motion ratio to play with.

To clarify that, the bottom of the spring mount moves less than the wheel in both single wheel and double wheel bumps. This means I can get smaller changes in wheel rate than steps in spring rate which gives me finer control over wheel rate. Also the total travel of the shock is less than the travel of the wheel which reduces the amount of force per inch of wheel travel. There is a formula that gives us the effective wheel rate when the spring rate is known (mr2*Spring Rate) or the square of the motion ratio times the spring rate. On the rear suspension for the Sprint-T there are two motion ratios, the motion ratio for a single-wheel bump or body roll and the motion ratio for a two-wheel bump which is just the motion ratio of the swingarm. The single wheel bump is the swingarm ratio times (the distance from the far wheel to where the swing arm attaches to the axle housing divided by the track).