Technical PtII-Ratio of Spring weight to unsprung weight unfavorable, what helps?

I guess I'm too simple minded...it's like the guy filling out the job ap...I'm a Land Beautification Engineer......I said, what do you do?..he said...Cut Grass........the simple answer took on a whole new meaning..........but keep it going...what I don't understand, I skip over and figure the guy cuts grass...hehehe

 

Also...........post some pictures of your stuff 31 Vicky......I'd like to see what we're arguing over.

 

This is what I'm working on now-
The entire Saga so far is there.
Be sure to check the links in the thread too.
http://www.jalopyjournal.com/forum/showthread.php?t=850807

Lots of pics

 

I'd like to know if this levered motor mount system is used in other forms of racing, in particular drag racing where weight transfer is paramount. With all the tricks that have been used to alter weight transfer, and in classes where engine setback or wheelbase alterations are not permitted this should be common practice.

 

When suspending the rear axle from behind you can use less spring rate than if it were mounted on top or in front of the axle. This works very well for spring/shock units (coilovers to us) and should also apply to "spring behind" transverse leafs. The rate can be reduced (lbs per inch) to allow faster reaction to load simply due to leverage. Does it really work? I suspended a 3545# O/T racer with 110# coilovers. The car scaled out at 1625# on the rear axle, 1920 on the front. I don't recall the static preload on the springs, or more accurately, the installed ht vs free length. It worked pretty well delivering consistent 60' times in the low 1.40s. The ladder bars were standard fare. I ran them pointing slightly down at rest. My theory was that the bars "lifting" the car at the X member also extended the axle centerline dimension. Not by much, but the arc of travel allowed for it and improved 60' times vs the bars level or pointing up. Since the forces were going to lift the car I sought to use that work to move the rest of the car forward at the same time that the tires were loading up to do their job.

I don't know if these observations will apply in whole or part to the actions and wt placement you're seeking, but it worked very well on a heavy car limited to true 10.5 X 29.5 tires.

 

There's been a few circle track racers say this is used there.
I've not been around circle track stuff so its almost all new to me, I can't say one way or the other. Maybe its common knowledge there, maybe its quackery, maybe it'd be equal to the secrets of the illuminati.
But I'd sure like to understand more.

 

I'm sure they do apply.
Do you remember how far behind the springs were?
On this one I'm doing now, the C of the transverse spring is 8" Behind the C axle. I'm more than reasonably certain this will multiply the effect. But I'm not sure how much, or where the loaded ladder bars are transferring the load from, and unsure of how to use this to more of my advantage. Not even sure which way to guess.

 

Man I am glad you said it!...As I was going to say the same thing but figured my post would be deleted again....I think since NASA canceled the space program, Alot of out of work rocket scientist joined the hamb....LOL Where should he put the motor mounts to get this sucker to go to the moon??...LOL (my post is just good humor No offense intended)

 

Pardon my "art", had some time to spare and thought this would illustrate what Highlander is getting at. A,B and C are the alternate mounting points, second pic is an exaggeration and third may help to demonstrate why the other end of a mount doesn't really matter since the load is still applied in the same spot. Last pic would also feel spongier since the bracket itself is less rigid.

 

Not too far off probably.

HehHeh...My first engineering job was in 1976. I was designing roof trusses and writing code for a production line that ran off a paper punch tape. (Used in the days of IBM cards and before Floppy disks.) I was also writing programs for a microcomputer. It sure beat building VW engines for a living.

I remember when they started cutting the aerospace budget. There were thousands of engineers out of work here.
I got laid off work when my contract expired & I went to the unemployment office.

The guy behind the counter was an out of work engineer. The guy who sold me lunch at Wendy's was an out of work engineer. The year I started college was the lowest engineering student enrollment in several decades. Even so, it was sometimes hard to get work. I ran heavy equipment and supervised a welding shop, and did computer work on the side.

I have a Punjabi friend who works at the local liquor store. He was a civil engineer in India for 20 years.
He tells me he has a better life here in California selling liquor than working as an engineer in India.

So it ain't all gravy.

But it beats stripping greasy Kubelvagens.

 

good pictures showing the fulcrum/pivot points. if some of the weight was ahead or behind the axle/pivot/fulcrum and the vehicle was in motion, either accelerating, braking or cornering would the lift point of the motor attachment matter?

 

Not completely sure what you mean. I was mostly partaking in the part II discussion though pic 3 does relate somewhat as far as static weight distribution. To be honest all this text is making my head hurt.

 

now that i think more about it, your picture helped me.
on the race car, if we removed the right motor mount completely the motor would want to fall towards the right front tire, and if the suspension in the rear was soft enough it would want to lift the the left rear of the frame. more of the weight of the motor would be on the transmission mount and closer to the right rear. the pivot point of the weight would be left front to right rear and flinging the car into a corner would amplify the loads.

 

Another thing, ladder bars are inherently bumpy going since you basically have turned the 3" tube of an axle into an anti sway bar. Can be helped with long bars mounted close together in the front, wide in the rear. The frame will twist less with torque applied on a narrower span too. Willys have some spindly frames but if you study some of the old gassers, the side mounted bell housings and forward ladder bar mounts were about on the same center making torque on the frame a non issue.

 

Hmmm, still not really grasping it, lots going on there.

 

it's late, i am tired, i reread it and i agree with you.

 

31Vicky yes I was talking about coils just for the example part of this. How you mount your coil has a huge effect on the rate that is seen - in a similar way as you moving your buggy spring back and forth on your teeter totter. I did kinda forget that you were running a buggy spring - that happens when we read too fast while the kids are piling into the car waiting to go to their game!! ha ha

Oh shit now I forget the whole point I was trying to make...oh yeah ....I was gonna say - it'd be fairly easy to make up a fixture to measure the actual force - whether it is a coil spring on an angle or a buggy spring shifted to and fro on a trailing arm. You can take a valve spring checker and and adapt it to fit in the area your spring mounts - inbetween your buggy mount or even to temporarily replace your coil. If you're too cheap (like me) you can even make the checker -use a 1-1/8" bore housing (think brake m/c seals or even a call to McMaster-carr - loaded lip seals work good) IIRC so long as you keep with the 1-1/8" bore your gauge will read directly in pounds. Not sure if this is more BS than you care to fart around with, but I know for certain I'm gonna make one like this for coil overs.

 

I happened to be at my friend's wrecking yard yesterday watching bubbles in my radiator, not good. Anyway he races dirt track, builds his own cars. He had a couple of books by a Steve Smith on chassis setup. Never heard of him myself, seems to be quite a prolific writer on the subject.

http://www.speedwaymotors.com/shop/Steve-Smith-Autosports/11.html

Couldn't find anything even close to it in the two books we thumbed through. I sent him an email, let you know what he says.

 

Here's the tech Andy did for a 1-1/8 bore load cell, it utilizes wheel cylinders.

http://www.jalopyjournal.com/forum/showthread.php?t=588650



Way better than guessing but if you want to split hairs to less than 50 lbs or so the gauge is not going to make it easy

 

Splitting hairs, maybe, but I've always understood the "polar" part like a bar magnet, i.e. the "poles" are the more or less heavy ends, in the present case most often front and rear. The point of "polar" being that we look at each "pole" of the bar in isolation lest the moments cancel out and tell us nothing.

As you implied in passing earlier, polar moments of inertia cut both ways. A vehicle with low PMI is easy to get into a spin and easy to catch again; a vehicle with a lot of PMI will tend to keep spinning once it's spinning but would be harder to get spinning in the first place. Both characteristics can be beneficial, depending on the situation.

Something I haven't seen in the theory around PMI is that there must be a corresponding polar moment of grip. That is, the effect of PMI will depend on the positions of the tyre contact patches relative to the axis of rotation. A low PMI has a greater effect if the wheelbase is long, as lesser inputs are required at the contact patches for any given inertia, and vice versa. I can't think why anyone would want a high PMI on a short wheelbase, though: if stability is the main consideration, a high PMI combined with a long wheelbase would be the stablest of all.

I'm all for empirical engineering, for rules-of-thumb developing in the field so that someone can make something without having to go back to first principles every time. The idea that making things should be restricted to an elite is anathema to me, and I oppose it with every fibre of my being. By the same token the theory is out there; it's open to anyone with the ability and inclination to tackle it.

Theory and practice should respond to one another. They should be in conversation; they should be dialectical, to use the language of Plato and Marx, among others. Most of the time they are. The nature of theory is that it has to correspond to the real world or be tweaked and refined until it does. It's ongoing.

One danger with rule-of-thumb engineering without theory is that it can be very easy to see something correctly but then explain it incorrectly. You could even say that there is nothing wrong with this as such: an argument can be made that nobody can understand anything except by making up some kind of story around it. The problem is when you start making subsequent deductions from the incorrect explanation.

It's a questionable cause-type fallacy, like post hoc ergo procter hoc. TANNERGANG, I'm sure your engine mountings worked, and that they arose from some fine intuitions about what you were trying to achieve, but if we accept your explanation of how and why they worked we'd have to throw out a huge chunk of statics and geometry that has been working perfectly for centuries.

The flipside of spring rate is, of course, travel. It might seem like six of one and a half-dozen of the other whether we set up leverage for a stiff spring with a short travel or a soft spring with a long travel. In practice it is often easier to deal with things like bushes and damper valving in the latter case. Wear interfaces are more lightly stressed, and assemblies might not need to be quite as rigid as otherwise. There is often a mass advantage.

 

What I see here, with reference to the first pic and being static ...
With spring force at position B, - the ladder bars would not generate any load at the frame mount neither up nor down.

With Spring In position A, the ladder bars would be placing a downward load on the ladder bar frame mount. That force downwards force would some how follow the curly cue to both the front and rear. And the further away from the axle the more force applied to the mount.

With spring in position C, the ladder bars would be placing an upwards force at their frame mount. Again that force upwards force would follow the curly cue to both front and rear and again the further away from the axle the more force.

does that make sense so far ? I'm pretty sure that the concept does and logic with some physics says it should be so. This particular application for reference is going to be with spring in position C

I get that far and start thinking how to use that concept to do a bunch of stuff .... balance the car, at least move the sprung : unsprung ratio the right way, get it to hook hard and not unload, not stand straight up, go straight- This is the goal I suppose and the things I am trying to achieve, so the question marks later in this post refer to accomplishing this. At least not make any of it worse. I see the dynamics of spring position C changing when the engine torque makes its way thru the chassis. There's a lot of concepts that come into play, CG, neutral line, anti squat that is see possibly moving , but which way??? What direction to guess in???

Moving objects around and choosing the placement will change those forces, adding weight as a last resort will also. But adding weight apparently has an effect on the polar inertia moment. Not quite sure how many axis or poles I need to be concerned about but I'd imagine there would be more than one. For instance placing the battery between the ladder bar frame mount and the axle would be different than placing it behind the axle. Adding 80 lbs to each side if the frame just before the kick up would have an effect on sprung weight, center of gravity and PMI, But 160 lbs mounted in the same for and aft location but centered over the drive shaft would be different PMI

Just for example - What I see the difference is that if the battery were behind the axle, it would certainly add to the sprung weight but at the same time add more upwards force at the ladder bar frame mount. While placing it between the axle and the mount would add some to the rear sprung weight and add some downwards force at the ladder bar frame mount to balance the upwards force. But which do I want?????? And why do I want it???

If my calculations from the previous post are correct, if i were to move things from a location near the ladder bar mount to back behind the spring it would have at least least a 16% amplification of that relocation. Is that what I want ???

 

I probably should add that the ladder bars are P&J style with a close mounting at center

 

I'm quite sure from your answers I've read that your an intelligent guy..but....as I start to understand what your talking about I think of the Amzoil salesman we used to have...if you asked him what time it was..he'd tell you how to build a watch....I understand you guys love to dig into theories and why mass is this and leverage is that.....I was raised up on a farm and we looked at the broken part and fixed it or figured out a way to make it work better with another application method...while I appreciate guys like you......and we need yall.......most of the time when your explaining something...YOUR SPEAKING GREEK TO A MEXICAN.....When I raced I'd have guys ask me how did I know this or that would work...and I'd say i just kept trying different stuff till it did what I wanted to do......I did it the hard way in the shop or at the track, you guys do it on paper in an air conditioned office.....you can explain why it does what it does and we are doing it and don't know why it is, but it is......but when it's all said and done....we're all in this thing working together...some use a pencil and paper..some use a torch and welder...hehehe

 

Pretty sure were on the same page with the spring mounts as far as the forward ladder bar pivot being loaded one way or the other with the spring on either side of the axle. The whole combination is basically two levers linked together and pivoting on the axle centerline, giving an advantage to the spring in example C which would tend to lift the frame at center.

Works with a pivot but not a solid member with the load point still the same as in the last pic. Curly cue was just a representation of a hypothetical Dr. Seussesque bracket going to another part of the frame. When it comes to redistributing weight I tend to think like a drag racer and put it all towards the rear bumper but sounds like to keep your "pole" happy, down low and near center sounds like the way to go.

TANNERs got a point too, sometimes you guys sound like your speaking Latin...oh wait, someone actually did.

 

Cogito Ergo Boggum.

Roughly translated: I think too much, therefore I bugger things up.

What engineers do with a pencil is model things. We make models with numbers and drawings which help us design useful stuff from ideas.

The problem is that only the simplest of things can be modeled with numbers conveniently. Complex devices and structures are often just too complex. Even with computers, some things are just too difficult to model that way.

So we do these calculations, but they are often mere guidelines. To really prove things will work you often must simply build and test.

 

What's the Latin translation for ...

I can think 100 times faster than I can build and thinking is free?

 

The same math was done long before computers were invented. Engineers designed those cars on a drawing board not by trial and error. If you look at the drawings they did, they had all the weights figured out before anything was built.

 

I can only add what worked for me in an O/T bracket racer and why it worked as it did. Springs were at 'C', bars faced down "1 hole", when force was applied to the rear suspension (forward mount) it was enough to not only raise the car but to extend the wheelbase about 3/8" due to the arc of travel. In an "enthusiastic" discussion at the track one night I placed a jack under the cross member and had one of em measure from the tread to the wheel opening. Then I raised the bar to level and the difference was 3/8". To my way of thinking that 3/8 helped move the car forward as well as up (upon load) and as an added advantage reduced 60" times. In pictures where the car was wheels up there was also additional space over the slicks vs the wheel opening being right on top, which was evidence that the bars were doing their job. The difference in my get up vs yours is that all the main mounts were pivots. Bar mounts and coilover mounts were like rod ends. What will the transverse leaf do would be my interest since it pivots side to side vs fwd and back.

 

If you want to add weight without it showing, use lead inside the frame. It can be melted and poured into any shape. To get the rear weight, put it in a bumper so it is as far back as possible.

Weight transfer only works under acceleration or braking. If you just lift off the throttle a little, you'll still have the bumpy ride.

You probably don't want to hear it but air bags would give the best ride.

 

Yup.

...and they had to use educated guesses (estimates) about some things as they developed the design.

You don't know how strong to make something until you know what it weighs, but you don't know what it weighs until you pick something you think will work, then plug in the numbers & see if it really does.

We have the same issues designing buildings.

We have to get the foundation laid out before we can lay out the steel, but until all the steel is worked out you don't know the weight of the building and can't size the footings. Until the footings are sized you don't know the dynamic response to an earthquake, but you can't run the analysis without picking some size to try.

And just how strong is an earthquake anyhow? We sorta pick one, based on historical data & current theory, but the next one in that area could be 10x worse because something far away that's never moved suddenly moves a lot.

It's like building a car. You test things. Sometimes they don't fit and you have to grind and bend. Sometimes you find that because one thing didn't work, 6 other things need changing. Everything develops in stages.