Marcus' Car9 - An Adventure...

[john hennessy]

are you guys really welding the inner parts of hidden tubes in a node, if you are, then i ask WHY?

imagine two tubes welded together at a 90 degree mitred corner, is this any weaker than one tube welded to the side of another tube at 90 degrees and the main tube cut off with the ajoining tube?

work out the length of weld and the mitred joint has more weld to it over a larger footprint.

if you had six tubes joining in a star pattern, any tube within the peripheral weld is not required.

imagin the same star joint but with two round wavy gussets on either side of the joint so that each tube was welded to the gussets and the gussets were welded to eachother, no weld would be inside the peripheral welds, just like the hub and spokes of a wagon wheel.

[horizenjob]

I'm in better shape than I thought at first. I can sit my diff at 7.5" at the nose. I'd like to be able to get it an inch lower but may just defer those types of mods. I'd rather not cut things up that take me a step back.

Tom, on your car the tubes extending out to the upper rail are to complete the truss and to provide fore and aft support. In this car the truss is there but it's in the bulkhead behind the driver's back. Basically all the same tubes are there, just in different places. The cricket legs are not very long and I think they would support my weight, maybe I should try that when I weld them in.

[horizenjob]

are you guys really welding the inner parts of hidden tubes in a node, if you are, then i ask WHY?

I have and I ask myself the same question. The last node i made I did not bring the tubes into the same point, I let them join the frame rail tube next to each other...

[a.moore]

are you guys really welding the inner parts of hidden tubes in a node, if you are, then i ask WHY?

imagine two tubes welded together at a 90 degree mitred corner, is this any weaker than one tube welded to the side of another tube at 90 degrees and the main tube cut off with the ajoining tube?

work out the length of weld and the mitred joint has more weld to it over a larger footprint.

if you had six tubes joining in a star pattern, any tube within the peripheral weld is not required.

imagin the same star joint but with two round wavy gussets on either side of the joint so that each tube was welded to the gussets and the gussets were welded to eachother, no weld would be inside the peripheral welds, just like the hub and spokes of a wagon wheel.

I was going back and forth on this years ago and was thinking along the same lines as you but also wondered if there weren't scenarios where it would matter (IE the weld isn't evenly loaded). I asked this question to Lincoln Electric at a seminar they held on MIG welding cages (namely for NASCAR) and they said weld it all since the hidden seam can be a place for a failure to start if it is left unwelded. It sounded like a logical enough reason.

[Lonnie-S]

I didn't have the great technical source that Andrew mentions above, rather I thought of Old Murphy and his various Laws. Based on that, I welded all the hidden joints and coped joining tubes to those welds, which I smoothed by filing.

If I were to do it all over, I'd do the "imperfect triangulation" approach that Justin and Cheapracer are using. Then there are no hidden welds and all welds are accessible and relatively easy to do. The sacrifice in strength from "ideal" joints is minimal. The benefits are many in contrast, I believe.

Interestingly, a week or so ago when I was researching a welding product on the Internet, I found a company online whose whole business is welded 3-space structures. They use the "imperfect triangulation" method extensively as was shown in their photo gallery of completed projects. There were very few "perfect" joints in their work.

Cheers,

[horizenjob]

I think you would weld all the seams to provide the best stability and endurance in the face of massive destruction during an accident. Once you get there you are already rolling the dice though and it's not clear it would make a big difference. Maybe it would help prevent you from dying with a horrified look on your face.

So I think I'm on the third spin for the cricket legs holding the diff rear cover. Basically I am moving from adding frame to mount the diff to "adding frame to mount the mount for the diff". In software engineering there is a saying that all problems can be solved with an additional level of indirection. So this way I weld something to the frame that takes a bracket or plate that the diff bolts to. So then I can change the height of the diff or even the type of diff and have a better chance of things working out. I don't need to weld 2 mounts that are 6 inches long and have their center to center distance be perfectly matching the diff cover. I was afraid I would weld it up mounted to the diff and the first time I unbolted it it would not bolt up again easily.

I had a good weekend, spent a couple of hours visiting with a fellow from my local car club who races a Factory Five Cobra. He lent me a T5 core and a SBF oil pan. This is being a huge help laying out the placement. One thing I learned is that I can't modify the front left of the oil pan much for clearance because that is where the oil pump lives. Funny how you can't see that until you have an oil pan in hand. Also the T5 has a pretty big bulge on the rear passenger side.

Here's a picture or two playing with the installed height for these parts. Need to borrow a flywheel and see what it's outside diameter is. This stock pan is just under 8" tall. I bet they call it 7.5" though and don't count the drain plug. They do make 7.5" pans with a side drain and also 6.5" pans (Aviaid).

BTW, it's pronounced Cah-Nein.

[seattletom]

Here's a picture or two playing with the installed height for these parts. Need to borrow a flywheel and see what it's outside diameter is. This stock pan is just under 8" tall. I bet they call it 7.5" though and don't count the drain plug. They do make 7.5" pans with a side drain and also 6.5" pans (Aviaid).

BTW, it's pronounced Cah-Nein.

Love the Boston twist on the pronunciation

Looks like you are at a fun stage of your build: Finding places for the big pieces. You might want to consider settling on the oil pan you will use, as this will drive all the driveline component heights and angles, including your adjustable diff mount. The pans shape could also impact engine offset options.

Great to see it coming together

[GonzoRacer]

BTW, it's pronounced Cah-Nein

Ain't that the latin word for "Dawg"????

[robbovius]

BTW, it's pronounced Cah-Nein

Ain't that the latin word for "Dawg"????

no way man, that's retahded

[john hennessy]

be aware that if you choose a high volume oil pump, dependant upon the make/model, even the stock pan may need to be enlarged in the oil pump area so when you get to that point, choose a pump that will fit in a stock pan.

alternativly, you could use a front sump pan of the same depth as a rear sump pan with a suitable front pickup pipe, then you can use any pump you want.

[GonzoRacer]

Yo, Marcus-
I the picture of the transmission, I can almost see that same reverse-light switch that cracked and leaked trans fluid all over the cockpit of the Slotus... It's a plastic nut with a metal center piece, with an electric "spade" connector on the end. The one I had was all painted silver, except for the spade. I thought it was all metal, didn't worry about it. Apparently, in one of our "take the motor out" repairs, we busted the little barstard without knowing it. Found out at the next event.

Now, I'm sure you would never overlook something like that and cause a leak in your transmission or anything... But now you know...

Regards-
JDK

[horizenjob]

Thanks for the advice guys, I need plenty of it.

I have found a motor to start off with and will get to pick it up next weekend. It's $100 in somewhat unknown condition. It was running when it was pulled. I need to get it an oil pump, flywheel and clutch. It will serve to look like an engine for the moment and let me finish the frame and should run for at least long enough to shake some things down. Basically I'm pretty ignorant on these motors so expect it will get me an education.

I bought a Ford Motorsports oil pump for it, standard volume and pressure for $18 new. Hard to beat that. I think there will be some things to like about using a motor with so much after market support! I need to pick a carb for it. Sigh, why is it even I can see how much better a $700 carb is than a cheap one just by looking at a picture.

This motor is coming with a nice road race pan that is only 7" tall and has baffles with trap doors. Have to pay for that though. That's about the clearance of the T5 so it's a good match and probably an inch lower than stock.

[horizenjob]

I fInally got around to redoing the FEA work for Car9. There was initial design work done in Grape to check the stresses and stiffness of the frame. As time went on and real world progress was made changes were done and it seemed like a good idea to revisit this.

So last weekend I made a new model from scratch and it is much more detailed. I am putting in the suspension and mounts for the motor and diff. It's been a lot of fun actually. I am repeatedly amazed how much difference small changes can make. My first pass thru I left out a pair of 6" long tubes that are part of the dash hoop. The dash hoop is an important part of this car and without it working properly something like %50 of the car's stiffness was gone.

The cars weight has risen a bit, for some reason it almost never goes down. There are several tubes here that I would swear weigh less than 1 pound each and yet they have succeeded in contributing to the total weight nevertheless! I need a "Reality Bites" t-shirt. I think the car is a little over built, something that happened because I am cautious and also the first examples have V8's.

Here is a picture showing the highest stressed tubes in the car. The tubes in red are carrying a bending load of 15 KSI interesteing. The highest axial loads are around 10 KSI in the diagonal tubes at the top front of the engine bay.

So with a load of 1000 lbs. up and down at the rear coilover mounts behind the driver's shoulders, the car is flexing 0.17". The car is ~21.5" wide at the tube centerline there, so how stiff is it in lbs. / degree?

When I get a little more checking in this model it will be posted in the FEA thread. The diff mounts are showing a pretty high stress with a thousand pounds of force distributed on them.

[Bobber]

Torsion = 2 loads x 1000 lb x 10.75" = 21,500 in lb / 12" = 1,792 ft lb

Torsional Rigidity = 1,792 ft lb / 0.453 degrees = 3,956 ft lb per degree

(0.453 degrees is from 0.17" deflection over 21.5")

Verify that the 1000 lb loads are acting 10.75" from the vehicle centerline

[horizenjob]

The loads are 21.5" from the centerline... So about ~2200 ft./lbs. I think.