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 Post subject: Re: My messy new shop
PostPosted: Mon Mar 26, 2012 7:57 pm 
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The voice of reason
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Hi Krepus. Making the parts accessable and replaceable is something I am trying to do. It's been the first comment I get when I show the drawings to people that I know are mechanics. I can imagine why... :) I have drawn a couple more versions today with minor changes trying to provide more room for removing the diff completely. It's hard to tell from just the software model wether it's doable or not. I was hoping to remove it from underneath, but the R160 has a very long nose so it may be hard. I was also hoping to panel in the floor in the back for aero, which would make it need to come out above. Maybe a hinged lid on the rear of the car...

It's a good point about a removable rear brace and I think I will go with that idea. Getting the brace out of the way will almost certainly make it easier to remove the whole diff in addition to just the rear cover. It also frees up the shape and where it mounts to the frame too.

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 29, 2012 2:30 pm 
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Here's a couple more pictures of the rear. I adjusted the rear lower tubes enough that the diff ( at least the R160 so far ) can be pulled out the back directly. I have also drawn in the tubes to bolt the suspension arms to. It seems like the bolt on shear tabs are worth going with so it is set up for that. This means the tubes that the suspension attaches to have to be about an inch behind the roll bar bulkhead to avoid them being difficult to bolt to or supporting their loads off axis etc. It still needs some work to draw gussets to make sure things are solid.


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Car9Gstab17rearB.jpg
Car9Gstab17rearB.jpg [ 114.51 KiB | Viewed 823 times ]
Car9Gstab17rearA.jpg
Car9Gstab17rearA.jpg [ 99.03 KiB | Viewed 823 times ]

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 29, 2012 8:02 pm 
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horizenjob wrote:
Here's a couple more pictures of the rear. I adjusted the rear lower tubes enough that the diff ( at least the R160 so far ) can be pulled out the back directly. I have also drawn in the tubes to bolt the suspension arms to. It seems like the bolt on shear tabs are worth going with so it is set up for that. This means the tubes that the suspension attaches to have to be about an inch behind the roll bar bulkhead to avoid them being difficult to bolt to or supporting their loads off axis etc. It still needs some work to draw gussets to make sure things are solid.
Car9 just keeps lookin' better!

Any thought to capturing the forward end of the trailing arms between the shear tabs? This would put the through-bolts into double shear and put the loads more on-center. Might make stronger mounts for the V8 cars with lots of push. Potential interference between the lower trailing links and the chassis diagonals could possibly be mitigated by shimming the rod ends towards the outer tabs. And stylish divots in the side panels could provide nice accents along with the needed clearance. 8)

The rear chassis design has really evolved nicely. Very clean! If you do need a removeable tube somewhere in the chassis, here's an interesting tube coupling product:
http://www.denunzioracing.com/shop/denu ... lings.html Nice clean solution. Good article about it in StreetRodder Magazine, Feb. 2011.

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"...the goal is to make the car look as if it has half as many parts as it really does. Keep it clean and simple." per Pat Prince as told to Peter Egan
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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 29, 2012 11:07 pm 
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Any thought to capturing the forward end of the trailing arms between the shear tabs?


Well I agree and have been thinking about it. One issue is the bodywork gets in the way if the trailing arms are not on the outside. I'll address that with a request for opinions below. Going with what's there in the picture now, I'd say use the long radius rods available in oval track catalogs. That length is sold as "3/4 radius rods" meaning 3/4" rod ends and 1.25" material swedged down for the rod end. This part would use a bolt more then twice as strong as a 1/2" bolt and the rod end itself would weigh about 3.5 times as much.

I should draw that part in just so you can see it. It would probably intimidate the competition. I would also say that single shear is what holds the flywheel on, the clutch too and also the car's wheels. The load is distributed across four mountings, but assume for a moment it's on one mount. Pick 3000 lbs. of force for a round number. Your motor could do that, but I am not sure where the traction would come from. You would be accelerating at 2g's. The off center load would be less the 250 foot lbs. of torque. The compression on the bracket would be about 1/3 the yield strength of a 1" strip of the bracket material. The actual load on the bracket at the "contact patch" of the bolt could be quite high, but I am assuming ( and drawing in ) some support around the bracket holes. Usually a tube welded thru and something like a washer welded on the face.

I am thinking of a bigger change to try and work out what you're saying though. I'll include a picture below of a typical OEM control arm which supports both the weight of the car and also a trailing arm into the mid span of the "wishbone". I see this a lot in cars. It makes the arm heavier, but it may not be so bad for us. The wishbones and radius rods weigh very little compared to the (rear) spindle 10+ lbs., disk 15-20 lbs. wheel 10-20 lbs. tire 10-20 lbs..

What I'm thinking is designing the control arms to have a clevis for the trailing arms. Then we have much more choice in wheel offset because we do not need to attach the trailing arms to the upright. It seems doable to attach to the upright, but it seems the choice is confining us a bit. Once we decide to attach the trailing arms to the upper and lower links then I can make the rear roll hoop just a couple inches narrower then the main frame rails and run the trailing arms straight back between the upper and lower frame rails. The trailing arms fit between the diagonal and the outside skin.

You would need another layer of skin on the inside to protect the passengers from the moving trailing arms.


Attachments:
Done 22.jpg
Done 22.jpg [ 94.59 KiB | Viewed 786 times ]

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 29, 2012 11:23 pm 
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Quote:
One issue is the bodywork gets in the way if the trailing arms are not on the outside. I'll address that with a request for opinions below.


Hi Marcus-
The bodywork (fenders, actually) and the 4-link arms can co-habitate quite nicely, as evidenced in the pic below:
Attachment:
Mallock Side View.jpg
Mallock Side View.jpg [ 171.12 KiB | Viewed 782 times ]
Note the slots in the fender to allow the bar to move with the rear suspension. Somewhere around here, I've got a picture of a 4-link on a Seven clone at Solo2 nationals with rather short 4-link arms that fit between the main hoop and the rear roll hoop. If there's that much room in your design, that would certainly get the arms inside the body.

Just my .02... For you, FREE!
:cheers:

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 Post subject: Re: My messy new shop
PostPosted: Fri Mar 30, 2012 12:19 pm 
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This might be going back a few pages, but do you think, for near single donor purposes, the gc8(impreza) front spindles could be used?

http://www.ebay.com/itm/140627289395

From what I've found, it seems to be set up stock with 54mm offset and 153mm backspacing, 15" and 16" wheels used as standard and is front steer...


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 Post subject: Re: My messy new shop
PostPosted: Sun Apr 01, 2012 12:51 pm 
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Hi Krepus. I can't tell much from the picture on Ebay because everything is hidden by that brake shield. I also looked for a model in the Sketchup collection but we just have the rear GC8 spindle there.

There needs to be more work done on wheel and tire choices, what that gives us for scrub on the front and then wether we can still use a clevis on the upright for the trailing arms or if we need to go with a clevis on the wishbone / radius rod. I was doing this and then diverted myself (again) to working out details of the rear frame, diff mount and suspension attachment.

Where we are now I would like to do the clevis on the suspension arms for the reasons you are bringing up. It just makes more choices of parts available and with that some cheaper routes for stock rims etc. It means thought that the orientation of the heim joints on the rear upright needs to become horizontal because the loads from accelerating and braking would be trying to pull the balls out of the joint the way it is now. So we need to either use clevis's to mount those or think of something else. I suppose the stock bushings handle this load too.

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 Post subject: Re: My messy new shop
PostPosted: Thu Apr 12, 2012 1:13 pm 
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Sorry for the slow updates. A computer died and it has taken some time to borrow a machine, restore backups and work on a much slower machine until I get the old one going again. Have been working hard on this though. I always thought the saying was "The Thrill of Victory and the Agony of da Feet!", but for me it's been "The Thrill of Victory and the agony of da Butt!". Seems to have been a loss of glamor there though. Sigh... Seriously, my butt was killing me the other day :rofl:


I asked for some help on issues in my frame from my old local car club. Some folks who build roll cages for SCCA folks are giving some advice and it's being helpful. One of my concerns was how I brought the main roll hoop's rear braces together into a single node. It turns out that is not legal in most organizations, so I have redrawn those supports to face more directly backwards and re-arranged the truss underneath them to provide good support.

The pickup points for the rear trailing arms are now more realistic. I am thinking of something like rectangular 1x2 tubing attached to the rear of the front hoop legs to provide bracing for the acceleration and braking loads.

It is allowed for the main roll hoop to be tilted in it's entirety by a significant amount. So it's been tilted by 8 degrees now to provide more room for the suspension and better possibilities for attaching the coilover and it's loads. I am still having trouble doing that - details, details. The rear suspension is moving forward 3 inches now for better weight distribution. A down side is it may be harder now to put the fuel tank behind the driver / passenger. Maybe that wasn't a good idea on a rear wheel drive anyway.


I haven't done the FEA on either of these changes yet


Attachments:
Car9Gstab22rearbracefixA.jpg
Car9Gstab22rearbracefixA.jpg [ 128.52 KiB | Viewed 642 times ]

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 Post subject: Re: My messy new shop
PostPosted: Sun Apr 15, 2012 12:05 pm 
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I did some FEA work to check where the trailing arms mount and also the changes to the rear end. Here's are pictures and comments about the trailing arm mount.

Looked at two situations, mounting the trailing arms directly to the front roll hoop leg ( a worst case ) and then using a section of rectangular tube welded to the back side of the roll hoop leg.

A 1000 pound braking load was used. It's a round number, it may not be enough since the car would often have outboard disk brakes. In this picture you can see the biggest load is where the roll cage hoop leg connects to the upper and lower chassis rails. The load is 28 KSI and the defection was .032" on the lower mount. Relatively high values for things on this frame, but it wouldn't break.

Attachment:
Car9Gstab23TrailingArmA.jpg
Car9Gstab23TrailingArmA.jpg [ 114.01 KiB | Viewed 607 times ]


Here is how it looks with a bracket to stiffen and strengthen the leg. I couldn't actually model that shape so I looked at a 1"x3" rectangular tube to replace the round hoop leg and 1"x2". It did lower the stress on the tube very substantially, but not as much as I would have expected. The deflection didn't go down as much as I expected either. After awhile I realized much of the defelction ( nearly half ) actually came from the rest of the frame, Doh! So the deflections are actually .0263" for the above case and .008" for this case. The stress reduces to 11 KSI.

Attachment:
Car9Gstab23TrailingArmc.jpg
Car9Gstab23TrailingArmc.jpg [ 119 KiB | Viewed 607 times ]


The interesting thing is in the first case the max stress occurs at the chassis rails, with the stiffer mount the stress occurs in the middle of the mount. Interesting subtlety.

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Car9 Roadster information - models, drawings, resources etc.


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 Post subject: Re: My messy new shop
PostPosted: Sun Apr 15, 2012 12:54 pm 
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The interesting thing is in the first case the max stress occurs at the chassis rails, with the stiffer mount the stress occurs in the middle of the mount. Interesting subtlety.


Yes, interesting... Does that imply that the stiffer mount is localizing the stress at that point --the middle of the mount-- while the other design distributes it on to the main frame rails? If so, is that a good thing? I would think you wouldn't want the stress very "localized" in either case, but rather spread out among several chassis elements. (But then, as we all know... I ain't no Engineer! :mrgreen: )

I'm enjoying this "4-link" exercise, Marcus, both for its own sake and because I might be putting something like that on my car one o' these days... Keep up the good work!

Regards-
JD Kemp

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"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom


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 Post subject: Re: My messy new shop
PostPosted: Sun Apr 15, 2012 1:57 pm 
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Sorry for the one track mind... Found a rear shot of a gc8 front spindle... Most of it, any how...


Attachments:
gc8 front spindle 2.jpg
gc8 front spindle 2.jpg [ 26.85 KiB | Viewed 587 times ]
File comment: Borrowed from Patrick Olsen of the NASIOC
gc8 front spindle.JPG
gc8 front spindle.JPG [ 41.7 KiB | Viewed 594 times ]
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 Post subject: Re: My messy new shop
PostPosted: Mon Apr 16, 2012 2:53 am 
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Krepus they look heavy, but I'll think about it.

Do folks think that color coding the tubing is a help? It looks "cheerful" now but may require sunglasses... Maybe it's more kid friendly now. I used colors from the "web safe" color pallette, but that reduces choices. The less bright colors didn't look that great they tended to look dirtier...


Attachments:
Car9Gstab25Colors.jpg
Car9Gstab25Colors.jpg [ 147.85 KiB | Viewed 565 times ]

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 Post subject: Re: My messy new shop
PostPosted: Mon Apr 16, 2012 5:01 am 
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The colors make it easier to differentiate between bars.

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 Post subject: Re: My messy new shop
PostPosted: Mon Apr 16, 2012 5:23 am 
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For a track car, they would be kind of heavy I guess...

RE:color... It's easier to see the "shape" with the color, seems to add some dimension.


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 Post subject: Re: My messy new shop
PostPosted: Sat May 12, 2012 12:27 pm 
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Hi folks, sorry for the slow updates. Progress is happening on several fronts.

I've decided to try and move the engine back further, about 4"-5". This required redoing the firewall and dash bulkheads. In doing that I found a mistake in my FEA model. I had left a diagonal in the firewall bulkhead from the transaxle version of the car. The nice simple and strong firewall is one of the good things about the transaxle car. After removing that and making the other required changes the car lost a lot of it's stiffness and required much work in FEA again to get it back.

The other thing is that I don't normally actually figure out the stiffness in Ft.-Lbs. / Degree but just look at the deflection of the suspension mounts because that's what matters really. It seems to have made it too easy for me to just pursue smaller deflections without really keeping it in context. I believe "Perfect is the Enemy of Good Enough", so will try to draw a line about where we are now and move forward with all the other things that need to be done.

There are a couple of things I like about the current frame. Using the dashboard area instead of the firewall for stiffness means engine / transmission choice and placement is more flexible. The firewall can be moved round and it's shape changed without incurring a couple of weeks of FEA work - I already did that. The other important benefit is that it provides an option for greatly increasing the stiffness with the addition of one small tube across the passenger seat. Thus a street and a more pure track car can both share the same frame.

Here are the numbers:
8000 Ft.-Lbs / Degree, Car9 as above
11,000 Ft.-Lbs. / Degree, Car9 with additional tube from mid-dash to roll hoop/upper rail
6000 Ft._Lbs. / Degree, Car9 with 14" upper frame rail height

The last number was because originally the car was drawn with the upper frame rail as high as I thought it could fit under the curve of the hood and scuttle. It became taller though when I lowered the car for track use and just dropped the bottom rail to be even with the oil pan. I'm not sure it looks right anymore and I wanted to see how that affected the stiffness, so I ran the numbers.

If you wanted the frame to look more Locostish you can just adjust the upper rail, I don't consider it a major or improper change to the car. The 6000 ft-lbs/degree is plenty stiff at over 6 times better then a normal Locost or Seven.

The other common adjustment would be to forgo the forward facing braces for the main roll hoop. Because of other changes caused by regulations for roll cages I haven't been able to stress those tubes as much as I wanted to, si it doesn't greatly affect the stiffness. I'll run the numbers later and post them too.

To replace the firewall stiffness the car will get a "Terry Hoop" for the dash. I haven't finished drawing it yet. For the FEA work I simulated that with an inner hoop of tubes which you can see in the FEA model.


Attachments:
Car9G-AxialStressA.jpg
Car9G-AxialStressA.jpg [ 124.35 KiB | Viewed 466 times ]

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