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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Dec 08, 2009 1:47 am 
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ok thanks for the info. seems like it should be fine then.
only the T-11 (sometimes labeled E71T-GS in .030 diameter) is the only one with impact problems; T-1 is too deep penetrating and takes gas anyhow, and T-8 is quite strong and reliable, but is very deep penetrating, extremely expensive, and doesnt come in small diameters. T-11 is the wire that was used on all the welds that cracked during the northridge earthquakes, and is now forbidden for structural use.

not to obsess or drag out that rabbit trail...

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Dec 08, 2009 3:06 pm 
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I bought my 110vac century mig with the gas setup. I had it for years trying to figure out why I was such a bad welder and I never could get decent penetration. I switched to flux core one day and thought I'd finally gotten the hang of it.

I recently converted back to gas since I'd be doing larger projects and didn't want the mess to clean up. Again, I could not get decent penetration so I switched back. It turns out it isn't just me:

http://www.lincolnelectric.com/knowledg ... xcored.asp

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Dec 08, 2009 5:46 pm 
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thats good to know. it seemed like the weld quality was more reliable, but i wasnt sure about the qualities of the actual material. it would be interesting to do vibration testing on a test specimen, but i dont have the equipment to do that...

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Dec 15, 2009 7:17 pm 
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Time for a quick update.

After looking at preliminary suspension designs (thanks Chet), I've realized that I don't understand suspension as well as I should. Its easy to make a suspension which will absorb bumps, but its much harder to make one that will be a winner on the track. Though I never intend to race my car, I am determined to do a good job on the new rear suspension. This means that I'm going to be doing some reading. I have bought 6 different books, which I will be ready as I get time. My exams finish on Dec 23rd, so maybe I can do some reading once those are done. The books I've bought:

Kimini (Have read already)
Engineer to Win
Chassis Engineering For High Performance Cars
The Race Car Chassis
New Directions in Race Car Aerodynamics: Designing for Speed
Metal Fabricators Handbook

Thats it for now.

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Sun Jan 03, 2010 5:47 pm 
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As stated in my last update, I've bought some books, and I've been able to do enough reading that I could design my suspension! I was determined to try to get my bottom A-arms as long as possible. Though this isn't the biggest factor in suspension design, in my design, the benefits of having it outweighs the benefits of not having it. It required quite a bit of work to get the geometry to work (since the bottom A-arm is angled upwards towards the wheel), but I'm happy with what I've got. I am currently constructing the rear end structure in solidworks. Its tricky, because I want to be able to drop the differential straight out of the bottom, I want the whole IRS to be enclosed in a "box", I want to maximize the trunk space, and of course, keep everything rigid and strong.

Some pictures of the preliminary design. Blue is the existing structure, pink is the new welded structure, and green in the middle bottom is a removable sub frame, which can be removed to take out the differential. Nothing is finalized at the moment:

Image

Image

Image

Image

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Jan 12, 2010 9:22 pm 
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I just got SolidWorks 2010, and I've been playing around with it a lot the past couple of days. I've also discovered rendering! I've had a chance to mess around with the PhotoView 360 (rendering program). Its really easy to render Solidworks parts with this program. I did the picture shown below in about 5 minutes, using the same assembly, as shown in my last post. I need to stop designing and start building....... Oh wait, its cold out....maybe I can use Solidworks a little more.....


Image

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Jan 12, 2010 9:57 pm 
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Is that bent square tubing going over the front of the differential?


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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Tue Jan 12, 2010 10:50 pm 
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Where did your rear roll center land up? Long arms are good, but you may have gone a little too far. With the lower arm angled like that the suspension is effectively in a 2" bump at normal ride height.

Your upper wishbones are an interesting shape also.

Don't be discouraged, but now is the time to work out all the thinking, before you weld it up.

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Wed Jan 13, 2010 12:08 am 
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Laminar wrote:
Is that bent square tubing going over the front of the differential?


Yes. I have a couple of bent square pieces laying around, and would like to use them.


horizenjob wrote:
Where did your rear roll center land up? Long arms are good, but you may have gone a little too far. With the lower arm angled like that the suspension is effectively in a 2" bump at normal ride height.

Your upper wishbones are an interesting shape also.

Don't be discouraged, but now is the time to work out all the thinking, before you weld it up.


The RC is 2" off the ground and does not move much in relation to the center of gravity. Camber gain is ~2Deg from ride height to full compression. I am happy with those results, because if I was to make either of those values any better, I would make my swing arm length too short. I understand your concern about the long arms, but I have found better results with these lower arms, compared to with ones that were shorter, and angled slightly down, towards the wheel. Maybe I haven't explored enough options? I will work at it some more...

Don't feel that you are discouraging me. If anything, you are encouraging me to learn more, which will benefit me in the long run.

Any suggestions/criticism is encouraged...


P.S. I'm using Solidworks to figure out the geometry. I know about Wishbone, and have used it, but prefer to use Solidworks.

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Wed Jan 13, 2010 2:31 pm 
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What are your inboard pivot point locations in the x and y axis? What is your rationale for the super long control arms? Are you trying ot minimize camber gain in compression, because it that's your goal it can be accomplished other ways. I've got a feeling your RC isn't going to be as stable as you think it is what with it being set up static in what looks like 2" of bump at ride height. I would recommend moving your lower chassis points up to the level of the lower upright pivot and then starting over from there. Also driveshaft angles aren't that critical which allows you to move that diff housing up some if you choose.

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Fri Jan 15, 2010 1:32 pm 
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I drew this crappy diagram in paint to try and illustrate why I don't like your proposed lower control arm configuration. In a nutshell it causes more movement of the bottom pivot of the upright in the lateral plane. This inward movement in bump/jounce can partly neutralize the camber gain effect of unequal length wishbones and cause the length of your swingarm to change dramatically from full droop to full bump. This can wreak havoc on roll center stability and what not. This position of the lower control arms, pointed up from the chassis to the uprights is where cars end up when they are lowered using only shortened springs. That's why "drop spindles" were invented and that's why many lowered cars without them, or some other provision to get the lower control arms back to level will handle like crap.


Attachments:
why.JPG
why.JPG [ 49.54 KiB | Viewed 1658 times ]

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Sat Jan 16, 2010 6:11 pm 
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Thanks Chet. Sorry its taken me a couple of days to reply, but I've been busy with school work.

I understand what you are saying. I did another look at the geometry you created for me, and it is much better than what I came up with. The original intent of the long arms was for the camber gain. However, I guess its not going to work out the way I originally thought. And to be honest, the structure in the rear end will be much simpler if I follow your design anyways. I love the Paint picture you drew. It explains your point well. When I can find some time, I will do some modifications to the design in Soliworks, and share it, to see what everyone thinks.


Thanks again for the input!

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Sat Jan 16, 2010 8:21 pm 
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Do the two diagonal braces directly behind the differential cross near their bottom? How do you plan on doing that and keeping a strong joint?


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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Sun Jan 17, 2010 9:56 am 
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On the suspension issue, smaller OD tires and lowering the upper shock mounts while maintaining the same ground clearance will help.

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 Post subject: Re: Jon's 5.0 v8 Build
PostPosted: Sun Jan 17, 2010 11:00 am 
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Miatav8,MstrASE,A&P,F wrote:
On the suspension issue, smaller OD tires and lowering the upper shock mounts while maintaining the same ground clearance will help.


Do you know what I just realized? I've been using the OD of my street tires for the suspension design. I probably need to be using the dimensions of my Toyo RA1 track tires. lol. Less than 5% of the driving I do will be with the RA1's, but the suspension geometry is more important when I'm on the track anyways.


Laminar wrote:
Do the two diagonal braces directly behind the differential cross near their bottom? How do you plan on doing that and keeping a strong joint?


Yes, they did cross near the bottom. It was done so that I could access both bolts that hold the rod ends, on either side of the X. That being said, the design was only preliminary, and it will be re-done to account for the changes in suspension geometry.

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