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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 3:44 am 
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Innovative packaging. While I'm not completely put off by running the structure through suspension members, I would be concerned about them coming into contact during periods of excessive movement. Is there enough room to allow for a shock to fail and completely collapse or an unexpectedly large movement well into the bump stops and full, unloaded droop? I am also wondering where you're going to place the shock & spring?

Another thought occurred to me; since you have both fore-aft movement and rotational movement constrained by the radius arms, couldn't you essentially "V" the lower rear lateral link to a single pick-up on the chassis side? That would still provide for toe control and adjustment and would reduce the number of mount points (and load points) in the rear chassis.

You could potentially even carry that idea into the radius arm(s) if it was designed right and save some weight and perhaps some complexity. The only real disadvantage that I see would be a very small amount of bounce and droop induced toe change based on the rotation of the uprights; gaining a very tiny bit of toe-in under compression and toe-out under droop. At least it would be working in the same direction as the corner. The rest of your rear suspension looks like it has more than enough compliance to absorb the added rotation of the uprights.

I'm sure you know this but I'll add it just for completeness:

That design would be similar to the rear suspension Lotus has used on some of the road cars created during their glory years. Although they tended to use a rigid, fabricated radius arm that also constrained toe adjustment along with simple upper and lower lateral arms there were essentially a single tube each. Frequently the upper lateral arm was also the drive axle. While that was innovative and did save weight, it caused rapid wear of the u joints and required the differential to be specifically modified to carry the loads. The same technique would not be compatible with modern CV joints.

Personally, I think reworking the lower lateral links into a "V" might be worth the effort just for the packaging benefits. I'd probably skip reworking the radius arms unless there was a noteworthy weight savings.

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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 1:17 pm 
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Hey Erioshi, good comments. Opinions and advice always welcome here.

I always imagined the type of lower wishbones you're talking about and for a long time that's what was in these drawings. I really liked the simplicity of the single bolt holding them on, It seemed easier to provide one strong mount location then two. I wanted everything in the rear built around a strong roll bar bulkhead.

I moved away from the wishbone and went with the parallel links because I was having trouble working out the bracing under the rear ward facing hoop, they also offer the advantages of being easier to set up, no toe change and adjustment of rear wheel placement.

It took me a lot of work to find a bracing scheme that I liked and it now turns out that it would allow the rear wishbone you describe. So I think I may revert to that and it will make the bracing a small step easier to work out also. I hadn't noticed I could back to that, good catch.

I did check for interference in a normal range of motion with a little to spare but not for something like spring or coilover mounting failure. I will try a little harder for that.

I am having trouble actually locating the coilover and I didn't expect that to be a problem when I started. :rofl:

Again, thanks!

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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 4:37 pm 
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Here you go, Erioshi. It occurs to me I need to think about provision for anti-squat. I thought that was going to be available with the lower parallel arms, but it occurs to me now that was wrong. I guess that can be done by adjusting the trailing arms to be non-parallel but will have to think about how to do that.

Does wishbone deal with this type of rear suspension ( that doesn't have wishbones really... )?


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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 6:12 pm 
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Are those the t-bird rear uprights or the subaru? I'm putting together a parts list for the next pull-a-thon at the local pull and save... Lol


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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 6:21 pm 
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Quote:
I keep trying to clean up the frame in the back of the car for the diff mount and the lower parallel links.
Nice improvement, Horizonjob! Simpler is gooder. I also like Erioshi's Y-style lower a-arms. Does it make sense to eliminate the fore-aft green cross-brace on the lower Y-arm between the upright's lower pivots? And then make the length of the rear, angled leg of the "Y" adjustable for setting toe? Could this be done with an adjustable clevis-and-pin on the inboard end of the angled leg?

Quote:
It occurs to me I need to think about provision for anti-squat. I thought that was going to be available with the lower parallel arms, but it occurs to me now that was wrong. I guess that can be done by adjusting the trailing arms to be non-parallel but will have to think about how to do that.
Does wishbone deal with this type of rear suspension ( that doesn't have wishbones really... )?
Wishbone should be able to do camber change under bump and roll with this set up, and I think it might be possible to fake it to analyze anti-squat as well. The anti-squat adjustment would be in the trailing-arms front pivot locations and one might have to ignore any "caster-rotation" effect and maybe toe-in change. There are non-free suspension analysis programs that should be able to do the job as well.
Would the anti-squat be adjustable or built-in?

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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 6:28 pm 
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Glad I was able to help contribute. To be honest, provisions for anti-dive and anti-squat are generally not on my radar. I don't disagree with the technologies, I just lack practical experience and data from working directly with them on a working race car.

As long as you are getting into the final parts of packaging, have you considered how you plan to package your swaybars and end links? Since there are no inboard pivot points I'm assuming the bars will need to be full length and run to the outer ends of the suspension arms. That is actually one of the subtle benefits of an inboard suspension; the pivot points allow for much shorter sway bars and compact, low mass linkages that can be easy to adjust. Any weight savings would probably offset by the added mass of the pushrods or pullrods.

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 Post subject: Re: My messy new shop
PostPosted: Wed Mar 21, 2012 7:20 pm 
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Thinking about anti-squat a bit more, couldn't you simply adjust the chassis side mounting points of the radius rods up or down to handle anti-squat? If I'm remembering correctly, the goal is to use geometry to direct the force vector (suspension load) from the radius rods further up into the chassis and closer to a line that passes through the car's CG and the rear contact patch?. If that's the case then adjusting the angle of the radius rods should allow for that. That, or I'm all wet, lol.

If my premise is correct, bringing the radius rods into a single chassis mounting point could allow for the force vector to be very precisely controlled. Other factors to consider are a locost's low CG and the fact your current radius rod design could be built with converging rods at the chassis to give a similar effect. A builder could raise the force vector by moving the lower radius rod's mounting point further up the chassis.

Also if I remember correctly, the primary use of anti-dive and anti-squat (in racing applications) is to control chassis height for aero reasons. Avoiding changes in chassis pitch and ride height are important for both full aero and flat bottomed cars that use high aero loads and small ground clearances to increase grip. Upsetting the car bottom to road relationship in both of those cases can really upset the car's dynamic balance. Unwelcome effects include situations like "porpoising" under braking; an example where anti-dive might be helpful if you couldn't redesign the aero package or otherwise use chassis set-up to fix the problem without giving up significant performance. Another potential benefit from anti-dive and anti-squat would be helping to keep wide tires flat on the the ground under straight line compression events like heavy braking or acceleration if the car's camber curves are too severe.

Caroll Smith talks about both anti-dive and anti-squat in fairly clear terms on pages 34-36 of "Tune to Win". The main drawback he mentions with anti-squat is that it can lead to a loss of sensitivity (or feedback) from the back end and also leads to "tire pratter", making the car harder to drive. He also suggests using the mounting points of the radius rods as a reasonable method of adjusting it. He very loosely suggests no more than 20% of anti-dive or anti-squat, and offers that cars with lower power to weight ratios (compared to the higher powered race cars he uses as examples) should have less anti-whatever and receive less benefit from it. His coverage of anti-dive also includes a few caveats, depending on how exactly it is being implemented. The main message seems to be that it's not a free ride and there are noteworthy side effects to understand and suspension tune around. In general there seem to be more issues with anti-dive than anti-squat.

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 22, 2012 7:39 am 
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I will 2nd Erioshi comments on not getting carried away with both anti-dive anti-squat. On these light wt cars and relative low power you should not need a lot of either. I have about 12% anti-dive and currently about 18% anti-squat and no ill effects. Adding more rear anti-squat has made a noticeable improvement in traction. [solid open axle with soft damping] I would suggest you look at some adjustability at the rear. The higher power cars are going to need a more anti-squat. Both Vettes and Vipers have massive amounts of anti-squat. But I'm guessing that must of our cars will have something less the 600HP.
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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 22, 2012 10:50 am 
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Krepus, the uprights shown there are the Subaru ones. Both the T-Bird and Subaru uprights are in the SketchUp drawings but they are in different "layers" of the drawing. You can click on the layers menu and show one or the other or even both at the same time to compare them. I would like two choices to help people get the parts easily and also to cover two levels of weight and power available. It turns out that the two uprights are very similar in dimensions, which I hadn't really noticed until I had them both showing once.

WRT to the anti-stuff, I didn't personally picture using much or any of that geometry, at least originally. I want to cover the possibility ahead of time though and understand what we would do to get at least roughly appropriate amounts. With the current design using those bolt on tear tabs it might be as easy as flipping the front or rear set of tabs upside down and bolting them back on. I don't know yet how much inclination one would need to get say, %20 anti-squat. DaveW roughly how many degrees of angle or inches out of level are your suspension arms?

At the beginning I was unsure if I would really make those tabs bolt on or just weld them on. As time goes on though I like the bolt on option. It will provide great information when a driver can try a couple of setups and report their results on one car. It is a good controlled experiment.

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 22, 2012 10:59 am 
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SeattleTom, this is what the rear wishbone looks like. This is a rough copy of the one on my FF and also what I've seen on old Lotus F1 and Indy cars. In real life the connection of the rod end used for toe-in is more robust, but you get the idea. The collar under the mount for the coilover uses a spherical bearing so the car's weight is not carried by bending the threaded portion of a rod end.


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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 22, 2012 11:44 am 
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Quote:
But I'm guessing that must of our cars will have something less the 600HP.


They will, but our weight is going to be a great deal less too. It will be interesting. I hope we can get really good weights on these cars for the track. I don't want them to be moving road barriers or tanks. Weight and safety were the two big reasons for going with a "cage with a locost welded on" approach. It seems easy to kid yourself about weight because of all the little things that add up. I was surprised that Lonnie ( I think? ) posted something close to 50 lbs. of fluids measured on his engine weight. It's so easy to ignore things like that.

Brake disks weigh more then I thought. Pinto front disks are 14 lbs. and the larger heavy duty units are 15-16. That includes the hub, which is part of the disk.

I am starting to collect data on the suspension and the results of initial Wishbone runs etc. I think I'd like to break that discussion out of this thread and create it's own thread for this. That will make it easier for people to find and use the information in their locosts.

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 22, 2012 1:54 pm 
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Anti-dive
My front control arms are on a 1* angle,
Front wt is 633lbs
Anti-squat
Rear wt is 622 w/o fuel + about 20lb wet and the arm is currently set a 4*.
The rear mount is multi- location and I can not recall the angles, I'm on the road and can measure the angle that it is set at this weekend.
My initail design had the CG lay-out was just over 12", but I'm sure that it is slightly high because since the design work did not include a roll bar, heater and trunk that was added later in the build.
Dave W


Last edited by davew on Sat Mar 24, 2012 9:58 am, edited 1 time in total.

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 Post subject: Re: My messy new shop
PostPosted: Thu Mar 22, 2012 4:53 pm 
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horizenjob wrote:
Brake disks weigh more then I thought. Pinto front disks are 14 lbs. and the larger heavy duty units are 15-16. That includes the hub, which is part of the disk.
You got that right. They are definitely a major contributor to unsprung weight...Although I've seen numbers more like 20-22 lbs each for the 11 inch Granada rotor/hub upgrade, vs the 15lbs range for the 9.3 inch Pinto rotor/hub piece. Definitely not light, but still about the same as a 16lbs SN95 11 inch Mustang rotor plus the sealed bearing hub of 5-6 lbs.

The Centric web site offers a great selection of basic rotor data if you search out the car they came from and look at the "image" of the rotor in question...This can also often, but not always, be seen in the similar rotor listings from Centric at Rock Auto.

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 Post subject: Re: My messy new shop
PostPosted: Sat Mar 24, 2012 9:57 am 
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Rear anti-squat
Went out and measured the trailing arm angle. My bottom arm is at 4*, I think that puts it at about 18%. I beleive that my original design was 12%, 18% and 24% settings. I will try to find the design layout to confrim.
Dave W


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 Post subject: Re: My messy new shop
PostPosted: Sun Mar 25, 2012 5:49 pm 
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Something that popped into my head while day dreaming about building a 7 at work tonight... Make the rear diff housing mounts for the r160 easily removable to allow for easy diff changes... I believe ratios from a 3.73 to 4.11 were available stock. For a track car, diff access could be pretty important....

Just a thought...


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