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Learning how to build Lotus Seven replicas...together!
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PostPosted: Thu Jan 21, 2010 8:12 pm 
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Joined: Wed May 13, 2009 6:04 pm
Posts: 87
Location: Missouri
More updates. Front suspension complete w/gussets less upper shock mount.
Rear suspension complete. Lower arms are 1"DOM w/0.5" rod ends and AN bolts on inner side, outer side is 5/8" rod ends with Grade 8 bolt (increased size is due to single shear mounting of rod ends, and do you know how much a 6" grip AN bolt is). For any body that cares a 8" 5/8" Grade 8 bolt has a grip of 6". Upper arms are 7/8"DOM w/0.375" rod ends and AN bolts on inner side, outer side is 0.5" AN bolt that grabs the upright and lower shock. Track width is stock Miata (56.2"), and camber is set currently at zero for simplicity. Still need to set upper shock mount back here also.


Attachments:
Compl. Rear Susp..jpg
Compl. Rear Susp..jpg [ 162.53 KiB | Viewed 2706 times ]
Compl. Front Susp..JPG
Compl. Front Susp..JPG [ 148.16 KiB | Viewed 2707 times ]

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PostPosted: Tue Feb 23, 2010 9:07 pm 
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Location: Missouri
More pics. The front suspension is complete. Here is the run down of the parts for anyone that cares.......
DR5885 Proma Stars w/250# 12" springs, installed at a 35 degree angle at 5" ride height. This should give approx. 3" of bump and 3" of droop, more enough to allow me to raise and lower the car and not run out of travel.

The rear suspension is still in-work since the upper arms need to be re-done. Using the same DR5885 shocks with 275# 12 springs, installed at a 45 degree angle at 5" ride height I had an interference between the arm and the spring cup (even mounting the shock upside down), and it only gets worse under droop. For anyone that is planning on using the upright mounting hole for the bottom shock mount take note. The below pic is at ride height and the shock is only angled over at 40 degrees.

Everything based around a natural frequency of 2.0 for the front and 2.2 for the rear.


Attachments:
Rear Shock Interference at ride height.jpg
Rear Shock Interference at ride height.jpg [ 149.6 KiB | Viewed 2513 times ]
Front Spring-Shock in Droop.jpg
Front Spring-Shock in Droop.jpg [ 146.68 KiB | Viewed 2512 times ]

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PostPosted: Wed Feb 24, 2010 2:17 am 
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Always Moore!
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Very nice work with the plate. Those arms look fantastic.

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PostPosted: Wed Feb 24, 2010 10:37 am 
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a.moore wrote:
Very nice work with the plate. Those arms look fantastic.


Thanks.......I'm assuming that you mean the front arms. I bent those plates up that way so that all of the load from the shock would load those plates in shear, instead of trying to bend the lower control arms.

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PostPosted: Sat Feb 27, 2010 1:46 pm 
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How is the spring seat attached to the rod/eye of the shock? Could you make a spacer that would move it farther away from the mounting eye and give you enough clearance to the arm?


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PostPosted: Sat Feb 27, 2010 2:15 pm 
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Mid-Engined Maniac

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jaf wrote:
...DR5885 Proma Stars w/250# 12" springs, installed at a 35 degree angle at 5" ride height. This should give approx. 3" of bump and 3" of droop...

Because the 250 lb springs are leaned over 35 deg (from vertical I assume), the actual vertical spring rate is 250 * cos(35), or around 142 lbs / inch. I'm guessing motion ratio is about 0.8, which means the actual wheel rate will be 142 lbs * 0.8^2, or about 92 lbs.

92 lbs is pretty low for wheel rate. Since you have three inches of droop, that implies an unsprung load of 3 * 92 lbs, or 276 lbs. Is it?

You'll probably find that you don't need nearly all that droop. Typically, only about 1" is needed before the springs rattle loose.

[edit] see posts below...

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Last edited by Anonymous on Sat Feb 27, 2010 6:39 pm, edited 1 time in total.

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PostPosted: Sat Feb 27, 2010 3:31 pm 
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Glen wrote:
How is the spring seat attached to the rod/eye of the shock? Could you make a spacer that would move it farther away from the mounting eye and give you enough clearance to the arm?


Already walked down that path............the seat just sits (a shoulder and the spring pressure hold it down) on top of the rod/eye of the shock. My go forward solution is to mount the shocks right side up and space it 0.5" off of the upright bushing and then rebuild the upper arms. I already broke down all of the tack welds on the arms to force me to do it correctly. This will also provide a little more shock/spring clearance to some other tubes.

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PostPosted: Sat Feb 27, 2010 4:27 pm 
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KB58 wrote:
jaf wrote:
...DR5885 Proma Stars w/250# 12" springs, installed at a 35 degree angle at 5" ride height. This should give approx. 3" of bump and 3" of droop...

Because the 250 lb springs are leaned over 35 deg (from vertical I assume), the actual vertical spring rate is 250 * cos(35), or around 142 lbs / inch. I'm guessing motion ratio is about 0.8, which means the actual wheel rate will be 142 lbs * 0.8^2, or about 92 lbs.

92 lbs is pretty low for wheel rate. Since you have three inches of droop, that implies an unsprung load of 3 * 92 lbs, or 276 lbs. Is it?

You'll probably find that you don't need nearly all that droop. Typically, only about 1" is needed before the springs rattle loose.


You're killing me. I was hoping to never have to go back to all of those painful calculations. I used a bunch of different methods with the intent of shooting for 2.0 and 2.2 front/rear natural frequencies, using both mathmatically calculated motion ratios and actual measured motion ratios. My calculated wheel rates are very close to yours and all I can tell you is that I can't wait to get this thing resting on all four wheels. I'm hoping that it isn't sitting up like a monster truck or that it collapses to the floor. I'm shooting for a sub 1200lb car with a 45/55 F/R wt%.

Good thing springs are relatively cheep, and since my front/rear springs are the same length, and relatively close in rates, I can quickly dial in the best rates. Wish me luck.

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PostPosted: Sat Feb 27, 2010 6:20 pm 
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There may be nothing wrong with your numbers at all, depending how much weight you have up front. Any idea? That's the advantage of creating a spreadsheet showing all component weights and location in order to the CG, weight on wheels, spring compression, that sort of stuff. However, it's safe to say that if you're using a similar drivetrain, you can't go wrong.

I'm not trying to rain on your parade, it's just hard-learned lessons I discovered myself. Ditto on spring prices - a buddy said that no matter how hard you try, it always takes three tries (three sets) before finding the right rate. Dang if he wasn't right on Kimini... I'm hoping to prove him wrong on Midlana.

AND... I made mistake on the shock inclination value, the correct value of cosine(35) is 0.82. (I used cosine(55). So, your 250 lb springs will be 250 * cos(35), or around 205 lbs / inch. With a motion ratio of 0.8 (a guess), wheel rate will be 205 lbs * 0.8^2, or about 131 lbs, which is much better. Still, since you have three inches of droop, that implies an unsprung load of 3 * 131 lbs, or 393 lbs, which is most likely way higher than it is.

So, even with my goof fixed, I think droop will still be much less than the 3" provided. That's not a bad thing, since it means you can free up more bump travel.

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PostPosted: Sat Feb 27, 2010 11:12 pm 
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No apology necessary. I think it was one of your earlier posts about "centered shock travel" along with some others on this forum that made me finally just bite the bullet and place the order for the springs/shocks. The sprung weight I used for the front wheel was 240lbs and then stepped it up/down by 30lbs to see how the spring rate would vary. We'll see how we come out in a few weeks, assuming I can get the rear upper arms nocked out.

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PostPosted: Sun Mar 21, 2010 8:06 pm 
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Okay rear suspension is fixed.......same type of solution as "Ivai" but I spaced the shock out so that I could run it right side up to make the adjustment easier to get to.


Attachments:
Fixed Rear Uppers Side.jpg
Fixed Rear Uppers Side.jpg [ 156.85 KiB | Viewed 1925 times ]
Fixed Rear Uppers.jpg
Fixed Rear Uppers.jpg [ 157.12 KiB | Viewed 1922 times ]
Fixed Compl. Rear Susp..jpg
Fixed Compl. Rear Susp..jpg [ 157.05 KiB | Viewed 1918 times ]

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PostPosted: Mon Apr 26, 2010 2:06 pm 
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JAF,

I am working on a suspension layout similar to yours and am struggling a bit. Any chance you could send me your Wishbone numbers as a reference? Thanks!

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PostPosted: Mon Apr 26, 2010 9:39 pm 
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skou wrote:
JAF,

I am working on a suspension layout similar to yours and am struggling a bit. Any chance you could send me your Wishbone numbers as a reference? Thanks!


Might as well share with everyone else.


Attachments:
JAF Wishbone.jpg
JAF Wishbone.jpg [ 163.37 KiB | Viewed 1648 times ]

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PostPosted: Tue Apr 27, 2010 7:27 am 
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On final assembly turn the shock so the damping adjustment knob is on the inside so you will not hit it with a wheel wt.
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PostPosted: Tue May 25, 2010 7:52 pm 
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Since I haven't even touched my build for a month due to other household projects I figure I could post an update. The steering rack (90 Miata manual rack) has been sucessfully modified. This turned out to be much easier than I anticipated. Here's some lessons learned for those in the same boat as me:

The large hex plug can be removed using a 7/8" tall nut.
I made a tool out of some scrap metal to remove the "keyed" plug.
I safely removed 7" of length from the rack and my bi-metallic Harbor Freight bandsaw blade zipped right through the rack with ease.
Instead of cutting welding the rack I just cut off the end and re-tapped that hollow end, which already has the proper starting hole diameter for the inner tie rod ends 18x1.5 thread.
I cut and hand ground the end of the rack to properly accept the stock locking washer.
Only the housing was dissected and welded back together.....and yes I know the rubber end of the housing in on backwards in the below pic.

Attachment:
Steering Rack Tools.jpg
Steering Rack Tools.jpg [ 137.68 KiB | Viewed 1387 times ]

Attachment:
Steering Rack.jpg
Steering Rack.jpg [ 128.61 KiB | Viewed 1387 times ]

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