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Learning how to build Lotus Seven replicas...together!
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PostPosted: September 12, 2018, 1:22 pm 
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Joined: February 8, 2007, 4:35 pm
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Location: Atlanta Ga
I redesigned the Sevens front end with rocker arms, and I wanted to see if same 1/2" heim joints could be used as bearings, in order to avoid having to machine the bearing housings for needle bearings.
The suspension is progressive, and the motion ratio can be adjusted by changing the rocker arms. Typical Gaz shocks were used as coilovers.


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PostPosted: September 12, 2018, 4:33 pm 
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Hi HRK. I had that drawn in on my Car9 plans for some time. Have you put the car on the ground yet? I think there is a flaw in that the rocker arm can rotate horizontally... It seems like such a good idea though... :(

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PostPosted: September 12, 2018, 5:06 pm 
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Yes, the car is actually sitting on wheels, it is about to be aligned for the first time. Those are Harbor Freight motocrossbike stands under each tire with some stoppers preventing it from falling to the ground.

I ran Dragon Hillclimb with it in June, and ended up second overall with 3.5 seconds behind my best time ever. I was happy with the performace straight out of the box, with eyeballed alignment and no testing at all. I did have to stop running after I found another issue in the suspension in Sunday morning, and I was 3 seconds ahead of the eventual Winner, Focus RS.

There are two heims per corner, one on each side of the rocker.

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PostPosted: September 12, 2018, 6:48 pm 
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hrk wrote:
There are two heims per corner, one on each side of the rocker.
It doesn't look to me like those rod ends (Heim joints) are getting used any harder than the ones on the pushrod. I don't see why they wouldn't work. Besides, if you have to replace them every hundred thousand miles, that's about forty five bucks...or 45 cents (and one minute's work) per thousand miles.

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PostPosted: September 12, 2018, 10:29 pm 
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Here is the video from first tests.

[youtube]https://www.youtube.com/watch?v=u3m6vK32IKU[/youtube]

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Last edited by hrk on September 12, 2018, 11:25 pm, edited 3 times in total.

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PostPosted: September 12, 2018, 10:46 pm 
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I can't see any reason why your set up wouldn't work well. The rod-ends are being loaded in their strongest plane. Being bushings (rather than needle bearings) they should have higher load capacity and last longer. As to which is the weaker link in a bottom-out situation, I'd say it's a toss up between bending the pivot rod ends at the threads, or your pushrod. Either are easily replaced so good spot to bend.

Honestly, I put some thought into rocker arm design and never considered dual rod ends..... I like it. :thmbsup:

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PostPosted: September 13, 2018, 9:22 am 
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Here is a photo during mock up to show the rod ends better. The rocker arms started as 1" square tube, same as frame, and got reinforced bushings for three bolts, and wrapped with 16 gauge bent plate for strength.


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PostPosted: September 13, 2018, 9:29 am 
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As the Brits say, it works a treat, though in my case I used spherical bearings mounted in the rockers.

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PostPosted: September 13, 2018, 9:45 am 
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Heims are cheaper than bronze bushings, and you don't need to ream them to fit...


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PostPosted: September 13, 2018, 11:23 am 
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TRX wrote:
Heims are cheaper than bronze bushings, and you don't need to ream them to fit...

The bushing in the rocker that the bolt passes through should be reamed, so it's a wash.

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PostPosted: September 13, 2018, 11:41 am 
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Or one can buy round mechanical seamless tube with 3/4" OD and 0.500" or .510 id , and weld it in. The bolts are nominal 1/2" so the tolerance is reasonable.
The bolt through the heim joints is torqued first, and then the rod ends to the frame, and it the rocker rotates freely without binding.

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