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PostPosted: Tue Apr 03, 2012 7:34 pm 
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Location: Cleethorpes
I'm not familiar with non circular bearings, but this is how the bearings are placed;
Image

And I could do this sort of thing to help spread the forces to both sides;
Image

Also I could use some of Titanium/Steel insert through the pivot. If the whole pivot went through the frame as a single piece of Aluminium, welded on each side, strength could be increased directly on the pivot.


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PostPosted: Tue Apr 03, 2012 9:22 pm 
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Location: Kuranda DH circa 1991
what kind of shock are you using in this thing?


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PostPosted: Tue Apr 03, 2012 9:31 pm 
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... just another idea.

you have RH seat stay where the shock is parallel to the top tube - so the compromise of this design is having the front mount sticking out from the top tube - this as has been menitoned will tend to twist the seat tube. Also the moment will need the mount to be failory beefy due to the unsupported tiwsting.

have you considered using rose joints in order to have the top mount inline with the seat tube? the top tube/seat tube join would be strong place to put the top mount.

the frame below - specialized epic has shock mounted that is not in line with the frame - the rose joints allow for the side-to-side movement as the rear stays move up and down.
Image


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PostPosted: Tue Apr 03, 2012 10:10 pm 
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Perhaps not the "best" design, but neat and simple.

Image


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PostPosted: Tue Apr 03, 2012 11:05 pm 
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Quote:
28.6mm for the downtube and toptube


What are you making this out of again?

Quote:
Perhaps not the "best" design


That's one way of putting it ;)[/quote]


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PostPosted: Wed Apr 04, 2012 1:18 am 
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merckx wrote:
what kind of shock are you using in this thing?


I'm going to build a fork leg.

MikeD wrote:
Quote:
28.6mm for the downtube and toptube


What are you making this out of again?


Aluminium



I've tried to place the shock so at the rear of the seattube, but it's too long and it gets in the way of the wheel. I think the double sided clamp is the best one so far, so I'm going to start on the bb pivot. Also I was thinking I could either buy a new frame or use one I already have to make a first prototype (just the front triangle) instead of building a new one. Could possibly use the dropouts too.


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PostPosted: Wed Apr 04, 2012 9:28 am 
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You're going to want bigger than 28.6mm for an aluminium main triangle. Look around at some production bikes.


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PostPosted: Wed Apr 04, 2012 10:26 am 
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Location: Kuranda DH circa 1991
the rear end is going to have a lot of pedal induced bobbing if the shock does not have some kind of inertia valve or propedal type valving ala fox..


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PostPosted: Wed Apr 04, 2012 10:48 am 
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Its easy to pick fault....so I'm not going to.

Why concentrate on "retro" designs and make the same mistakes. I would be looking at modern designs where big R&D budgets have optimised the pivot positions and axle paths over the years. To do something different will take a lot of R&D and prototype building, great if you have the capacity.

Modern MTBs mostly fall into these categories:

4-bar e.g. specialized FSR and their licensees
"Faux bar" single pivots with linkage activated shocks - Kona, Turner, Orange ST4, Scott spark
VPP & DW-Link - Santa cruz VPP, Giant Maestro bikes
Single Pivot - Orange 5 etc

Pick up a copy of "what mountain bike" this month and they test 2012's trail bike of the year 120-150mm travel - loads of pictures of good trail FS bikes and you will notice they fall into distinct categories.

There is a reason why no one makes bikes like the GT RTS, Trek 7000 or that SBIKE any more.

Remember to think about positioning the brake caliper to avoid "brake jack" , and the practicalities e.g. will the end of the shock catch my legs?


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PostPosted: Wed Apr 04, 2012 1:57 pm 
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Had a bit of a scribble... hope this helps!


Attachments:
File comment: hastily scribbled illustration!
onesidedpivot.jpg
onesidedpivot.jpg [ 88.37 KiB | Viewed 384 times ]
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