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The "Frankenfork" Linkage-type fork

EVRAC

Monkey
Jun 21, 2004
757
19
Port Coquitlam, B.C., Canada
Built for my mech. eng. degree final project last year. Just got it assembled and tested for the first time.

7" Travel. Almost perfectly linear wheelpath, exactly like a normal fork, with standard rake and trail geometry.

Nice rising rate, floating shock arrangement.

Very stiff front-to-back, and torsionally.

Very smooth motion due to bearings throughout.

Weighs a tonne though.

Successful first prototype. Not sure if I'll bother with a second. Fun project.



https://picasaweb.google.com/101728978993585111636/Frankenfork?authkey=Gv1sRgCI6KqbPsh4XbyAE&feat=directlink
 

EVRAC

Monkey
Jun 21, 2004
757
19
Port Coquitlam, B.C., Canada
Looks amazing dude. Any compensation for brake effect? Any ideas on how to lighten her up? How does it steer?
Seems fairly neutral on brake induced front end compression.
Lots of ideas for weight savings. There is just way too much metal in there. Every web and edge could be half as thick. Maybe carbon legs?
Steering precision is excellent. The extra mass is out quite a way from the center of steering rotation, so you do feel the extra rotational inertia resisting steering input.
 

tacubaya

Monkey
Dec 19, 2009
720
89
Mexico City
Built for my mech. eng. degree final project last year. Just got it assembled and tested for the first time.

7" Travel. Almost perfectly linear wheelpath, exactly like a normal fork, with standard rake and trail geometry.

Nice rising rate, floating shock arrangement.

Very stiff front-to-back, and torsionally.

Very smooth motion due to bearings throughout.

Weighs a tonne though.

Successful first prototype. Not sure if I'll bother with a second. Fun project.



https://picasaweb.google.com/101728978993585111636/Frankenfork?authkey=Gv1sRgCI6KqbPsh4XbyAE&feat=directlink
 

marshalolson

Turbo Monkey
May 25, 2006
1,770
519


that is an awesome school project. check out the old school look fourneles, the ultra pimp version of the original AMP fork.
 

EVRAC

Monkey
Jun 21, 2004
757
19
Port Coquitlam, B.C., Canada
nor does / did brodie build crazy-link bikes. i scratch my head.

oh, and rad work on that fork! still waiting for you to develop a mad gearbox bike...
I had a complete solid model of a new gearbox and frame, but I've dropped it in favor of just buying a Zerode.

My next projects are a few custom shop tools and maybe another version of the pedals.
 

LMC

Monkey
Dec 10, 2006
683
1
I had a complete solid model of a new gearbox and frame, but I've dropped it in favor of just buying a Zerode.

My next projects are a few custom shop tools and maybe another version of the pedals.
a gearbox of your own design or a g-boxx frame?

can you post pics of this?
 

marshalolson

Turbo Monkey
May 25, 2006
1,770
519
I had a complete solid model of a new gearbox and frame, but I've dropped it in favor of just buying a Zerode.

My next projects are a few custom shop tools and maybe another version of the pedals.
awesome man. really cool project. what leverage ratio did you plug into that fork?

2.5" -> 8" ?
 

marshalolson

Turbo Monkey
May 25, 2006
1,770
519
how about a 6-7 speed planetary hub that is 150x12mm, disc compatible, and not stupid heavy. :D

come on man. get on it ;)
 

buildyourown

Turbo Monkey
Feb 9, 2004
4,832
0
South Seattle
I have long thought that this style of fork integrated into the frame design would be the wholly grail of stiffness and weight. The only reason is hasn't existed for a DH bike is it requires one company to build the frame/fork from the ground up. Still surprised Spec or Cannondale haven't tried it.

Nice work.
 

SuspectDevice

Turbo Monkey
Aug 23, 2002
4,157
359
Roanoke, VA
I have long thought that this style of fork integrated into the frame design would be the wholly grail of stiffness and weight. The only reason is hasn't existed for a DH bike is it requires one company to build the frame/fork from the ground up. Still surprised Spec or Cannondale haven't tried it.

Nice work.
 

eatmyshorts

Monkey
Jun 18, 2010
110
0
South OZ
Its amazing how much time everyone debates how much/how little brake feedback there is through the back of a dual suspension mountain bike. No one really looks at the front..

Having a 64/71 deg head angle, with the suspension fork following close to that angle for a wheel path certainly encourages a lot of brake dive.. not to mention the mechanical friction of the rotational load applied through the lowers on the stanchions under braking..
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
EVRAC - f**king rad. Really, really awesome.

Its amazing how much time everyone debates how much/how little brake feedback there is through the back of a dual suspension mountain bike. No one really looks at the front..

Having a 64/71 deg head angle, with the suspension fork following close to that angle for a wheel path certainly encourages a lot of brake dive.. not to mention the mechanical friction of the rotational load applied through the lowers on the stanchions under braking..
Agreed, however people are all used to the identical dive characteristic, axle path and steering geometry that you get with ANY model telescopic fork. Given how hard it is for the companies out there to get it right when axle path and steering geometry are fully constrained, introducing more variables would require so much R&D to get right that most companies just aren't willing to touch it. Linkage DC forks also have the issue of being unable to compensate for changing headtube stack heights, and leading link forks in fact generate MORE dive under brakes than telescopics.

I think there is definitely potential for a linkage fork to be built that makes good use of anti-dive characteristics and the ability to change the shock rate without messing the axle path or steering geometry though.
 
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eatmyshorts

Monkey
Jun 18, 2010
110
0
South OZ
Agreed too.. Considering how long it has taken manufactures to get it right with rear suspension... Would be very interesting see the circus act if everyone jumped on the linkage fork bandwagon..
 

fluider

Monkey
Jun 25, 2008
440
9
Bratislava, Slovakia
I think the suspension kinematics has been well explored over the past few decades. So, for suspension designers it shouldn't play some significant role.
I'd be much concerned about customers' (anti-)attitude ...
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
haha, shall we revisit the RM "open-source" linkage fork? I was just perusing that thread recently.

I still really want to make a small floating brake for a fork. I think that would be massively fun to experiment with.
 

Steve M

Turbo Monkey
Mar 3, 2007
1,991
45
Whistler
haha, shall we revisit the RM "open-source" linkage fork? I was just perusing that thread recently.

I still really want to make a small floating brake for a fork. I think that would be massively fun to experiment with.
haha, I have more than just a few ideas if anybody anywhere wants to volunteer manufacturing time... may or may not have been running numbers for the past 18 months :)
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
do you have a concept for a brake bar or linkage fork? The complete fork would be impressive but a massive challenge...I've been tossing around the idea of a mount-able brake bar for common forks, something that would just bolt on then attach above the crown. The problem is skirting the lowers, but I haven't really tried that hard. Should be easy on a dorado or other inverted fork.