I’m going to uni in september so I’m trying to learn some CAD skills relevant to bike design. Here’s some of the designs I’ve come up with in the past few weeks.
This is my latest, the Dipper, with 115mm rear travel and a 6 bar layout.
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This is my earliest, the Comet, it has 145mm travel with the same 6 bar layout, and a chainstay mounted idler pulley.
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Recently I made a discovery. I was inspired by the new Polygon Collosus DH bike’s claims of being a 6 bar (technically true, but only 4 of those bars determine the axle path, like a VPP, and the other 2 determine leverage rate) and thought “what if it actually was a 6 bar?” It produced the flattest Anti-Rise curve I’ve ever seen!
This discovery prompted a redesign.
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How’s the anti squat? Curious to see more about what you’re doing here?
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Not entirely as flat as the AR, it sits just above 100% at sag. Because of the idler, I could tune it to an acceptable level.
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The front end always goes smoothly, I still havent learned how to do brake brackets yet for the rear. Regardless, the new redesigned Comet is taking shape! I’m designing it around parts I already have so it’s a 205 shock (60mm stroke gets 150, 65mm gets 160) and a 160/170 fork, so more of an all mountain/enduro bike now.
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6 bar is lots of hype right now. A question, what are you trying to get in AR/AS/LR?Kickback that you can’t get with a 4bar?
Personally I think lots of 6-bar stuff is only being used to get around patents or visual IP from other brands. Secondary maybe shock placement for packaging.
More bars equals more pivots equals more opportunity for problems.
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it would be interesting to mock up a 4 bar version of that same suspension layout while trying to achieve similar numbers. @Constellation maybe you could try that just for fun and for some design validation?
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@Spencermon You read my mind. I’ve been doing that this afternoon, can’t get the anti-squat as consistent with the 4 bar, the anti-rise is different, probably not enough to be perceptible. Leverage rate is different as well. There’s just an extra layer of fine tuning available with the 6 bar.
@earle.b I’m trying to get a consistent anti-rise (and other consistent handling characteristics,) that’s achievable with 4-bar but you can really fettle with a 6-bar to iron out any compromises with pedal kickback etc. Anti-squat is pretty much dealt with entirely by the idler pulley placement, but because the chainstay and (by virtue of being placed on the chainstay) the idler are rotating around their own instant centre, you get a more consistent and flatter anti squat on the 6-bar than the 4-bar. I’m not fussed about the ultimate pedalling performance or anything like that, but if I don’t have to reach down for a climb switch, thats a win in my books.
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In engineering generally, many problems can be solved by adding complexity to increase control over more individual characteristics of a mechanism. That can be suspension kinematics, engine control, harmonic behaviour of a structure, you name it. At first, it is always deceiving to learn, that you can control that one thing just by adding one more link, mass damper, control unit, sensor… and it works in theory, but don’t forget that you have to deal with the complexity in the long run!
More complexity is more stuff to produce, more quality control needed, more tolerances to hold, more maintenance to do asoasf
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It is hard to produce a complicated linkage. Every small mistake changes numbers dramatically.
More pivots and bearings also create drag and more stiction. You get less compliance. Usually have to use less compression damping to combat that.
I personally have not ever felt pedal kickback, and I ride a very high anti squat bike, so Im not sure it is worth chasing.
They use o chain because the chain is flopping around and creates pedal movement and it also lets you move your feet while rear wheel is locked up to balance better. So not because pedal kickback from anti rise.
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I got some resin prints off a friend. They might be for the old designs but it’s still interesting to get them in hand so I can get a feel for where they’d flex etc on a full scale bike. Some of the bits are rather flimsy.
Haven’t posted anything here for a while, so i thought I’d do a little update. I considered dropping the 6-Bar in favour of simplicity, but a friend convinced me that it was a dumb idea, because I’m trying to develop my skills.
Additionally, I’ve been inspired by the new Orbea Rallon, and converting my concept to a dual purpose Enduro/DH bike has heen quite easy, as fitting a 225mm shock only requires a link that’s 20mm deeper than the one for a 205mm shock.
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Plus, the 4 bar version looked boring, too much like a Slash/Sight/HB916. I don’t want to make something that’s been done before and established, I want to do something new. If I had the funds to get 3D printed lugs etc I’d definitely be moving faster with the project xD
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