Single pivot location via linkages?

benpinnick

Ahh, the fulcrum. Man that was a beast.

bluechair84

Yeah, they're the kind of thing I'm going for - but hopefully significantly lighter! Thanks for the offer Nick. If I can't get quite what I'm looking for I'll be in touch. I think I'm pretty much there with the linkage variation... I just need a garage now to start it in! Should be moved into a house with a lot more space in a month.

The Rookie

Been having a think, while it won't gve the same as a single pivot it would do what you want, 2 equal length links (upper and lower) running parallel, centre of the gearbox on the line between the frame end pivots and axle between the two dropout end pivots. Mount the front end higher than the rear for a rearward axle path in bump and as long as the frame end pivots are one above and one below the chain then no pedaling feedback!

I think....

nicklouse

The Beginner wrote:

Been having a think, while it won't gve the same as a single pivot it would do what you want, 2 equal length links (upper and lower) running parallel, centre of the gearbox on the line between the frame end pivots and axle between the two dropout end pivots. Mount the front end higher than the rear for a rearward axle path in bump and as long as the frame end pivots are one above and one below the chain then no pedaling feedback!

I think....

Oh the lawwill patented design. But not great for a gearbox design.

benpinnick

Bluechair - yes Im pretty sure IIRC it ran straight SS - no tensioner. The VPP was fixed on the BB. Mine doesn't have that linkage/dropout kit on it, but I did ride ones that did, and yes it did work.

bluechair84

benpinnick wrote:

Bluechair - yes Im pretty sure IIRC it ran straight SS - no tensioner. The VPP was fixed on the BB. Mine doesn't have that linkage/dropout kit on it, but I did ride ones that did, and yes it did work.

Yeaj, I was originally thinking the instant centre was the pivot point. I was looking at the wrong data when I thought that eould be true. I've now got a single pivot point using links like the blade

The Rookie

nicklouse wrote:

The Beginner wrote:

Been having a think, while it won't gve the same as a single pivot it would do what you want, 2 equal length links (upper and lower) running parallel, centre of the gearbox on the line between the frame end pivots and axle between the two dropout end pivots. Mount the front end higher than the rear for a rearward axle path in bump and as long as the frame end pivots are one above and one below the chain then no pedaling feedback!

I think....

Oh the lawwill patented design. But not great for a gearbox design.

Not sure why it wouldn't work with a gearbox design as long as the criteria I mention are stuck to?

Basically an old Jaj' IRS design on a bike!

YeehaaMcgee

I'm still uncertain "why" you're doing this, when there's already what is largely the same bike, available. If you're curious, pick one up and try it.
The reason they're not more commonplace may then become apparent.

bluechair84

I doubt I'd be able to get hold of one to test for long enough to make any conclusions about. It's worth putting the feelers out there though to see if I can get a longer ride on one. Though I have ridden an old GT IT1 once. The thing was so heavy I could barely get it going enough to tell how the suspension felt! And, as for reasoning - I'm not trying to reinvent the wheel. I want to learn some new skills and experiment with a design I'm curious about. If it turns out it doesn't ride well at all, I don't really mind. But I am hopeful that it will descend really well. I'm well aware that its pedalling efficiency will be a bit naff but, I'm just designing that out of it's priorities. I've been reading Ken Sasaki (?)'s essay on suspension designs and it makes for encouraging reading to be frank.

YeehaaMcgee

Hmm. I'm a bit concerned that this whole effort is going to cost you a considerable amount, and you may ened up with something you don't like at all. I would wholeheartedly suggest trying out a few pre-existing ideas first, and seeing their various strengths and weaknesses. Stand on the shoulders of giants (and a few malformed midgets ) so to speak.

nicklouse

bluechair84 wrote:

I've been reading Ken Sasaki (?)'s essay on suspension designs and it makes for encouraging reading to be frank.

it also helps you see through all the bull.

just been looking at your file as is you will be needing a tensioner. you will have almost as much as the the tank. (it is in the online libary have a look).

only had a quick look will look more later.

bluechair84

nicklouse wrote:

bluechair84 wrote:

I've been reading Ken Sasaki (?)'s essay on suspension designs and it makes for encouraging reading to be frank.

it also helps you see through all the bull.

just been looking at your file as is you will be needing a tensioner. you will have almost as much as the the tank. (it is in the online libary have a look).

only had a quick look will look more later.

He's particularly damning of Ellsworth... of which I'm an owner :shock:
Yup, needs a tensioner. Originally I positioned the VPP at the gearhub axle but realised anti-squat from the chain was too important. Do you think it conflicts with any patents?

YeehaaMcgee

Hang on, i thought you were completely eschewing anti squat?

bluechair84

YeehaaMcgee wrote:

Hang on, i thought you were completely eschewing anti squat?

The design has changed quite a bit - I originally designed the frame so it pivoted about the gearhub so that no chain tensioner would be required, but the more I learnt about anti-squat, the more I realised I couldn't get away from the need for it. Like you've said before, it'd be a pig to ride! It might have been your post that got me going in that direction actually, the more I looked at the design after your contributions, the more problems I could see with it.

YeehaaMcgee

Ok, I see.
But, are you still going with the gearhub design? and if so, why?

Or I guess I'm just being nosy and asking, what are your design objectives by now?

bluechair84

YeehaaMcgee wrote:

Ok, I see.
But, are you still going with the gearhub design? and if so, why?

Or I guess I'm just being nosy and asking, what are your design objectives by now?

Big objectives, a frame which can tackle trail riding and light dh comfortably with an adjustable fork and pair of wheels. At the moment, I take both Lyrics and Revs on riding hols, along with xc and dh wheels. All fits in the boot fine and takes 15 min to swap around, but i want a frame which can better handle both types of terrain over a riding holiday. A gearhub gives a wider range of gears than 1x10 for xc, but is secure and doesn't need and guide system, so never a dropped chain. The xc side is why i opted in on the anti-squat, the high pivot improves big hits, and i'm planning on adjustability

YeehaaMcgee

It will need a guide if you've got chain growth.

But honestly, sounds like you need my Marin Wolfridge

supersonic

Or third generation Idrive lol

YeehaaMcgee

I can;t think of any I-drive bike that's as versatile, frankly, sorry, Berk.
(that's a proper noun, not an insult by the way!)

supersonic

GT Distortion and Sanction - top machines!

bluechair84

Ho-hum... I had an old iDrive - an XCR. And a Freedrive which is more like the current iteration found on the Fury. Didn't like them both I'm afraid. The suspension felt 'muted' when stood.

As for the guide - I'm hoping it will only need a chain tensioner.

YeehaaMcgee

If this were Dragon's Den, I'd have to say I was out of the deal. That thing's going to weigh a ton with a gearhub, and two drivechains. Far better off with a 2x10.

Aaaand, it will still drop the chain. Rear mechs are chain tensioners, but don't alleviate the problem.

bluechair84

YeehaaMcgee wrote:

That thing's going to weigh a ton with two drivechains.

Weigh weenie :roll:
Yeah, with the design now moving away from zero chain stretch; pivoting at the gear hub, to designed-in anti-squat, I might need to go down the chain guide route. Chain stretch on the current design is something like 11mm (IIRC), so not vast. I'll be experimenting. There won't be any shifting ramps on the ring to encourage a chain drop - I discovered that moving to a custom chainring rather than just taking two off a triple helped.

YeehaaMcgee

bluechair84 wrote:

Weigh weenie :roll:

About as far from it as you could imagine
But you mentioned it as an XC machine.
The idea is just to vague by now to be worthwhile, IMO. There's plenty of bikes out there that can do what you want them to. Built by experienced manufacturers, some with lifetime warranties on frames (and bearings, looking at Marins)

bluechair84

For sure, and for all the slating my Moment has had, it's a decent versatile machine. But you know, I just want to learn a few things, make something myself that fits my needs. By XC, I mean just trail riding, moorlands, trail centres... all mountain riding... not XC racing. There will be compromises and issues, but I'm really looking forward to making it! Space is holding me back right now, but it's about a month before I move into my new house with a proper garage - that's when it'll really kick off.
All of the little niggly things about how the frame will work will all be figured out, it's mostly all done now. Bearing sizes and the BB shell are final focuses. After building it, I'll have the challenge of getting it destruction tested to see if it will hold up to proper abuse. I'll end up with a thread about where I could send it eventually.

bluechair84

Just to be clear, it's a 150 / 180 aggro frame, designed with an adjustable fork in mind (or most likely in my case, two forks that can be swapped over).

YeehaaMcgee

Aggro frame?
It strikes me that it's become a highly ambitious project, with no real aim. I'd suggest building a simpler hardtail, to teach yourself about the actual construction process, rather than (what I think will turn out to be) wasting a ton of money on something that isn't going to be particularly great. In the meantime, you may come up with a truly novel groundbreaking concept.

There's already bikes out there to do the kind of riding you're after. Bionicons, for example. Or, like I mentioned previously, my own much loved Wolfridge, which is a devastatingly capable all rounder machine, which really will do anything, from lapping lift assisted gnarly DH tracks, to 10 hour enduros.

I'm concerned that your desire to build "something" has overtaken your need to build something "good", and that what started out as a practical engineering challenge has devolved into some kind of fetishistic tinkering.

bluechair84

YeehaaMcgee wrote:

fetishistic tinkering.

Hey, What I get up to in my own leathers is none of your business, unless you're taking photos...

A hardtail was the initial plan, it bloomed from there. It is a big project, but one that I'm happy to undertake. There will be learning challenges as I go