[dw]

Right, you run numbers to make sure things will be strong enough, but you get to a point where you don't really know what the numbers mean untill you tinker around with it. For pedal kickback for example, you can calculate how much pedal kickback you'll have in some quantifiable units but you don't know how much is acceptable until you build up a bike and ride it to see if you can notice it or not, then it's an optomization game from there. The same could be said for structural analyisis, there's a point where you just don't really know what the variables are, I can calculate the impact force of a 200lb rider hucking off a 8' roof to flat but I don't know how that will affect the structure of the frame if the rider lands rear wheel first, how far on the rear wheel, tweaked out a little bit, and such. Hopefully the safety factor would account for variables like that but you really don't know until you have done some testing. Like DW points out the two really do go hand in hand, I'd consider a design that was built in CAD and used some FEA and such along with thourough testing to be superior to the homegrown tinker toy bike but computers and analysis can only take you so far.

You got it man, I mean, take the Sunday for example. A bike at first developed on "paper", using all of the aplied science and math I am so fond of, then tested for over a year in the real world. The beauty of the development cycle that I used is that every time I talked with Sam, Bryn, Matheiu etc... about performance, the performance traits always matched expectations. This gave the riders a lot of confidence to suggest performance changes that they knew they wanted, and it let me deliver new prototypes that reflected those changes almost immediately. We went through 3 years of what I would be satisfied with of "normal" development in a little over a year and 3 frame revisions. It really let us hone in on and modify exactly the performance traits that we wanted to affect, without casuing any detriment to traits that we really loved. Thats pretty awesome IMO, and thats the real power and efficiency of all this mathematical work.

dw

 

[dw]

yeah i know...but try to take a big drop and see what the physical constants do to your ankles....

hahahahha

that bike would suck!

 

[dw]

Are you wearing a dust mask? I'll bet you're getting loopy from inhaling fiberglass. Really we're not that funny.

ok im coming down now. must have been the fiberglass. Stupid low budget breather...

Only about 5 more pieces to go and I am done. Insulating blows.

 

[ssaddict]

Is it any better than roofing?

Ya would think in a place where it never rains you wouldn't need to do much maintainance.

 

[binary visions]

Insulating blows.

No kidding... I have to wonder about people who do it for a living. I see some guys, throwing up insulation with no masks, no gloves, no long sleeves, nothing.. I have to wonder about the contents of their lungs and how much of that sh!t works its way into their skin. ITCHY!

 

[ssaddict]

Ya mean you arn't suppose to do it that way?

 

[zedro]

No kidding... I have to wonder about people who do it for a living. I see some guys, throwing up insulation with no masks, no gloves, no long sleeves, nothing.. I have to wonder about the contents of their lungs and how much of that sh!t works its way into their skin. ITCHY!

i did that in edmonton for work. Although i was wearing a mask, after 3 days i quit because i woke up one morning and couldn't breath.

 

[leprechaun]

zedro,
Since your pivot is so high(and there is a pulley mostly negating chain pull) i'm curious if you still get a firming up sensation due to an inchworming effect?I would assume you do,but in a good way.I would think that due to the pulley that it would still be very active,but at the same time have anti squat designed in? One of those thing that has to be ridden to know.
Is this what you and DW are refering to as driving force?
Also does the front wheel push when cornering due to chainstay lenghtening?Since the Filing Cabinet has the highest pivot i've seen you should be the one to ask!!
I've been working(on paper) on a sliding pulley for my ASX so i can control the feedback i experience in the granny gear. A cable actuated,springloaded pulley that could be able to shift between the granny and middle rings in place of a front der.Personally i think that the whole single pivot with a pulley design is great and want to incorperate it into a multi speed system-at least until we have a transmition to work with!!
Thanks, Krispy

 

[zedro]

zedro,
Since your pivot is so high(and there is a pulley mostly negating chain pull) i'm curious if you still get a firming up sensation due to an inchworming effect?I would assume you do,but in a good way.I would think that due to the pulley that it would still be very active,but at the same time have anti squat designed in? One of those thing that has to be ridden to know.
Is this what you and DW are refering to as driving force?
Also does the front wheel push when cornering due to chainstay lenghtening?Since the Filing Cabinet has the highest pivot i've seen you should be the one to ask!!

well, Private Joker who took a short pedal on the bike up a hill said it felt like an XC bike.

The bike simply pedals neutral, it doesnt feel like it firms up (that would usually be due to chain effects which the design does not capitalise on) and doesnt "inchworm" (unless your in a low gear harmering up a hill trying to get to the chairlift, especially if your pulling the handlebars alot, but its very subtle). Also i do not run any ProPedal on the DHX to keep it more active, and it handles bumps well under power (no feedback). Basically this bike weighs 10 pounds heavier than the Stinky it replaced, yet pedals 10 pounds lighter than that power hogging slush-bucket.

Also despite what people assume, the chainstay actually gets shorter under hard or slow techy cornering if you load the front end (ie. decompressing the rear which gets shorter) or simply staying neutral on the bike. On fast corners you can stay rearward to lengthen the wheelbase. Really its a different cornering style than on my Stinky, and it was a worry before i tried it, but cornering ended up being immediatly and noticibly easier to handle.

there may be one draw back that i've just become aware of but havent fully substantiated, is that when you arent carrying enough speed through a techy rock garden and the front wheel gets hung up, pedalling through it may cause it to jack, further driving the front end down and then its OTB from there. Of course this is more rider incompetance than anything else, i'm just wondering if the suspension design is amplifying the mistake.

Personally i think that the whole single pivot with a pulley design is great and want to incorperate it into a multi speed system-at least until we have a transmition to work with!!

stop stealing my ideas before i get a chance to produce it

 

[ChrisKring]

heh, that bike sounds pretty wild, even on that one though, driving force will be higher than chain pull force. You could have a single pivot bike with a pivot 1 million kilomenters above the rear axle and a 450mm chainstay length, with a standard gearing, and drving force effect will be higher still. Its just one of those universal constants.

Dave

I just sketched the free body diagram. DW is correct.

The only way the chain pull force would be higher than the driving force is if the chain pull force was on the bottom of the cog. (assuming the instant center is higher than the cog)

Or if the instant center was approaching the ground. Then chain pull force would induce squat while the driving force produces anti squat. If it wasn't 6pm on Friday I would fire up Mathcad and make a model of this.

Again, do a FBD and like your prof. said things will be much more clear.

On a similar topic,

DW: how do you model how much the rider mashes the pedals verses spining circles? I guessing you determined that through trials. Or, did you throw a bunch of racers on a trainer with a power meter and cadence sensor attached to the computer to analyse their pedal strokes? It would be so easy to design the right amount of anti squat if everyone pedaled the same.

Also, I got ripped. Michigan Tech didn't let me build a FS bike for a design project. We just got to play with 600cc go carts (FSAE). Damn that was fun.

 

[ÆX]

Ya mean you arn't suppose to do it that way?

i did blow in 2 weeks ago in our house. that stuff is bad too. there was no ventalation in the attic. i am also doing my show as i put the steel siding up.
not is it fiberglass but out side in texas wind is not bad.

 

[leprechaun]

FINE THEN JUST MAKE IT!
Really it's a pain in the ass for me since i have little acess to the hardware i need to make it.
So far i have a MRP seat tube brace to mount on the seat tube and to take the load i am thinking of a rubber MRP type wheel that can roll on the outer bashring so it can't flex into the rings. But i need the cog! A der pulley will last about 1 mile! I'm trying to get a Balfa one but that is not so easy...
What are you using?I should call Lance Canfield,maybe he will get me one of his

 

[zedro]

I just sketched the free body diagram. DW is correct.

man, you guys take this more seriously than i do. The comment was an exageration of the infintly horrible design these guys made...sheesh, i can draw vector diagrams too... :

 

[ÆX]

exept maybe the bike that was designed the previous year at my school, which had a pivot higher than a BB7 but didnt run any pulley system whatsoever

these guys didnt know jack about bikes tho, and got a friend and Balfa to design and build the whole thing, yet they won the design award anyway (the faculty later realized they got burned and wont even mention the project ever happened at all, and it kinda screwed up my chances to win the award the next year ). Not surprisingly, i've never seen the bike on the trails.

sounds like my first 2x4. it coasted like a dream.

 

[zedro]

FINE THEN JUST MAKE IT!
Really it's a pain in the ass for me since i have little acess to the hardware i need to make it.
So far i have a MRP seat tube brace to mount on the seat tube and to take the load i am thinking of a rubber MRP type wheel that can roll on the outer bashring so it can't flex into the rings. But i need the cog! A der pulley will last about 1 mile! I'm trying to get a Balfa one but that is not so easy...
What are you using?I should call Lance Canfield,maybe he will get me one of his

i can get you a Balfa one, my shop has one for 25$cnd. I made my own since the Balfa ones are too wide. I shoulda got it done properly at the machine shop, but found an alternative...

Receipe:

ODI lock-on collar conveniently with fit a cog on the outside, and a skate bearing on the inside. Then its a matter of making side plates and bolting them together.

I made another one using a casette freehub shell cut at the end which can fit a bigger bearing.

 

[zedro]

sounds like my first 2x4. it coasted like a dream.

something about big oversized pivots that makes me all sweaty.....

this one had an even higher pivot....

you could mod it no?

 

[ÆX]

something about big oversized pivots that makes me all sweaty.....

this one had an even higher pivot....

you could mod it no?

i traded it for a ktm 540
it was to big for me and i sold it.
the guy ended up killing it off a
big flat drop with too light of springs.
it was still set up for me.

there was no room to mod it. it had a lot of problems at the bb pivot. i didn't
beef it there enough. it was a great proto and did evenything it was asked to.
mainlly tell me what i could do better!

 

[zedro]

it was a great proto and did evenything it was asked to.
mainlly tell me what i could do better!

yeah, i know that feeling...

 

[UiUiUiUi]

FINE THEN JUST MAKE IT!
Really it's a pain in the ass for me since i have little acess to the hardware i need to make it.
So far i have a MRP seat tube brace to mount on the seat tube and to take the load i am thinking of a rubber MRP type wheel that can roll on the outer bashring so it can't flex into the rings. But i need the cog! A der pulley will last about 1 mile! I'm trying to get a Balfa one but that is not so easy...
What are you using?I should call Lance Canfield,maybe he will get me one of his

try one of the canfields
they use ti pulleys with a good bearing inside
they work flawless on both my canfield bikes for one respective two seasons now

 

[dw]

zedro,
I've been working(on paper) on a sliding pulley for my ASX so i can control the feedback i experience in the granny gear. A cable actuated,springloaded pulley that could be able to shift between the granny and middle rings in place of a front der.Personally i think that the whole single pivot with a pulley design is great and want to incorperate it into a multi speed system-at least until we have a transmition to work with!!
Thanks, Krispy

Trek patented EXACTLY this in 1999-2001 or so. I have the patent in a box in storage. Ill dig it up and let you guys know the #.

Remember that weird little pulley mount on the Trek Deisel frames? That is what was supposed to bolt to it. Pretty neat I thought. I always wanted to do something similar, just with a bit more "complexity" We had a lot of discussions about htis back inthe day on MTBR. Myself and Kyle K (PDC) had a thread about this going for about a month where I was trying to explain how to analyze such a system. Man, those were the days... hahaha

 

[dw]

FINE THEN JUST MAKE IT!
Really it's a pain in the ass for me since i have little acess to the hardware i need to make it.
So far i have a MRP seat tube brace to mount on the seat tube and to take the load i am thinking of a rubber MRP type wheel that can roll on the outer bashring so it can't flex into the rings. But i need the cog! A der pulley will last about 1 mile! I'm trying to get a Balfa one but that is not so easy...
What are you using?I should call Lance Canfield,maybe he will get me one of his

Krispy, get a profile hub driver and mount that to your shaft, or find an old cassette body and then you can change gear sizes. There are those old school aluminum derailleur pulley replacements too. Any shop that did a lot of business in the mid 90s should have one of those kicking around. Heck, I think I have one from an old AC guide. If you cant find one let me know and ill mail it to you!

Dave

 

[dw]

sounds like my first 2x4. it coasted like a dream.

one of the coolest bikes ever.

 

[dw]

Is this what you and DW are refering to as driving force?

When I refer to driving force, I am literally referring to the force that is pushing the bike and rider forward as you accelerate. It is really a reaction force that can be broken down as chain force, amplified through a lever (your wheel and cogs) and "anchored" at the ground through traction force between the tire and the ground itself.

BTW, It was good to talk with you and Scott again out at the show man.

Dave

 

[thaflyinfatman]

Excellent thread! Learnt a lot from this one.

 

[thaflyinfatman]

I
DW: how do you model how much the rider mashes the pedals verses spining circles? I guessing you determined that through trials. Or, did you throw a bunch of racers on a trainer with a power meter and cadence sensor attached to the computer to analyse their pedal strokes? It would be so easy to design the right amount of anti squat if everyone pedaled the same.

Yeah, I wondered that too (and how CoM shifts, and how pulling up on the bars would affect pedaling, if at all, etc)! Maybe it's not the kind of info DW wants to give away though...

 

[loulou]

I made a bike, a long time ago, where the pulley is far enough from the crank, so that i can use two chainrings.(I planned on using a rotated front E type derr. but i must say i still finger shift!) I still use this bike with two baby seats. 7'' travel is perfect for carrying kids on trails.
I agree that acceleration force is a good way to counteract pedaling downforce.
high pivot bikes work well, but the design(geometry and shock levers) has to be adapted for the way the suspension works.
As for that single pivot VS four bar VS VPP, I think there is a lot of marketing hype involved.
For example: the VPP has supplanted the fabled Horst link as the most desirable system, but has any one noticed that the VPP rear brakes very much like a single pivot?
In my opinion the only reason, apart from structural preferences, to go multi pivot is to get a shorter radiused path (and perhaps as an added bonus benefit from the subtle benefit of a floating caliper)
The only use of the VPP is to limit chain growth in the last part of the travel.
The reason they pedal good is in the shock compression curve, they present an early rise in their rate that work as threshold to filter pedaling forces.

 

[loulou]

one of the coolest bikes ever.

eh! a carbon fiber balsacore 2 D.o.F, 18'' in. square travel DH...
THE COOLEST! :mumble:

 

[flymybike]

Krispy, get a profile hub driver and mount that to your shaft, or find an old cassette body and then you can change gear sizes. There are those old school aluminum derailleur pulley replacements too. Any shop that did a lot of business in the mid 90s should have one of those kicking around. Heck, I think I have one from an old AC guide. If you cant find one let me know and ill mail it to you!

Dave

Krispy
The driver is a good way to go if it works in your application. I have to disagree with DW. The aluminum pulley wheels won't work, I've tried. They will disinigrate in one ride, seriously! They are made for a non-loaded application, not in the tensioned side of the drive system.
BTW I have the TI cogs available for special peeps like you! It will last. call chris, he will set you up.

 

[leprechaun]

thanks for all the friendly info on the pulley system guys!
Trek can bite me! It doesn't matter if Twreck has the patent since i'm only gonna make 1 for myself!

 

[vitox]

eh! a carbon fiber balsacore 2 D.o.F, 18'' in. square travel DH...
THE COOLEST! :mumble:

hey loulou i have read and enjoyed all of your 3 posts so far but this one i plain dont understand.....

 

[zedro]

hey loulou i have read and enjoyed all of your 3 posts so far but this one i plain dont understand.....

translation:

2 d.o.f = 2 degrees of freedom (ie. the rear axle has....)

18" square travel = the theoretical box in which the rear axle can travel inside

 

[vitox]

fack


alex



i thought it only was to increase damping and decrease effective leverage.

and that was how much before the first gemini?

 

[loulou]

i had never seen Zedro's bike before, very very nice! Alex BCD 2x4 is amazing, has anyone heard of a 2 D.o.F. suspension on any vehicle before?
Only in this business!

 

[zedro]

i had never seen Zedro's bike before, very very nice! Alex BCD 2x4 is amazing, has anyone heard of a 2 D.o.F. suspension on any vehicle before?
Only in this business!

heh thanks....surprised you havent seen it at Bromont before.

i think those Mars rovers have 2 D.o.F?....

 

[ÆX]

fack


alex



i thought it only was to increase damping and decrease effective leverage.

and that was how much before the first gemini?

thanks, it just came to me. i never saw the rover.

i made and raced the biek for one season in '98.

this first gen had 4:1 for the high pivot and 2:1 for the bb area.

gen two had equal leverage 2.5:1.

1.5 stroke for the bb abd 1.75 for the high pivot

i love that bike. it would rule if i could get a gearbox in there too!

 

[loulou]

did not go much to bromont this summer...
hey, were you in the concordia group that made the dh bike project...
in any case, your bike is really nicer.
i am gearing up for making a few frames this winter.
i will do a little 3D modeling and f.e.a., but i still think actual frames and swing arm protos are so quick to make and ...well more realistic! i'll keep this forum informed!
as for the Mars rover, i thought they just had high pivots, but i see them everywhere now...

 

[zedro]

hey, were you in the concordia group that made the dh bike project...
.

that group was the year before me, but basically they had other people do everything (ie. some ex-student friend and Balfa, etc) and presented the bike as their own work and won the design prize. People knew what they did and eventually the school found out, which is why they dont talk about it now.

I did this project 100% on my own the following year, all machining was done at the school (exept the BB threads which i had my friend at Pauls cycles get done at the Balfa shop), welding done at some crappy moto place in Laval. I didnt bother entering the design contest tho, considering the bad taste the last bike project had caused for one reason....

 

[loulou]

well i am happy to have helped you; i cutted these threads. the bb i.d. was just right!
are you still in montreal?

 

[zedro]

well i am happy to have helped you; i cutted these threads. the bb i.d. was just right!
are you still in montreal?

heh thanks

yeah i'm still in montreal