the gearbox thread
- Thread starter xy9ine
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good to see she is still performing well.
thats easily the coolest shaped front triangle ive seen.. nice paint job too. How about a carbon rear end to match?
i dont suppose you know off hand how dodzy's high pivot rig is going for him too?
re: pivot hight. Given the fore/aft position of the pivot which was determined by my gearbox config this is the position that gives neutral pedalling given the chain line, my height and wheelbase. In that respect it's great. Ie neutral pedalling. It also eats up bumps like mad with the rearward axle path. No downsides that i have encountered yet.
Some would say it needs a floating brake do to brake induced squat, I would say it's not something I notice and if you look at Fabien Barel floating brake set up it mimics the behaviour of a high pivot bike without a floater.
Dodzys bike is retired in his garage. Needs a few tweaks for race worthyness.
Some would say it needs a floating brake do to brake induced squat, I would say it's not something I notice and if you look at Fabien Barel floating brake set up it mimics the behaviour of a high pivot bike without a floater.
Dodzys bike is retired in his garage. Needs a few tweaks for race worthyness.
^ For Metzy
A question concerning inboard brake setups
I've been searching around but cant really find an answer for this. Say I were to run a nonconcentric pivot, as in a single pivot with the "gearbox" drive sprocket in front of the pivot, yet somewhat inline with the swingarm - pretty much picture a motorcycle, or dirtbike. On the Driven sproket of the system I want to put the inboard disc brake - In hopes that since the main swingarm pivot and gear box are non concentric, i can acheive a lower overall width by having them inline and having the rotor on the center of the gearbox aka internally geared hub.
Ok thats the setup, now how would it react when braking forces are applied, i.e. squat or jack? would it be unique to how the chain forces are - negative or positive chaingrowth or is it affected differently. Since chain growth/shrinkage is almost unavoidable with this setup, unless you were to run a third chain and make the main pivot a jackshaft setup (and add more weight) I'm assuming brake interaction with an inboard setup and non concentric pivots is unavoidable as well.
Let me know what you think and if there are any references or resources i could research on this that already exist.
A question concerning inboard brake setups
I've been searching around but cant really find an answer for this. Say I were to run a nonconcentric pivot, as in a single pivot with the "gearbox" drive sprocket in front of the pivot, yet somewhat inline with the swingarm - pretty much picture a motorcycle, or dirtbike. On the Driven sproket of the system I want to put the inboard disc brake - In hopes that since the main swingarm pivot and gear box are non concentric, i can acheive a lower overall width by having them inline and having the rotor on the center of the gearbox aka internally geared hub.
Ok thats the setup, now how would it react when braking forces are applied, i.e. squat or jack? would it be unique to how the chain forces are - negative or positive chaingrowth or is it affected differently. Since chain growth/shrinkage is almost unavoidable with this setup, unless you were to run a third chain and make the main pivot a jackshaft setup (and add more weight) I'm assuming brake interaction with an inboard setup and non concentric pivots is unavoidable as well.
Let me know what you think and if there are any references or resources i could research on this that already exist.
I have a great reference for this situation. There is some good moto info around about the 'reverse torque" created under engine braking. this is the same as using an inboard brake. Depending on the specific geometry of the suspension it is likely the chain will reduce the amount of squat.
Imagine traction force at rear wheel contact patch. This tends to rotate the swing arm about the pivot. If the pivot is at ground level there will be no rotation. If it is high and back you will get squat. Weight transfer dominates in practice and all you really feel is dive in the front + rear wheel is so light under brakes the traction force in minmal........ unitl you get bumps then you can get loading and unloading........gets complicated.
a little info attached.
Imagine traction force at rear wheel contact patch. This tends to rotate the swing arm about the pivot. If the pivot is at ground level there will be no rotation. If it is high and back you will get squat. Weight transfer dominates in practice and all you really feel is dive in the front + rear wheel is so light under brakes the traction force in minmal........ unitl you get bumps then you can get loading and unloading........gets complicated.
a little info attached.
Attachments
Sure - and the torque from braking (engine or otherwise) is tending to lift the rear wheel off the ground in a 'squatting' setup. This lowers the mass force on the rear contact patch, reducing grip.
Thanks for the link metzy, would you mind sharing what book or source thats from? I'm picking up Foale's book on motorcycle suspension soon, that wouldnt be it would it?
That picture is OK, but I would most likely be using the same size sprocket front and rear, would this present a difference? the IC (or whatever the term for braking forces) would be alot different if the braking force vector or w/e was parallel with the the swingarm line throughout compression, right?
I've read that a bigger rear sprocket creates "squat" and vice versa creates "jack" as well, but what do the same size sprockets in the same nonconcentric arrangement cause?
It is my quess that the effect will largely dependent on the chaingrowth, positive growth causing squat (I know the pedalling effects on positive chain growth promote squat, not sure if the braking effects would be inverse) and negative growth the opposite.
That picture is OK, but I would most likely be using the same size sprocket front and rear, would this present a difference? the IC (or whatever the term for braking forces) would be alot different if the braking force vector or w/e was parallel with the the swingarm line throughout compression, right?
I've read that a bigger rear sprocket creates "squat" and vice versa creates "jack" as well, but what do the same size sprockets in the same nonconcentric arrangement cause?
It is my quess that the effect will largely dependent on the chaingrowth, positive growth causing squat (I know the pedalling effects on positive chain growth promote squat, not sure if the braking effects would be inverse) and negative growth the opposite.
That is from Gaetono Cocco's book. You can find it on Amazon but I would recommend staying with Foale's book. The Cocco book has some inaccuracy in it that can confuse things, especially for someone trying to learn.
Has anyone tried replacing the bottom bracket with an internal drive "hub"? Obviously, this would require some modifications to the size of the bottom bracket, but here's what I'm thinking.
Using a Rohloff type hub, replace the BB. The gearing would start at the axle that currently goes through the BB, go through adjustable gearing, just like the rear wheel, and then there would be an external gear, around the axle but able to move independently, to drive the wheel. This way, frames could be standardized to accept a specific "hub", just like they currently accept standard BB sizes. Basically, I'm reversing the direction of the hub. Instead of the chain driving the axle, the axle drives the chain. There could either be a fixie hub on the wheel, and the new "BB" would allow the pedals to move freely, or a standard hub could be used on the rear wheel. The benefit of the fixie hub is less unsprung mass and the ability to shift without pedalling, but the chain will always be moving.
I've been thinking about this for a little while, but unfortunately lack the means/ability to try it out myself. I hope one of you can take it and run with it!
Using a Rohloff type hub, replace the BB. The gearing would start at the axle that currently goes through the BB, go through adjustable gearing, just like the rear wheel, and then there would be an external gear, around the axle but able to move independently, to drive the wheel. This way, frames could be standardized to accept a specific "hub", just like they currently accept standard BB sizes. Basically, I'm reversing the direction of the hub. Instead of the chain driving the axle, the axle drives the chain. There could either be a fixie hub on the wheel, and the new "BB" would allow the pedals to move freely, or a standard hub could be used on the rear wheel. The benefit of the fixie hub is less unsprung mass and the ability to shift without pedalling, but the chain will always be moving.
I've been thinking about this for a little while, but unfortunately lack the means/ability to try it out myself. I hope one of you can take it and run with it!
you have just described one of the things i have been working on for the last year or so. Its a simple and good idea but tricky to actually impliment, mostly due to space restrictions, maintaining an acceptable q factor etc..
not all places have big resources,Man, where do these places come up with the money to build such custom fab intensive products! Send some this way!!
I am currently designing a toned down and cheaper DH frame, that will be easier to sell 
. all the earnings will go into funding a gearbox bike.
I searched but couldn't see if someone had already posted this.
"The Bomb Boxx9 of Bouncing Betty, a new limited edition frame, packs 9 powerful speeds into this lethal machine.
They perfected high performance and then took it over the top, the result is going to lay an assault on the DH world cup scene! Take your ride to the next level, drop the Bomb!
From Taiwan.
"The Bomb Boxx9 of Bouncing Betty, a new limited edition frame, packs 9 powerful speeds into this lethal machine.
They perfected high performance and then took it over the top, the result is going to lay an assault on the DH world cup scene! Take your ride to the next level, drop the Bomb!
From Taiwan.
The bits the frame that go down past the shock look poorly designed,why not either run all fat square tube or.... That X looks weak as. It can only be as strong as the X bit or the welds below it. Otherwise looks long lasting. Are they for sale,or is it proto? I know it says limited run,but what does that mean?
Yeh!? What is news mate? Been quiet on your www?
I believe this was shown at eurobike in 2006, but with no follow-up in '07, meaning that it's most likely a dead project. It was also exactly the same bike at the suntour booth, labeled suntour and painted white.I searched but couldn't see if someone had already posted this.
"The Bomb Boxx9 of Bouncing Betty, a new limited edition frame, packs 9 powerful speeds into this lethal machine.
They perfected high performance and then took it over the top, the result is going to lay an assault on the DH world cup scene! Take your ride to the next level, drop the Bomb!
From Taiwan.
I really hope suntour can get it's s--t together on this. We really need an affordable box. The german g-boxx will be better I'm sure, but it's dangerous to have all our eggs in one basket, so to speak.
Ah, if it's from that long ago no wonder I couldn't remember seeing it before. Remembering last week is hard enough
Hot little teaser from diamondback. The sabbath arrives May 12th.
http://www.diamondback.co.uk/index.aspx
http://www.diamondback.co.uk/index.aspx
With Quad Deuce brakes!
Very nice man, way to get out there and do something special. Looks cool and definitely some sweet little custom features on there. I dig the BB/freehub, nice idea.
thanks man, i was stoked to watch yours get built up. I have been working on this since january for school kind of off and on. its nice to be done.
DC your bike is so F***ing nice(design). Well done mate.
Very nice work mate. Was waiting on someone (else) thinking FFW was the goods!
I like the way you routed the chain going up the to the gears; its nice and out of the way
definitly a sick design w/ the der. in the frame, i am def. a fan of that style
I don't think so. I emailed db usa, they said no. Emailed db uk, they said they were in negotiations to distribute it in the us. I never heard back.
I like the zip-tie friction drive on the rear hub. Very slick.
How'd you mount the freewheel to the crank spindle? I don't think those cranks have splines all the way across the spindle, so a simple adapter is out. Did you just put it together and weld it in place?
Yea he welded it right onto the spindle. Serves its purpose, but might be tough to remove the one crank without a sawzall haha.
Die grinder works wonders.
I got a question about the Ratcheting type cvt's like Lahr's and Honda's and any before it.
It seems like most of the designs, including his are able to transfer a variable output in a single direction independent of the direction of the input (although usually not optimized for reverse direction input). In other words if you back pedal you will still be pedalling, so say you need to ratchet through a tight set of rocks your back pedal stroke will be creating the same forward motion as a pedaling forward - making it tricky i would assume. Do you just throw another sprag clutch inline before the input? Also does anyone know the weight of Lahr's cvt (just the removable transmission part, no input or output drivetrain)? thanks
::Edit:: oh damn 600th post. giggidy giggidy
It seems like most of the designs, including his are able to transfer a variable output in a single direction independent of the direction of the input (although usually not optimized for reverse direction input). In other words if you back pedal you will still be pedalling, so say you need to ratchet through a tight set of rocks your back pedal stroke will be creating the same forward motion as a pedaling forward - making it tricky i would assume. Do you just throw another sprag clutch inline before the input? Also does anyone know the weight of Lahr's cvt (just the removable transmission part, no input or output drivetrain)? thanks
::Edit:: oh damn 600th post. giggidy giggidy
lahr cvt = 3lbs i believe
in answer to your 2nd question, in the case of the lahr i suppose it would really depend on the profile of the cam. If the cam follower responds to the direction of rotation being reversed without getting stuck then no need for another sprag, as there will already be one just before the output.
If i were to guess id say he doesnt have an additional sprag for if the pedals are reversed as they are relativley heavy and 3lbs is light for such an assembly.
in answer to your 2nd question, in the case of the lahr i suppose it would really depend on the profile of the cam. If the cam follower responds to the direction of rotation being reversed without getting stuck then no need for another sprag, as there will already be one just before the output.
If i were to guess id say he doesnt have an additional sprag for if the pedals are reversed as they are relativley heavy and 3lbs is light for such an assembly.
Being that its at the output won't it have already been through the ratcheting part of the cvt, and transfered into forward motion tho (assuming the follower can follow the cam bidirectionally)? A sprag would only stop feedback from the back wheel at that point (allow it to coast) right? Thats what I'm kinda caught up on with my design, bidirectional input = unidirectional output. I could easily throw another sprag in but its so mechanically simple right now, I don't wanna clutter it so to speak.
3lbs is impressive, I thought I heard 9lbs or something but that must of been something else.
i think ive maybe misunderstood your question,
from what i can gather the way you have it set up you will need another sprag so that the whole cam follower assembly only moves in the one direction, although without pictures its hard to tell as im trying to visualise your setup..
im working on something similar at the moment.
I guess look at it as if the Cam is the driven member of the input. I'm not sure if thats the inversion the Lahr CVT uses for bicycle use though now that I think of it.