Home Made Bikes

Author Message
flag R-M-R
Posted: Apr 17, 2020 at 19:09 Quote
There are weirder designs out there and there's nothing crazy about his kinematics.
flag dirtysanchez44
Posted: Apr 18, 2020 at 1:59 Quote
R-M-R wrote:
There are weirder designs out there and there's nothing crazy about his kinematics.

Forces like straight lines.

Also best of luck to the downtube when it’s getting loaded almost perpendicular. What wall thickness is that DT? Im guessing that’s the reason you’ve got the support stay.

I guess it’s only a bike so you can do what you want...

Definitely an eye catcher though and the jig is pretty neat!
flag SleepingAwake
Posted: Apr 18, 2020 at 2:22 Quote
It does look a little unconventional, but in the end the forces are not going to any bigger or smaller than with a linkage design that gives you more progression.
flag R-M-R
Posted: Apr 18, 2020 at 3:06 Quote
jgmu97 wrote:
Also best of luck to the downtube when it’s getting loaded almost perpendicular. What wall thickness is that DT?

Anything can be strong enough with enough material. Notice the gusset plate over the down-tube. I can't say whether it will definitely hold up, but he's taking the right steps.
flag dirtysanchez44
Posted: Apr 18, 2020 at 3:13 Quote
SleepingAwake wrote:
It does look a little unconventional, but in the end the forces are not going to any bigger or smaller than with a linkage design that gives you more progression.

With a linkage or bellcrank design, you are at least getting the forces working axially with the shock. That just isnt the case here, based on the pivot location and shock angle.

OP, do you have any plots of your kinematics to show from CAD or Linkage or a computer code?

R-M-R wrote:
jgmu97 wrote:
Also best of luck to the downtube when it’s getting loaded almost perpendicular. What wall thickness is that DT?

Anything can be strong enough with enough material. Notice the gusset plate over the down-tube. I can't say whether it will definitely hold up, but he's taking the right steps.

True, but in my eyes that is excess weight along with compliance in an area where you want it to be rigid so your damper can do the best job at dampening the inputs and keeping your bike stable with the best rear wheel traction..

Load paths are an interesting topic!
flag Grumposaur
Posted: Apr 18, 2020 at 7:16 Quote
jgmu97 wrote:
SleepingAwake wrote:
It does look a little unconventional, but in the end the forces are not going to any bigger or smaller than with a linkage design that gives you more progression.

With a linkage or bellcrank design, you are at least getting the forces working axially with the shock. That just isnt the case here, based on the pivot location and shock angle.

OP, do you have any plots of your kinematics to show from CAD or Linkage or a computer code?

R-M-R wrote:
jgmu97 wrote:
Also best of luck to the downtube when it’s getting loaded almost perpendicular. What wall thickness is that DT?

Anything can be strong enough with enough material. Notice the gusset plate over the down-tube. I can't say whether it will definitely hold up, but he's taking the right steps.

True, but in my eyes that is excess weight along with compliance in an area where you want it to be rigid so your damper can do the best job at dampening the inputs and keeping your bike stable with the best rear wheel traction..

Load paths are an interesting topic!

Shock is always loaded axial as the mounting points are shafts and cannot transfer a moment to the shock. A shock is always acting as a pure compression member.

(At least not in their normal working plane: sideways flex between rear triangle and frame can cause shock 'bending" and thus binding)
flag dirtysanchez44
Posted: Apr 18, 2020 at 8:35 Quote
Grumposaur wrote:
jgmu97 wrote:
SleepingAwake wrote:
It does look a little unconventional, but in the end the forces are not going to any bigger or smaller than with a linkage design that gives you more progression.

With a linkage or bellcrank design, you are at least getting the forces working axially with the shock. That just isnt the case here, based on the pivot location and shock angle.

OP, do you have any plots of your kinematics to show from CAD or Linkage or a computer code?

R-M-R wrote:


Anything can be strong enough with enough material. Notice the gusset plate over the down-tube. I can't say whether it will definitely hold up, but he's taking the right steps.

True, but in my eyes that is excess weight along with compliance in an area where you want it to be rigid so your damper can do the best job at dampening the inputs and keeping your bike stable with the best rear wheel traction..

Load paths are an interesting topic!

Shock is always loaded axial as the mounting points are shafts and cannot transfer a moment to the shock. A shock is always acting as a pure compression member.

(At least not in their normal working plane: sideways flex between rear triangle and frame can cause shock 'bending" and thus binding)

Yes I realised that was the wrong terminology... You are correct as they’re not fixed mountings so can’t transfer a moment.

How much does the shock have to rotate during the travel of the rear wheel? Seems like there will be a lot of forward motion based on the geometry of the link.
flag shirk-007
O+
Posted: Apr 18, 2020 at 8:55 Quote
Draw an arc from the upright and you will see how far forward the shock moves.

From rough memory this layout gets you about the same amount of LR progression as what GT got with the split seat tube Sanction frames.
flag Grumposaur
Posted: Apr 18, 2020 at 9:05 Quote
jgmu97 wrote:
Grumposaur wrote:
jgmu97 wrote:


With a linkage or bellcrank design, you are at least getting the forces working axially with the shock. That just isnt the case here, based on the pivot location and shock angle.

OP, do you have any plots of your kinematics to show from CAD or Linkage or a computer code?



True, but in my eyes that is excess weight along with compliance in an area where you want it to be rigid so your damper can do the best job at dampening the inputs and keeping your bike stable with the best rear wheel traction..

Load paths are an interesting topic!

Shock is always loaded axial as the mounting points are shafts and cannot transfer a moment to the shock. A shock is always acting as a pure compression member.

(At least not in their normal working plane: sideways flex between rear triangle and frame can cause shock 'bending" and thus binding)

Yes I realised that was the wrong terminology... You are correct as they’re not fixed mountings so can’t transfer a moment.

How much does the shock have to rotate during the travel of the rear wheel? Seems like there will be a lot of forward motion based on the geometry of the link.
Obviously more rotation than every "looks like a session" design.


But that is not on common at all for example my Tues has a similar change in orientation as the bike goes to max travel:
Large frame with shock removed for saddle clearance check. eye-eye about 10mm shorter then minimum length of shock at full bottom out. Saddle tube stick up 140mm.
My late 2016 YT Tues Comp. All stock delivered with GX-derailleur 7 speed narrow range cassette 17 Guide RS and black Boxxers

The shock rotates from being parallel to the down tube to more horizontal at max compression.
(video from the web with a shock in there: https://www.youtube.com/watch?v=IVQLUo0VT7w)

It just a design choice, also it doesn't mean perse more rotation in total. In a Session, or what ever, the shock stays vertical, but the actuating link is rotating more. So it is always important to have smooth shock bushings and bolts.

photo

That link is normally horizontal/forward side slightly up.
flag BikeRider3
Posted: Apr 18, 2020 at 9:08 Quote
Shock rotates roughly 19 degrees throughout travel, all of the components are just placed in position currently so the shock to upright angle is a little smaller than it will be eventually.
flag dirtysanchez44
Posted: Apr 18, 2020 at 9:46 Quote
I traced it in CAD, got the MR changing from around 2.6 at static to 2.5 at fully compresse, so slightly progressive Is that in the right ballpark OP? Obviously this is a good estimate based on where i dropped my points so its not going to be bang on.
flag BikeRider3
Posted: Apr 18, 2020 at 9:51 Quote
jgmu97 wrote:
I traced it in CAD, got the MR changing from around 2.6 at static to 2.5 at fully compresse, so slightly progressive Is that in the right ballpark OP? Obviously this is a good estimate based on where i dropped my points so its not going to be bang on.

LR is around 2.8 with a similar level of progression you mentioned. Version 2 of this frame which I'm currently working on the design of will use a different shock size and have more progression.
flag jamieridesbikes
Posted: May 8, 2020 at 10:44 Quote
Question for anyone who has made a jig using aluminium extrusion: did you use any heat shielding to protect the beams when brazing? Bit worried I'll warp it with the torch while tacking.
flag suravida
Posted: May 8, 2020 at 14:05 Quote
If you wrap your fixture when tacking your flame is waaay too big. Hell, my first ever frame I built on a wooden board, which did not catch fire when tacking, so you should be OK.
flag jamieridesbikes
Posted: May 8, 2020 at 15:12 Quote
I didn't think to space out the arms from the frame so they're only about 4cm from the tubing.
More concerned that my big steel cones to hold the head tube and BB in place will suck up a lot of heat and affect the alloy they are fixed to.

Maybe I'm over thinking, but if you managed with a wooden jig I'll probably be ok!

 


Copyright © 2000 - 2024. Pinkbike.com. All rights reserved.
dv56 0.102951
Mobile Version of Website