Linkage Mechanism- any engeneers here?

[alonstar]

Hey!!
I hope there is anyone who can help me with this topic..
For the stucture of a folding mechanism of foldable bicycle,
im trying to achive a mechanism, when pushing the seatpost to the front of the bicycle, the rear wheel will also be pushed simultaneously to the center of the bicycle under the frame.
after the short description i will try and explain the wanted outcome it visually:


how should i link the arm to the seatpost? i need a linkage system that will convert the movements.
any genious out there?
the "linkage system area" represnts the space to use extra arms or axis.

Thank you all!

 

[DaLanMan]

So you are looking for a collapsing fold, like you would get from a folding chair (which collapses up but same process)

Just a thought.. You may not want to put a point on your bike that is in line with the direction of motion that has a collapsing process in it.

I have already fished a kid off the street who managed to partially fold his bike on himself.

If you have it so that it is going to potentially capture the rider in the procese...

Hey, i am not gonna judge you, you gotta capture friendship where you can ::laughing;:

 

[RunForTheHills]

You are either going to have really small wheels or or the top tube will be too long for a comfortable ride with a fold like that. Most folding bikes fold to the side for a reason. That said, the Brompton folds under like that before folding again to the side. The seatpost slides down into the frame. With your method, it would be difficult to adjust the height of the seat for different riders.

 

[Chalo]

Since a bicycle drive chain can carry many hundreds of pounds of tension when it's being pedaled, keep that in mind when vetting ideas for your folding mechanism. It's no good to have a folding mechanism that does what you want, but breaks when you try to climb a hill.

Also keep in mind that with bicycles, everything has been thought of and tried multiple times, and designs you've never seen before most likely have deal breaking problems that kept them from becoming common.

 

[marka-ee]

Also keep in mind that with bicycles, everything has been thought of and tried multiple times, and designs you've never seen before most likely have deal breaking problems that kept them from becoming common.

true, the dominant factor: "patents". I remember seeing somewhere a very elegant folding bicycle design that got held up because of a patent issue. I can't put my finger on where I saw the design but when I saw it as an engineer I thought that it was extremely elegant.

 

[Papa]

I didn't even get to question at- hand... sorry. Your steering geometry jumped out at me - It is radically unacceptable... I don't have immediate access to my images ATM, but just plugin "bicycle steering geometry" into Mr G and replicate what you find. Here's one..,

Geometry of Bike Handling – Calfee Design

calfeedesign.com

 

[alonstar]

So you are looking for a collapsing fold, like you would get from a folding chair (which collapses up but same process)

Just a thought.. You may not want to put a point on your bike that is in line with the direction of motion that has a collapsing process in it.

I have already fished a kid off the street who managed to partially fold his bike on himself.

If you have it so that it is going to potentially capture the rider in the procese...

Hey, i am not gonna judge you, you gotta capture friendship where you can ::laughing;:

Hey thanks for your reply, i believe, if made and designed correctly, it wont be dangerous..
when you say a collapsing fold, is that a thing? should i look for this type of fold on go after it?

 

[alonstar]

You are either going to have really small wheels or or the top tube will be too long for a comfortable ride with a fold like that. Most folding bikes fold to the side for a reason. That said, the Brompton folds under like that before folding again to the side. The seatpost slides down into the frame. With your method, it would be difficult to adjust the height of the seat for different riders.

View attachment 348598View attachment 348599

Hey hey thanks for your reply.
brompton indeed made such a great job.
in my drawing the sizes are far from the actual proportions i have in my more serious sketching and CADing.
the wheel will be small around 18INCHES.. its true that the seat will not be properly folded in differet heights- a topic i will have to work on.. about my question, you know how can i make the linkage of the arms to act the way i described?
thanks

 

[alonstar]

Since a bicycle drive chain can carry many hundreds of pounds of tension when it's being pedaled, keep that in mind when vetting ideas for your folding mechanism. It's no good to have a folding mechanism that does what you want, but breaks when you try to climb a hill.

Also keep in mind that with bicycles, everything has been thought of and tried multiple times, and designs you've never seen before most likely have deal breaking problems that kept them from becoming common.

Hey thanks for your reply!!
Im not sure i understand, why the folding mechanism would bother or inturrept the paddling?
if connected correctly, and tested with the high enough pressure- it should be ok isnt it?

i do realise that mostly has already been tried and invented, but i will still shoot my shot! who knows, might be a succes or might be a failed try, either way i will learn a lot.

Do you have any idea about the linkage system? how should i link the arms?
thanks!

 

[alonstar]

I didn't even get to question at- hand... sorry. Your steering geometry jumped out at me - It is radically unacceptable... I don't have immediate access to my images ATM, but just plugin "bicycle steering geometry" into Mr G and replicate what you find. Here's one..,

Geometry of Bike Handling – Calfee Design

calfeedesign.com

The drawing i uploaded is far from my actual design, i added the stem and all just to make clear when the parts are.
I would love to send you privatly- my sketching of the bicycle and we can discuss geometry.

Do u have an idea on the linkage system?

thanks!

 

[Chalo]

Hey thanks for your reply!!
Im not sure i understand, why the folding mechanism would bother or inturrept the paddling?
if connected correctly, and tested with the high enough pressure- it should be ok isnt it?

If the pivoting chainstay, the frame member that holds the bottom bracket, and the top run of the drive chain form a triangle, then the drive chain will try to get shorter when pedal force is applied, and that may break something at the pivot or linkage.

The best way to avoid this is to have the front chain sprocket coaxial to the folding pivot. In turn, that means you'd need to have another stage of chain drive running from the cranks to the pivot.

Do you have any idea about the linkage system? how should i link the arms?
thanks!

Because your diagram implies a much smaller angular range to fold the seat mast than to fold the chainstays/rear wheel, I think using a set of sector gears would be a good way to do it. You can change the radii of both sides to get whatever ratio you want.

You could provide bosses in the frame to pin the sector gears in the folded or open positions.

 

[RunForTheHills]

Hey hey thanks for your reply.
brompton indeed made such a great job.
in my drawing the sizes are far from the actual proportions i have in my more serious sketching and CADing.
the wheel will be small around 18INCHES.. its true that the seat will not be properly folded in differet heights- a topic i will have to work on.. about my question, you know how can i make the linkage of the arms to act the way i described?
thanks

I don't think there would be a good way to synchronize the forward movement of the seatpost to the swinging of the rear wheel under the bike. It won't be a 1:1 movement. The rear wheel will have to travel much further than the seatpost and you will have to exert a lot more force on the seatpost to make that happen since you will have a gearing ratio of 1:2 or 1:3 if you have to move the wheel two or three times as far as the seatpost.

If you look at a video of the Brompton being folded, there is a quick release lever that releases the back wheel. Gravity starts it's swing downward as you lift the back of the bike and then you can just plop the bike down on the dolly wheels on the back of the rack once it swings past the middle point. The effort is very low and doesn't require much force.

 

[DaLanMan]

A breaking fold joint (I think I have that name memoreised correctly, no promises._ Is usually guided by outside linkages (armature, that move, but does not fold it works as a guide rail) Which can have the distance traveled measured y the various linkages.

So that is a memory from a very very long weekend with PhD's and Engi's of all sorts talking trains, and the attempt by one of the passenger lines making an extendable ramp so people did not get drench in inclement weather...

I am a little stunned I memorized that after all these years, that is my takeaway... I think there may have been a momentary adrenal kick recognizing that their is finally something cool that I understand.

I was told that as the end of the event the things talked about were giving a percentile value of it being successfully reached. The reason for it getting a 38% "the excess weight would be the major cost factor" The wheels weigh over 10k pounds....

I also recall something vaguely about guides not being safe du them beign both greasy, and also able to pinch the crud out of you.

 

[Dui ni shuo de dui]

Hey!!
I hope there is anyone who can help me with this topic..
For the stucture of a folding mechanism of foldable bicycle,
im trying to achive a mechanism, when pushing the seatpost to the front of the bicycle, the rear wheel will also be pushed simultaneously to the center of the bicycle under the frame.
after the short description i will try and explain the wanted outcome it visually:
View attachment 348581

how should i link the arm to the seatpost? i need a linkage system that will convert the movements.
any genious out there?
the "linkage system area" represnts the space to use extra arms or axis.

Thank you all!

I'd say something like this should work, in theory (forgive my MS paint skills):



Basically it's a large gear attached to the seat post and a smaller gear attached to the swingarm pivot axle. With the appropriate gear ratio you could get the desired travel distance for each to reach their ideal resting spot.
You wouldn't need the whole 360 degree for the gears, they could look like half moons.