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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 3:37 pm 
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Joined: Wed Oct 31, 2007 10:32 pm
Posts: 7518
Location: Los Angeles / Glendale, California
I definitely applaud the work here, even though it doesn't look pretty at all. I appreciate experimentation!

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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 3:42 pm 
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Posts: 94
Craigagogo wrote:
To take your idea another step further...

Support the post at the clamp as you have done but have no support at the end of the seat post.

Now you would have a cantilevered beam @ the seat which resist the bending moment that is supported rigidly at the clamp and intermittently at the end of the post in the frame.

This allows for large deflection of seat for the first 2.0 +/- mm of movement at the lower end of the seat post. Then as the first 2.0 mm of lower post deflection is observed, secondary flexing due to the further deflection of the seat post that is supported between contact with the frame and at the clamp. You could tune this effect with an elastomer at the base of the seat post.

Yes, you can try that. But, I get the naming of the product, OK! :beerchug:


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 Post subject: Re: Kai-ming's seatpost
Posted: Fri Aug 10, 2012 3:42 pm 


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 3:45 pm 
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prendrefeu wrote:
I definitely applaud the work here, even though it doesn't look pretty at all. I appreciate experimentation!

But the ugly bit is hidden inside the seat tube, you wouldn't know if I didn't show you the first photo. :?:


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 4:50 pm 
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Location: by Crystal Springs (Sawyer Creek Trail)
Could you show us some stress analysis?


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 5:03 pm 
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justkeepedaling wrote:
Could you show us some stress analysis?

As I have said, this is concept design, stress analysis is not necessary :smartass: . I would rather spend the time to ride it. :mrgreen:


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 5:35 pm 
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Just my 2 cents... Seems to me the flex is in the x/y direction, not z. Also, the clamp force/contact area seems to be important, as this would determine the magnitude of deflection. If in the extreme where one would preferr maximum deflection the clamp force would be minimized. Seems like a floating pivot would decouple this. For example, and rubber gasket between your aluminum adapter and the post. You might need to go to a smaller post to get the room for the elastomer.

If you look closely at the frame designs that have pensil thin stays or the new trek and cannondale seat tube designs, they are designed to yield motion in the z direction.

That said, my understanding is that it's z compliance that improves comfort. But that's my assumption.

Another thought... Try to incorporate some dash pot elements. Simple springs do attenuate peak forces, but do not have energy dissipative paths.

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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 5:44 pm 
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Posts: 94
ergott wrote:
Do you have any way of evaluating just how much "flex" you gained with this?

crohnsy wrote:
kai-ming wrote:
crohnsy wrote:
You need to post scale pics. Please quantify how much weight you saved in this configuration....

:thumbup: :smartass:


I forgot :noidea: , reduced weight is of secondary importance. :smartass:



Then quantify the amount of flex you are getting please. You are an engineer please provide data to validate your claims

kai-ming wrote:
justkeepedaling wrote:
Could you show us some stress analysis?

As I have said, this is concept design, stress analysis is not necessary :smartass: . I would rather spend the time to ride it. :mrgreen:

There is a simple test you may try to get the amount of flex. With the seatpost installed, anchor the bike at bb/dropouts, put static weight/vibrator at the head of seatpost to stimulate the load of rider then measure the deflection/responses. :smartass:
justkeepedaling, it would be a little tricky to do vibration analysis, my major is Vibration. You will be charged if you insist to have the analysis done. :mrgreen:


Last edited by kai-ming on Fri Aug 10, 2012 8:59 pm, edited 2 times in total.

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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 6:03 pm 
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ras11 wrote:
Just my 2 cents... Seems to me the flex is in the x/y direction, not z. Also, the clamp force/contact area seems to be important, as this would determine the magnitude of deflection. If in the extreme where one would preferr maximum deflection the clamp force would be minimized. Seems like a floating pivot would decouple this. For example, and rubber gasket between your aluminum adapter and the post. You might need to go to a smaller post to get the room for the elastomer.

If you look closely at the frame designs that have pensil thin stays or the new trek and cannondale seat tube designs, they are designed to yield motion in the z direction.

That said, my understanding is that it's z compliance that improves comfort. But that's my assumption.

Another thought... Try to incorporate some dash pot elements. Simple springs do attenuate peak forces, but do not have energy dissipative paths.


My design is not the same of the pencil thin seat stays one, but similar in the way that it will flex continuously down below the seat tube clamp to make smooth ride on bad road surfaces. With regard to dash pot elements, you may try that, I am satisfy with my post which I consider simple and clean in concept. As others say it looks ugly when expose to view, making the details pretty/presentable is easy with proper tools and a little time.


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 6:26 pm 
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Location: Los Angeles / Glendale, California
kai-ming wrote:
The post is lighter than any post that I have ever own. :P


Since weight is a nice side-benefit to your method, what is the weight after your modification?
Just curious.

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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 7:40 pm 
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Posts: 210
Location: Czech Republic, Europe
To be honest, isn't something like this much better choice if You want flexy and comfortable seatpost? I've seen many more variations, where seatpost was made from two or more thin pieces. This is just example picture, that I quickly found using google.


Attachments:
seatpost.jpg
seatpost.jpg [ 25.21 KiB | Viewed 525 times ]

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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 7:41 pm 
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prendrefeu wrote:
kai-ming wrote:
The post is lighter than any post that I have ever own. :P


Since weight is a nice side-benefit to your method, what is the weight after your modification?
Just curious.

Just removed the saddle and rear light, it weight 207g(without cleaning it, there is grease left in the holes of the lower sleeve). There is potential weight reduction with a weaker super-lightweight seat tube collar, I have one carbon fibre collar that may be tuned, however, I do not have it with me now.


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 7:47 pm 
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Martin1977 wrote:
To be honest, isn't something like this much better choice if You want flexy and comfortable seatpost? I've seen many more variations, where seatpost was made from two or more thin pieces. This is just example picture, that I quickly found using google.

Don't know how it will perform and the weight ?
My one is smooth, rode it for a year, solid for everyday ride.


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 7:50 pm 
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Posts: 1136
Location: by Crystal Springs (Sawyer Creek Trail)
If you're gonna pull the Engineering card, you at least have to show some Engineering. Stress analysis and FEA nodal simulation using something like Patran to show deflection under load. Also, the load on the seatpost isn't static, so you have to take that into account as well. If not, then this has absolutely nothing to do with Engineering.

Nevertheless, good weight. You could have gotten a lighter post to begin with, but as far as modifications to a heavy one go, this is the only route possible


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Fri Aug 10, 2012 8:18 pm 
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justkeepedaling wrote:
If you're gonna pull the Engineering card, you at least have to show some Engineering. Stress analysis and FEA nodal simulation using something like Patran to show deflection under load. Also, the load on the seatpost isn't static, so you have to take that into account as well. If not, then this has absolutely nothing to do with Engineering.

Nevertheless, good weight. You could have gotten a lighter post to begin with, but as far as modifications to a heavy one go, this is the only route possible

Not without vibration analysis taken into consideration. :roll:
All those are just theoretical which I have little interest. Please don't keep asking for the same thing, I have said it before (not really like to say that again), what I am doing here is a concept design with sound engineering sense which I consider clean and simple. Riding it and happy with the result is all I wish to prove to myself.
The purpose of the thread is not playing cards with you. If you think you are a better engineer, show me your works, not just talk, talk... endless talk.
Pulling card? I have my engineer registration card, I will show you before I charge you if that is what you wish to see.

p.s. It appears that you wish to start the flame. If open-fire is not your intention, ignore statement no.2, just forget about engineering, you do not need to have the necessary basic engineering knowledge to ask questions.


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 Post subject: Re: Kai-ming's seatpost
PostPosted: Sat Aug 11, 2012 4:56 am 
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Location: Western Australia
Whenever I see a hole, I think stress riser, stress riser, stress riser. Especially since a seatpost is under repetitive loading. And it looks very, well, rough.

However, I can see exactly what you did design wise and all I have to say is

:beerchug: :thumbup:

I'm considering this one of the rare gems of WW. Some innovation! If this concept could be extrapolated into a more elegant design and manufactured one piece, I would actually use it. Granted it would take some proper engineering work to move it through some stages and the collar heights would have to be adjustable. Could the flex be controlled by wall thickness rather than drilling? Easier to make and easier to use with adjustable collars.

Great stuff! A nice change from 'what saddle should I buy'. Or any 'off the shelf' component threads. High five for the innovation.

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 Post subject: Re: Kai-ming's seatpost
Posted: Sat Aug 11, 2012 4:56 am 


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