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Old 2019-08-18, 10:39 PM   #1
leo
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draft for new seatpost adapter

Hi,

I truly do like the Moocow Unicycle company for it Open Source approach.
I once ordered their Saddledapter, however, ended up never using it; it's bolts are too tiny, my tools will bend. And the nuts to tighten the seat are unreachable, because of the walls that are meant for strength.
Last week I discovered there already is a v3, but I already spotted a design-flaw; the sink'ed-in bolts will never make much contact; the tighter you spin them, the less contact area it will have.

And so I thought about drawing the one I have in mind for long:
  • Make it compact and smooth.
  • Have the bolts go very tight along the seatpost
  • Allow to reach the seat-nuts.
  • Have decent size bolts, such that you can use bigger tools to tighten.
  • Don't have thread, but use a nut, such that you can replace it.
  • Have bolts on both sides, for nicer -more direct- application of force; and to be able to apply it straight (as in symetric).
  • As it consist of two separate halfs, I think it's unlikely to break 100% at once.
  • the post will go in for 29mm (in stead of 20.something)
See rendering images below.

I don't know how much of a fortune it will cost to realize these, probably much as I did a lot of round edges (which aren't that obvious in the renderings). But I wonder if there is any interest in such.
So please let me know what you think of it, especially if you think they could be better.
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Old 2019-08-18, 10:55 PM   #2
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One more picture of a slightly different version:
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Old 2019-08-19, 08:26 AM   #3
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The design appears to have a serious stress concentration between the square corner at the top of the the post socket and the square corner nearby on the outside. The cross-section also seems very thin there.
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Old 2019-08-19, 11:47 AM   #4
finnspin
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I personally have no interest in these, as I haven't been breaking seatposts much in the last years, and if I wanted one, I'd take the proven strength of the Moocow design over the elegance of yours. I think it's pretty cool though that you make use of the open source approach, as that isn't really a common concept for mechanical parts, at least outside of 3d printers.

Two points I marked:
Name:  seatpost-adapter_2.png
Views: 186
Size:  54.3 KB
  1. OTM pointed this one out already, the way the diameter decreases there is pretty bad from a structural point of view. I see the radii, but you are still going to see an increase in stress there. The effect of stress risers is unfortunately even bigger when looking at fatigue strength, which seems to be the issue with most seatposts.
  2. Those two internal chamfers don't serve much function (tiny bit of weight decrease maybe), and will be pretty expensive to make. I'd leave them out.

Quote:
Allow to reach the seat-nuts.
I'd need to check in CAD (or better a 3d printed prototype), but I think your design will make it impossible to use seats with allen bolts, at least in the more "extreme" seat angles, as it will be hard to get an allen wrench in there. Mad4one uses these:

Which is what I would use if I used a moocow seatpost adapter, or regular socket head allen bolts, depending on your seat.
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Old 2019-08-20, 01:17 AM   #5
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Quote:
Originally Posted by finnspin View Post
the open source approach, as that isn't really a common concept for mechanical parts
It's then called Open Hardware.

Quote:
Originally Posted by finnspin View Post
I think your design will make it impossible to use seats with allen bolts
Mine need to fit a 28mm tube, so the shown post is now option.
Probably the nuts will solve the tightening problem that the Moocow gives me, but then still it's bolts to clamp the clamp are far too tiny.
And drilling the hole to 28mm will make it scary thin.

Based on above feedback (plural) I've adjusted my design.
However there will ever and ever be a weakest area.
I guess with this one the top plate edges are the first to break.
But being significant thicker than the posts I mentioned before, I guess the whole thing -times two- is strong enough for my own kind of use.
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Old 2019-08-20, 03:07 AM   #6
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The sharp corner at the end of the post hole will still focus stress.

You could radius this and put a small step as the post stop.
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Old 2019-08-20, 07:51 AM   #7
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I might be a little slow this morning but what's the point of a seat post adapter that's more expensive than a seatpost?

This is a genuine question, not sarcasm. I just don't get it.
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Old 2019-08-20, 07:55 AM   #8
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Quote:
Originally Posted by Garp View Post
I might be a little slow this morning but what's the point of a seat post adapter that's more expensive than a seatpost?
Assuming the adaptor is more durable than the tube, it can be reused on many posts that consist of any length cut from plain tube.
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Old 2019-08-20, 09:42 AM   #9
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but will you be able to tighten the adapter enough on the seat tube so the seat won't spin around. After I UPD, it does already sometimes happen that the seat is twisted and then I only have to unscrew the bolts at the frame to turn it back. With the adapter there are 2 places where the seat can twist and I would need to loosen 4 additional bolts.
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Old 2019-08-20, 10:07 AM   #10
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Quote:
Originally Posted by Setonix View Post
With the adapter there are 2 places where the seat can twist and I would need to loosen 4 additional bolts.
LOL. Either of the connections can correct the alignment.
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Old 2019-08-20, 11:54 AM   #11
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If you put the split 2mm off centre you could add a central rib to the base. Then make the other side interlock underneath it so when it is fitted to the saddle base both sides see advantage of that rib. However small it is it will help considerably with strength.
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Old 2019-08-20, 07:08 PM   #12
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Quote:
Originally Posted by OneTrackMind View Post
The sharp corner at the end of the post hole will still focus stress.
You could radius this and put a small step as the post stop.
Ah right! Good point.

Quote:
Originally Posted by Garp View Post
what's the point of a seat post adapter that's more expensive than a seatpost?
Because actually I need it in odd sizes, that aren't available.

Quote:
Originally Posted by Setonix View Post
With the adapter there are 2 places where the seat can twist and I would need to loosen 4 additional bolts.
I don't understand what you mean. In my case you release 4 bolts if you want to twist one way OR the other 4 bolts if you wish to move the other angle.
(or -in my case- simply twist the tube on the other end).

Quote:
Originally Posted by rogeratunicycledotcom View Post
If you put the split 2mm off centre you could add a central rib to the base. Then make the other side interlock underneath it so when it is fitted to the saddle base both sides see advantage of that rib. However small it is it will help considerably with strength.
With the Pitfighter-III laying in front of me I was thinking the same.
In deed has 1 mm ofset (times 2 halves), I will play with that.

One different approach I thought of is doing it like below BMX seatpost;
it's super-neat as it also cuts the need for a seatpost-clamp; look how finger-friendly that could be.
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Old 2019-08-21, 02:20 AM   #13
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Just my two cents:

The sharp edges would probably cut the crap out of my hand. Not a huge worry for muni, but my hand would be touching it all the time on my street/trials uni. I own one of the Mad4One setups, and I slightly cut my finger when trying something SIF. I ended up wrapping tape around the adapter.

I am no longer breaking seat posts like I once did. I am a more gentle rider now, I infrequently UPD, and when I do it's normally on grass or dirt. When I UPD, I typically either catch the uni or slow the fall with my hand before letting go. But, beginners seem to have the kind of UPDs where the saddle slams into the street. At a certain point, that stopped happening to me.

Side note: Some riders were complaining about the weld on the Nimbus seat post...in another thread. I looked on my trials uni, and I have that seat post. I also noticed that the slight inward tapering of the post in the final inch helps me get my fingers around the saddle in the middle section.
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Old 2019-08-21, 05:48 AM   #14
slamdance
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Breaking? I just don't want it to twist.

Is this clamp equal or superior to the standard nimbus clamp for the seat post?

If I have to take out a tool after each time I fall to straighten it out? I don't want it. It has to work like a collet. Good luck
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Old 2019-08-21, 12:25 PM   #15
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Quote:
Originally Posted by elpuebloUNIdo View Post
Just my two cents:

Side note: Some riders were complaining about the weld on the Nimbus seat post...in another thread.
I think that is the post where they were talking about it breaking when ridden hard... the seatpost has been redesigned since then and they are considerably stronger now. We changed the press tool to add a small rib down the centre.

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Last edited by rogeratunicycledotcom; 2019-08-21 at 12:26 PM.
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