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 Finding the flex?
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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/07/2019 :  05:07:30  Show Profile  Reply with Quote
Did some GoPro work trying to find the source of the light fishtailing in the upright build. I don't think it's in the rear triangle. The chainstays and seatstays don't seem to flex in these videos. I think I verified that after seeing them, but taping a couple of popsicle sticks to the chainstays, setting them 0.75mm from the rim, and riding again. I got no rub at all. Unless I am not conceptualizing this correctly, if I were getting flex in the stays, the fulcrum would be the axle, and I'd get the evidence out near the rim -- sort of like the brake rub some get under power.

I think the weave here is moving around the seat tube, so I'm beginning to suspect I need to stiffen the front triangle, the top tube (being the smallest, at 28mm) being my first suspect.

https://youtu.be/Wv9HiDGxOJ0

Maybe I can splint the front triangle tubes with some angle aluminum stock and test for decreased weave.

--SpiderMonkey

SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/07/2019 :  12:04:03  Show Profile  Reply with Quote
It's not the stays. It's the front triangle. Video of that coming soon. Stay video here:

(4k60 takes a while to process. If it still looks low res, try again later.)

https://youtu.be/pAO5Mgt0A80



--SpiderMonkey

Edited by - SpiderMonkey on 11/07/2019 12:04:50
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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/07/2019 :  12:31:49  Show Profile  Reply with Quote
Video showing front triangle flex is here: https://youtu.be/s_9MUytw8FM

It shows how much the top tube is deflecting, but I believe I'll be stiffening all of the tubes in the front triangle.

This cool chart...



from here: (http://www.thetallcyclist.com/2016/09/theoretical-framebuiling-part-2-tube-size-and-butting/ and based on this study: https://www.sheldonbrown.com/rinard/fea.htm)

Shows the strain on different parts of a DF under different conditions. When pushing hard, the down tube is taking half the beating, to the seat tube's 30% and the top tube's 10. At least if the data on which it's based are good.

Since it won't cost much (in $$, time, or weight) to stiffen the entire front end, that's what I'll start with. Since it has a very nice road feel, I plan to run a couple layers of uni on the sides of each tube, and then a braid over that, using a larger braid, so that when it's pulled tight to fit the smaller tube, the fibers will be more oriented parallel to the tube axis.

--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/11/2019 :  08:17:07  Show Profile  Reply with Quote
about 3/4 of the way through reinforcing the upright bike. I reviewed my emails and saw that I'd misunderstood the layup of my down tube, so the torsion there is (now) expected. I reinforced it with 4x layers of braided CF, so those fibers are running about 45 degrees to the axis. I expect this will transfer more torsion to the join, but I've got a backup plan to deal with that if it starts to cause problems.

I reinforced the top tube with 3x layers of unidirectional on the sides followed by a 45 degree sleeve, since this needed a bit more stiffness out of plane, and doesn't see much torque.

Seat tube is left. I'll wrap that with some heavier 45 degree cloth at the bottom 1/3, then put 3 plies of uni down there, feathering to 2x and 1x toward the top, since there's much less force up there (and the top of the tube has a thick aluminum tube in it from the seat anyway). I'll cover that ugliness with a layer of 3k plain weave. I've got some intermediate mod plain, so I'll use that just to get the extra stiffness.

The bike will weigh probably half a pound more, maybe 3/4, which isn't bad. A plus to this is that with the tube walls much thicker, composed of more woven material, there's less worry about their taking damage from clunks and drops.

--SpiderMonkey

Edited by - SpiderMonkey on 11/11/2019 19:43:48
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Garrie L Hill
human power supergeek

USA
1842 Posts

Posted - 11/11/2019 :  13:53:32  Show Profile  Reply with Quote
Klunks and Drops. ....... Sounds like a product liability law firm! They are probably in the same office building as Dewey, Suhem, and Howe LLC.

Garrie "carbon based lifeform" Hill
HPRA Co-Dictator of the East
for pics of some of my time and money sucking projects
http://s58.photobucket.com/albums/g277/cfbb/
and videos
http://vimeo.com/5513519


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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/11/2019 :  20:05:22  Show Profile  Reply with Quote
My wife may want to grab one of their cards should she continue riding bikes I make.

--SpiderMonkey
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warren
human power expert

USA
6560 Posts

Posted - 11/12/2019 :  13:35:23  Show Profile  Visit warren's Homepage  Reply with Quote
ROFL
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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/19/2019 :  17:51:06  Show Profile  Reply with Quote
Well, after I added probably too many extra layers of CF, the upright frame feels different. It feels really heavy to me now, though it's 1630g, only up 200g from before. Some of that will be removed when I sand it back to smooth.

The wife rode it in the dark tonight and said it doesn't wag anymore. I rode it 3 miles and didn't notice the wag, but then I hadn't noticed it so much before, either. I'm tempted to do more video recording, but then whatever flex I see will look like too much, so probably going with "feels fine to the intended rider" is the smartest policy.

Still the most comfortable upright I've ridden in a long time, maybe ever, and it's too small for me. Last ones I've ridden make me want to chuck them in the bin after 3 miles. This one feels fine.

I don't know that I'll make another upright, though. Too many damn tubes.

--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/20/2019 :  15:32:19  Show Profile  Reply with Quote
against my better judgment I shot some video and it confirms there's a lot less flex in the frame. Ride and response feel good to me, so I think I'm going to re-set the cable stops, put a finish on it, and call it done. The bike built up feels no different than before, so that's good. The wheels (CR-18s, 32 spokes, XT hubs, Deore LX rotors) aren't exactly lightweights, but at ~23 pounds, it's lighter than any of the adult bikes we've got in the garage.

--SpiderMonkey
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warren
human power expert

USA
6560 Posts

Posted - 11/21/2019 :  09:08:47  Show Profile  Visit warren's Homepage  Reply with Quote
That's still pretty light for a take apart bike. I still think about rebuilding my suitcase pack-able lowracer in CF but that would mean I'd actually have to start riding my bikes again and I have been lacking in that department.
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SpiderMonkey
recumbent guru

USA
725 Posts

Posted - 11/21/2019 :  16:16:55  Show Profile  Reply with Quote
quote:
I have been lacking in that department.



Me too. A flood a few months ago literally destroyed my favorite route into work. A month worth of rain fell in one hour, and the Creekside trail I ride was under 18 feet of raging torrent. It picked up the pavement and threw it into the woods. It covered concrete spillways under tons of large rocks. I rode it once afterward, and had to carry my bike over a lot of ankle-breakers. Probably $15 million or more in damage.

--SpiderMonkey
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