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 Starting the Kid CF bike
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 07/09/2019 :  07:09:49  Show Profile  Reply with Quote
I agree indicators are overrated. The nice thing about a 'bent is the real front indicator is right there in your field of view, between your feet. But I did feel like a moron erasing the mark after thinking I was so clever in reindexing the twister.

I did rig up the derailleur and shifter and tested it, and I was able to get perfect indexing with the new middle index notch and the original big ring notch, with no derailleur fouling on the main tube either in the granny, just mounting with a single 2mm spacer on the BB right side. So that'll be good.

For the next few adult bikes (next project is an upright for the wife) we're going with microshift thumbies. Micro-friction on left, so works with any front derailleur. Right side is 9-speed shimano index or friction, so again works with anything, or if the indexing goes wonky in the middle of a ride, you can move it to friction and be happy until there's enough time to adjust properly. They're really pretty shifters, and not too pricey at ~$80 a set. Should last forever.

Kid's hands do better with these twisters for now, however.

I think I'm actually going to stick another index notch into this one. One thing I dislike about front index shifting is that the final drop to the granny is sort of an uncontrolled chain throw. Whereas with friction or micro-steps on that side, you get a slower, more controlled drop, that fast, spring-loaded toss toward the center is in my experience more likely to result in a chain drop. I figure another index notch on the way down will give a small pause in the cage-slap toward center that should mitigate that.

If there are too many chain drops, I'll rig up a DIY jump-stop on the post. I generally have real jump-stops on all our bikes, since to me they're cheap, light insurance against annoyance.

--SpiderMonkey

Edited by - SpiderMonkey on 07/09/2019 07:12:08
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mecheic
Starting Member

United Kingdom
5 Posts

Posted - 08/05/2019 :  01:29:35  Show Profile  Reply with Quote
great effort and looking good...
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 09/14/2019 :  17:41:24  Show Profile  Reply with Quote
Haven't done much on this lately. School's started, and the wife wanted an upright for her short commute, so that jumped the line in priority.

Fingers killing me today. Upright dropouts are a lot more fiddly to make. Lots of drill, file, and hacksaw, but these should work out well for that.



I should have this bike wrapped up inside a month, then I can get back to finishing the kid bike. It needs the seat stays finished, then some seat fabric designed and made. After I get her on the bike again and confirm body position, I'll design her steering mast and flipit, and after that it'll just be a matter of cable stops and buildup.



--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 10/06/2019 :  20:35:10  Show Profile  Reply with Quote
I've been mostly working on the wife's upright, but this weekend I finally made another test at a finish for the bike(s) I'm working on. I had no luck earlier with Duratec Sunshield, which was a bummer because it's got good built-in UV protection, it's really nice and glossy when cured, and it's nice and tough. I was trying some liquid dyes I was told would work with it, but they didn't. They never fully mixed, and left gooey spots. I decided to try some try powdered pigments. Test looked OK, so the kiddo said she wanted gold, and I ended up with this.



I was going for a transluscent pearlescent finish, so this is actually a little too dense. It looks less dense than it does in real life. The color is wild. The opacity changes depending on the angle of the light/viewer. Spots that show CF weave from this angle will be covered in opaque gold from just a bit to the side.

The kid loves it, and wants to name the bike Gold Fang, so I guess it's a hit.

The finish is pretty good. Can use a little high-grit sanding, and when I see what that does to the opacity, I'll probably just put another layer of this down clear.

It's meant to be sprayed, but brushing works OK. I thin it with 10% MEK, then mix the pigments for 2 minutes. Then, I pour off the batch into 5g servings. I catalyze it with 2% MEKP at that point (about 4 drops) and then I've got about 4-5 minutes to both stir and brush it on before it gets a little gummy. After the point of gumminess, you can actually stipple it on and it will add color density and lay flat and not produce bubbling. The odd bubble is fairly easily removed with a heat gun on low.

I get a few boogers in the mix, probably from the cheap brush, but those should sand out.









--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/01/2020 :  11:16:18  Show Profile  Reply with Quote
I think I've got the seat mesh figured out pretty well. It wasn't so difficult to make, so if it performs well, I'll probably make the next couple of suitcase-bike seats the same way. (Considering just ordering a pair of seats from Thorseat, cutting in half, and using nesting tubes to make them separable.)







https://www.crazyguyonabike.com/doc/page/?o=1mr&page_id=598418&v=g

--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/02/2020 :  16:41:16  Show Profile  Reply with Quote
Finished up the mesh: https://www.crazyguyonabike.com/doc/page/?o=1mr&page_id=598457&v=t

Seat at short rider size.


Seat at tall rider size.


Top mesh


--SpiderMonkey
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alevand
human power expert

USA
3696 Posts

Posted - 02/03/2020 :  06:43:24  Show Profile  Visit alevand's Homepage  Reply with Quote
Mesh seat looks a little narrow to be comfortable. My seats sag a couple of inches, are 14 to 16 inches wide. I like how mesh is removable. Looks like you are adding padding to the top?

C:
Tony Levand
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/03/2020 :  08:38:06  Show Profile  Reply with Quote
It would be if it were a typical mesh seat. It's not a mesh sling seat. You don't sit down in it. You sit on top of it (on top of a pad). It's a seat to be used same as a hard-shell, like a Bacchetta Euromesh, which is very similar in dimensions. This seat is 22cm wide the entire length. A Euro mesh is 25cm wide at the butt, 21 wide at the top. (This one's for a kid who's going to grow into a skinny woman.)

This seat is very close to the same dimensions as the famous M5 shell (medium). The M5 is 20cm at front of the butt pan, 24 at the hips and shoulder, 19cm across the top.

The length of this one is variable, which is why I designed it this size. The 2-part mesh is also to accommodate that. It'll also break in half for the suitcase. A growing kid won't outgrow it -- unless she gets to 6 feet, although I rode an M5 medium for years despite the fact that it didn't fit well.

Of course the trick is keeping it tensioned well enough that the pad doesn't sag too much. (Same trick necessary with the euro mesh seat.) To be determined if the mesh and tensioners are up for the task.



The design I plan to use for the adult version will be 24cm wide. My Azub seat is 27cm wide and that's really more than necessary. If it doesn't work for my butt (or my wife's) I'll buy a shell from Thorseat, chop it in half, and mod it with tubes to make it take-apart-able. My wife rides her 20-24cm wide butt-pan M5 seat every day on the trainer, so I think 24cm should work -- it'll depend on the tension and pad.

--SpiderMonkey

Edited by - SpiderMonkey on 02/03/2020 09:00:43
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alevand
human power expert

USA
3696 Posts

Posted - 02/04/2020 :  07:18:23  Show Profile  Visit alevand's Homepage  Reply with Quote
It wouldn't be hard to make the frame wider. (no pun intended)

C:
Tony Levand
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/04/2020 :  20:44:26  Show Profile  Reply with Quote
No, but I suspect if it doesn't work, it'll won't really be the width but be because of some kind of utter failure to tension it enough to keep the tubes from pressuring the cheeks through the pad at the bottom, and at that point I'd just go for a shell. I don't think that'll be the case. (and another slice of pad would probably solve that). I've ridden a Euromesh, and it feels fine, but maybe this Phifertex won't work out.

I am not a big fan of sling seats. They're OK when finally tensioned correctly, but wife and I are always more comfortable on shells with pads. I get numb legs, butt, feet with much greater frequency on a sling when I don't have the tension just right somewhere.

--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/08/2020 :  13:56:32  Show Profile  Reply with Quote
So after doing all the mesh and seat fabric in order to get a better idea of what the steering flipit and mast angle/dimensions should be, they ended up being...
Almost exactly the same as the Azub steering mast. (Within half a CM!)

Anyway, decided to design the flipit with a bit more rigor using Fusion 360 so I could have a better idea of the interference, etc. This will be the base design, with carbon tow / filler / fabric to bond and finish over the bits.



--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/10/2020 :  06:58:26  Show Profile  Reply with Quote
The flipit setup jig came out well, but now, of course, a different idea came to me (in my sleep).



It would pretty much be the same as this, but instead of using the pre-made, flat bar stock along the sides, I'd use fabric and lay it up directly on the base stem cylinder, bringing it in slightly on the hinge side so that the whole assembly wouldn't be so wide.

As designed here, with a lock-nut on one end, the entire width would be about 53mm. The main tube is about 53-54 in that same spot, so probably not an issue. Keeping it this size does make fabrication a bit easier, since I can just bond in a hollow CF tube axle directly through the side of the 28mm mast stock, with some plastic washers on either side, to be held by a through M6. That hollow CF tube will be nominally 2.5mm wall, but it'll be bonded in, then surrounded by CF-chop + epoxy putty, then layered over with fabric. The bottom of the mast tube was OD 28mm, 1.5mm wall, but I bonded in another tube, 25mm OD, 1.5mm wall, so that's now 3mm wall for the bottom 60mm. With a thick axle going through it, it should be plenty strong to take the tiller forces, I think.



--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/11/2020 :  08:36:48  Show Profile  Reply with Quote
This morning after I woke up for my geriatric earlywhiz, suddenly a different flipit design idea popped into my head. It would be a lot narrower. It will be simpler to build, too, since I can wrap around the plate/fin hinge here a lot more easily than with the side-plates design.

I'd use 6.5mm CF plate in the center (and it would be thickened by the bonding/wrapping process, if I wanted, by laying a few more layers around the sides and over it). I'm not sure which would be stronger, but I think either design would be strong enough.



The mast bottom would have a couple plates bonded in like so:



--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/18/2020 :  18:30:07  Show Profile  Reply with Quote
My flipit/stem design seems good so far.





The plates seen here are going to be the bottom of the steering mast. The stem's 45mm high. I cut some custom slide plates/washers from my super-sophisticated materials bin, type G for garbage. (HDPE from an old protein powder jar) The plates slide nicely, and the whole things feels really, really stiff. I tested it on the fork steerer and it clamped down really well with the single M6. I custom-rolled the base cylinder for this design on that steerer tube (with a few layers of packing tape inside) so it's a really close fit even before you start tightening the M6 in the stem. In fact, it grips tighter and stretches less than any of the commercial stems I've got around the garage. (I use expansion plugs in the carbon steerers too.)



--SpiderMonkey
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Balor
recumbent guru

Russia
925 Posts

Posted - 02/19/2020 :  03:48:03  Show Profile  Reply with Quote
That is my experience as well - I have made a 32mm tube clamp using carbon fiber and a couple of captive m8 nuts for VPS 'arms' and it grips really teaciously even by clamping it with a single m4 nut and bolt (because I've botched the mounting place of the second one :)).

Makes one wonder why chinese carbon stems suck so much... (while their bars/seatposts are decent) They usually use glued in and threaded aluminium inserts that are prone to 'pulling out' of carbon though.
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/19/2020 :  07:44:22  Show Profile  Reply with Quote
pulling through of embedded nuts in CF is what got me started on CF years ago. The stem that came with my nocom just had regular hex nuts embedded behind a way-too-thin layer of CF. The CF broke and the nuts pulled through. They hadn't even been filed or nicked to provide any mechanical tooth. Fixing those (because I had to) was what got me started doing my own CF work.

The stems I've gotten from China have been OK, but the ID has been a bit too large and they seem to stretch a bit too much -- the sides of the assembly nearly meet in the middle. The one I'm thinking of has 2x M5s that thread into 2x M5 OD inserts that run in from the other side.

Of course, the aluminum-block pinchers I've got on other bikes (like to stop seat stays on the volae) also stretch and deform over time. Overbuilding in CF with fat flanges embedded seems to yield a better part, but I think keeping a minimal gap between the diameters helps a ton.

--SpiderMonkey

Edited by - SpiderMonkey on 02/19/2020 07:45:38
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/23/2020 :  12:08:26  Show Profile  Reply with Quote
Almost done...

Got the plates on the mast and it seems to be pretty darn stiff and strong.



Entire steering column should come out < 360 g with final tweaks. Not bad for a completely adjustable setup.



I decided the simplest way to get a set screw for dialing in the steering angle would just be a tee nut in the base of the mast and making a landing pad on the top cap. I gouged up a cheap top cap and put a hunk of scrap CF plate on it.



I put down a couple layers of fiberglass then 4x layers of CF over the top, overlapping the stem a little so it'll make its own custom overhangs down the side. That way I won't have to worry about the thing spinning and moving the stop block after it's on.

Once that is set, the only thing left is to give the pieces a final sand, put on the finish, and put the bike together.

--SpiderMonkey
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/24/2020 :  06:33:12  Show Profile  Reply with Quote
I finally got the hang of properly mixing, thinning, and applying Duratec Sunshield with a brush. The back half of the kid recumbent, plus the seatstays and the seat clamp are finished. Need to do the front half, steering mast, and boom.

The key seems to be a little more thinner than I was using.

Wear a respirator with a good charcoal filter. This stuff REEKS, and although the distributor told me it was mostly just a nuisance, I didn't buy that line.

The finish meets my requirements for looking good -- it lets the CF texture come through while smoothing out surface wiggles and somehow making the chaotic layup layers look nice too. The photos can't quite capture how the opacity changes with light and viewing angle. Looks kind of like a fade here, but it's not. It's a fairly consistent layer, with varying opacity based on the angle.

It's also providing UV resistance in the clearcoat itself, and adding UV resistance in the form of a physical pigment barrier. It's also a nice, durable clear. Takes a polish if you need to sand it back. It stands up to cleaning solvents and grease, another plus. (Water-based spar urethane was a huge failure on that -- dissolved in simple isopropyl.)







--SpiderMonkey

Edited by - SpiderMonkey on 02/24/2020 06:35:11
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SpiderMonkey
recumbent guru

USA
689 Posts

Posted - 02/24/2020 :  16:24:11  Show Profile  Reply with Quote
My little set screw and top cap solution seems to have come out just about perfect.







--SpiderMonkey
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