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 Folding bike to recumbent lowracer build attempt 2
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ElectricStreamliner
New Member

Australia
79 Posts

Posted - 02/25/2020 :  19:23:01  Show Profile  Reply with Quote
Picked up a folding bicycle for $50 yesterday. Will start a new recumbent bicycle build.






Thoughts:

Odd shaped head tube, looks difficult to use. If I dismantle it I can determine an appropriate replacement tube.

Front wheel drive would be easy with derailleur that attaches to the axle bolt.

Will learn from previous build mistakes:
Effective welding jig, actually tack weld everything and check alignment before creating modern art.
No galvanized steel this time, will get proper steel for welding.
Lower amperage less blow through.
I think I will build the jig so everything is read to be welded then get a quote on professional welding.

I'll do bit more thinking before designing what kind of frame, either z frame or straight.

alevand
human power expert

USA
3706 Posts

Posted - 02/26/2020 :  06:11:45  Show Profile  Visit alevand's Homepage  Reply with Quote
Ive cut a hanger off a drop out and welded it to the fork.

C:
Tony Levand
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Balor
recumbent guru

Russia
946 Posts

Posted - 02/26/2020 :  06:50:49  Show Profile  Reply with Quote
I don't think it even has a hanger on the frame - it seem to have a 'bolt on' hanger in fact.

Edited by - Balor on 02/26/2020 06:55:59
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ElectricStreamliner
New Member

Australia
79 Posts

Posted - 02/27/2020 :  00:36:00  Show Profile  Reply with Quote
Today's progress.



Bicycle dismantled, 6.9kg binned. 8kg left.

Parts pictured
fork/headtube 1.1kg
crank/bottom bracket shell 2kg
front wheel 1.4kg
back wheel 2kg
chain, brakes, gear shifters, deraileur 1.5kg

Total weight left 8kg

With 8kg already I'll be trying to design a light weight low racer frame. The one I made before was 4.2kg.

I've bent out the front fork to fit the back wheel, surprisingly easy with a couple 1 meter pipes. It got a bit messy handling the chain and derailleur.



Notes:

Threaded headset, I need a replacement stem.

The headtube is 45mm diameter tapering down to 37mm in the middle. It will be tricky to weld to.






Edited by - ElectricStreamliner on 02/27/2020 00:50:33
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ElectricStreamliner
New Member

Australia
79 Posts

Posted - 03/04/2020 :  02:32:27  Show Profile  Reply with Quote

Getting there, it's good to be at a stage where it rolls with a push.

Not sure if the rake and trail is any good. Not sure if the frame welds will hold up. Will find out when it's done.
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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 03/04/2020 :  06:20:19  Show Profile  Reply with Quote
quote:

Not sure if the rake and trail is any good. Not sure if the frame welds will hold up. Will find out when it's done.



Since this is, IMO, the most important aspect in whether or not you'll want to ride the bike, I encourage you to get it right. Head tube angle looks steep, might just be the photo. What's wheelbase, HTA, and rake (offset)? I used an onscreen protractor to try and estimate, but there's a lot of room for error. Still,

If the head tube angle is 84 deg as measured my lousy way
If rake/offset on that fork is 30mm (my 406 forks are 33mm)
And wheel is 405 with a 45mm tire on it,

Then trail would be negative 4mm.

I aimed for ~50-60mm of positive trail on the bike I just finished, with a 105cm wheelbase. That meant a 69 degree head tube angle, and 57mm of trail. The bike handles very well, but it's still very nimble. It holds a line better than her LWB, which has very little trail (despite the super slack heat tube angle) because it has so much fork offset. You can see here (https://youtu.be/7TcT5GWwrSo?t=90) how it handles for her, and at this point, she had less than 5 minutes total ride time on it.

I based goal that on my experience with my other well-mannered recumbents, and poorly mannered ones. The last one I had with a steep head tube angle (the Performer FWD discussed in a thread here a couple weeks back) had a short wheelbase and a somewhat steep head tube angle (75.5%) was always more work to steer than I wanted. I didn't consider it dangerous, but you had to be on top of it all the time. That bike had trail of 35mm, and a wheelbase of either 93 or 100 cm (some disagreement from Performer on that, and I didn't measure when I had it.)

The others on the forum with more lowracer time than I've got (although I do have thousands of miles on my NoCom) may disagree, but I think that a lower, more laid-back bike needs a bit more capability to hold a line (trail, wheelbase, or both) rather than less. When you're flat and on-axis with the wheels, your weight shifts translate into "quicker" handling already. Quicker = exhausting, to me. I'm not racing, and even if I were, it wouldn't be in a peleton.

I have never measured the NoCom's trail, but estimating from here, it looks like the HTA is about 68 degrees, and the fork has very little rake, so about 75mm of trail? (Mine's downstairs, so I'll try to measure later.)



In my opinion, the NoCom is very well mannered (especially when it's moving fast) but most people -- especially new riders -- think it's twitchy as hell.

I think 50-60 mm of trail is a decent target for a SWB. I think 60-70 might be a better target for a lowracer. You can calculate here: http://www.yojimg.net/bike/web_tools/trailcalc.php

--SpiderMonkey

Edited by - SpiderMonkey on 03/04/2020 06:52:50
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Balor
recumbent guru

Russia
946 Posts

Posted - 03/04/2020 :  07:28:54  Show Profile  Reply with Quote
Actually, a steep steering angle and NEGATIVE offset is best bet for high and low speed stability, but you may end up with too much tiller for your liking w/o remote steering.
A bike w/o fork flop don't need as much trail either, becase it's return to center force does not need to fight flop force ('turn in force').

A negative offset also allows for a disk wheel that actually ADDS to crosswind stability, not only makes one faster.
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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 03/04/2020 :  08:00:32  Show Profile  Reply with Quote
I know you're a big proponent of that, and the physics defy my attempts to understand it, so I fall on the side of "if it's such a good idea, why isn't it everywhere?" Is it that everyone's an idiot, too mired in past designs (even recumbent makers, motorcycle makers?) or are foot/frame clearance issues the problem (on an upright, b/c these could be solved by recumbent makers who are already selling a product that's goofy-looking)?

And where's the crossover? Because the short trail bikes I've ridden handle horribly. Where does it suddenly get better? I guess you need enough negative rake to generate positive trail at that angle?

Even if that is the aim here, I think the design needs to carefully set that up.

Looks like with the current head tube angle, flipping the fork around would generate 50mm of trail from -30mm of offset (but the tire would be in the frame at that point)

--SpiderMonkey

Edited by - SpiderMonkey on 03/04/2020 08:10:52
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Balor
recumbent guru

Russia
946 Posts

Posted - 03/04/2020 :  09:01:56  Show Profile  Reply with Quote
quote:
Originally posted by SpiderMonkey

I know you're a big proponent of that, and the physics defy my attempts to understand it, so I fall on the side of "if it's such a good idea, why isn't it everywhere?" Is it that everyone's an idiot, too mired in past designs (even recumbent makers, motorcycle makers?) or are foot/frame clearance issues the problem (on an upright, b/c these could be solved by recumbent makers who are already selling a product that's goofy-looking)?

And where's the crossover? Because the short trail bikes I've ridden handle horribly. Where does it suddenly get better? I guess you need enough negative rake to generate positive trail at that angle?

Even if that is the aim here, I think the design needs to carefully set that up.

Looks like with the current head tube angle, flipping the fork around would generate 50mm of trail from -30mm of offset (but the tire would be in the frame at that point)

--SpiderMonkey



Physics is not strightforward to be fair:
http://recumbents.com/forums/topic.asp?TOPIC_ID=7507
(And I might be getting some stuff wrong still).

Anyway, steep angle and negative offset for enough trail DO work and was utilized by, say, Patterson great effect:

http://www.bicycle.tudelft.nl/ProceedingsBMD2010/papers/patterson2010application.pdf
http://www.bentrideronline.com/messageboard/showthread.php?p=1603671#post1603671

Also, here is my other resent post from BROL, about negatively offset disk wheel:

(In a thread that is also about very steep angle/negative offset bike, worth a read in entirety):

https://www.bentrideronline.com/messageboard/showpost.php?p=1638693&postcount=86

And yea, tire will hit the frame on this particular bike. And negative offset on SWB results in less tire/crank/foot conflicts, but possible wheel-leg conflicts on a lowracer, that's how it is on my MBB but does not matter much - it's predictable and does not lead to fall.

And yea, would not work on DF bikes very well due to same wheel-foot conflict as on SWBS unless you make your wheelbase huge (and that would in turn require 'tiller' which is very likely suboptimal on DF).
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Balor
recumbent guru

Russia
946 Posts

Posted - 03/04/2020 :  09:19:53  Show Profile  Reply with Quote
Btw, I'm actually toying with idea of additional *aerodynamic* return to center force via a control surface that would double as attention getting device, basically a 'weatherwane rudder' that is coupled to steering.

It will provide a return to center force which curve is perfectly coupled to inrease in steering sensitivity (both quadratic), unlike, say, one from spring/negative flop (fixed value) or positive trail (linearly increasing) and will counter exceesive 'turn out of the wind' steering input due to sideforce/trail couple exactly like a negatively offset disk wheel (which would not work well on a fully faired HPV - mostly hidden in the fairing).
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alevand
human power expert

USA
3706 Posts

Posted - 03/04/2020 :  15:04:30  Show Profile  Visit alevand's Homepage  Reply with Quote
It nice to have some trail, 1.5 to 2.5 inches, which in this case would need more angle on the headset, since reversing the fork would cause the tire to rub on the frame..slice the top of the square tube near the fork a little more than half way through, close it up and weld it. I use a pipe in the fork tube and a rope to hold it closed. Check that the v-brake and derailleur don't interfere with knees.


C:
Tony Levand
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ElectricStreamliner
New Member

Australia
79 Posts

Posted - 03/06/2020 :  02:43:19  Show Profile  Reply with Quote
Made a seat and attached it to the frame, it is secure. Attached the front part of the frame to the head tube. It's straight but a little too short for my legs. While pedaling my legs won't bump the chain or fork as the bottom bracket is fairly high.


No trail. It is annoying that there is fork offset, I actually forgot that bicycles have that.


Seat feels secure.

Waiting on a quill stem to show up in the post.



To sort out trail and my long legs I will am thinking I'll cut the frame

Edited by - ElectricStreamliner on 03/06/2020 02:52:36
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Balor
recumbent guru

Russia
946 Posts

Posted - 03/06/2020 :  03:48:36  Show Profile  Reply with Quote
Ouch, my legs went numb just by looking at this picture!
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SpiderMonkey
recumbent guru

USA
690 Posts

Posted - 03/06/2020 :  11:25:53  Show Profile  Reply with Quote
Just to keep the right terms, if you're inclining the head tube further back, you're changing the heat tube angle, not the rake. Rake is the amount the fork is curved forward. (Same as offset, but that's generally applied to forks that achieve the difference with straight-line differentials, mounting the legs non parallel to crown, sticking the dropouts further out, etc.)

You could always take some of the rake out of that fork by bending it, but since you're going to have to cut the frame and reweld anyway, simpler just to give it the right head tube angle to get desired trail with the existing rake.

I suggest measuring the rake, then using the web page calculator above to calculate for 45-70mm of trail, depending on how you want it to handle.

--SpiderMonkey
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alevand
human power expert

USA
3706 Posts

Posted - 03/06/2020 :  17:26:14  Show Profile  Visit alevand's Homepage  Reply with Quote
Ive straighten forks by, putting a pipe in or over the neck and the forks in the garage rafters and pulled down, checking a little at a time.


C:
Tony Levand
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Jerry
human power supergeek

USA
1527 Posts

Posted - 03/07/2020 :  10:57:21  Show Profile  Reply with Quote
I have straightened and bent forks using my conduit bender and also using just pipe. Careful as you can crack a fork if you go too fast!
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ElectricStreamliner
New Member

Australia
79 Posts

Posted - 03/08/2020 :  03:59:50  Show Profile  Reply with Quote

It's pretty straight.


I raised the seat (32cm) and lowered the bottom bracket (44cm). Trail corrected. I did not move the seat. The bottom bracket is at the correct position for my legs now.

The seat is 26 degrees.

Can't wait to stick a chain on tomorrow and hopefully get my quill stem in the mail.

Edited by - ElectricStreamliner on 03/08/2020 04:10:05
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ElectricStreamliner
New Member

Australia
79 Posts

Posted - 03/09/2020 :  03:42:05  Show Profile  Reply with Quote

Pretty much done. I went for a ride down the street and back and across field. Got a couple scratches grazes from the ground and the chain.


I had an issue with bending the power idler bolt. So I got a new bolt and used a couple nuts and welding to reinforce the bolt.

Front wheel drive is troublesome. Low speed turning is not possible as the front wheel throws the chain off if you turn the wheel.
I was bumping my thighs on the handlebar as the stem was not long enough but some flat shoes helped me ride it.

Overall I am satisfied that I built the bike and rode a recumbent. I think I'm interested in building a trike or pedal car next.

Edited by - ElectricStreamliner on 03/09/2020 03:46:43
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warren
human power expert

USA
6528 Posts

Posted - 03/09/2020 :  12:22:04  Show Profile  Visit warren's Homepage  Reply with Quote
Looks good but it will need some tweaking to make it something you will want to ride. That's a part of any building process.
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