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alast
Starting Member

New Zealand
21 Posts

Posted - 05/24/2017 :  01:43:41  Show Profile  Reply with Quote
Hi All,
It's been a couple of years since my last build:
http://www.recumbents.com/forums/topic.asp?TOPIC_ID=6367
I've read plenty about MBB but I'm still curious - what are they like to ride(scarce here in New Zealand) & for my use (fast commute,day tour & maybe road TT) can they be any improvement over this?:



I've ridden about 3000Km on this bike & it's been great.

After looking heaps at French MBB I've eventually opted to try a Cruzbike geometry first, a fairly unashamed influence:



The design has 2" more wheelbase than the Vendetta but apart from that they are very similar.

First step was to jack out some reasonably light CroMo MTB forks & lengthen some chainstays:





After remeasuring the forks & chainstays I adjusted the drawing to achieve 3" trail. With the fork offset the steerer angle is 70 deg.
The other design criteria are seat height, BB height, seat angle (20deg)& length to suit me.

I don't intend to make the size adjustable. I'm planning to make the
forks & chainstay separable so I can pivot the chainstay forward to fit the forks in the steerer tube & assemble the bike.

I reckon with the tube dimensions as planned it'll come out a similar weight to the RWD above, about 30lbs.

Any suggestions for tweaking the geometry & nominated material dimensions gratefully received.
Bigger pics here:
https://www.flickr.com/photos/86404869@N00/with/34820257016/


Cheers
Andrew



Edited by - alast on 05/24/2017 01:48:32

Balor
recumbent guru

Russia
512 Posts

Posted - 05/24/2017 :  09:10:44  Show Profile  Reply with Quote
You may want to modify the forks for no offset while leaving the angle as sharp as possible and make the boom length as short as possible while still maintaining at least neutral weight distribution and being able to reach the bars.

The shorter the boom, the less pedal feedback is, the less unstable equilibrium flop of the front triangle is (due to CG of front triangle on the highest point above the steering axis), and most importantly - it reduces massive steering inertia which is the real bane of MBB, not pedal feedback.

Without going into exotics like negative angles and remote steering, I'd recommend an angle of 80+ (preferably 90) and slight negative offset (simply reversing the forks will do) and boom about 20-30cm combined with bars of modest width, you are going to have a ride that has no wheel flop whatsovever (be it either conventional or unstable equilibrium flop), little steering inertia, and manageable pedal feedback and tiller, kinda like this:




My prototype with negative angles rides just beautifully, unfortunately fabricating remote steering is harder than I've thought, I'll have to order a few parts custom-made I guess.
Plus, too much negative angle makes negative offset too apparent when it comes wheel-thigh conflict with large wheels and lower seat.
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Balor
recumbent guru

Russia
512 Posts

Posted - 05/24/2017 :  09:21:46  Show Profile  Reply with Quote
Btw, based on trail/angle values of cruzbike Vendetta, btw, it actually has less offset than usual, about 3cm or so.
Anyway, it is good that you've chosen to avoid French geometry, it is simply *bad*. It is rideable, few things (even RWS) are truly absolutely unrideable, but really subpar when it comes to handling.
Cruzbike is a step in a right direction but they did not go far enough - boom too long, head angle still not steep enough, way too short wheelbase.
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warren
human power expert

USA
6032 Posts

Posted - 05/25/2017 :  10:19:13  Show Profile  Visit warren's Homepage  Reply with Quote
Your original build looks pretty ideal to me, but I certainly appreciate the need to build and test something new!
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alast
Starting Member

New Zealand
21 Posts

Posted - 06/05/2017 :  00:57:41  Show Profile  Reply with Quote
A bit further along the frame build & a story about the process:

3D Modeling the 2D drawing



Unwrapping 3D elements to generate a 2D mitre pattern:



Gluing the 2d mitre patterns onto the tubes:



TIG welding the main tubes:



Next is the seat tube & then the rear wheel stays.
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warren
human power expert

USA
6032 Posts

Posted - 06/05/2017 :  19:46:41  Show Profile  Visit warren's Homepage  Reply with Quote
Nice!
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Patrick Bateman
New Member

USA
69 Posts

Posted - 06/10/2017 :  19:10:35  Show Profile  Visit Patrick Bateman's Homepage  Reply with Quote
I'm actually look at a Bachetta stick bike tomorrow, possibly to replace my Cruzbike Silvio.

MBB FWD may be the most efficient recumbent bikes out there, but bicycling is supposed to be fun and my Silvio is consistently terrifying.

It's not "unridable" by any means, but my other bikes are just less scary. For instance, my Catrike 700 isn't as fast overall, but it's just a joy to ride. Stable, predictable, responsive, comfortable, fun. (Full disclosure : I weigh 250lbs and maybe my Silvio would be funner if I didn't.)

I've built a bunch of MBB FWD bikes and here's what I've found:

1) use the same geometry as a road bike. Same heatube angle, same trail, etc.

2) stretch the wheelbase, particularly with shallow seat angles.

If you made a spreadsheet that documented the various changes to the "real" Silvio and Vendetta over the years, you'll notice the same trend.

I've frequently wondered if something like the NoCom could be done with FWD.

I've posted a bunch of threads about this here and at BRO if you're interested


Edited by - Patrick Bateman on 06/10/2017 19:12:13
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Balor
recumbent guru

Russia
512 Posts

Posted - 06/10/2017 :  22:38:05  Show Profile  Reply with Quote
Yea, flop + steering inertia results in a pretty scary experience.
It will do you good to minimized it while trying to end with something you can actually fit in :)
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alast
Starting Member

New Zealand
21 Posts

Posted - 06/12/2017 :  18:41:05  Show Profile  Reply with Quote
Catching the odd hour or two in the workshop. I carefully cut the T piece on the seat tube from a donor bike with the two thread inserts in place to be used to screw the seat on. I got halfway through the weld & realized I put the inserts on the underside. I finished the weld, cut the seat tube & rewelded it turned through 180 degrees - hence the neat weld scar.



Patrick & Balor, I've followed many of your posts - thanks for your contributions. This bike's wheelbase is 50mm longer than a Vendetta, the trail is the same at 3". Once complete I'll give it a decent go to evaluate. If I just don't like it I'll convert it to a twist chain FWD.

Balor, it seems like your radical design shows much promise but it comes at a heavy cost to aesthetics! It'd be a good exercise to sharpen the looks once the geometry is refined.

Seat stays next.

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Balor
recumbent guru

Russia
512 Posts

Posted - 06/12/2017 :  23:47:36  Show Profile  Reply with Quote
Unless you are building a parade bike, ergonomics will trump aesthetics every time :). But anyway, it is indeed a rough prototype.
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alast
Starting Member

New Zealand
21 Posts

Posted - 06/14/2017 :  00:32:13  Show Profile  Reply with Quote
I've got the top seat stays on - I decided that 3/4 x .049 was unnecessarily heavy & used the seat stays from my donor bike (5/8" tapering to 1/2" , about .049" wall thickness). I used the dropouts & I'll tweak the measurements to fit the bottom stays to the dropout lugs.



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alast
Starting Member

New Zealand
21 Posts

Posted - 06/21/2017 :  02:09:02  Show Profile  Reply with Quote
Bottom seatstays installed:





I think I'll weld in the front seat mount next & then set the BB position with the seat installed.
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Balor
recumbent guru

Russia
512 Posts

Posted - 06/21/2017 :  05:42:06  Show Profile  Reply with Quote
Great progress!

quote:
Originally posted by Patrick Bateman
MBB FWD may be the most efficient recumbent bikes out there, but bicycling is supposed to be fun and my Silvio is consistently terrifying.

It's not "unridable" by any means, but my other bikes are just less scary.



By the way, I think this is particularly noticeable for us clydes (both power efficiency AND scare factor) because ALL of our body parts are heavier - including the legs that have to swing around as you steer, too!

I've just completed two consequitive 220 km rides in two days and finally feel like I'm getting the hang of it... after about 5k kilometers. And it still steers like a barge you must balance on one wheel :). It is just I got used to those pecularities enough that they no longer feel as scary.

I think making MBB of carbon, especially the boom and the crankset is nearly mandatory if 'long-boom' designed is to be maintained.

Edited by - Balor on 06/21/2017 05:59:21
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dual45
Starting Member

USA
8 Posts

Posted - 06/21/2017 :  23:37:49  Show Profile  Reply with Quote
Pretty interesting design! Subscribed
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alast
Starting Member

New Zealand
21 Posts

Posted - 06/25/2017 :  02:19:53  Show Profile  Reply with Quote
I welded the front seat mount on, fixed the seat, shortened some Tiagra cranks down to 155 & fitted the crankset. I adjusted the length of rope until the seat /pedal distance felt OK. The BB rotated up & back a bit more than my drawing.



I could perforate my seat some more & move it forward 20mm which would:
- put more weight on the front wheel (probably a good thing?)
- lengthen the boom & lower the bottom bracket (probably more pedal steer = bad?)

Next is the boom including fixing it to the stem clamp & fabricating handlebar clamps. Cruzbikes have that exaggerated fat boom for rigidity. I've got 1 1/4" x .035 Cromoly that I'd like to use to keep the weight down. Should I add weight & beef it up at the handlebar end (like my drawing)?
Cheers
Andrew
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Balor
recumbent guru

Russia
512 Posts

Posted - 06/25/2017 :  04:27:20  Show Profile  Reply with Quote
quote:
Originally posted by alast
I could perforate my seat some more & move it forward 20mm which would:
- put more weight on the front wheel (probably a good thing?)
- lengthen the boom & lower the bottom bracket (probably more pedal steer = bad?)

Next is the boom including fixing it to the stem clamp & fabricating handlebar clamps. Cruzbikes have that exaggerated fat boom for rigidity. I've got 1 1/4" x .035 Cromoly that I'd like to use to keep the weight down. Should I add weight & beef it up at the handlebar end (like my drawing)?



Pedal steer is overrated, steering inertia is highly UNDERrated on MBB. You want the boom as short as possible.
As for more weight - it depends on how powerful you are and how steep/loose climbs that you do.

Note that you have a longer wheelbase than Vendetta (and about the same seat height), so even with less front weight bias you are will likely climb steeper grades with similar (or maybe even less) wheel spin.
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nickyfitz
Starting Member

France
33 Posts

Posted - 06/26/2017 :  07:19:32  Show Profile  Visit nickyfitz's Homepage  Reply with Quote
Hi Andrew

Very nice build! Respect!

I've built a number of MBB-FWD bikes with HiTen frame tubing from discarded low quality steel frame bikes in my builds, and specifically for the boom I've telescoped a top tube inside a down tube to get the required length and allow some degree of adjustment. I couldn't possibly claim that my booms are particularly torsionally or laterally robust, but this hasn't had any detrimental affect on steering so I don't see why you'd need a larger diameter boom tube (as per the earlier Vendettas). I can't really see why Cruzbike use such a huge diameter boom. However, I have found that any "play" in the mounting of the bar ends can have a negative impact, as can the mount for the boom at the top of the steer tube.

If you're up for some experimenting, I'd recommend you try a "hamster" style tiller bar as well as the classic handlebar set up used by Cruzbike. With a well reclined seat angle the Cruzbike-type bars readily contact my thighs when turning (particularly as I prefer to keep the bar width as narrow as possible for aerodynamics) and a tiller bar becomes more suitable with highly reclined rider positions. I admit it was a weird experience using the hamster tiller for the first time, but I rapidly adapted to it and I find that control is every bit as good as with the "classic" handlebars, but without the thigh contact steering constraint. The length of the tiller gives good leverage to control the torque of the boom around the steer tube. With "classic" bars I found it was best to have my arms well extended to control this torque.

Hope this helps you. Pics of my different handlebar set ups below. (My bikes are less pretty than yours!)

Good luck and have fun. I look forward to seeing the completed bike and hearing your experience of how it rides.

Tiller with hamster bar:


Tiller with narrow handlebar:


Handlebar on short tiller:


Handlebar on forward-facing stem:


Nick

Previous bikes:
https://www.flickr.com/photos/139728134@N08/albums/72157673027547665
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Johnsfwdbent
recumbent enthusiast

USA
112 Posts

Posted - 06/26/2017 :  17:06:02  Show Profile  Reply with Quote
Nick the reason that cruzbike uses such a large diameter boom is because it is aluminum. And you guessed it! Aluminum flexes a lot more than steel for the same given diameter.
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nickyfitz
Starting Member

France
33 Posts

Posted - 06/27/2017 :  05:40:55  Show Profile  Visit nickyfitz's Homepage  Reply with Quote
I'm sure you're right John. Nevertheless, while the tubes of aluminium DF bikes are of noticeably larger diameter than their steel counterparts - for the same reasons of stiffness - the Cruzbike booms are absolutely huge! I think I noticed that their most recent Vendetta model has a boom with a slightly reduced diameter, so perhaps they were initially over-engineered?

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Speedbiker
human power expert

USA
3678 Posts

Posted - 06/27/2017 :  08:33:22  Show Profile  Reply with Quote
When you consider that the pedal steer is resisted by the handlebars and the entire load travels through the book, stiffness is very important. Especially with a performance bike meant for climbing the steepest grades by the strongest riders. If you don't plan to pedal hard or climb steep grades, the boom could be much smaller.
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nickyfitz
Starting Member

France
33 Posts

Posted - 06/27/2017 :  10:44:26  Show Profile  Visit nickyfitz's Homepage  Reply with Quote
I think you've nailed it. The reason why I don't notice a problem with my puny boom is because I've only got puny legs :-)
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alast
Starting Member

New Zealand
21 Posts

Posted - 07/06/2017 :  20:15:40  Show Profile  Reply with Quote
Thanks Nick, Thom, John & Oleg for the clues about boom stiffness, swing weight etc.
I decided that the 32 x 0.9 mm boom would be a reasonable compromise between weight & stiffness. I figure I've gained a bit of stiffness through lack of adjustability. It was a bit of a mission to get the boom constructed that way - no room for error.
The frame's basically done now, brakes & gears next.











Nick, you've been bitten bad by the building bug!
What's your favorite bike at the moment? I'm guessing that the hamster/tiller/big wheel MBB was the final in your series of MBB experiments? What was you evaluation of MBB in general?

I'm looking forward to the learning curve of riding MBB. I'll get all the bits on before engaging that phase 'though.

Cheers
Andrew
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Jerry
recumbent guru

USA
906 Posts

Posted - 07/07/2017 :  15:22:22  Show Profile  Reply with Quote
Nice looking Tig welds there my friend. I have welded for 50+ years, can't anymore because of health issues and can't see. When I try using my old cheaters or glasses, I see several arcs! The bike looks cool also. it will be nice to see the finished bike.
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alast
Starting Member

New Zealand
21 Posts

Posted - 07/09/2017 :  02:04:34  Show Profile  Reply with Quote
Hey Jerry,
I hear what you're saying!
Since I got bifocals I have to weld without glasses (I'm short-sighted)
With any luck I've finished welding for this bike:



All the cabling is taped in place.
As it is here it weighs 28lbs (12.7kg).
I start learning to ride MBB tomorrow!
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Jerry
recumbent guru

USA
906 Posts

Posted - 07/09/2017 :  20:13:01  Show Profile  Reply with Quote
Ha! My arms are way too short for no glasses. Good luck with the learning curve. I think most of the people who have some much trouble with MBB are not that coordinated to start with. Nice job. with the build.
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alast
Starting Member

New Zealand
21 Posts

Posted - 07/10/2017 :  03:29:16  Show Profile  Reply with Quote
I launched the MBB today - 43km & stayed upright (well, recumbent but upright!)



On the open road I'm fine but tight maneuvering is still a bit sketchy. I can see pedal steering will very quickly be absorbed by proprioception.

Already there's a lot to like about this bike:
  • The riding position is easier with the seat 40mm lower than my RWD 700C - flat footed stops
  • The off-road drop bars are very user friendly with a clear view over them, two riding positions (over& under the hoods), plenty of leverage against pedal steer, easy to get off the bike at a stop.
  • The bike's rear stays have a nice amount of give without feeling noodly (at least for speeds up to 36kmh on the flat!).
  • [*]The front transmission feels very solid, smooth & quiet

    I dunno if I'm gonna get used to the bar-end shifters, I miss changing gears with fingers hovering on the brake levers (twist shifters). I might lash out & get some brifters but this would mean new brakes also. The short bit of hill I rode was damp & a bit gravelly, inducing a tiny bit of wheel slip - par for the course on any FWD.

    I'll have to get a bit more confident before I ride my regular commute or tackle some decent climbs on this bike, hopefully that will come quick. It already feels fast on the flat, I'm sure I'll get quicker when I don't have to think about balance & can freely put power down.

    Edited by - alast on 07/10/2017 03:31:08
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