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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/25/2010 :  11:52:17  Show Profile  Reply with Quote
quote:
Originally posted by DocBB

Too bad I'm sorry for you I hope you'll get better soon.

and if you really want to get rid of the bike , would you sell it to me?



The bike is to bent the ride again

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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OpusthePoet
recumbent guru

USA
678 Posts

Posted - 07/25/2010 :  21:28:23  Show Profile  Visit OpusthePoet's Homepage  Reply with Quote
From looking at the pictures I think wheel flop might have been the culprit, making the steering do things the rider never intended.

Opus

My gas is up to $.99 a burrito, $5.99 for premium and I'm only getting 20 miles to the regular burrito.
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/25/2010 :  21:37:49  Show Profile  Reply with Quote
quote:
Originally posted by OpusthePoet

From looking at the pictures I think wheel flop might have been the culprit, making the steering do things the rider never intended.

Opus

My gas is up to $.99 a burrito, $5.99 for premium and I'm only getting 20 miles to the regular burrito.



The bike just started swaying from side to side, until it was no longer under me.

The yellow oval is where I left the road - The red arrow is where I ended up! The pic doesn't show the large rocks or the drop into the creek


and this is why you wear helmets


"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx

Edited by - nigel schroder on 07/25/2010 21:42:49
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LongJohn
recumbent guru

China
581 Posts

Posted - 07/26/2010 :  01:05:07  Show Profile  Visit LongJohn's Homepage  Reply with Quote
Augh!!!

Nigel, thank God you walked away from that!!
To bad to hear it is to hard to ride, and you would like to hack it up.

It takes some time getting used to the steering. Some people learn this faster than others.

I would set it aside. Forget about it, and try again in a couple months.

Would be sad to see so much work go to waste...

Thomas
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tom porter
recumbent enthusiast

161 Posts

Posted - 07/26/2010 :  04:35:30  Show Profile  Reply with Quote
My recommendation is to forget MBB all together, especially if you want a high performance bike. It's almost impossible to get right. All you save is a little chain weight anyway. Look at the proven fast lowracers on this site. I'm nearing completion on my newest lowracer and will post photos/articles as I go. This is this the general opinion of WISIL riders/racers. I'll be happy to answer any questions that you may have about my build.


O---o
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25hz
human power supergeek

Canada
1223 Posts

Posted - 07/26/2010 :  05:12:38  Show Profile  Visit 25hz's Homepage  Reply with Quote
Too bad about the crash, Nigel. Hope you aren't too busted up.

Swing booms are the only style of bent where rider skill was the speed limiter. Of course, down hills or other artificial means can put you outside your skill zone, but for just riding on the flat, it took me a few hudnred km before I felt confident enough to go on the road with them. Then, on hills, for the longest time, I would ride the brakes going down them, and that was on hills that I could hit 90+ kph on other bents without feeling uncomfortable. The biggest thing for me, and biggest "relief" was being able to completely relax on downhills, or even sprinting, once I switched back to anything with a rigid boom. MBBs are cool, but I think other designs have more advantages to their design than the negatives that their drivetrain produces.
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warren
human power expert

USA
6528 Posts

Posted - 07/26/2010 :  05:49:19  Show Profile  Visit warren's Homepage  Reply with Quote
I agree with Tom. MBB bikes are just fine when ridden in a nice slow sedate manner. That is not my personal riding style. Wow that helmet did exactly what it was supposed to. It was destroyed to protect your head.

-Warren.

Edited by - warren on 07/26/2010 05:53:21
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alevand
human power expert

USA
3706 Posts

Posted - 07/26/2010 :  09:29:15  Show Profile  Visit alevand's Homepage  Reply with Quote
Speed wobble is a scary and mysterious thing, you dont know you have it until your going too fast and the bike starts wobbling violently and uncontrollably. The only thing you can do is slam on the rear brake and hope to slow down to under the threshold speed before you loose it. Trying to fight it by holding the handle bars stiff only makes it worse, my experience anyway. Looks like you would have been brain dead without the helmet.

Good Luck with the bike.

C:
Tony Levand

Edited by - alevand on 07/26/2010 09:50:23
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/26/2010 :  11:40:43  Show Profile  Reply with Quote
Thanks for the support guys

I'm going on holiday for a few weeks ,so I'll have time to rethink the design. I should be able to reuse from the headset back, just need to change the head angle and add the boom.

I still can't believe I walk away from that crash

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/26/2010 :  15:33:32  Show Profile  Reply with Quote
quote:
Originally posted by Alan

quote:
Originally posted by nigel schroder

I still can't believe I walk away from that crash



You DaMan Nigel.
Did you have your kevlar shorts on when you crashed?

You get the award for most helmet damage in Recumboland crash. Amazing!

Tinkerville Racing


Cobbling up wunderbikes to make 'em faster.





No I don't own any kevlar shorts, but amazingly I didn't rip any of my clothes.

Maybe I should invest in a kevlar body suit

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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triked
recumbent enthusiast

USA
126 Posts

Posted - 07/26/2010 :  19:49:39  Show Profile  Reply with Quote
You must have a really hard head to destroy a helmet like that without any significant injury. Glad you are relatively unhurt.

-Ed
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LongJohn
recumbent guru

China
581 Posts

Posted - 07/27/2010 :  00:07:16  Show Profile  Visit LongJohn's Homepage  Reply with Quote
Hi,

I am very surprised at the amound of "anti" MBB! I have been riding a Flevoracer for the last 12 years and put well over 100,000 km on it.
Yes, the first month was eary, but after that I never again found the bike to be unstable. Unforgiving yes, but definitely not unstable.

What I am surprised about is the two camps that have formed over the years; there are two groups of people that think that their geometry set-up is better than the other (I would call it: Flevo vs python).
I have been riding a flevo a long time and I really like the steering. I can imagin (but there the difference in filosophy) that a Python bike would have more pedal steer.

Like I said; leave it for a couple weeks and reconsider. It will take some time getting used to.

Cheers,

Thomas
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/27/2010 :  00:35:35  Show Profile  Reply with Quote
quote:
Originally posted by LongJohn



Like I said; leave it for a couple weeks and reconsider. It will take some time getting used to.

Cheers,

Thomas



Hi Thomas
The bike was very ridable and I got the hang of it a lot quicker than my first RWD low racer. But it was just to unpredictable.I do still love the design ,so I will give it some thought ,but it is so bent now
that it needs to be cut which ever way I go

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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OpusthePoet
recumbent guru

USA
678 Posts

Posted - 07/27/2010 :  20:55:39  Show Profile  Visit OpusthePoet's Homepage  Reply with Quote
There are two kinds of speed wobble. One is called "shimmy" and is a higher-frequency shaking caused by elastic interactions in the frame and is almost impossible to predict or control once it gets started. The other is lower in frequency but higher in amplitude and is cause by steering geometry of the bike. This one is usually called a "tank slapper" and can get violent enough to throw the rider off the machine. The problem with trying to fight a "tank slapper" is you only have a fraction of a second to use muscles to damp it out before it throws you off, and the things that make a bike fun to ride are the same things that make a "tank slapper" possible. The two things that work together to prevent tank slappers are lots of trail, combined with lots of friction in the steering. Conversely, having steering with little trail and very low friction steering makes for a nimble feeling bike.

One factor known to help prevent "shimmy" is a very stiff frame from side to side.

Opus

My gas is up to $.99 a burrito, $5.99 for premium and I'm only getting 20 miles to the regular burrito.
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Larry Lem
human power expert

South Sandwich Islands
2541 Posts

Posted - 07/27/2010 :  21:12:01  Show Profile  Reply with Quote
I still love the simplicity of the drivetrain. No power-robbing pulleys and a short chain. Maybe I'll try some experiments after Battle Mountain.

Larry Lem
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/27/2010 :  21:31:37  Show Profile  Reply with Quote
quote:
Originally posted by Larry Lem

I still love the simplicity of the drivetrain. No power-robbing pulleys and a short chain. Maybe I'll try some experiments after Battle Mountain.

Larry Lem



I think if I was going to do this design again ,I would use duel 26" wheels and make it a mid-racer.

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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25hz
human power supergeek

Canada
1223 Posts

Posted - 07/28/2010 :  03:58:43  Show Profile  Visit 25hz's Homepage  Reply with Quote
You could always make the front end like the MBB, but make it rear steered like the one dude on the Python list did. his seemed very stable according to his videos. The problem with speed wobbles on a MBB, if/when you get them, is it's just not the front wheel going crazy, it's the whole front end AND your legs. The way it starts to thrash your body makes it hard to recover. I had a large number of high speed wipeouts, but they were all low sides in less threatening ground areas.
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alevand
human power expert

USA
3706 Posts

Posted - 07/28/2010 :  04:45:29  Show Profile  Visit alevand's Homepage  Reply with Quote
Speed wobble is mysterious. Yes, frame torsional stiffness is key, I think. Instead of using the tear drop down tube and two bottom tubes, a single larger diameter tube would have many times the torsional stiffness without a weight penalty, since it scales as diameter to the forth power for round tubes and width to the cube times height for non-round sections. Flexing of the rear fork may have something to do with it too. Speed wobble is a resonance that occurs at a specific speed and not just on MBB bikes, the Mango crashed at Battle Mountain. Rear steering is not an answer for a high speed bike!

Mango crash:
http://www.youtube.com/watch?v=i5Dapy1xUq0

A dramatic motorcycle crash:
http://www.youtube.com/watch?v=RmtoOmq3ppw

skate board crash:
http://www.youtube.com/watch?v=yRuBDAIkhZU


But watching this video, the very skillful rider recovers. I may have to rethink the torsional stiffness theory.

http://www.youtube.com/watch?v=HtjQ4SK4GXk

These are all interesting and entertaining:

http://www.youtube.com/results?search_query=speed wobble&aq=f

C:
Tony Levand

Edited by - alevand on 07/28/2010 05:10:00
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LongJohn
recumbent guru

China
581 Posts

Posted - 07/28/2010 :  08:15:53  Show Profile  Visit LongJohn's Homepage  Reply with Quote
Tony,

I don't see how these speed-wobbles are related to what Nigel experienced.
I think what Nigel experienced was an overcompensation of a steering action induced by ??? (fill in the blanks).
This could have simple be related to the steering geometry.

What we do know, is that steering of a bike is very complex. Several universities have spend there share of time researching it.
Also the Lord of the Chainrings has done his share.
Stability of a MBB bike is something totally different from that. Which implicates that you would have to depend on "previously succesfull geometry".

If there is a deviation in geometry you might get stability issues.

I don't expect this is related to frame stability...

Thomas
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/28/2010 :  12:33:22  Show Profile  Reply with Quote
quote:
Originally posted by alevand


Flexing of the rear fork may have something to do with it too.

C:
Tony Levand



I used the rear fork like this trying to get a little suspension in the back end.

After the crash the back wheel still spins straight and round but the axle has been bent. Do you think this was caused by the fork flexing side to side before the crash?

I have seen other people use forks like this has anyone else ever had problems with this type of flexing?

When I rebuild the bike do you think that I need to reinforce the back end? or do I need to start all over again?

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx

Edited by - nigel schroder on 07/28/2010 13:06:16
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25hz
human power supergeek

Canada
1223 Posts

Posted - 07/29/2010 :  04:26:19  Show Profile  Visit 25hz's Homepage  Reply with Quote
MBBs do weird **** when they wipe out. Not being a physicist or an engineer, the main reason I can come up with, from repairing post-wipeout damage, is because the CoG moves left and right of centre.

When you steer, especially in extreme control, or over control moments, as your legs are moving left and right of centreline, this obviously also moves the CoG, and that amount of movement with the forces present in a wipe-out, might be what is causing rear wheels and frames and forks to twist like they do. If the CoG is lined up with centreline and the wheels, pushing sidways on the CoG makes the bikes rotate in an arc with the pivot being the contact patch of the tires, and the bike goes over. With the MBBs, turning displaces the CoG to the side of centreline and the contact patches, so now, lateral force on the CoG adds lateral force to the contact patch before the CoG can be raised a little more than normal to still rotate up and over to the side. That spike in loading, during a wipeout, might be what is causing the twisting that happens.

With a more normal 2 wheel bent, even during a wipeout, the only thing that's moving left and right of centre, is the relatively low mass arms and handlebars/tiller.
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 07/31/2010 :  15:57:08  Show Profile  Reply with Quote
When I start the rebuild I still want to keep it FWD,so there are two options that I'm thinking about.

Option 1 --- Big front chainrings and idler's

Option 2 --- Small (standard) chainrings and a step up/mid drive.

The front wheel is a 406

I want to be able to race on the road at speeds between 35-60kph and maybe add a full fairing at a later date.

What are the pro's and con's of the two options?
and what do you think will work best?

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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tom porter
recumbent enthusiast

161 Posts

Posted - 07/31/2010 :  18:03:15  Show Profile  Reply with Quote
I've built several FWD's with a small tire (349,406,451). Tried every possible way except one. Big chainring 72T/52T double with a 451, was OK with a 42 - 120 inch gear range, used two pulleys, shifting wasn't very crisp though. Intermediate drive on the other two, 349 had triple crankset with normal chainrings and about 6 speeds on the intermediate on a 8 speed cassette body, single speed freewheel on wheel hub. Finally the 406 had a single chainring with 3 speeds on the intermediate drive shifted with a modified front derailleur ond a 9 speed cassette on the wheel, thes both shifted crisply. Only issue is clearance for the knee on the right side. Seemed to be OK for others who rode these bikes. The best way I think would be a single chainring with a 3 x 8 hub on the wheel using two pulleys, if I was going to attempt this again I would use this.

O---o
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nigel schroder
recumbent enthusiast

New Zealand
190 Posts

Posted - 08/01/2010 :  19:49:43  Show Profile  Reply with Quote
quote:
Originally posted by tom porter

I've built several FWD's with a small tire (349,406,451). Tried every possible way except one. Big chainring 72T/52T double with a 451, was OK with a 42 - 120 inch gear range, used two pulleys, shifting wasn't very crisp though. Intermediate drive on the other two, 349 had triple crankset with normal chainrings and about 6 speeds on the intermediate on a 8 speed cassette body, single speed freewheel on wheel hub. Finally the 406 had a single chainring with 3 speeds on the intermediate drive shifted with a modified front derailleur ond a 9 speed cassette on the wheel, thes both shifted crisply. Only issue is clearance for the knee on the right side. Seemed to be OK for others who rode these bikes. The best way I think would be a single chainring with a 3 x 8 hub on the wheel using two pulleys, if I was going to attempt this again I would use this.

O---o



Hi Tom

can you please add some close up pic's of this Fwd of yours
(http://www.recumbents.com/wisil/porter/images2004/porterFWDDualSusp9.jpg)

And what are the size's of all the cogs?
and what did you have to do to modify your front derailleur?

cheers Nigel
(ps: I'm away on holiday for a couple of weeks, so look forward to seeing something when I get back, no rush)

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
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tom porter
recumbent enthusiast

161 Posts

Posted - 08/02/2010 :  10:47:16  Show Profile  Reply with Quote
Hi Nigel,

This bike was built in 2003 so the only pictures are the ones posted. The front derailleue had the cage shorted and mounted almost upside down. The intermediate drive is a Shimano 8 speed cassette body with pawls removed, this is a pretty common thing. Gearing is vitually unlimited. The single chainring was mounted on a sliding boom for tensioning. If your interested in building something on the order of this let me know, meanwhile I think most of the bits are stashed somewhere nad I'll have look around. I probably can come up with some refinements of the design if your'e interested.

Tom Porter

O---o
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