Incredibly Stable Recumbents

[Rick Youngblood]

Does a ventisit seat offer

Does a ventisit seat offer more cushion, or is it just for staying dry?

For me it's just more comfortable. I used it on the stock seat and my CF custom seats, and also on other past recumbents. I personably like it a lot, however it may not be for everyone. I also personally prefer the comfort model over the standard, it's a little more cushier.

 

[Robert Holler]

Just a heads up,
We have

Just a heads up,

We have Ventisit comfort cushions in stock. I absolutely love mine.

They can be a "like it or not" thing. For me I had to add the stock foam from the OEM cushion (not the dense one just the filter) and it is perfect. It looks awesome too.

Robert

 

[LarryOz]

I do like the Ventist cushion

I do like the Ventist cushion as well.
The main reason is that is at least allows my sweat to evaporate (a little), but if not, it at least let is "drip down" so I am not so terribly wet. This mostly happens with multi-hour rides.
It is a little on the rough side compared to the original "soft" Cruzbike pads, but I think you kind of get used to it.
I have noticed small abrasions on my back from it, if have really sprinted hard and pushed my back into the seat too much.
You definitely would not want to go shirtless with it. I think it would pretty much take you skin off!

 

[ratz]

Skin?

I don't go shirtless on these bikes for other reasons; I'll spare your imagination.

 

[LarryOz]

Too late for that!

Imagination already kicked in - wow!

 

[MrSteve]

Fascinating

-and entertaining.



The obvious cure for your mysteriously numb finger tip is to not use that hand.
You know, ride one-handed.
Or, ride with no load on the affected hand.


An unobvious approach is to approach your numb fingertip problem by considering
your whole fingertip-support system: Spine, through your arm, to your fingertip.

Your finger tip may be responding to muscular/skeletal stimuli and their effect on the nerves.

It's up to you to track down the cause.

Have fun,

-Steve

 

[Lief]

@Rick said:
It's like your

@Rick said:

It's like your MBB/FWD skills don't stop after the first few thousand miles.

I will attest to that.
I found an email I sent to friends/family after I got my Silvio 1.0 (Sep 2009) where I described a wobbly feeling in the front-end after 30mph on my regular morning descent. If memory serves I didn't crest 35mph on that descent for quite some time because I didn't like that wobble - felt like it was right behind the headset.

Later, when my grandfather asked me about it again, I couldn't explain it but it was gone. At the time I chalked it up to some maintenance effort or other which tightened up the "looseness".
In retrospect - that maintenance was time on the bike and muscle memory and "relax".

I regularly pedal up to 38 (40+ if I'm feeling saucy) on that same descent now on the same bike and the wobble is never felt.
That change happened somewhere between 1,000 and 3,000 miles.

After about 5-6,000 miles I took advantage of a clear run in an area east of Seattle on a hill called Lakemont Blvd (http://goo.gl/AJwG4g) and topped out at 50mph. I didn't have the guts to let er go.
But stable? Yes.

Then, somewhere around 8,000 miles, after several episodes of easy recoveries in mild front wheel slips in gravel, leaves, etc I said to myself - "having four points of connection to the steering is really the cat's meow" - it is very difficult to be surprised by a small slip; having multiple points of connection and the extra mass of your legs resisting changes in direction contributes to that stability I think.

Shortly after that epiphany I tried riding no-hands for the first time since mile 2,000. Back in the late 'oughts I gave up riding no-hands as impossible. This time it was 2 min of adjustment and just like butter!

I haven't done it at speeds over 30mph but in a safe place, I'll open a cranky wrapper with both hands and continue pedalling at 18-20mph without any fear. I don't recommend it, use your own judgement, but it certainly feels as safe as the ride is long; stable, relaxed, and easy.

ONE caveat - the Vendetta 2.0 does not enjoy that same level of 'no-hands stability' at speed.
My running theory is that
A) on my Silvio 1.0 I'm sitting more upright - I get to use more of those oblique muscles in my hips and torso to maintain balance like you do in a kayak
and
B) I only have about 1,000 miles on the Vendetta. Perhaps I'll be singing a different tune in 2015.

 

[Andrew 1973]

"ONE caveat - the Vendetta

"ONE caveat - the Vendetta 2.0 does not enjoy that same level of 'no-hands stability' at speed.
My running theory is that
A) on my Silvio 1.0 I'm sitting more upright - I get to use more of those oblique muscles in my hips and torso to maintain balance like you do in a kayak
and
B) I only have about 1,000 miles on the Vendetta. Perhaps I'll be singing a different tune in 2015."

For the record, I have witnessed Jim Parker riding his Vendetta with his hands in this position...
alt="Not actually Jim Parker"

 

[LarryOz]

Yes - I have too (Seen Jim do that very thing!)

Of course he has been riding a V for longer than anyone I suppose.
I started on a Silvio 2.0 - I only rode it for about 3 months, but I never could ride it no hands.
I have had a V2.0 now for about 3 months (but have not been able to ride it nearly as much on the open rode).
I have already been able to tentatively ride no hands (but for a very short time).
The V appears to be more balanced for me for some reason, but it might have helped that I rode the SIlvio many miles before switching.
I am hoping to be able to do this someday on it! (well the inverted position from this one actually)

 

[Rick Youngblood]

Like this?

 

[LarryOz]

There you go

-I always wondered what that "rotate clockwise" thingy-button did if you clicked it twice.
I guess I was a little on the "slooooow" side yesterday... haha.
love your avatar by the way - awesome!

 

[Andrew 1973]

back to stability

One time, when heading home from work back when I lived in SC, I was cruising along a beautifully smooth length of pavement on a rear flat tire! I didn't realize until making a left turn at a three way intersection (I was intent on making the green light, so I was pedaling at quite a pace). As soon ad I began to round my turn, the rear tire rolled on the wet road surface and the back end of my Silvio fishtailed as if I were riding on ice!

My heart felt as if it leapt into my throat, but I was able to keep upright. It was almost instinctive.

 

[Lief]

Caveat on my Caveat:
I can

Caveat on my Caveat:
I can still do ^that^ on the Vendetta too (just ask Tim Turner) - it just isn't AS easy to recover.

So, perhaps what I should say is, yes it's stable, I can still ride and pedal no hands but if you get off line recovering is more difficult and has to be well predicted - you have to pay closer attention.

Recovering, in the more upright position of the Silvio 1.0 is just that much easier.**

that said - I'm NEVER going to have a no-hands race so it's all just monkey-business which *MIGHT* be an indicator of perceived handling stability when learning simply because it's such an edge case.

** I suppose if it matters to any new buyers - deciding between a more upright position and more reclined - I could illustrate the differences in no-hands riding in my cul-de-sac between the S 1.0 and the V 2.0. Probably not.

 

[hamishbarker]

Ok, so I have implemented the

Ok, so I have implemented the linearized bicycle stability equations used in the jbike6 matlab software on the open source sage mathematical software which I mentioned in my previous post.

This is going to be a bit too theoretical but nonetheless interesting. If you don't like maths, probably best to skip it. If you do like maths and/or are interested in what makes a bike be able to run stably without any steering input (no hands) have a look at the jbike6 website and especially the paper published in the proceedings of the Royal Society:
http://ruina.tam.cornell.edu/research/topics/bicycle_mechanics/*FinalBicyclePaperv45wAppendix.pdf
http://rspa.royalsocietypublishing.org/content/463/2084/1955

I have made a rough stab at capturing the vendetta's geometry and mass distributions to see what the software would spit out, and

Before going to the vendetta plot, the first plot below is the variation of the stability eigenvalues of a typical racing (DF) bike and rider combination, with velocity in meters per second along the bottom, and the eigenvalues on the y axis. This is all for small amplitude steering and lean motions, but the equations have been well benchmarked against full non-linear mechanics models and are good for showing trends in stability.

Notable points: The speed at which the yellow line starts is the speed at which oscillatory (weaving) behaviour starts to happen naturally. Below this speed, the bicycle will just fall over one way or the other (the pair of green lines which come together represent those "solutions" which can happen in a fast way (the upper line) or a slow way (the lower line). I'm not sure how there are two ways for a bike to topple over. Perhaps one way is with the steering towards the topple (which probably would go slower) and another way with the steer away from the topple. Anyway, after the two lines come together, but while the green line is still positive, it means that the weaving motions are amplified (growing) (the frequency of weaving is varying according to the yellow line/pi (or might be 2pi). So the bike is still unstable.

BUT, where the green line goes below zero (at about 5.4m/s for this bike model), the weaving dies away, and the bike will run stably without steering torques input. So, no-hands riding is then possible.

Above about 9m/s, where the red line becomes positive, this indicates instability for the case of "capsize" which is that the bike leans one way, the steering makes it then lean further and eventually the bike will go zooming around in a tightening circle and lay down. But this mode of instability is very slow growing and is no trouble for normal cyclists to counteract with either a steering input or a lean.

Now on to the vendetta curves (second graph). It looks very different. At this stage I have made a rough model by making a mass of 28kg in the form of two cylinders (i.e. legs!) which are fixed to the handlebars in the approximate geometry for where they are on a vendetta. Of course, on a real vendetta this isn't quite correct, since the end of the legs (feet) moves pretty much exactly as the handlebar/boom rotates, while further back along the legs there is less movement (and none at all at the hips). but at least it might give some indication of trends.

So what do the curves tell us? Well, see the yellow line now starts at about 11.5m/s (26mph). Perhaps this could be the instability that bumblief mentioned in his post above? Note that the low speed "topple" modes go all the way out to 11.5m/s - that is, active steering is required. (it's always possible to ride in unstable speed regions, as long as the controller (grey matter/muscles/senses) can react faster than the instability). Note there is an odd yellow loop at 2-3 m/s. Some sort of oscillating instability mode perhaps, but more likely a figment of the rough model.

Note also, the green line never crosses zero, so the bike is always unstable. Either the model is wrong, or when people ride a vendetta no hands they are still putting in sufficient (perhaps small) steering inputs with their feet. Since it isn't easy for most people to ride a V or silvio no hands, I'm guessing probably the latter.

If anyone wants to use the maths or help contribute to putting together a better model of the moments of inertia of a vendetta or silvio and rider, have a read of the paper and then have a look at the sage (open source, free, computer maths package) code
https://cloud.sagemath.com/projects/97da2c46-dec0-423e-b73e-a66455d08018/files/vendetta-linear-dynamics-eigenvalues.sagews

 

[Andrew 1973]

Ummm...

 

[ratz]

Cool

So on a DF Bike 6m/s is the optimal ghost rider speed. That would have been very useful to know when I was 13.

I didn't read the papers yet and it looks like a mighty fine first pass at trying to extend the study; nicely done. The results really do make sense but they do seem right shifted to the high side compared to the real world, Oscillation seems to die out around 8-9 mph and is gone for sure at 12-14mph so 4m/s at which point it's a flop syndrome from gravity induced fake steering input;. I suspect that the model doesn't yet account for the Leverage from the length of the boom and the feet being so far in front of the wheel. The length of the boom is going to both add power leverage and dampen the input.

Yep neat.

 

[hamishbarker]

Apologies to Mr Baloga for

Apologies to Mr Baloga for blowing mind/boring sensless...

I would agree about the higher speed thing. Measurement and a less rough calculation of the moment of inertia of the critical boom/leg/crank/chainstay masses will change things.

Do you think there is any speed at which the V is stable (with feet on the pedals) and not requiring (possibly small and not normally noticed) steering inputs? (i.e. would be a no-hands stable speed like on a df?) The lower of the green line pair is very close to the axis, so it's only a very slowly amplifying topple mode. The other one is much faster growing, still slower than that for a df.

the leg masses and their rotational inertia in all three axes (two medium/fat cylinders - depending on the physique!) and center of mass as I estimated, are included in the model as being rigidly connected to the handlebar/fork (in case of vendetta, also the boom) assembly. The biggest rotational inertia of the legs about the vertical axis is through the boom will add a little more mass, but compared to the legs probably small (although it's boom plus cranks and chainset plus chainstays all a long way from the headset axis of rotation, so maybe not so small). The tilt in the steering axis (which also effects wheel flop - a vertical headset gives zero flop), trail and rake (offset) are all modelled although just typical values, haven't measured the Vendetta's.

It will be interesting to refine the model and see how much changes. The model is linearized equations, so valid for small displacements only, but in the conventional df case has accurately predicted.

 

[Eric Winn]

Self-stability

I skimmed through the papers and I'm not really into math all that much but I get the feeling their reference model doesn't quite accommodate some of the funky dynamics of FWD-MBB. I think the FWD-MBB design adds some more complexity to BOTH the holonomic (hinges and ground contacts) and non-holonomic (non-slip rolling) constraints. Based on my riding experience my gut tells me more on the holonomic side but I'm really reaching to make sense of this stuff.

The self-stability bit paints a mental picture of doing roll down tests of bicycles sans riders which gets me to really wonder what a Vendetta would do in this scenario but I'm not too inclined to use my Vendetta to find out.

Interesting stuff though.

-Eric

 

[DuncanWatson]

Hey Andrew, now that you are

Hey Andrew, now that you are relocated up to Washington state, you should be able to find some nice long steep hills - I'm sure Lief and Robert know of some. I'm hoping to break into the 50+ MPH this springs.

Sacramento River looks like the Amazon River, muddy and murky!

I can point out some Hills on the Eastside that I use for max speed runs. I hit 52 on my raptobike a couple of times. I hit over 40 on my standard commute route. I need to scout the route to make sure those speeds are still safe

 

[cranky cyclist]

I was able to wave at some friends going downhill at 29 MPH. I don't think that I could have done that on my DF. Maybe?