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Balor
recumbent guru

Russia
514 Posts

Posted - 01/28/2017 :  04:10:22  Show Profile  Reply with Quote
Examples: Bipolar and KrankiKobra:

http://en.openbike.org/wiki/Bipolar

The discussion on 2WS got me thinking, and those Python-based prototypes seems quite rideable - if prone to rear caster precession:





To compensate for wheel flop (due to CG of wheel above steering axis, unless 90 "true caster" angle would be used with negative offset) and add some steering damping to cancel steering wobble, a simple 'flop stop' from inner tube rubber can be used:

http://velomobile.org/forum/viewtopic.php?p=4810526#p4810526

Simple, cheap and should last forever. Easily removable, too.

While I don't like inherent HUGE steering inertia, negative trail and CG-based wheel flop (that overbears negative 'conventional' wheel flop and makes the bicycle fold as soon as rider is out of the seat) of a Python, turning a rear wheel into a caster with more conventional (or even less conventional like my negative angle MBB, heh) FWD design seems to be beneficial for two reasons:

1. Tighter turning radius inherent in 2WS designs
2. Makes the bent somewhat 'foldable', together with MBB on the front it makes it MUCH more compact when 'folded' this way than conventional rigid boom designs.

So, you can have your long wheelbase (better weight distribution, better ride quality) AND tight turning radius AND ability to fit into somewhat tight storage space (very important for transportation in cars or trains).

It is somewhat of a mystery how it would behave under heavy front braking, though.
While I don't think that it is a good idea to cram TWO novel steering features into one design, I think it is certainly worth investigating in the future.

Anyone familiar with similar FWD/rear caster designs and how they work in practice?

Edited by - Balor on 01/28/2017 06:06:59

Speedbiker
human power expert

USA
3756 Posts

Posted - 01/28/2017 :  06:14:24  Show Profile  Reply with Quote
I believe stability gets worse with speed. The opposite of what we like. No amount of keyboard pseudo-engineering will fix that. There are stellar designs based on conventional geometry. Why waste time on that which does not work?
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/28/2017 :  06:28:07  Show Profile  Reply with Quote
quote:
Originally posted by Speedbiker

I believe stability gets worse with speed. The opposite of what we like. No amount of keyboard pseudo-engineering will fix that. There are stellar designs based on conventional geometry. Why waste time on that which does not work?



You *know* or you *believe*?

I *know* that Python FWD design gets more and more unstable at speed (due to negative trail forces overpowering negative steering flop forces) - unconventional rear end or not, hence I will not waste my time building one.

I don't *know* how adding a swing caster rear wheel would affect handling on a design that is less radical than a Python (say, FWD-twist chain).
If you do, I'm very interested in hearing reasons why, so I would not waste my time doing things that do not work, right.
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/29/2017 :  01:27:42  Show Profile  Reply with Quote
I see. Well, in my case 'winning races' seems fun, but entirely optional (hence, I'm unlikely to accomplish that and it is fine by me). I like fast stuff, but I also like things that are practical, too.
I agree that this addition will not help at high speeds, but I also fail to see how it would contribute to instability at speed (which may be entirely my own failure at grasping underlying physics).
What it should accomplish is better low-speed manoeuvrability that I'm having trouble with on my current MBB (in theory) and 'limited foldability' (undeniable).

Since no definite arguments against are forthcoming and evidence suggests that it is quite rideable, I guess I'll add this to my list of 'features to try out'.
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/29/2017 :  23:43:25  Show Profile  Reply with Quote
Spent some time mulling about it. I think that turning rear into a caster should not in fact upset balance, because it does not actually affect initiating a turn in any way, but picks up gradually, without 'pushing CG from behind' like RWS designs do (now THAT is what makes RWS inherently unstable).

Kinda like Ackermann geometry, only for front-back, not left-right wheels - the point is not to 'add' to front steering (that would introduce instability indeed), but only to remove resistance to turning fixed rear wheel adds - namely, minimizing sideslip forces.

I've googled an interesting article, by the way:
https://www.researchgate.net/publication/229038090_How_a_rear_steering_system_may_improve_motorcycle_dynamics

Unfortunately, only abstract is available:

Two types of rear steering systems are compared: a self-steering wheel coupled with a spring-damper assembly and a controlled steering wheel, whose steering angle is governed accordingly to a first-order relationship between front and rear steering angle. In general, any rear steering system transfers energy from weave mode to wobble mode. Thus, both solutions stabilise high-speed weave, but increase instability when braking. The passive system shows unexpected reactions when accelerating in cornering condition, whereas the active system is almost neutral.

It is actually stated to stabilize high-speed weaving!
The 'weirdness in acceleration under cornering conditions' would only apply to a RWD design. Braking instability is something I've predicted myself.
I'll try to find a full version and be back with results.

Anyway, come to think of it, this WOULD help me in races - I'm not racing my current MBB on local races (time trial) exactly because it is taking place on a narrow road with 3 turnarounds. Having to stop and flintstone to turn around would cost me too much time to even bother, not to mention I'll only make a laughing stock of myself.

My current MBB has similar wheelbase to my new design and similarly limited steering angle, and I'm missing 'just a little bit'. Passive rear steering might give me just that little bit.

And other motorcycle article on the same subject:

http://papers.sae.org/950198/

Again, converse of what was proposed by Speedbiker is stated:

quote:
While the study found that the rear wheel self-steering system has a potential to improve the motorcycle stability under high speed straight line operations, it was also found that it adversely affected the motorcycle stability in turn maneuvers.


It is found to increase high-speed stability, but negatively affects turning... which is strange, because Python rider in "Futon Express" videos seemed to have no trouble doing figure eights and commented that it actually makes it easier.

Maybe it is due to some combination of braking and cornering? Oh well, instead of buying full version of the articles, I'll better spend funds to equip my prototype with optional rear triangle that would include a caster pivot. If it will not work out, I'll simply remove it.

Edited by - Balor on 01/30/2017 02:18:39
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/30/2017 :  05:44:55  Show Profile  Reply with Quote
Found one article on sci-hub. A few relevant tidbits:

quote:
Later, two researchers from Honda (Hikichi and Tezuka, 1995) proposed a work
about the stabilising effects of a self-steering rear wheel. The system described in the
paper is designed to damp weave mode in straight running and cornering. The authors
assume that weave oscillations are sustained by the sideslip force on the rear tyre, and
therefore better stability can be achieved reducing the sideslip angle.
This principle is
applied to stabilise a 400 cc road sport motorcycle, whose rear wheel is mounted on an
inclined rear steering head in order to generate a positive trail. With this geometry, the
lateral tyre force has an aligning effect that tends to reduce the sideslip. Steering motion
is controlled and limited using a spring-damper assembly. The paper presents both
simulations and experimental results, meaning that Honda has already built a 2WS
prototype. Results show a noticeable improvement of the weave stability, but it must be
remarked that the testers did not appreciate the large behavioural changes due to the
additional steering system.



quote:
It has been found that the passive system has good effects on the stability, causing a
strong reduction in the weave oscillations that occur after the motorcycle is excited with a
lateral impulse.
On the contrary, there are not stabilising effects on the wobble mode, that
becomes unstable in braking conditions. A configuration with preload MPS = 8 Nm,
damping coefficient CPS = 200 Nms/rad, and stiffness KPS = 1000 Nm/rad has been
selected as best compromise, but the steering system should be anyway inhibited when
the brake is activated.


So, it should, in fact, be very advantageous for streamliners - by converting high-speed weave after 'being excited with a lateral impulse' (say, a wing buffet) into a rear wheel wobble that would in turn be damped by a steering damper in this system.

It does produce instability on rear braking, so the author recommends to lock out rear pivot under braking. Might be possible by doubling the braking cable and activating rear brake along with 'rear steer brake' - kinda like tilt lock, a cheap mechanical disk brake will do the trick... or skip rear braking altogether, heh.

Conclusion: Definitely worth a try.
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alevand
human power expert

USA
2932 Posts

Posted - 01/30/2017 :  06:13:50  Show Profile  Visit alevand's Homepage  Reply with Quote
Is weave the same as "death wobble"? I haven't experienced it in a streamliner, but I have on a motorcycle. Speeds are much lower. I think Sean Costin experimented with two wheel steer on his Monkey Hand bike and concluded it wasn't beneficial. Probably not a good idea, if the bike weaves and you put the brakes to slow down and it goes into a wobble mode, or visa-versa. All wheel steer, like the cars that have it, is probably better for low speed maneuvering and at small front steering angles would steer opposite, so the bike would steer as if the wheel base were longer at speed. I don't know what effect this would have have. Rohorn experimented with 2 wheel steer on some reclined mopeds and had generally positive remarks on exiting corners.

C:
Tony Levand

Edited by - alevand on 01/30/2017 06:35:07
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/30/2017 :  06:50:40  Show Profile  Reply with Quote
No, weave is different from wobble. For reducing wobble you need a steering damper - a set of rubbers + dragging mechanical disk brake should do the trick for 'low-tech' implementation.

Here is sci-hub link:
http://sci-hub.cc/10.1504/IJVD.2008.019090

I think you may glean more information from this article, I never claimed superior knowledge on recumbent building or mechanical engineering.

Btw, wobble is apparent from second 'KrankiKobra' video, but he had no steering damper at all plus it was destabilized by chainstay-mounted camera.

Edited by - Balor on 01/30/2017 08:04:14
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Speedbiker
human power expert

USA
3756 Posts

Posted - 01/30/2017 :  08:49:06  Show Profile  Reply with Quote
Should be advantageous on a streamliner? Definitely worth a try? HA HA HA. Please, please try it!

Robert Horn went way beyond testing dual steer on mopeds. He built and successfully race track tested a full power racing recumbent motorcycle with dual steer. It's too had this site frustrated him to the point of not posting any more. He has built and proven designs you guys theorize about.

"10 minutes of research on the internet can make anyone an expert"
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/30/2017 :  09:27:54  Show Profile  Reply with Quote
quote:
Originally posted by Speedbiker

Should be advantageous on a streamliner? Definitely worth a try? HA HA HA. Please, please try it!




I will. Why all the venom, though? Do you have anything constructive to contribute? You've worked with Sean Costin for instance, Tony said that he tried something on one of his recumbents. So, if you are speaking from experience about adding passive rear steer, why don't you share it? After all, that is what internet is about - dissimnation of knowledge that you can learn from other's people mistakes and share your own - so other people will not have to repeat them.
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/30/2017 :  12:22:53  Show Profile  Reply with Quote


I spoke with Robert. No, he did not try it. He thinks that this might be fun to just mess around with, but his AWS system was designed to address a specific problem 'conventional' recumbents should not have, and self-steering AWS is unlikely to solve anything that would remotely interest him (namely, going REALLY fast), so he is not interested.

Advocating half-baked theories certainly does not help the sport, but testing them and then publishing the results fairly does. If it was not published - it might as well never happened.

If you cannot be bothered explaining me what you actually tried and how it turned out, maybe you can point me to someone who will? I expressly stated my desire to learn SPECIFICS in my original post. Did you actually test for slow speed minimum turning circle reduction, for instance?

And besides, making a self-steered rear on a FWD is actually not hard at all. I can simply ask builder to add a separate head tube and mock up a rear triangle, kinda like this:



Plus some rubber bands for damping and basically that's it. *shrugs*
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purplepeopledesign
recumbent guru

Canada
685 Posts

Posted - 01/30/2017 :  14:36:38  Show Profile  Reply with Quote
Yeah... we tried that too. Sometime in the early 90's probably. Actually, my late friend Dan Trayling designed it and my mentor Paul Smith welded it. Anyway, I just stood by and watched, then helped them take it apart and toss it on the pile of tubular metal source material. Can't be sure but part of it may have turned into Dan's 17 lb CLWB circa 1994. Those of you who've seen it will remember it for the fabric seat tensioned by nylon strap.

Anyway, Balor (and other newbies), you're on a forum with people that have building recumbents for decades. I've been messing around since 1986 and I'm not even close to being an old-timer around here. Heck, I was even out of the scene working a career that when I came back, nobody knew me... well, except Georgi and Sam, but that's another story. First I saw Ollinger was in 1990 at Portland with a composite SWB low racer. I think it was white. I have an actual paper photograph somewhere. If he says it was done and failed, then it was done and failed. There's nothing to stop you from building it for yourself to learn, but understand that if one of the people with a pyramid of failed bike frames behind them says it's can't work, then it's been tried every which way.

I learned a long time ago that when mentor-types start telling stories, it's best to listen. When you come up with the new sliced bread and they say it won't work, I don't keep poking with "but, it has too" arguments. The smart thing is to ask why, then understand the why. If you come up with a way around it, the only way to prove it is to build it. And let me tell you, it's far better to build it and watch it fail by myself. The problem with a public failure is that if you trumpeted it first, the rest won't take you seriously afterwards until you come up with something truly new.

:)ensen.



Those who claim to be making history are often the same ones repeating it.

Video of my trike
http://www.youtube.com/watch?v=MdSLRD_2vzc
Photos of my trike
http://www.flickr.com/photos/purplepeople/

Edited by - purplepeopledesign on 01/30/2017 14:36:59
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Speedbiker
human power expert

USA
3756 Posts

Posted - 01/30/2017 :  15:48:48  Show Profile  Reply with Quote
There is so muchnyou can do without delving into the fringe. People have been rearranging bikes since the 1800s. There is little you can try that wasn't tried before. Possibly decades ago. We now know what works. Now, refine it. I remember when 23 mph would win most nonfaired bent races, 32 faired. Now you need 30 and 40+! That was accomplish thru experimentation, yes, but not crazy fringe stuff. I'm currently involved in 2 projects chasing the elusive 30mph on 200 watts goal. And that's with a bike for the road. No, it won't be rear steered, dual steered, or pivoting back wheel. But it does have a very high level of refinement. I'm sorry if that level of design is beyond people here who wish to experiment. But I feel there is nothing formus in the fringe. If you do believe it, build it! But don't write endless posts about what you think you know, but will never prove. Less BS, more building!
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/30/2017 :  22:13:24  Show Profile  Reply with Quote
quote:
Originally posted by purplepeopledesign
I learned a long time ago that when mentor-types start telling stories, it's best to listen. When you come up with the new sliced bread and they say it won't work, I don't keep poking with "but, it has too" arguments. The smart thing is to ask why, then understand the why. If you come up with a way around it, the only way to prove it is to build it. And let me tell you, it's far better to build it and watch it fail by myself. The problem with a public failure is that if you trumpeted it first, the rest won't take you seriously afterwards until you come up with something truly new.

:)ensen.




But that's the whole point! I've asked if that was tried before, and if it was - what was the result, so I can understand it myself.
A reply 'no, it will not work' does not actually help anyone understand anything - this is just speaking from authority to accept something on faith. I don't do 'faith'. I do experiments.

Anyway, I trust Speedbiker's experience that it "will not work". Question is, 'will not work FOR WHAT"? Would it help going really fast? That is not my point in the slightest, I have other things going for that. I want to know will it help with slow-speed minimum turning circle reduction, for instance.

quote:
Originally posted by Speedbiker
I'm currently involved in 2 projects chasing the elusive 30mph on 200 watts goal. And that's with a bike for the road. No, it won't be rear steered, dual steered, or pivoting back wheel. But it does have a very high level of refinement.


That's entire problem. We have different design goals, and something that 'does not work' for you might in fact 'work' for me.

Can someone, please, explain me what EXACTLY was done, what EXACTLY it accomplished and how EXACTLY it failed?

If Speedbiker is too busy building his refined bikes so he cannot find time to educate me, maybe you can, purplepeopledesign?

Edited by - Balor on 01/30/2017 22:18:34
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purplepeopledesign
recumbent guru

Canada
685 Posts

Posted - 01/30/2017 :  23:29:07  Show Profile  Reply with Quote
Any steered rear wheel tends to put any vehicle (of any number of wheels) into immediate oversteer. You can see this if you build any small model, even in your imagination. So looking at a bike with 50/50 weight distribution going in a straight line. Now steer the front wheel, creating a turn radius for each wheel. As it goes in the circle, the front wheel is pulling the CoM towards the center of the turn radius. If you let go of the steering, the CoM pulls back and the vehicle tries to straighten out. Now take the same bike and steer the rear wheel. As the bike goes in a circle, you see the rear wheel pulling the CoM towards the outside of the turn. If you let go the steering, the CoM pulls back and tries to decrease the turn radius... a form of negative feedback. Whether there is traction on any wheel, oversteer or understeer doesn't matter since the the difference is that one wants to continue in a straight line and the other tries to do the opposite. This is why forklifts must not be driven in reverse at speeds that can overpower the steering, and why many fork drivers use reverse to traverse the length of the warehouse. This is also why the original Honda 4WS system would first parallel steer the rear wheels for some large angle before countersteering them. It is also why that Krankicobra weaves. If not for the rider using the front steering to compensate, the rear wheel would throw it into a spin. Positive, negative or zero trail only affects the magnitude of the problem, but doesn't make it go away... as in this video.

https://www.youtube.com/watch?v=_qHP6oJlXnk

:)ensen.

Those who claim to be making history are often the same ones repeating it.

Video of my trike
http://www.youtube.com/watch?v=MdSLRD_2vzc
Photos of my trike
http://www.flickr.com/photos/purplepeople/
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/30/2017 :  23:53:52  Show Profile  Reply with Quote
quote:
Originally posted by purplepeopledesign

Any steered rear wheel tends to put any vehicle (of any number of wheels) into immediate oversteer. You can see this if you build any small model, even in your imagination. So looking at a bike with 50/50 weight distribution going in a straight line. Now steer the front wheel, creating a turn radius for each wheel. As it goes in the circle, the front wheel is pulling the CoM towards the center of the turn radius. If you let go of the steering, the CoM pulls back and the vehicle tries to straighten out. Now take the same bike and steer the rear wheel. As the bike goes in a circle, you see the rear wheel pulling the CoM towards the outside of the turn. If you let go the steering, the CoM pulls back and tries to decrease the turn radius... a form of negative feedback. Whether there is traction on any wheel, oversteer or understeer doesn't matter since the the difference is that one wants to continue in a straight line and the other tries to do the opposite. This is why forklifts must not be driven in reverse at speeds that can overpower the steering, and why many fork drivers use reverse to traverse the length of the warehouse. This is also why the original Honda 4WS system would first parallel steer the rear wheels for some large angle before countersteering them.



Up to this point I agree with you completely, in fact see my reply to Tony at his FWD-RWS thread.

quote:
Originally posted by purplepeopledesign
It is also why that Krankicobra weaves.


Umm... no. It weaves because the rider is inexperienced and this is a goddamn Python - MBB design that is notoriously unstable by itself even if you do not put your BB at the level of your head.

There are two videos in original post, similar self-steering rear end on an other bike does not prevent the rider from effortlessly moving in a straight line and doing figure eights - because he has Python mastered, and even claims greater stability... which, again, I don't take on faith, but I do trust my own eyes.

"As the bike goes in a circle, you see the rear wheel pulling the CoM towards the outside of the turn. If you let go the steering, the CoM pulls back and tries to decrease the turn radius... a form of negative feedback. "

Like I already stated, rear self-steering is drastically different from 'forced rear steering' because it does NOT pull the COM anywhere, it only minimizes sideslip forces by realigning the wheel. The turn itself is initiated and maintained by a front wheel, but I think removing resistance to turn that rear wheel provides should positively affect minimum turning radius, which should be really beneficial for a bike with long wheelbase and limited steering lock.

Again, can you please describe what exactly have you tried and how exactly did it fail?
If you tried 'just rear steer' - this is different. Even if you tried all wheel steer with 1:1 ratio - this is also different.

Edited by - Balor on 01/31/2017 00:02:04
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purplepeopledesign
recumbent guru

Canada
685 Posts

Posted - 01/31/2017 :  02:16:48  Show Profile  Reply with Quote
Your goddamned Python is only half the problem. Remove the loose rear wheel and it will become as stable as a Python. The rider in that video is not going fast enough to activate the dreaded negative trail. Slow enough and with the weight on it, the Python will mostly steer straight and provided it is built with some precision, the inner ear decides the balance. Add the pivoted rear wheel and it flops around enough that the rider must compensate. So, if I had to guess, I'd say that video shows just how much skill the rider really has.

IIRC, Dan wanted to try a bunch of stuff so Paul built variable head angle (slotted plates and bolts) with zero offset fork. I no longer recall the exact results, but I know they tried zero, positive and negative head angles. I think zero was hardest to get moving. Positive (aimed ahead of contact) was better in straight line but would immediately oversteer with anything resembling a turn, and negative would start to oscillate with any speed. Then they put slots on the fork to move the hub around and depending on where they put the axle sometimes the handling would reverse. I remember that none of it was rideable to the point where any of us was confident it could be paraded, never mind raced. The only memory I'm sure of now is that it didn't work.

Here's where you think self-steer is different and I don't. First, look up free-to-caster. Same thing except typically the front wheel, like a shopping cart. There are some experiments with it at the Yahoo Tilting Group.

Of every combination, nothing worked. You say that handlebars make a difference. But, if the loose rear wheel were to find it's way then we could have ridden it... possibly even no hands. But in some combos we could barely get moving, never mind letting the rear wheel wander on its own. Even when we could get rolling, at no point was anybody every confident enough in stability to let it go on it's own, and trust me on this, I'm willing to let a machine float on it's own if I think it might do it. Letting a loose rear go might be easy enough to try on a stable multi-wheel machine. In fact, just push a shopping car in reverse. But not that two wheeler.

So, now you have my why. Still disagree? Now you have to show me to prove it. And because this is a forum and not just cafe, you have to show everyone else too.


:)ensen.

Those who claim to be making history are often the same ones repeating it.

Video of my trike
http://www.youtube.com/watch?v=MdSLRD_2vzc
Photos of my trike
http://www.flickr.com/photos/purplepeople/

PS: Edited for spelling and clarity.

Edited by - purplepeopledesign on 01/31/2017 02:24:42
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/31/2017 :  04:34:50  Show Profile  Reply with Quote
quote:
Originally posted by purplepeopledesign
IIRC, Dan wanted to try a bunch of stuff so Paul built variable head angle (slotted plates and bolts) with zero offset fork. I no longer recall the exact results, but I know they tried zero, positive and negative head angles. I think zero was hardest to get moving. Positive (aimed ahead of contact) was better in straight line but would immediately oversteer with anything resembling a turn, and negative would start to oscillate with any speed. Then they put slots on the fork to move the hub around and depending on where they put the axle sometimes the handling would reverse. I remember that none of it was rideable to the point where any of us was confident it could be paraded, never mind raced. The only memory I'm sure of now is that it didn't work.



Wait-wait. You are talking about FWD (with fixed wheel)/RWS here, or is it all wheel steer, or some combination thereof?

Edited by - Balor on 01/31/2017 04:39:01
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Tom Schneider
recumbent enthusiast

112 Posts

Posted - 01/31/2017 :  05:25:53  Show Profile  Reply with Quote
Sometimes (many times?) KIS needs to be used. Last S was dropped to keep it simple.

Tom
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/31/2017 :  05:40:30  Show Profile  Reply with Quote
quote:
Originally posted by Speedbiker
If you think you have a new idea, BUILD IT and see. But please stop asking us to verify your fringe ideas.



Well, that is exactly I was intending to in the first place. Than you came along and basically told 'don't do it, it will not work', and provided no reasons beyond "because conventional geometry is best". And since when recumbents even have a 'conventional geometry', anyway? DFs have - because UCI. There are many very distinct recumbent designs, which one are you talking about?

And what is 'fringe' when it comes to recumbent design, anyway? If you ask that question to 'elite cycling athletes' 100 out of 100 would say that fringe is 'anything that is not UCI-compliant'.
There are no 'fringe' designs, only designs that do not work in full spectrum of conditions you may meet while bicycling. 'Python' is exactly one of those designs, because it will never be fast, and I know that.

Anyway, now I'm conflicted - I find idea appealing based on my admittedly limited understanding on the principles behind it, but I don't want to build something that patently does not work... yet, I've been given no reasons why it should not work!

So I am asking again:

Did anyone actually try to build a rear caster, FWD-FWS - not RWD, not AWD, exactly rear caster and how it performed OR can explain what might be wrong with it at theoretical level, just like Jensen did with explaining RWD design... which he did an excellent job with btw, but unfortunately, it is irrelevant to the discussion?

By the way, since Honda rear self-steered prototype motorcycle was 'not liked' by test pilots, I am fully prepared that I will not like it either, but I will keep an open mind - which test pilots were unlikely to. After all, 'not liking something' and 'refusing to ride this dangerous thing because it wants to get me killed' are different things, and there are people refusing to ride Cruzbike MBB with 'quite conventional' geometry with latter complains, while Maria Parker quite successfully finished RAAM on one!
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Jerry
recumbent guru

USA
981 Posts

Posted - 01/31/2017 :  06:02:07  Show Profile  Reply with Quote
quote:
Originally posted by Tom Schneider

Sometimes (many times?) KIS needs to be used. Last S was dropped to keep it simple.

Tom



Ha, ha, that made me laugh. I use the KISS method and sometimes the SWAG method.
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purplepeopledesign
recumbent guru

Canada
685 Posts

Posted - 01/31/2017 :  06:57:40  Show Profile  Reply with Quote
Standard geometry that Thom speaks of is front fork steering. Head angle between 69 and 80 with trail between 0 and 3 inches. You see this on UCI bikes, motorcross, low racer, high racer, delta trikes, FIM, drag bikes... everything. Drive doesn't matter. All those machines will coast downhill with stability.

For the tests, they didn't even bother with drive. Just rear wheel steer. Sit, keep feet flat on the ground and someone else pushes. If it will roll, the rider tries to lift his feet. If the design will coast with stability for any useful distance, then we can decide how to pedal it.

Irrelevant?

One method taught me by my mentor is to also analyze each component separately. So, if a pivoted rear wheel will not be stable then adding it to any machine must automatically add instability. If you start with a Python like above, you start with a system that is already unstable above ~15 kph. Now add instability from a rear caster and you get a floppy bike. When a highly-skilled test pilot has trouble with control, it is a safe bet that regular people will have much more trouble.

One last thought, then I'm going to have my coffee: I have my signature line because I used to make those silly claims. Then I learned that almost always, someone beat me to it, usually by decades. Then, one day, I realized why all university programs start with basics. If a student cannot understand past work, they will not understand the future, let alone discover it.

:)ensen.


Those who claim to be making history are often the same ones repeating it.

Video of my trike
http://www.youtube.com/watch?v=MdSLRD_2vzc
Photos of my trike
http://www.flickr.com/photos/purplepeople/

Edited by - purplepeopledesign on 01/31/2017 07:07:21
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Garrie L Hill
human power supergeek

USA
1692 Posts

Posted - 01/31/2017 :  06:57:45  Show Profile  Reply with Quote
M&M's

Garrie "carbon based lifeform" Hill
HPRA Co-Dictator of the East
for pics of some of my time and money sucking projects
http://s58.photobucket.com/albums/g277/cfbb/
and videos
http://vimeo.com/5513519


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warren
human power expert

USA
6117 Posts

Posted - 01/31/2017 :  07:56:16  Show Profile  Visit warren's Homepage  Reply with Quote
Great ideas that don't work well:
http://www.recumbents.com/wisil/misc/great_ideas.htm

Yes these things have been tried over and over and there are reasons why they are not used. Usually this means unintended deceleration incidents (UDI).
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/31/2017 :  08:52:39  Show Profile  Reply with Quote
quote:
Originally posted by Speedbiker

Balor, thanks for the long, rambling waste of bandwidth. Do what you want, which usually means 99.8% arguing online and .2% actually doing something. To each his own.



It takes at least two to argue online.

quote:
Originally posted by purplepeopledesign

For the tests, they didn't even bother with drive. Just rear wheel steer. Sit, keep feet flat on the ground and someone else pushes. If it will roll, the rider tries to lift his feet. If the design will coast with stability for any useful distance, then we can decide how to pedal it.

Irrelevant?



Was the front wheel fixed?

quote:
Originally posted by purplepeopledesign
One method taught me by my mentor is to also analyze each component separately. So, if a pivoted rear wheel will not be stable then adding it to any machine must automatically add instability. If you start with a Python like above, you start with a system that is already unstable above ~15 kph. Now add instability from a rear caster and you get a floppy bike.



That is exactly why I do not consider Python example very conclusive either way - because I will not be riding one, and he certainly cannot test stability by a high-speed downhill run, you need an experiment with controlled variables.

quote:
Originally posted by purplepeopledesign
When a highly-skilled test pilot has trouble with control, it is a safe bet that regular people will have much more trouble.



Yea, this is exactly why I began my tinkering with MBB. While it does make me much faster uphill (tested time and time again, quite objectively), it IS hard to learn and remains hard to control even after you get used to it, and in some cases obstacle avoidance that you can perform on any other design would be impossible on MBB due to huge steering inertia.
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Balor
recumbent guru

Russia
514 Posts

Posted - 01/31/2017 :  09:34:47  Show Profile  Reply with Quote
quote:
Originally posted by warren

Great ideas that don't work well:
http://www.recumbents.com/wisil/misc/great_ideas.htm

Yes these things have been tried over and over and there are reasons why they are not used. Usually this means unintended deceleration incidents (UDI).



Well, it also states: Don't design in a vacuum!
This is exactly what I'm NOT doing :). I'm trying to get feedback on my design idea, but so far information is inconclusive.

It seems you, along with Jensen (and likely Speedbiker, too), confusing RWS (which I know does not work, *know* why it does not work and will never truly work and hence will not attempt doing) with SELF-steered rear.

The bike is steered with front wheel quite conventionally, what self-steered rear should do is to remove negative (out of the turn) slip angle that does nothing but slows you down and robs rear wheel of centripedal force provided by camber thrust of the tire.

P.S.
http://www.recumbents.com/wisil/brown/steeringandride.htm

"The difference between the direction these patches are pointing and the way the wheel is pointing is called the ’slip angle’. As cornering force increases, slip angle increases until it reaches a point of maximum cornering force. Beyond this point, the tire will break free and slide. The maximum cornering the bike can achieve will be if it is balanced so that both tires meet their limit at about the same time. Having the rear wheel skid slightly before the front gives up a tiny bit of cornering power, but gain in control and “feel” is more than worth it.

Remember to think in terms of balance. Tire width can be used to help tune the steering."

While he is right that tires may fine-tune the steering and narrower tires give more cornering power, it is not about slip angle (this is from steering with your handlebars at low speeds and auto tires), but camber thrust.

I've tried emailing him recently, but go no answer. He is allright, I hope? Notify him that he needs to make a minor correction to his treatise.

Edited by - Balor on 01/31/2017 09:59:50
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