www.recumbents.com - Carp Front End
www.recumbents.com
www.recumbents.com
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password
 All Forums
 www.recumbents.com
 Technical / Bike Building
 Carp Front End
 New Topic  Reply to Topic
 Printer Friendly
Previous Page | Next Page
Author Previous Topic Topic Next Topic
Page: of 10

warren
human power expert

USA
6470 Posts

Posted - 07/07/2016 :  12:44:17  Show Profile  Visit warren's Homepage  Reply with Quote
I saw a video of an Akira style feet-forward motorcycle and think that the front fairing may work well for this bike. It has hemispherical wheel covers on the front wheels, which seems weird, but they allow a nice transition into the front hardshell fairing. Almost like a ball and socket.
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 07/07/2016 :  14:16:13  Show Profile  Visit alevand's Homepage  Reply with Quote
If the hemisphere were the radius of the wheel, then it could be fixed, as it would steer freely inside.

The fabric stretch only allows about +/- 35 degrees steering. I haven't encountered a windy day yet, I suspect it would get scary at speed..

C:
Tony Levand
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/28/2019 :  08:32:21  Show Profile  Reply with Quote
I've been considering VPS in my "delta quad" project - I need plenty of suspension (lots of sag actually) to prevent losing steering in case front wheel falls into a big pothole.
However, "brake steer" phenomenen is off-putting, and zero or negative fork flop is absolutely essential.

So, VPS can be "simplex" like Rohorn's moto, or "Duplex" with virtual pivot points above and below.
If you make "Duplex" steering with upper "trapezoid" having higher lateral axis displacement in a turn, shouldn't it compensate for same displacement at contact patch (by tilting steering axis a bit to the other side compared to "simplex" steering), leading to (near)zero displacement and zero brake steer if you it just right?

It will result it effective "negative steering" angle I presume, but I'm not a stranger to negative steering angles :) just add some negative offset to get enough trail... or you can compensate by having fork with some positive rake angle.

Btw, what's up with Robert's post? They are entirely missing both from this forum and bentrider.

Edited by - Balor on 09/28/2019 09:55:08
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 09/28/2019 :  09:34:23  Show Profile  Visit alevand's Homepage  Reply with Quote
Yes.

The simplex magnifies the effect, especially with high mounted links. The upper arms in the duplex would be in tension during braking, thus stable even with a wider trapezoid. Best to have pivots as close as possible, without hitting the spokes.


C:
Tony Levand

Edited by - alevand on 09/28/2019 09:42:00
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/28/2019 :  10:06:36  Show Profile  Reply with Quote
quote:
Originally posted by alevand

Yes.

The simplex magnifies the effect, especially with high mounted links. The upper arms in the duplex would be in tension during braking, thus stable even with a wider trapezoid. Best to have pivots as close as possible, without hitting the spokes.


C:
Tony Levand



Yea, I've played about in CAD and finally got my head around this system. Wider "tranpezoid base" is good too, and helps with steering lock.
Btw, what's wrong with mounting vps fork pivots as close to the ground as possible (just so long as frame attachment points don't contact the ground with maximum suspencion compression, provided you have any)? Way below wheel axles.

Will make the system very rigid, eliminate brake chatter and will still allow for decent steering lock just like mounting it way above wheel axles... would not fit your fairing?
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/28/2019 :  15:29:38  Show Profile  Reply with Quote
quote:
Originally posted by rohorn

quote:
Originally posted by Balor


Btw, what's up with Robert's post? They are entirely missing both from this forum and bentrider.



Too many keyboard experts giving out bull$hit advice. I asked Bryan to delete my account and posts there - he was kind enough to do so. With very few exceptions, I don't want to be even remotely associated with the feeble minded/bodied there.

Just for your amusement:

A great article on diamond quad configurations is in the May 2008 issue of Racecar Engineering - I read it when it came out - sorry I didn't scan it: https://www.zinio.com/gb/racecar-engineering/may-08-i81533

In the mean time, my $0.02 on what I've been doing: https://www.odd-bike.com/2019/07/guest-post-robert-horns-rohorn-two.html





Thanks! In fact, I've been reading that very article (on your moto) just now... I am not that much into moto stuff, too clumsy and I need every bit of execise I can get, but it all makes total sense. Finishing quote from Kevin Cameron is all too true (very moving).
I'll make sure to buy that article you mentioned, I suspect there are "undewater stones" to this system I cannot fanthom yet, especially if combined with leaning which might or may not be a good idea - at least Pulse existed and was quite rideable, but you cannot make new things without taking some risks.
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/28/2019 :  16:10:17  Show Profile  Reply with Quote
Thank you! Well, pretty much what I suspected - not as good as conventional quad (still better that tricycles though, they were not even contemplated) when it comes to driving kinematics but potentially much better aerodynamics and something they did not pay much attention as well - much easier to make using "off the shelf" bicycle components.

The leaning version is exactly what I'm trying to make (a free leaner with tilt lock and damping), and exatly like it was written I'd be needing lots of travel on "centerline" wheels, and according to my preliminary mockup in Shook's shell desigh/CAD I can have enough (10+cm) travel OR conventional head tube but not both, that will greatly limit view over the fairing even with a 20" wheel and I am unwilling to go lower.
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/28/2019 :  16:25:21  Show Profile  Reply with Quote
By the way, do I need to worry about "brake steer" if I am to make steering geometry closer to yours?
As I understand, Levand's implementation was somewhat compromised by high link attachment points, amplifying lateral wheel displacement... and your moto MUST deal with high speed braking reliably but you also have AWS, and his bent didn't - and I am unlikely to have it as well for now, though it is very tempting, but I have to get other systems working reliably first.

Going full duplex might solve it in theory, but more complex and bulkier, plus might result in yet unforeseen consequenses - fun to try if was not considered before, but I'd hate to repeat something that was already tried and found wanting.

Edited by - Balor on 09/28/2019 16:37:39
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  03:43:31  Show Profile  Reply with Quote
*sigh* Levand seemed to know exactly what he was doing, and did note that his brake steer phenomenon is mostly due to high pivot attachment points, but it was a result of his specific design constraints. Changing "tried and true" formula might have worked, and might not. That's how progres is made, by trial and *error* - even if you have "aerospace" budget.
Considering everyone else to be idiots might be intellectually satisfying in short term, but likely lead to misery and depression to the long run... but what do I know?
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 09/29/2019 :  06:46:24  Show Profile  Visit alevand's Homepage  Reply with Quote
I see you've recovered from your race crash, hope your doing well.

Yes, the constraint was replacing the fork on a mono tube frame and retaining enough maneuverability to ride down the steep curved path behind my house, thus the high mounted links. If it were limited to the small steering angles needed on a flat race course it would still be on the bike. I changed it after I went uncontrollably down the hill and skinned the bark off a tree with the linkage "wing" appendage. I could easily ride no hands, though. A space frame is best suited for the VPS as in all of Rohorn's designs. Yes some experimentation is need to for the duplex, maybe that's why the OEC design is the way it is. The VPS-MBB bike had no such problems, but then again, steering was limited and it had low mounted pivots very close to the spokes. The problem there was the MBB at high speeds was just scary. It felt much better if I unclipped.

The only thing VPS does for you is to remove the head tube, thus a larger wheel can be fit in the fairing, or a lower fairing on front of a LWB bike without the head tube sticking out, otherwise its not worth the effort. So Oleg, if you are building a unfaired bike to go though and dodge potholes, maybe a standard fork would be better, unless you want the "wow" factor.

C:
Tony Levand

Edited by - alevand on 09/29/2019 07:59:46
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  08:22:53  Show Profile  Reply with Quote
quote:
Originally posted by alevand

I see you've recovered from your race crash, hope your doing well.

Yes, the constraint was replacing the fork on a mono tube frame and retaining enough maneuverability to ride down the steep curved path behind my house, thus the high mounted links. If it were limited to the small steering angles needed on a flat race course it would still be on the bike. I changed it after I went uncontrollably down the hill and skinned the bark off a tree with the linkage "wing" appendage. I could easily ride no hands, though. A space frame is best suited for the VPS as in all of Rohorn's designs. Yes some experimentation is need to for the duplex, maybe that's why the OEC design is the way it is. The VPS-MBB bike had no such problems, but then again, steering was limited and it had low mounted pivots very close to the spokes. The problem there was the MBB at high speeds was just scary. It felt much better if I unclipped.

C:
Tony Levand



Hate to sound like a broken record, but problem of MBB is 'two-fold' wheel flop and steering inertia, and had nothing to do with VPS.

If you dedicate a lot of time and effort (and blessed with good kinaestetics) you will learn to steer with your legs, that don't suffer from limited leverage... and that is likely why MBB topic is so polarising.
Some people find 'leg steering' easy, some (like, say, me) never get it fully.

On my '90+' deg bents I've minimised steering inertia by making boom as short as possible and nullified both kinds of flops... still not exactly as effortless as RWD design, but tons better.
Only problem left is tired arms on long (100+) km rides.

If you'had made the boom significantly shorter, and went for positive, not negative tiller, I bet you'll find it much tamer - *most* of flop problems are dealt by VPS.

But it would be a very different bike, likely one you'll not be interested to make.

As for VPS plus suspension, I think modifying existing MTB forks with VPS attachment points at dropouts like on Horn's first VPS bike will be the way to go.

I think you can even simply add 35mm clamps (or newfangled 35mm diameter stems) on the lowers, hence possibly a 'no-weld' project even.
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  08:36:46  Show Profile  Reply with Quote
quote:
Originally posted by alevand
The only thing VPS does for you is to remove the head tube, thus a larger wheel can be fit in the fairing, or a lower fairing on front of a LWB bike without the head tube sticking out, otherwise its not worth the effort. So Oleg, if you are building a unfaired bike to go though and dodge potholes, maybe a standard fork would be better, unless you want the "wow" factor.

C:
Tony Levand



Well, 'beheading' the steering axis is the whole point.
Here is preliminary pics (shook's Shell Design program):




As you see, there is room for head tube, suspension travel but not both.
On a 'diamond quad' design you have to be wary of of either front or rear wheel 'seesawing' over central wheels if either falls into a pothole, hence plenty suspension travel is essential.

I think I need to create a separate thread for this project here, but it is still in 'alpha' stage, I'm considering options.

Btw, VPS is actually pretty good for other reasons - fork flex is nearly eliminated, hence better steering with lighter components, better suspension kinematics.
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 09/29/2019 :  09:16:06  Show Profile  Visit alevand's Homepage  Reply with Quote
HI, There is a problem with the diamond quad, in that it will scrub on turns. The four wheels need a common point (Ackerman) to steer about. Usually the out riggers are lightly loaded with only one in ground contact at a time. As with a trike, it would be harder to avoiding potholes with 3 tracks. I dont know if castors would work here. A quad may be better with 50/50 weigh distribution, the four wheels could be the same size as the rear shown. http://pedalcarracing.info/

On my bike the head tube protrudes, Ive found that the smallest nose is best on cross winds:

C:
Tony Levand

Edited by - alevand on 09/29/2019 09:28:21
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  10:03:03  Show Profile  Reply with Quote
It will if all wheels are fully loaded BUT Pulse that I've got idea from have them very lightly loaded and they are used only in turns (will still scrub, but that's manageable).
http://www.autocycles.org

Using a castor was suggested already, but I have no idea how it will interact with lateral weight transfer and resulting side loads.

Note staggered side wheels - that's because I want to use iLean for side wheels, and make me a free-tilter. Ilean deals with tilting and serve as a suspension of sorts, with tilt lock I'll be able to enter/exit and stand at red lights unassisted and with out bomb bay doors, and by installing a 'tilt damper' I will (at least I think I will) have balancing kinematics of a bike with much higher CG (leans slowly - wider window for steering corrections, resists wind gusts) with a much lower CP.

Having a BB concentric to front hub is very tempting will solve a LOT of problems from weight distribution and wheelbase perspective, but combining it with suspension and adequate Q-factor is challenging to say the least.

Something to consider:
https://protobikes.org/my-bikes/

https://protobikes.files.wordpress.com/2012/12/hpb-crop.jpg

Edited by - Balor on 09/29/2019 10:09:53
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 09/29/2019 :  10:59:40  Show Profile  Visit alevand's Homepage  Reply with Quote
I-lean was dropped because of tire scrub. You may find yourself beached, with the drive tire in the air.

C:
Tony Levand
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  11:59:44  Show Profile  Reply with Quote
quote:
Originally posted by alevand

I-lean was dropped because of tire scrub.


Like on the Pulse, suspension sag will have to be manipulated JUST right so tires simply lightly touch the surface. This way they contribute almost nothing to rolling resistance and there is little scrab - they simply 'move out of the way' and provide some tilt damping via moto steering damper.

quote:
Originally posted by alevand
You may find yourself beached, with the drive tire in the air.


Actually, much worse is to find your steering hovering in the air! Hence, again, requirement for front/rear suspension with lots of sag.

I'll make an unfaired prototype first and see how bad is that in practice.
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  14:12:20  Show Profile  Reply with Quote
And Robert's posts are gone again. *sigh*
Well, I should be the last person to complain about people that dabble in 'reinventing the bike' having eccentric personalities, or I'll be missing a log in my own eye...
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 09/29/2019 :  15:43:36  Show Profile  Visit alevand's Homepage  Reply with Quote
Well, he probably got fed up deleted his account again for the next 6 years because of us idiots, he's done some cool stuff. Looks like he's putting hub steering on the rear wheel for thrust vectoring..

Adleweder velomobile has had a virtual pivot in the steering for years..

C:
Tony Levand
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/29/2019 :  17:39:57  Show Profile  Reply with Quote
Well, I freely admit being an idiot because it took me two years to finally get my head around virtual pivot steering...
And I *still* don't get what benefit 'simplex' steering has over duplex steering except, of course, being less complex mechanically and simpler suspension setup (which is damn handy, but unrelated to question at hand)? It does not solve any 'weirdness' related to OEC Duplex steering, but actually exacerbates them - if by 'weirdness' we mean lateral wheel displacement.

If this page is of any indication:

https://cybermotorcycle.com/gallery/oec/OEC-1930-Duplex-Steering.htm

Duplex had a metric ****ton of trail due to a some 'rake angle' plus lots of 'virtual negative offset' but little flop - which explains why it was so stable that it resisted steering input.
If you put, just like Robert said, link attachments closer together for less 'virtual negative offset' and lateral contact point displacement and leave rake angle at 72deg, you'll get pretty much the same kinematics as Robert's moto but with LESS lateral wheel displacement unless you'll have lower link attachment points at ground level, right?

And by manipulating front and rear trapezoids, you can eliminate it altogether, hence you'll not be needing a ton of trail to counter brake steer, though Robert claims NOT to have any problems with brake steer...
*shrugs*
Maybe I'll be able to afford a test mule to test this 'simplex vs duplex' hypothesis, I likely missing something.
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/30/2019 :  01:20:22  Show Profile  Reply with Quote
Doh! I *am* an idiot - this 'lateral wheel displacement' is actually what constitutes trail due to negative offset! I have absolutely same dynamics on my MBB!
And I don't remember *any* brake steer ever with negative offset of 6cm... So, will it simply get worse with more displacement, or I am missing something more and this brake steer is due to steering axis itself shifting about, especially if you have to consider 'simplex-specific' "tilting" if you look at it from the front?
After all, shouldn't LWBs with tons of *positive* offset get same brake steer, but resulting in steering 'self-centering' in a turn?

Edited by - Balor on 09/30/2019 01:42:59
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/30/2019 :  03:59:03  Show Profile  Reply with Quote
Ok, I finally get it (I think):
Brake steer moment is due to lever arm between *instantaneous* virtual point location for a *given steering angle* and tire contact patch.
On a conventional steering, negative offset actually results in *self-centering* brake steer moment, and positive offset - *turn in* moment.

On VPS though steering axis itself shifts as you steer, and a LOT, so while initially we have negative offset and a ton of trail, it seems as though the more we turn, we get what amounts to massive positive offset and negative trail (and negative flop)?

On the other hand, that's pretty neat actually!
At high speeds where large trail force is essential steering is done by very small steering angles, trail stays positive, brake steer moment arm - extremely short, all is well.
At larger steering angles that are only in effect at slow speeds the bent behaves like a Python with negative trail and negative flop that provides stabilizing force instead. That's the best of two worlds! And *exactly* what I need for my 'diamond quad'!

You cannot have that with a conventional steering tube.... well, admittedly, you *can* have same 'positive trail/negative flop' pair with a negative steering angle, but to get enough negative flop with negative angle you need truly massive negative offset, plus steering tube that is sticking 'in the wrong direction' making things rather awkward.

Btw, if your bent had more forward weight bias, negative flop force will likely overcome brake steer force and you would not have needed massive trail. Rohorn's moto have 50/50 weigth distribution and much larger weight, hence small wonder he has no brake steer woes... not to mention only small steering angles most likely.

Tricky stuff! Ok, now how to combine it with suspension and utilise it to best effect...
Go to Top of Page

alevand
human power expert

USA
3541 Posts

Posted - 09/30/2019 :  06:09:34  Show Profile  Visit alevand's Homepage  Reply with Quote
Brake force is proportional to weight. Positive trail causes the contact patch to move to the outside of the turn, the instantaneous center moves to the outside with trailing links. There is a magical point, depending on geometry, where you can ride in circles with no hands. Oodles of trial is nice, except with a fairing in a cross wind makes it unmanageable.

C:
Tony Levand
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/30/2019 :  06:46:24  Show Profile  Reply with Quote
quote:
Originally posted by alevand

Brake force is proportional to weight. Positive trail causes the contact patch to move to the outside of the turn, the instantaneous center moves to the outside with trailing links. There is a magical point, depending on geometry, where you can ride in circles with no hands. Oodles of trial is nice, except with a fairing in a cross wind makes it unmanageable.

C:
Tony Levand




Yea, I've heard that before... but why though? Why 'trail' makes balancing harder on a fully faired singletrack vehicle in a crosswind?

Here is post from BHPC:

"A surprisingly important part of handling is the relation between CP and trail. If it is fairly forward, and you have considerable trail, the bike will castor with the wind and get blown around. I had to moderate the trail on Oscar. With less the steering was very light, but the bike was only gently pushed away from the wind, and naturally corrected itself. This makes sense with the work Matt Weaver did. Next version (if I ever build it) will have the front wheel a bit further forward and should be able to cope with a bit more trail. "

I've failed to extract more information about this aspect and what 'work' by Matt Weaver he alluded to.
He used to have a site that is now dead, I presume?

Edited by - Balor on 09/30/2019 06:49:06
Go to Top of Page

Tom Schneider
recumbent enthusiast

132 Posts

Posted - 09/30/2019 :  09:08:59  Show Profile  Reply with Quote
quote:
Originally posted by alevand

I-lean was dropped because of tire scrub. You may find yourself beached, with the drive tire in the air.

C:
Tony Levand



Tire scrub could be reduced or eliminated by using a real differential between the 2 cranks so they both are in the same direction. The function would be the same i-lean.

Tom
Go to Top of Page

Balor
recumbent guru

Russia
750 Posts

Posted - 09/30/2019 :  09:14:07  Show Profile  Reply with Quote
quote:
Originally posted by Tom Schneider

quote:
Originally posted by alevand

I-lean was dropped because of tire scrub. You may find yourself beached, with the drive tire in the air.

C:
Tony Levand



Tire scrub could be reduced or eliminated by using a real differential between the 2 cranks so they both are in the same direction. The function would be the same i-lean.

Tom



You sure? I think they will function the same - because of effective track width changing while leaning.
But it would not work as 'kind of suspension' for 'speed bump' types of obstacles anymore. Not as simple to make as well.
Go to Top of Page
Page: of 10 Previous Topic Topic Next Topic  
Previous Page | Next Page
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
www.recumbents.com © 2019 www.recumbents.com Go To Top Of Page
Snitz Forums 2000