FWD MBB with 100 degrees steering angle and negative offset.

[Balor]

First, a few sketches to to show that it works at least on paper:
With 'superman' tiller:

With USS:

(Sorry, I'm a total n00b when it comes to CAD)

A bit of history:

I have a 'Zockraish' clone myself, it has steering angle between Zockra and Vendetta - 65. I like it, and I used to pedal feedback very quickly and now do not notice it at all. However, it was not tailor-made for me and a bit too small, so I wanted to order a custom one (due to me being a relatively poor Russian, ordering Cruzbike is NOT an option, or I'd do it, of course).

After reading this articles:

http://www.recumbents.com/wisil/brown/alltogether.htm
http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

I thought that going like 80-85 angle might be a good idea, to minimize wheel flop.

But than I've seen this:

http://www.fastfwd.nl/index.php?id=35

And I've been struck with an idea:

What about 100 steering angle? That is going to make heavy (hence - 'floppy') front triangle completely self-stabilizing up to inclines of 10 degrees. And situation is actually exacerbated by weight of legs, eventually you learn to correct for that, but it takes effort.

Of course, such an angle is tailor-made to actually maximize pedal feedback, but why not? I think bar-pulling is more effective than pushing against the seat - I definitely output more power this way.

After mulling about, I've understood that it might have much less pedal feedback than it might appear too:

Pedal feedback depends on:

• Head tube angle (in case of Zockra in is nearly parralel to pedal force vector, hence almost no feedback)
• Q-factor
• Boom length - acting as lever.

So, if my bike is to have double steering input due to head angle, having boom lengh of nearly 1/3 of Vendetta would likely make pedal feedback LESS than on Vendetta!

Also, the shorter boom is, the less inertia it has (remember, moment of inertia of a pendulum is mR^2, and since most of the mass of the front triangle is concentrated at end of it - feet, cranks, etc - r^2 is 1/9!), hence the steering would be much quicker and lighter.

Of course, you cannot make boom TOO short, otherwise you'll get crank-frame interference, but boom being about equal to crank legth or about 170 cm might be best. (might be even shorter with shorter cranks).

So, benefits of such a design (again, on paper, I'm in a process of ordering a prototype, but since I'm poor and cannot be picky - it takes much longer than I hoped) include:

• No wheel flop - front triangle is actually self-stabilizing. It might be less of a problem on Cruzbike, but on my 65 head angle MBB it is HUGE PITA. I do randoneering and I have to move the bike around a lot, including being very tired.
• Less pedal feedback.
• While you have limited ability to rotate your entire body to get to the cranks as you turn, on shorter boom you do not actually have to!
• Possibility of having front triangle suspended by a trailing link suspension:

With concentric bottom bracket pivot. This way there would be no chain grown, and if you run internal gears, you can fine-tune gear ratio (as in - chain angle) to get perfect pro-squat that would completely eliminate pedal bob - in all gear ranges.

Since FWD non-MBB with 'negative' angles and offsets exist (FastFWD, Ming, etc) and seem to just fine, there seems to be nothing preventing FWD MBB bikes from benefiting from such design, in fact it seems they would benefit all the MORE.

I understand that any 'Cruzbike tribesman' first desire would be to rip this concept apart to maintain status quo of Cruzibke design being the best thing ever, and I daresay - bring it on!
If it sounds too good to be true, it probably is. Maybe I am missing something?

 

[McWheels]

Not sure I want to start an argument I can't win, or in fact recognise what the winning argument is, but here's some food for thought from the guy who designed Chris Boardman's 1996 gold-medal winning bicycle, pretty much from scratch.

 

[Bentas]

First, a few sketches to to show that it works at least on paper:
With 'superman' tiller:

With USS:

(Sorry, I'm a total n00b when it comes to CAD)

A bit of history:

I have a 'Zockraish' clone myself, it has steering angle between Zockra and Vendetta - 65. I like it, and I used to pedal feedback very quickly and now do not notice it at all. However, it was not tailor-made for me and a bit too small, so I wanted to order a custom one (due to me being a relatively poor Russian, ordering Cruzbike is NOT an option, or I'd do it, of course).

After reading this articles:

http://www.recumbents.com/wisil/brown/alltogether.htm
http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

I thought that going like 80-85 angle might be a good idea, to minimize wheel flop.

But than I've seen this:

http://www.fastfwd.nl/index.php?id=35

And I've been struck with an idea:

What about 100 steering angle? That is going to make heavy (hence - 'floppy') front triangle completely self-stabilizing up to inclines of 10 degrees. And situation is actually exacerbated by weight of legs, eventually you learn to correct for that, but it takes effort.

Of course, such an angle is tailor-made to actually maximize pedal feedback, but why not? I think bar-pulling is more effective than pushing against the seat - I definitely output more power this way.

After mulling about, I've understood that it might have much less pedal feedback than it might appear too:

Pedal feedback depends on:

• Head tube angle (in case of Zockra in is nearly parralel to pedal force vector, hence almost no feedback)
• Q-factor
• Boom length - acting as lever.

So, if my bike is to have double steering input due to head angle, having boom lengh of nearly 1/3 of Vendetta would likely make pedal feedback LESS than on Vendetta!

Also, the shorter boom is, the less inertia it has (remember, moment of inertia of a pendulum is mR^2, and since most of the mass of the front triangle is concentrated at end of it - feet, cranks, etc - r^2 is 1/9!), hence the steering would be much quicker and lighter.

Of course, you cannot make boom TOO short, otherwise you'll get crank-frame interference, but boom being about equal to crank legth or about 170 cm might be best. (might be even shorter with shorter cranks).

So, benefits of such a design (again, on paper, I'm in a process of ordering a prototype, but since I'm poor and cannot be picky - it takes much longer than I hoped) include:

• No wheel flop - front triangle is actually self-stabilizing. It might be less of a problem on Cruzbike, but on my 65 head angle MBB it is HUGE PITA. I do randoneering and I have to move the bike around a lot, including being very tired.
• Less pedal feedback.
• While you have limited ability to rotate your entire body to get to the cranks as you turn, on shorter boom you do not actually have to!
• Possibility of having front triangle suspended by a trailing link suspension:

With concentric bottom bracket pivot. This way there would be no chain grown, and if you run internal gears, you can fine-tune gear ratio (as in - chain angle) to get perfect pro-squat that would completely eliminate pedal bob - in all gear ranges.

Since FWD non-MBB with 'negative' angles and offsets exist (FastFWD, Ming, etc) and seem to just fine, there seems to be nothing preventing FWD MBB bikes from benefiting from such design, in fact it seems they would benefit all the MORE.

I understand that any 'Cruzbike tribesman' first desire would be to rip this concept apart to maintain status quo of Cruzibke design being the best thing ever, and I daresay - bring it on!
If it sounds too good to be true, it probably is. Maybe I am missing something?

Would you just build it ,so we can all find out!

 

[Balor]

I'm not a welder, and lack workplace to do so. But I've already ordered a frameset (in May, in fact). Though, since I'm relatively poor and cannot afford top-quality workmanship, it takes longer than expected. I'll keep you posted.

Not sure I want to start an argument I can't win, or in fact recognise what the winning argument is, but here's some food for thought from the guy who designed Chris Boardman's 1996 gold-medal winning bicycle, pretty much from scratch.

Why argument? It actually confirms my claims . So long as you keep enough offset to have enough trail, any angle goes.
Reverse angle is to make it actually self-stabilizing, not just 'flopless'.
It might be worth to fine-tune it to keep 'boom length' fixed and as short as possible. But greater angles will make leg-wheel contact in turns less severe with lower seat - due to wheel 'lowering' as you turn it (in this case, this is more of a plus).

Of course, there is a problem of having either a very long tiller, or remote steering, and due to negative angle remote steering is not easy to implement. (Wheel is in the way).

One way is to use Bowden cables for steering, aircraft quality, 2.5mm thick or something, using Teflon lined-housing or route the wires over idlers.

 

[Jerrye]

One way is to use Bowden cables for steering, aircraft quality, 2.5mm thick or something, using Teflon lined-housing or route the wires over idlers.

Gears could work, and would be more dependable than a cable. If you worked out your angles, you should be able to find something that would work, perhaps even something off the shelf, cheap and readily available.

The Cruzbike Sigma used a universal joint for steering, but I think the angle here would preclude using one of those.

 

[ratz]

Why argument?

That just because we've all been online for too many years and these topics usually go off the rails. However if there is a safe place to actually discuss this topic I would guess these forums are the right place. yet I'm not sure enough of us actually understanding the topic to actually discuss it; that or all the engineers are out riding and enjoying the summer weather ...

so carry on and have fun.

 

[Robert Holler]

The Cruzbike Sigma used a universal joint for steering...

Horrible

 

[McWheels]

For a reverse angle front wheel, and to avoid leg strike, perhaps you need to get over the top of it in a high racer sort of way, and also have maybe a 20" to 24" front wheel so you can maintain a mostly horizontal human aspect. Like Mike Burrows says, once it's at this angle the problem is the pilot-monkey ergonomics, not the mechanics.

Mike Burrows with enclosed FWD racer

Leaning trike with reverse angle front wheel

A home-built FWD MBB low racer. Demonstrates the space problems if the wheel angle was reversed.

 

[Balor]

My latest iteration, calculated with both with 700c 28mm wheels, seems to minimize all possible conflicts, straight path to fork-mounted spool and shortest possible boom I've managed to cram into design so far.
The 'boom' is actually more of a 'steering bar stem' in this case (with a DM tab for DM front dérailleur, chainstay angle is perfect)

It is plenty high, no going around it, though there are quite rideable and popular stick bikes like Bachetta 700c with similar seat height, and much higher pedal height too (something that does NOT work for me at all, I get numb feet and my power drops).
It might be possible to make it quite a bit lower, but I'm very interested in making cable spool-actuated stick steering (at least, sometime in the future).
I've got the idea of stick steering here:
http://www.bentrideronline.com/messageboard/showpost.php?p=1349812&postcount=9
(See next page for better pictures)
Stick steering axis would be clamped to the frame and hidden under seat, which has advantages of tensioning the wires, and adjusting distance and angle of sticks.

Besides obvious 'no thigh interference', stick steering allows fully unimpeded visibility and is very conducive to pulling for power.
Cable spool actuation was recommended by Thom Ollinger - seems very inobstructive and lightweight. If you use cable thick enough and, perhaps, use TWO of them in parallel, it should be plenty reliable.
In my case, two spools on sticks translate pulling into wires that bend around a spool on a fork.
Unfortunately, you'll need to have them connected by gears to work as intended with steel cable, but this is doable.

 

[RojoRacing]

It's too much of a project for me to undertake in my free time. I would love to try a negative rake setup as I think it would probably self straiten unlike the current CruzBike models. I'd be more curious to feel the problems in handling it would bring to the table. Nothing is ever free as the saying goes.

 

[Balor]

It's too much of a project for me to undertake in my free time. I would love to try a negative rake setup as I think it would probably self straiten unlike the current CruzBike models. I'd be more curious to feel the problems in handling it would bring to the table. Nothing is ever free as the saying goes.

Well, nothing is free indeed, but in this case this is more about needing to have a very long tiller or remote steering, not handling. There are negative rake FWD models like Ming and Munzo, Burrows experimented with zero rake and negative offset and all of them handle just fine. It is trail that is important.
Of course, none of them were MBB, but since distance to steering axis would be 3-4 times less, steering inertia should be an order of magnitude less AND you'll have self-stabilization without any need for 'flop stop'.
However, it would likely feature a 'funny' behaviour in sharp cornering due to tendency for steering OUT of the turn, but you can get used to that.

Of course, practice rarely fully coincides with theory, but so far I'm pretty damn sure that it will work out as intended, but long tiller I'll have to implement at first due to material constraints would add steering inertia of it's own.

 

[Balor]

Finally, a video of my prototype:

'Self-straightening' is readily apparent, even with relatively mild negative angle (7 degrees)

But I really want to try remote steering to avoid long tiller, but it needs to be it really robust AND narrow enough to fit between the legs even with all the articulation required for turning while pedalling.
After a LOT of googling around think I've found one.
http://www.ihpva.org/projects/tstrike/lwbbike/lwbbike.htm

Stay tuned.

 

[Balor]

While adding remote control is underway, I've been researching other stuff to add to my prototype.
One of disadvantages of MBB compared to RWD recumbent designs is relatively limited steering lock and hence - turning radius (because your legs are attached to the steering).
Not THAT bad, but still. It is especially apparent on my MBB, with wheelbase of about 135cm (but it has it's own advantages: plushy ride AND better climbing due to less load transfer). I even abstained from participating in a local time trial races because they take place on a remote stretch of a narrow road with one (or three) turnarounds, and it is impossible for me to do it quickly and gracefully enough.

I've contemplated two wheel steering, but it is too mechanically complex (especially on my design).
But if I am to add a 'swing caster' real wheel, it seems to me that I'll be getting '2WS' basically for 'free'.

Dual wheel steering Python, 'Bipolar':

A three-wheeled bike prototype made by an archetypically crazy Russian, heh:

There is even an article that states that a self-steered rear would increase high-speed stability (but might introduce instability when braking and acceleration).
https://www.researchgate.net/public...eering_system_may_improve_motorcycle_dynamics

Acceleration is not a problem due to FWD, as for braking - we'll see. I'll be asking to add a swinging rear end to my prototype in addition to current 'fork clamp'.
This way I get to test both concepts, and will simply saw off one that would not work as well .

 

[Balor]

Pretty much done, only paint and shipping is left. Hopefully, I'll get my prototype right at the beginning of the season.

 

[Balor]

Unfortunately, due to a series of misfortunes it is not "quite" finished yet, but at least it is rideable now.

Final sketch:

A few finished photos:

This one with underseat steering 'partially' installed.

Video of underseat steering in action:

Unfortunately, while rideable, underseat steering suffer from very weird leverage rations due to remote mounting points being offset from steering axis - otherwise you'll get nonexistent steering lock due to how front triangle a welded up.
This is due to design being very 'evolutionary', unfortunately. I'm using superman bars for now... which are like 4" wider than I've asked for .
Not being a builder yourself is frustrating sometimes.

Anyway, how it rides:
In one word: wonderfully.. at least for me, because I, for some reason, cannot grasp the concept of 'leg steering', and my arms are inadequate to damp both two-fold wheel flop and massive steering inertia of conventional MBBs.

Negative angle that puts CG of front triangle below the steering axis + negative wheel flop allows for a self-centring action of steering in all speeds and conditions, which makes the ride very pleasant and much safer in loose (sand, gravel, wet) conditions.

I should note that due to HUGENESS of superman bars (that are, in turn, are above steering axis now) they now cause the bike to turn outside of the lean a little bit, hence the bike lacks positive self-stability without rider (because with rider on top leg weight is added to the front triangle).

Due to short boom, there is no problem with steering inertia whatsoever. I think I could have get away with longer boom, which would allow for shorter superman bars (hence no need for remote steering and much more manageable weight and size of the bars) and proper 'lean into turn' passive self-stability without rider (make the bike easier to wheel around).
Also, with bars tiller a BIT shorter, steering gets even better - I've tested that by moving my hands up on the bars as I ride. Only a few cm makes a noticeable and welcome difference.
Still, I've had to trouble of clocking 100 km the first day I've ridden it, hitting nearly 70 kmh on a steep hill and it gets better as I ride it, too.

P.S.
I've also tried chain steering:

Unfortunately, it turned out to be unviable due to chain tension 'bucking' the frame and leading to massive steering slop.
Since than the frame got shortened and reinforced, so I may try it again... only I'll have to order remote steering tube clamp, because the one on the picture was 'used up' on the underseat steering .

 

[Balor]

Oh, and about climbing. The bike is heaviest of my crop yet, 25kg with superman bars, and I'm not in the best shape due to health issues, but at does not "feel" inefficient at the very least. More data is needed.
One thing I should note - due to huge width and length of the bars (and short boom) pedal feedback feels nearly nonexistent.
It is a mixed blessing - I firmly believe that bar-pulling is one of things that "make" MBB.

 

[super slim]

I like the design!
Could you use tie rods, instead of chain for the remote steering, similar to what is used on trikes!

 

[Balor]

Well, that is an other possibility. What I don't like about tie rods, is nonlinear actuation and some slop in the bearings (unless you use extremely good ones... which I'm not ).
Right now I'm trying to 'conquer' the underseat steering, but I suspect I'll need much longer levers.

Chain, on the other hand, is completely slop-free if you tighten it good enough, and should stay slop-free if you use a quality chain.
Plus, actuation is completely linear (though you can still play with steering ratio if you want to).
It is a very viable way of remote steering for non-MBB bikes to be sure, but for MBB structure must be completely rigid under tension, and that is a few hundred kg (due to leverage).

 

[bladderhead]

Behind the seat, the rack is the frame. Very neat.

 

[bladderhead]

A fear hundred kg? How much weight can that chain take? Going down a steep hill, approaching a turn, and it snaps? How quickly can you learn to do no-hands?