Fully suspended MBB with 90 deg steering angle.
- Thread starter Balor
- Start date
bladderhead
Zen MBB Master
Could you take the horizontal part at the top of the black rectangle and replace it with a longer piece that extends backwards?
Balor
Zen MBB Master
Certainly not now, plus I'll be missing wide range of adjustability. Once I'll have everything dialled in (and besides, I may not LIKE this arrangement) I may order an other one from scratch, maybe even lacking any adjustability but much lighter and stiffer.
There is still some offset issue to iron out, plus I want to play around with all wheel steer.
bladderhead
Zen MBB Master
That should be interesting. Can't wait to see it. Good idea for commuting - it will wiggle easily through the pedestrian barriers and around the pedestrians.Balor said:
Balor
Zen MBB Master
Well, this is mostly to make turnarounds on narrow roads. Longer wheelbase is great in all respects except this
.It will certainly add some more weight, though - plus, you can use it to have some extra self-centring (any trail you add to both your wheels would be cumulative - hence, you can, say, end up with zero trail up front, but some/lots in the back).
Fortunately, remotely steered rear does not need a very strong arrangement, because it is not subject to pedal forces.
Balor
Zen MBB Master
Ok, I've got it, assembled with one gear (33x11) and one brake and went for a short night ride (otherwise I'll not get any sleep ).
So, how it handles? Lugging it around is still a pain due to heavy and somewhat floppy front triangle (real steering angle turned out about 88 deg or so), but once you sit down and push the pedals the beast transforms.
Steering is absolutely rock-stable at any speed past snail pace, mentioned wheel-calf conflict is not noticeable with 40mm tires. It does not feel like your typical MBB at all - even pedal steering effect is barely noticeable at speed!
I'll need to try this on one guy that tried my previous bents before and did not like them, whether he'll 'ride off' this time
Suspension works wonderfully and allows one to simply fly over huge potholes that my neighbourhood supplies in abundance.
Low BB feels and pedals great.
Fit... is tricky though, like I suspected the builder made the frame a bit larger than I asked for, and given very limited tolerances it feels I'm overextending a few mm even on 150mm cranks. I actually have cranks as short as 140mm, but those are road double and it will result in rather 'virtually tall' gearing with cranks that short.
I'm contemplating cutting a notch in my seat to move it forward those missing few mm.
Pictures after I'll finish assembly.
).So, how it handles? Lugging it around is still a pain due to heavy and somewhat floppy front triangle (real steering angle turned out about 88 deg or so), but once you sit down and push the pedals the beast transforms.
Steering is absolutely rock-stable at any speed past snail pace, mentioned wheel-calf conflict is not noticeable with 40mm tires. It does not feel like your typical MBB at all - even pedal steering effect is barely noticeable at speed!
I'll need to try this on one guy that tried my previous bents before and did not like them, whether he'll 'ride off' this time
Suspension works wonderfully and allows one to simply fly over huge potholes that my neighbourhood supplies in abundance
.Low BB feels and pedals great.
Fit... is tricky though, like I suspected the builder made the frame a bit larger than I asked for, and given very limited tolerances it feels I'm overextending a few mm even on 150mm cranks. I actually have cranks as short as 140mm, but those are road double and it will result in rather 'virtually tall' gearing with cranks that short.
I'm contemplating cutting a notch in my seat to move it forward those missing few mm.
Pictures after I'll finish assembly.
bladderhead
Zen MBB Master
You can get pills for that.Balor said:
Balor
Zen MBB Master
Maiden voyage!
https://www.strava.com/activities/1670046779
I daresay it is fast enough for a FS bent with body position (low BB) and crank length I'm not familiar with yet.
"Cruzbike cockpit' with 'seagull bars' is great and short cranks allow for comfortable arms position without my knees hitting anything in the process.
I should note that road on that track is very bad, with lots of potholes and rough, weathered asphalt. Funny enough, front suspension seems much 'smoother' than the rear - likely due to heavy front weight bias (hence much larger suspended mass) and rearward axle path.
Among 3 MBB bents I've tested (Zorkra Clone, MBB with negative angle and this one) - this is the most easily steered bike, despite front triangle weighting a ton. One-handed operation is trivial, riding no-hands is ALMOST doable even for an oaf like me! I bet I'll get the hang of it eventually.
Basically, ride has a 'relaxing' quality that my previous MBB bents sorely lacked. You don't feel like being from one small hand twitch from lying in a ditch Yet, you can 'swing the boom' for power and pull the bars and stomp the pedals and get rewarded with feel of power NOT being lost anywhere.
I should note that suspension does NOT bob at all at least when cruising on flat ground - something that came as a surprise for me, actually.
https://www.strava.com/activities/1670046779
I daresay it is fast enough for a FS bent with body position (low BB) and crank length I'm not familiar with yet.
"Cruzbike cockpit' with 'seagull bars' is great and short cranks allow for comfortable arms position without my knees hitting anything in the process.
I should note that road on that track is very bad, with lots of potholes and rough, weathered asphalt. Funny enough, front suspension seems much 'smoother' than the rear - likely due to heavy front weight bias (hence much larger suspended mass) and rearward axle path.
Among 3 MBB bents I've tested (Zorkra Clone, MBB with negative angle and this one) - this is the most easily steered bike, despite front triangle weighting a ton. One-handed operation is trivial, riding no-hands is ALMOST doable even for an oaf like me! I bet I'll get the hang of it eventually.
Basically, ride has a 'relaxing' quality that my previous MBB bents sorely lacked. You don't feel like being from one small hand twitch from lying in a ditch
Yet, you can 'swing the boom' for power and pull the bars and stomp the pedals and get rewarded with feel of power NOT being lost anywhere.I should note that suspension does NOT bob at all at least when cruising on flat ground - something that came as a surprise for me, actually.
Balor
Zen MBB Master
Yea, that would take 24" front wheel and larger rear shock an I intend to try that indeed, to see how 'small positive' (about 89 deg now) angle compares to 'small negative' angle.
It will switch from about 66mm of trail and 1mm of flop to 54mm of trail and 1 mm of negative flop (head tube rising when steering, that would be a tiny fraction of a mm during normal operation, flop is calculated at 90 deg of steering rotation).
Trail difference is rather large actually, but difference in flop is very small. Still, like I said, the bike has a large front weight bias (for FWD traction, though I suspect I went a bit overboard here too) and hence flop play a large role in 'controllability' - it makes Pythons rideable with negative trail, for instance, because your CG is EXACTLY on top of steering tube and you lifting up and down your entire weight when you steer.
I suspect it will make the bike easier to wheel around, but make little noticeable difference on actual operation, except when starting a bit...
All in all, 'negative angle' is good on bikes with small wheels (like Minq or Munzo), with large wheels negative angle needs so much negative offset for decent trail that you run into wheel/calf interference and (again, see Munzo) on FWD-TC where you can have remote steering without massive technical hurdles.
It will switch from about 66mm of trail and 1mm of flop to 54mm of trail and 1 mm of negative flop (head tube rising when steering, that would be a tiny fraction of a mm during normal operation, flop is calculated at 90 deg of steering rotation).
Trail difference is rather large actually, but difference in flop is very small. Still, like I said, the bike has a large front weight bias (for FWD traction, though I suspect I went a bit overboard here too) and hence flop play a large role in 'controllability' - it makes Pythons rideable with negative trail, for instance, because your CG is EXACTLY on top of steering tube and you lifting up and down your entire weight when you steer.
I suspect it will make the bike easier to wheel around, but make little noticeable difference on actual operation, except when starting a bit...
All in all, 'negative angle' is good on bikes with small wheels (like Minq or Munzo), with large wheels negative angle needs so much negative offset for decent trail that you run into wheel/calf interference and (again, see Munzo) on FWD-TC where you can have remote steering without massive technical hurdles.
Balor
Zen MBB Master
Installed longer rear shock, based on my precision eyeball-o-meter steering angle is now like 90.2 or something
A very, very minor tendency for weight-based self-center is observed now, it still flops a into a lean due to large weight imbalance around the steering axis - but this is actually a good thing for passive self-stability. It is much easier to wheel around now, at least.
On the bike I've noticed no discernible difference, but I've tried cruising no-handed and actually succeeded!
No-handed pedalling will surely take some training because, like I said, I'm a bit of an oaf, but certainly seems doable.
The shock does bob a bit (like, a mm) during climbing under power, and not at all during steady state cruising even when really pushing it.
Only thing that worries me now is that wall mart bike pivots (donor limitations) have a tendency for developing slop. We've predicted that and actually used 'industrial quality' (think IGUS) polymer bushing instead of just metal-on-metal friction, but I'm not entirely sure how it will work out, too.
Theoretically, the pivot should have been done by using a very large axle and angular contact ball bearings - think head tube.
Since this design shows great merit, we may do exactly that for my next prototype if slop in the pivot becomes a problem.
A very, very minor tendency for weight-based self-center is observed now, it still flops a into a lean due to large weight imbalance around the steering axis - but this is actually a good thing for passive self-stability. It is much easier to wheel around now, at least.
On the bike I've noticed no discernible difference, but I've tried cruising no-handed and actually succeeded!
No-handed pedalling will surely take some training because, like I said, I'm a bit of an oaf, but certainly seems doable.
The shock does bob a bit (like, a mm) during climbing under power, and not at all during steady state cruising even when really pushing it.
Only thing that worries me now is that wall mart bike pivots (donor limitations) have a tendency for developing slop. We've predicted that and actually used 'industrial quality' (think IGUS) polymer bushing instead of just metal-on-metal friction, but I'm not entirely sure how it will work out, too.
Theoretically, the pivot should have been done by using a very large axle and angular contact ball bearings - think head tube.
Since this design shows great merit, we may do exactly that for my next prototype if slop in the pivot becomes a problem.
dtseng
Well-Known Member
Most MTB and cruzbike sofrider and quest all use that kind of pivot, but all in the rear wheels. For front wheel, I think the lateral stiffness is important. Then I look at DF bike front wheels, the axles are usually 9 mm in diameter. The axle length (or front fork opening) is standard 100 mm. Therefore, I would think that using front wheel hub (or similar structure) as pivot would have sufficient lateral stiffness.
Balor
Zen MBB Master
Yea, actually my first MBB bent had a steel hub with 9mm solid axle as rear suspension. It, too developed play eventually, but you can adjust the cones.
Unfortunately, welding it is tricky - not a whole lot of real estate to work with, plus heating may interfere with proper tempering of bearing races.
Balor
Zen MBB Master
Erm, if you take a Flevobike, leave everything else equal but make steering angle vertical you are going to have a perfectly *unrideable* recumbent:
*Massive* negative trail with no negative flop to make up on it even on at slow speeds (like on a Python) plus with 90 deg steering pedal steering is not a problem with long tiller and wide-ish bars - but will *certainly* be a problem on a flevo with rudimentary USS bars, and any tiny swerve will be amplified by negative trail, neatly folding your bike in half. Please don't!
Negatively offset forks are indeed not very good structurally and aestetically (though it worked well on my negative angle prototype - it just didn't have ENOUGH, plus way too long bars).
With a light and not too long front end, a design like this also has merit (and in fact was already ridden for a LOT of kilometres by Zimin):
80 deg steering angle, no (or very small negative) offset. Unfortunately, the project is halted for now...
It still has nearly 2x less flop for a given trail than traditional 70 deg steering, 2x less 'mbb-specific' flop that is NOT affected by reducing trail, less inertia due to no offset and shorter boom and still decently forward weight distribution (in fact, 30 cm 'boom' and -6cm of offset results in about 30/70 weight bias which seems too extreme to me - especially if are not planning suspension. I doubt I'll be having any problem with wheel spin though
)
Balor
Zen MBB Master
Went for an offroad ride - MTB tires steal about 5 km/h average, but allow for a very good offroad grip.
https://www.strava.com/activities/1701534847
https://www.strava.com/activities/1701534847
dtseng
Well-Known Member
A re-designed Flevobike with vertical steering axis and 60mm trail. The short wheel base is for maneuverability in the concrete jungle and not for setting speed record on down hill glide. The pivots will use cartridge bearings to increase side-way stiffness. The only purpose of using vertical steering axis is to eliminate the front fork. This is more of a Balorbike.
Last edited:
Balor
Zen MBB Master
Oh, that seems good (more like 'Balorkara' ), but:
a. You sure you can properly calculate amount of elastomer-assisted travel? During front braking you will encounter much higher shock-loading forces than going over bumps (ton of brake dive... though same is with Flevo, Chinkara or my own bent for that matter), so front wheel may touch the frame and that will certainly cause loss of control.
b. Wheelbase is way too low if you ask me. With decent recline your head will likely be past the rear axle, I"ve heard multiple times that that is not good for proper steering... in my case, 130cm allows to make a complete turnaround on a narrow two-lane street, but results in 70% load on the front wheel. I think something like 110 would be fine.
c. The lower your BB, the easier it is to start, stop, and less brake dive (lower suspension pivot). Plus, with lower CG (and longer wheelbase) makes for less suspension bob - though in your case it is addressed by chain forces I see (but will result in a change in chain tension when suspension goes though the travel). If you do not expect to set speed records - make BB as low as possible (in my case it does not prevent me from reaching high speed, though Vendetta it is not).
And make sure you can reach the pedals
), but:a. You sure you can properly calculate amount of elastomer-assisted travel? During front braking you will encounter much higher shock-loading forces than going over bumps (ton of brake dive... though same is with Flevo, Chinkara or my own bent for that matter), so front wheel may touch the frame and that will certainly cause loss of control.
b. Wheelbase is way too low if you ask me. With decent recline your head will likely be past the rear axle, I"ve heard multiple times that that is not good for proper steering... in my case, 130cm allows to make a complete turnaround on a narrow two-lane street, but results in 70% load on the front wheel. I think something like 110 would be fine.
c. The lower your BB, the easier it is to start, stop, and less brake dive (lower suspension pivot). Plus, with lower CG (and longer wheelbase) makes for less suspension bob - though in your case it is addressed by chain forces I see (but will result in a change in chain tension when suspension goes though the travel). If you do not expect to set speed records - make BB as low as possible (in my case it does not prevent me from reaching high speed, though Vendetta it is not).
And make sure you can reach the pedals
