Paul,
No problem with negative feedback - that's exactly what I need.
Good point with the toe in/out. The "axle" will need careful alignment even
with vertical wheels. Cambered ones would be much trickier to jig up. Another
dead end ticked off!
All brakes at the front wheel is definitely a no no, I agree. I want all wheels
braked. But the front one has to be strong in my case. Kettwiesel has almost
all weight on the rear wheels, so having two strong brakes there and nothing at
the front makes perfect sense. Your trike's CoG is also pretty far rear which
explains the front wheel skidding. But my rickshaw would have about 70 % of
weight on the front when empty, so rear wheels would skid at first light touch.
Two SWB lowracers I have tried so far have never locked their front wheels,
even under very hard braking. Rear wheel, on the other hand, skids pretty
easily and is not sufficient for an emergency stop.
Coupled rear brakes mean the cable force splits equally between them via a
torque arm or pulley. If one wheel locks, it doesn't mean the other one loses
braking power. Of course, actuating two brakes with one hand means only half
force for each - poor man's ABS :-).
Another thing I'd like to ask you guys about: what is your favourite
construction approach for building self-supporting cargo boxes? I'm thinking
thin plywood walls reinforced with wooden beams at upper edges and corners, and
light steel frame and thicker plywood floor at the bottom. Or how about sheet
aluminium riveted to the frame? Or latticework of thin steel tubes covered with
fabric, like an old aircraft? Or fibreglass? Or something completely different?
Conditions: smooth on the outside and as light as possible while being strong
enough to carry the required load and able to survive occassional knocks from
loose heavy items.
Regards
Mirek
______________________________________________________________
Od: "paul needham" <paul.2.needham@xxxxxxxxx>============================================================
Komu: python@xxxxxxxxxxxxx
Datum: 03.12.2018 23:26
Předmět: [python] Re: Python trike cornering stability
Mirek
Please don't camber the rear wheels , I gave up on that as unless you
get a line from the ground contact patch through the axle exactly
vertical you will introduce either toe in or toe out of the rear wheels
increasing the drag significantly. The Hase Kettweisels have adjustable
length and go to great trouble to ensure the rear camber of the wheels
can be altered to match changes in length to address this issue. Camber
will not increase cornering speed just remove the axle on the outside of
the hub from the total width of the vehicle.
The front disc brake is problematic , having ridden over 8000km on a
trike with both brakes on the front wheel I don't recommend it at all !
It is far to easy to lock up the front wheel [ with either the disc or v
brake ] and then you loose all steering and have no way of slowing it
down any further !
Neither do I recommend both rear brakes being coupled ? there is no
ability then to brake with one wheel should one lock up ?
Again the majority of the Hase Kettweisels are in use and perfectly safe
with 2 rear wheels independently braked , I had one before my Python and
had no issues what so every with it's braking performance and safety [
not something I could say about my Python I am afraid ]
Sorry to come over all negative , however it takes the same amount of
time to build a successful trike as it does to build a failure , and we
want you to succeed !
My first build is here :- Python trike Mk1
<http://forum.atomiczombie.com/showthread.php/8210-Building-a-python-trike?highlight=>
and second ongoing build here :- Python trike Mk2
<http://forum.atomiczombie.com/showthread.php/9476-Building-a-python-trike-Mk2?highlight=>
sadly some of the pictures are missing as Postimage decided to change
there server address , if you want any pictures please just ask.
Good luck with the build Paul
On 03/12/2018 13:03, mircosoft@xxxxxxxxxx wrote:
OK, here's a sketch.
The vertical white lines show the overall length limit: ceiling height
in our basement (262 cm). The brownish rectangles in the cargo area
are two cardboard banana boxes, the minimum capacity limit. Track
width is about 70 cm, adding a few centimetres if possible by adding a
few degrees of camber or by increasing the overall width a bit.
Lowering the main beam even further is possible, although it will
require modifications to the rounded front of the cargo box (and I
sure want it rounded). Transmission would be done by some internal
gear hub. Cargo box forms a structural part of the vehicle, the thin
metal frame underneath is only there to bolt things to and to spread
point loads over plywood sidewalls and floor. I'm not sure yet how to
connect it to the main beam: either the beam would bifurcate and
attach at three widely-spaced points (as pictured), or it would attach
to the two frontmost crossbeams (lighter and simpler, but I'm not sure
about strength).
Paul,
Miles would be at least 50 % loaded. When there's nothing big to
carry, I'd use a bike.
Front disc brake just saved my life again last Wednesday (on a bike),
so I for certain don't want anything weaker there. The other lever
will control coupled rear brakes. Parking brake is a good idea and
would be quite easy to incorporate somewhere in the mechanism.
You're right, tilt lock/unlock makes a vehicle switch between bike and
trike mode, which basically means reversing the steering. That could
be pretty tricky to handle.
Mirek
______________________________________________________________
Od: "paul needham" <paul.2.needham@xxxxxxxxx>
Komu: python@xxxxxxxxxxxxx
Datum: 29.11.2018 00:04
Předmět: [python] Re: Python trike cornering stability
Mirek
You will lose some width by using front forks to hold the rear wheels
, mine is 76cm to the centre of the rear wheels the hubs themselves
add another 4cm [ each ] to the width then there is the fork and
wheel nut etc.
With 100kg load that will probably match the weight of the rider and
trike [ mine is 17kg ] it should help with cornering.
Do you think your miles will be equally split between empty and loaded ?
You can get the seat lower by having the main frame at 12cm I have
the seat at 20cm just a matter of adjusting where the rear forks meet
the frame.
Having camped in Holland 4 times with a trailer I agree it can be
tiresome at times , however it does NOT restrict the python turning
circle which is good.
Disc brake on front may be of limited use ? both my brakes are
currently on the front wheel and it is all to easy to lock that wheel
up and loose steering in the skid.
I would suggest a parking brake , I really need one !
As for tilting and a tilt lock I think this would be very dangerous
both for you and others , if you have your feet down you just set off
as if it where a bike if you artificially stop it tilting you won't
be able to judge when to release the lock and any situation where you
need the tilt for balance will cause it to roll over ?
regards Paul
On 28/11/2018 13:26, mircosoft@xxxxxxxxxx wrote:
Thank you all!============================================================
My plan is 20" wheels, about 80 cm of track width (legal limit is 90
cm overall and I'd use standard front hubs with axles fastened at
both ends), wheelbase about the same as Vi's machine, cargo capacity
at least 100 kg (plus rider), seat as low as possible (that means
just above main beam which is at wheel hub height), weight under 30
kg if possible (the value to improve upon is my current setup of 16
kg bike + 17 kg trailer = 33 kg), disk brake front, drum brakes
rear, underseat handlebars attached to the front fork.
Target environment is standard streets and roads with occassional
bits of cyclepath when available.
According to Vi's video, it seems like it's OK to just lean the
upper body (legs lean with the front wheel anyway) to get enough
stability even with narrower track width than mine. So leaning of
the seat is not needed - good, that eliminates whole lot of design
difficulties. Riding it would be OK for me (I can ride Python
bikes), but it would need secure locking for others and low speeds.
Trailers are a good solution if one can't have a dedicated cargo
vehicle, but otherwise they're not very practical (in my opinion).
Small trike + big trailer = two wheels more than necessary (more
weight and drag). Big trike + big trailer = too much weight to be
able to pull (and hard or impossible to push). Anything + trailer =
two heavily loaded nonbraked wheels, and also two vehicles to park.
If I ever build this, I promise to post pictures and feedback at
Openbike :-).
Mirek
Od: "paul needham" <paul.2.needham@xxxxxxxxx>============================================================
Komu: python@xxxxxxxxxxxxx
Datum: 28.11.2018 09:05
Předmět: [python] Re: Python trike cornering stability
Mirek
First the trike stability depends on height of c of g from ground [
on a
recumbent general through the riders navel ]
Width of trike foot print where vertical line through c of g touches
ground [ foot print is triangle drawn between tyre contact patches ]
Also speed and angle of corner.
If you make the trike tilt in any way you have built a Python bike and
will have to learn to ride it !
So what height do you want the seat from ground ?
Can the trike not tow a trailer , lot easier than towing with a bike ?
What sort of load do you anticipate ?
Where are you riding ? roads , dedicated cycle paths etc ?
all the best Paul
Od: "Steffen R" <big.skangster@xxxxxxxxx>
Komu: python@xxxxxxxxxxxxx
Datum: 27.11.2018 19:09
Předmět: [python] Re: Python trike cornering stability
Hi Mirek,
I hadn't had big issues with mine as far as I remember. But the
bike itself
was kind of a load already its 40+ kg. It also had a short and
quite wide
wheelbase.
Am 27.11.2018 07:51 schrieb "Vi Vuong" <dmarc-noreply@xxxxxxxxxxxxx>:
Hi Mirek,
I experimented with a trike with off-center front wheel. It was more
stable going into right corner as I can lean in. See
https://youtu.be/as5fB8cQX7g
Left turn was okay at normal speed.
Vi
On Nov 26, 2018, at 12:16 PM, <mircosoft@xxxxxxxxxx>
<mircosoft@xxxxxxxxxx>
wrote:
Hello fellow pythoneers,
I'm looking for someone with personal experience with a non-tilting
cargo
trike, like this:
http://en.openbike.org/wiki/File:Gavin-Katts.jpg
My goal is to replace a bike+trailer combo by something equally
capacious,
but faster to ride (i.e. lighter and more aero), easier to start,
stop and
park.
The only problem is I have no idea what it will do in high speed
turns.
Long wheelbase, centre of mass closer to the single front wheel
than rear
axle, front wheel contact patch moving into the turn - everything
says it
would topple easily when not loaded heavily. I can live with some
instability, the question is: would I have to slow down for every
turn so
much that it offsets all the aero and weight benefits over the bike
and
trailer?
Tilting front end is also an option, but I'd prefer to get along
without
one if possible.
Thank you for any input.
Regards
Mirek
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