[python] Re: Python trike cornering stability

  • From: paul needham <paul.2.needham@xxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Mon, 3 Dec 2018 22:26:21 +0000

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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