Folding Python delta trike

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Feb 7, 2008
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Nottinghamshire England
Yes that's the video , well found !

40' is plenty , you can almost chase your tail with that.

I think suspension is defendant on what you are trying to smooth out ?
MTB's go for 5cm - 10cm [ 2"-4" ] however they go off road.
I want between 2.5cm - 5cm [ 1" - 2" ] for the awful tarmac I ride over on footpaths and streets , whilst the bumps are not big neither are they isolated , I can ride for a couple of km over really poor surfaces .

Python construction section 5 this is the easiest to implement and would fit in with your design very well.
easy to change hardness/travel by moving pivot about or changing elastomer values ?

Paul
 
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Jan 23, 2023
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Wageningen, the Netherlands
I think suspension is defendant on what you are trying to smooth out ?
Dutch bike infrastructure and road quality are excellent. I'll mostly be riding on smooth tarmac or shell paths so I definitely don't need MTB levels of travel. That's why I'm thinking maybe balloon tires alone are enough.

Python construction section 5 this is the easiest to implement and would fit in with your design very well.
easy to change hardness/travel by moving pivot about or changing elastomer values ?
That's certainly an elegant solution, I skipped over that so thanks!

Some thinking out loud. I can only get very short pivot arms on the rear wheels because of the short wheelbase. Well, I could get them to be longer, but then I wouldn't be able to have triangulation / a rear attachment for the seat. The suspension in the guide has maybe a 50cm moment arm on the wheel and a 9cm arm on the elastomer, and it can probably get about 3.5cm of travel at the wheel before the inner tubing hits the outer. I can't get more than a 15cm arm on the rear wheels, so the same elastomer would have to be about 2.7cm from the pivot for the same travel.

Edit 2: I was a little confused about the calculations but I think it's correct. The same relationship between the arms means the same force on the elastomer, so the same compression distance, multiplied again by the same arm ratio to get the same wheel travel distance. Just the travel angle goes from 4 degrees to 13 degrees.

Edit 3: wait that's assuming a single rear wheel. I have two so the force is half, and for the same desired wheel travel the elastomer bolt then needs to be half the distance to the pivot (1.4cm). That's almost bolt to bolt, but maybe it's still possible.
 
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Dutch bike infrastructure and road quality are excellent. I'll mostly be riding on smooth tarmac or shell paths so I definitely don't need MTB levels of travel. That's why I'm thinking maybe balloon tires alone are enough.
I know , that's why I try to ride there every year :D(y)
That's certainly an elegant solution, I skipped over that so thanks!
Yes it is , just a bit short on values for the elastomer , somewhere I have a piece of paper with a possible suitable value circled , however that of course is dependent on your weight and the possible moment arms.
Some thinking out loud. I can only get very short pivot arms on the rear wheels because of the short wheelbase. Well, I could get them to be longer, but then I wouldn't be able to have triangulation / a rear attachment for the seat. The suspension in the guide has maybe a 50cm moment arm on the wheel and a 9cm arm on the elastomer, and it can probably get about 3.5cm of travel at the wheel before the inner tubing hits the outer. I can't get more than a 15cm arm on the rear wheels, so the same elastomer would have to be about 2.7cm from the pivot for the same travel.
In your position I would build first without and try balloon tyres , if they work and are not to draggy and you don't mind the extra weight then that is the simplest solution ?
As your rear arms will pivot it would be easy if it does not work to build new arms with suspension and then try that ?

Paul
 
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Anything which compromise the stiffness/level of a python trike, suspension, tilt, to soft tyres etc. will also effect the steering/handling.
So make it as simple as possible. A good aspect of a the python is that it has a separate front and rear frame, so each part can be modified/re-made at a later point if needed.
I ride on 1.6" tire and they are comfortable enough.
 
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Jan 23, 2023
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Thanks guys, I'll go with no suspension and if I really need it I can always make new rear arms later.

Played around a bit with bigger wheels. With 24" wheels the folded size goes up quite a bit so I'm not going to do that.
Of course I knew that before I started, but playing around with Sketchup is fun and I didn't feel like designing the seat today..


Anyway now I know I'm going with 20" wheels, 70mm SA rear drum brakes and a 7 or 8 speed front gear hub with roller brake, and 55mm Big Ben Plus tires. Maybe I should just order those so there's no turning back.
 
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BB: can I go with one with plastic press fit cups, and hammer it into a piece of 35mm ID pipe? I don't have easy access to a lathe for BSA thread.
Just recover one from an old bike , easiest option
maybe a view of where it is going ?

Paul
 
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You can get them new but at a large price from frame-builder suppliers but almost everyone buys a secondhand steel framed bike not just for the BB but buy the right donor and you'll get other usable bits too. Alternatively try freecycle.org for free donors near you. You'll probably have to patch over some of the holes they align with the std frame to waterproof it. Avoid lugged frames as the lug will have frame tube sized holes in it rather than the smaller holes you'll find in the non-lugged frames.
 
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Most my bikes, so fare, has press fit BB into a home made tube, works a threat.
I'm using 1 1/2 inch tube with 1.6mm wall.
If you cut away the blue line on the side of the tube and weld it up again, it makes a perfect fit.
My first 2 was welded with a stick welder and 2mm electrode.
 
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A python can have a shorter chain than a conventional bike which might interfere with the
shifting of gear, so it's very important to have the central front chainring inline with the rear central chainring.
The BB comes in different width and it's very difficult, without trial and error, to find a combination
which works.
I have always used a BB for damaged treads, like this one,
https://hollandbikeshop.com/en-gb/branded-bicycle-parts/contec/contec-bottom-bracket/contec-complete-bottom-bracket/contec-cbb-150-bottom-bracket-universal-110mm-silver-457704/
I think it's different from the press fit BB.
Another thing to consider when you design the front frame is that most rear wheels, your front wheels, are not symmetric, they are normally wider on the cassette side.
 
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Jan 23, 2023
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Thanks for the suggestions. The reason I don't want to go with a salvaged shell is because I'm trying to stop accumulating parts that I can't throw away (because I might be able to use them later). A shell from a donor bike often comes attached to other parts.. I do plan on getting a second hand 28" wheel with a Nexus Inter 8 roller brake gear hub and using the 28" rim to replace the bad one on my daily upright bike.

A python can have a shorter chain than a conventional bike which might interfere with the
shifting of gear, so it's very important to have the central front chainring inline with the rear central chainring.
The BB comes in different width and it's very difficult, without trial and error, to find a combination
which works.
(..)
Another thing to consider when you design the front frame is that most rear wheels, your front wheels, are not symmetric, they are normally wider on the cassette side.
Thanks, this is definitely something to consider. My plan is to make the BB adjustable forward/backward to get the right distance from the seat and to tension the chain. Lining the BB up sideways so the chainrings are in line is no problem, but then the width of the BB still determines if the pedals/cranks are the same distance from the middle of the wheel/frame. I was looking at data sheets for gear hubs, I can get the distance of the chainring from the center of the wheel from there, but I'm not sure what the relationship is between the BB width and the front chainring distance. In other words, how far on the axle does a crankset chainring go?

Awesome, that's exactly what I want! That'd allow me to use a 40x2.5mm aluminium tube. Aluminium is often extruded, so there is no weld line to remove.

maybe a view of where it is going ?
My current idea for the BB is something like this:

The frame tube is 35x35x1.5 mm steel. A piece of 40x40x2.5 mm aluminium tube slides over that to adjust BB, and a 40x2.5 mm aluminium BB shell is welded under that. Then a bolt or maybe set screws keep it in place on the square tube.
 
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Nov 20, 2022
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West Virginia, USA
You can use a series of holes drilled across and then use a hitch pin to secure it. Might rattle a bit, but I’d trust it more than a bolt. Easier to do with no tools as well.
 
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