[python] Re: Some News

  • From: Patrick van Gompel <patrick_van_gompel@xxxxxxxxxxx>
  • To: <python@xxxxxxxxxxxxx>
  • Date: Tue, 15 Feb 2011 18:17:39 +0100

I uploaded some more pictures. I hope it's more clear now. Mind the bulbs ;-)

Some answers to your questions (I hope you don't mind putting it on the list):
1- No, I bought this seat as a curved rectangle. There's a nice dutch dealer 
who sells a lot of stuff for bike builders: 
I bought the cheapest (most unfinished) one for about 35 euros. Sending those 
things is expensive though. Of course I could have built one myself, but for 
only 35 euros it would be quite a bit of work and testing to get the right 
shape. Not in the bike pictures is the seat material I put on top of this 
wooden seat. I made a seperate photo of this (blue stuff). The same kind a 
material (but black and less durable) is used by many recumbent manufactures 
(at least in NL). It costs 25 or more euros for a new one which is overpriced 
imo. A few years back I bought a square metre for 40 euros. Aparently this 
material is used as a filter for garden ponds and I was able to order it at a 
garden centre. I think that dealer I mentioned sells the same material (blue 
and black): http://www.elfiets.nl/main.php?sNewPage=Ligfietskussens
2- Yes, I used a CAD program. Usually I start with paper and pencil for a 
design (whatever it is), but using the 3D environment of a computer program 
gives me a lot of feedback. Whether things will actually fit is much easier to 
see and simulate. Like for example whether your chainline is not touching the 
frame. You can download my drawings now (cycle.free-creativity.com) You may use 
them any way you want, but I didn't plan to put them online and they might be 
unlcear and with errors. So please use them wisely :-) One error that I 
discovered: the attachment for the rear derailleur is a bit close to the gap 
where the wheel axle goes. This means that when I detach my front wheel I have 
to be a bit careful.
3- Yes, all was done at home. Well, I did have some 'supervision' of my dad, 
since I'm rather new with metal working. The welds are done with a TIG welder, 
so that's why the weld surface looks rather neat compared to other methods.
4- Although I didn't go the most environment friendliest way by using old 
bicycle parts, it was a rather cheap bike for me. Except for the seat, rod 
ends, chain, front tire and mudguards, all bike parts are second hand. Bike 
parts are the most expensive things of a bike, so I had a lot of savings there. 
Stainless steel was about 4 euros a kilogram when I bought it, so that's rather 
cheap compared to the rest. So to (roughly) sum up: seat 35, rod ends/caps 20, 
chain 15, tire 15, mudguards 15 which totals 100 euros which I had to spent to 
make this bike. I guess another 100 euros value for the stuff that I had laying 
around or bought second hand.
To be honest: it's the machines to make the bike that I think are really the 
most expensive.

Same here: I had never welded before, untill I wanted making bicycles. I 
started practising to weld on some steel bars, then stainless steel with 
smaller thickness. First things I made were for good use, but for which finish 
and strenght didn't mattered that much. My first real project was a bicycle 
trailer for big loads. Although it went rather well, 1mm tube thinkness was 
sometimes a problem in corners (I blew a hole in it with the torch). This 
python is my second 'real' project.
Welding class sounds good! Wanted to do that myself (and safe me for my initial 
troubles), but I thought it was too expensive here. So I just gave it a go... 
Problem is: I never know wether I'm doing it he right way and whether my welds 
are strong enough. So far nothing cracked though. Good luck with your classes, 
a python would be a nice project indeed.

There's no front derailleur on my python ;-p  I thought 9 gears would be 
enough, especially since I knew it would take quite some time till I could 
cycle it in the 9th gear. And this bike is more like a prototype to see what 
can be done with center steering. My goal was to make a trike, but I didn't 
like the tadpole designs (hard to make a hook for the trailer and the long 
chainline is a pain in my eye). So I hope to attach the front of this Python to 
the back of a Jetrike. <- if anyone has tried this before, please let be know.
Anyway, some more pictures of the BB attachment on my website. Initially I 
designed this differently (like you mentioned with bolts going through the 
tube), but then I saw the Jetrike design and thought that was a neat and simple 
solution. I was woried about the problem that the nuts and bolt would squeeze 
the 40x40x1.5mm tube too much and I would end up with a wrecked part. Though, I 
gave it a try and I think I was lucky because of a thing I hadn't foreseen: the 
square tube bends outwards and it comes in contact with the bolt. It can't bend 
any further because the bolt blocks it. See the last picture of the BB 
adjustment. Notice that the bolt is straight and the top part of the square 
tube is curved upwards. So I think it will hold, but time will tell.

That was a lot of writing, but I hope it was of some use,. If you want more 
info, please ask.

Hi Patrick,
Thanks for posting a few pictures on your web site.
I really like your design, it is very clean and looks fast and comfortable.

I have a few questions for you:

1- Did you make the seat yourself? - If yes, can you tell me how you did it ?
2- Did you draw your python with  some sort of engineering design software (ie: 
AutoCad) or did you improvise a drawing on a piece of paper ? - If you have an 
AutoCad drawing would you be willing to share it with the rest of us ?
3- Did you do the fabrication/welding yourself or did you get someone else to 
do it ?
4- What do you figure the cost of your python is right now ?

The reason I'm asking all these questions is that I have been wanting to build 
a Python for over a year now and am slowly gathering ideas and designs for a 
project. I'm taking a welding class next week and
 I might be able to weld a frame for the course project. However, I don't have 
any CAD drawing to go by or anything close to a project plan and would like 
something to start with.

One thing I noticed on your design is the way the front derailleur is attached 
to the frame using the two steel plates and the 4 bolts. Overtime you might 
find that the bolts will loosen up a bit and that the front derailleur might 
move forward as you push on the pedals.
One quick solution to make sure this problem doesn't occur would be to secure 
both plates onto the frame by drilling 2  holes through the frame and plates 
and insert 2 threaded bolts. 

Thanks and have a great day.



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