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The Jaculus is my version of the Python. The Jaculus is quite similar to the Python since it is designed with the same things in mind. Especially for the Pivot angle i have looked at other Pythons.

During the borring classes at highschool i came up with a design for a recumbent. I had never heard of the python and did absolutely not know whether the designed bike would be rideable. The Jaculus has (just as any Python) a huge negative trail, while all other bikes have a little positive trail. Everyone told me that bikes with negative trail would be unrideable. So I did forget a bit about the designed bike.

Five Years later I heard about the existence of the Python project. Apparnetly it IS rideable. After the purchase of welding equipment there were no obstacles for making my own python.



The following things were kept in mind while designing: The bike has to be fast, so it has to be low. The bike has to be able to cope with normal trafic, so it can't be extremely long. Waiting for replacement parts is annoying, So as manny standard parts as possible. For rideability a pivot angle between 60 and 65 degrees is a safe option.

This resulted in the following design, Which is refined on paper (and beermats).


The shortcommings of this bike are: It is made from 2 mm steel tubing, so it is heavy. The frame would have been straighter, lighter and easier to make, when the rear fork would have contiued to the lowest point of the frame. The pivot could have been mounted far easier to the rear frame. (The pretty stupid solution can be seen in the foto below.) There is not enough space for the mounting of all parts.

Shopping list

  • Racingbike (for parts and wheels)
  • 2,5 m square steel tubing of 15 x 30 mm, 2 mm wall.
  • 1 m square steel tubing of 40 x 40 mm, 2 mm wall.
  • 1 m steel strip of 30 x 3 mm
  • Steel bracket housing
  • Flevobike pivot
  • Recumbentseat.
  • Derraileurpad
  • Nuts and bolts to mount the seat.


The tools I used to build the frame:

  • Electrode welder
  • Angle grinder
  • Drill
  • Vice
  • Plumber wrench
  • Lock jaw pliers
  • Bar clamps (3 is the minimum)
  • Carpenters rule
  • Try square
  • Iron saw
  • File
  • Wooden blocks (to temporary fasten things)

I worked in a rather cramped shed, but that didn't bother me much.


I started work at the rear fork. This is the easiest part of the bike, so it is suitable to get accustomed to welding.

I cutted two 42 cm pieces of the 30 x 15 mm tubing. I flatned one end (3 cm) of both tubes. This is to make it possible to mount the rear wheel. The other end I cut at an angle to weld it nicely to the 40 mm square tubing. Then I made the bend at the lowest point of the frame. I did this by cutting 3 sides of the square tubing and bending the other side. The 3 cutted sides are welded at the right angle.

Next I started work on the frontframe. I did cut two 76 cm pieces of the 30 x 15 mm tubing. I did cut these two pieces at 35,5 cm from the end, to be able to bend them. At this bend I atatched a piece of the strip, to provide a mount for the front wheel. Subsequently I welded the brackethousing to the two pieces of the front fork.

Next I did cut away some steel to make room for the pivot housing. It to a lot of efford to get this straight, but after an hour of grinding, fitting and bending I decided to try it. It seems that it worked out fine.

The result

Dit was het eindresultaat. Het voortandwiel loopt aan tegen het frame, daar moet ik nog flink wat metaal wegslijpen, maar dat kan wel, want ik heb toch veel te dikke buizen gebruikt.

Na het monteren van alle onderdelen begon ik aan het leren fietsen. Ik had begrepen dat een python zelfs voor flevo rijders een hele uitdaging zou zijn. Dit bleek voor mij gelukkig niet te kloppen. Na een paar minuten reed ik al echt stukjes en binnen een kwartier kon ik de fiets overal heen sturen en durfde ik al het verkeer in te gaan. Een echte aanrader is om de eerste dagen werkhandschoenen te dragen bij het rijden.

Zoals op de foto's te zien is is het stuur nogal verwaarloosd. Dit komt omdat het stuur van een python echt totaal niet nodig is om te sturen. Het stuur (bij mij een houten stokje aan een kant) dient alleen om een plek te bieden voor de remgreep.

Future improvements

I am planning to build a Python with an adjustable pivot angle.

This future Python will have a BB as pivot, instead of the flevobike pivot.