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The Velassi


Evolution of Vélassi design

While I really did my best to have the Vélassi as functional as I can, this is still a prototype and I lmade a few mistakes. It did work and is fully usable but there is room for improvement.
I recently finished what I consider to be the final design of Vélassi ‘Version 2’. But experience have shown that even after the start of the manufacturing I still did design modifications.

What will be new:

  • New steering geometry
The big one, steering geometry. The present Vélassi steering geometry is fundamentally adapted for handlebar atop the steering axis (I reused a rans Stratus fork) and did not work properly at low speed with under seat steering as there is no stabilisation effect due to the arms and handlebar weight, neither with the ‘tiller effect’. With a remote steering, you can adopt the best possible geometry without having concerns about ergonomy. I will use a ‘reversed’ fork on a very upright steering head, angle 82°, quite similar to what was done by Mike Burrows on his LWB version of ‘RatCatcher’ (also here). I will left the V-brake where they are, so they will be behind the fork
This geometry will allow a higher steering angle and smaller turns, as fork steering is now limited to ~45°
  • New wood
Oak is nice, hard and stiff but it is heavy and gluing it with epoxy is problematic as it lack porosity, hence the reinforcment with threaded rods I made. This reinforcment was quite long to made and has a significant weight. So the version 2 frame will be done in light wood (fir) which have no gluing problem (failures being generally in the wood aside the gluing zone) and there will be no reinforcment threaded rods.
  • A bit different frame structure
Fir being less stiff than oak and due to the new frame geometry being much longer, the torsional stiffness shall be looked at closely.
  • There will be a bit more wood in critical places (that’s ok, fir is lighter than oak).
  • Beams axis will be spaced as much as width clearance permit.
  • Some shear plates may be added to improve torsional stiffness, but frame will not became a complete torsional box.
  • Instead of using 20×20mm beams, I will use 9×50 or 9×40 beams, this will also allow to have the beam axis space wider than on the original version, to improve torsional stiffness.
  • Front diagonal was centered, so poorly participating to torsional stiffness. It will be now doubled and set on each frame side.
  • Frame design is much more simple with less parts and less complex cuts.
  • Other frame modifications
    • A thin front protecting plate will be installed to avoid dirt in the head bearings (and to have room to sign the frame).
    • The plate near the rear folding axis will be removed to have a more aligned chain line (I can’t remove it now because the suspension intermediate plate is articulated there).
    • The seat plate support will be less angled to allow easier seat reclining (I had to gouge the seat plate to recline the seat at its present position) and the rear back support is also be set a bit more backwards. Some stiffening on the back of the seat plate will be added to help install a luggage carrier, if needed.
    • Seat and bottom bracket will be a bit higher, with height difference reduced
    • I am convinced by short cranks (152 mm), so the clearance between bottom bracket and wheel will be reduced
    • Handlebar axis will be set a bit more backwards.
  • There will be a top shear plate behind the steering which will create a compartment to be used for electronic stuff (USB converter from dynamo current and GPS tracker if needed). That might also be used as small bag support.
  • Bottom bracket will be done with two aluminium plates in order to be capable to install a mid-drive motor
  • There will be a real pneumatic shock instead of the rubber blocks.
  • Rear wheel dropouts will have independant holes for trailer to avoid messing with wheel shaft and nuts for trailer attach.
  • A chain retainer plate on the wheel sprocket will allow unfolding rear frame without having to deal with chain on sprocket (like what is done with chain pulley).
  • Chain pulley shaft will be set directly in the rear frame, not on a separated part, as the load are quite high and this part was never well maintained (it ended up glued on the rear frame).
  • A traditional town bike chain guard will be installed on chainring (single speed chain is too wide for chain tubes)
  • A kickstand will be installed (made in wood, as it will be quite specific and also to save weight).

There is a drawback to this new design, the top beam is significantly higher than in former design (by ~50 mm), so it is more difficult to seat. However yet I often have my leg going over the bottle when installing, so this is not much different.

(c) Pierre ROUZEAU
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Page mise à jour le 24/09/2019 17:17