Wednesday, March 27, 2013

Yet Another Design

Right Side

Why another design?  I would like to change a few things on the newest handcycle.  These include:

  • Move the seat closer to the ground in order that I am more comfortable with my hands to the ground at stops and that I can crawl on and off the bike more easily.  
  • Get rid of the chain running between my legs (that required a chain guard!).
  • Change the fork design relative to the headset bearings. I would like the bearings to not have the "give" or play between the fork and base that the ones I have used permit.  In particular the bearing in the existing fork use a rubber seal that must be compressed.  For the new design I will probably use the same bearing that I use in the retractable wheels' axle.  They are indeed solid. 
  • Design the neck of the base to have an interior "beam" of carbon fiber in order that I cannot produce deflection in the bike's neck when powering up the handcycle.
  • Move to a larger rear wheel for comfort sake (650c or 700c).
  • Allow more room between the chain and the neck of the base especially during turns.  The existing bike's chain-neck interaction is problematic during startups when I may suddenly steer pretty wide in order to maintain balance. Again, this occurs at very low speed. At higher speeds, the handbike can lean into turns (with the retractable wheels up).  Of course, now that I have the retractable wheels the steering/balance problem at initiation of movement may alleviate itself.


The most obvious change in the design is relative to the chain.  This new design has two chains -- one that runs nearly horizontally and another that runs vertically thus removing the problem of the chainline.  The latter chain is hidden by the chain guard enclosure.

I am testing the retractable wheel design on my current handcycle.


Left Sde

The design will probably change before I have a chance to build it -- but that is the nature of design!

Retractable Wheels (Training wheels?)

Design of Retractable Wheels

For me to use the handcycle, I found quite quickly that I would need some training wheels and most likely some sort of steadying device when at a stop.  Hands to the ground did not quite do it.  Of course, when I am getting on and off the handcycle, I find that the need for stability is ever present.

So I designed two retractable wheels (inline-skate wheels), connected by an carbon-fiber axle. The wheels "hide" themselves (aerodynamically speaking) when not needed, by rotating up and back into the recess behind the seat.  Since there retractable mechanism is built from carbon fiber, the device maintains a low weight.

Nearly completed -- Still need to add lipstick to the handles/wheel supports
The concept is simple enough.  I use a lever arm to rotate the wheels into place.  Both wheels fit on an axle. The axle runs through a bearing set built into each side of the seat.  A spring-loaded plunger pull-pin locks the arm/wheels into either retracted or lowered position.  The reason for the axle -- and the connection between both wheels -- is that when coming to a stop or when moving, I will have the use of only one hand at a time to raise or lower the wheels. The spring plunger allows for the device to find and lock its position easily.  The pictures provide a better explanation.

The parts to the retractable wheels