Cruzbike construction continued..

Apart from the seat, the new bottom bracket (on top of the front wheel) and the front fork dropouts are the new artifacts to be fabricated.



The new dropout is pictured on the left ( courtesy the cruzbike yahoo group ) .



The reason these dropouts are used is that the width of front(~100mm) and rear(~130mm) hubs are different. If you notice the picture carefully, the arm that attaches to the front fork is at a different level than the rest of the dropout, about 15mm inside. This allows using a 130mm hub along with an ordinary front fork of 100mm.

These can be machined out of 4-6mm steel (or aluminium) plate.

The bottom bracket.

The bottom bracket for a cruzbike sits on top of the front wheel. My initial design used a bottom bracket cut out of an old Hero jet cycle ( the ones used by doodhwallas ). However, apart from the weight, there is another big flaw .

Since the bottom bracket 'triangle' changes every time the length of the top tube is changed ( when a person of different height is riding ) , or when a front fork with a shock absorber changes height, one of the angles of the triangle has to be variable. (see the attached picture, courtesy )

The design I used is similar to the one in the cruzbike kit . It uses a standard BB with a telescoping boom , but an additional pivot allows the angle to change. Got this done on the second attempt.

Another advantage of this (somewhat expensive) procedure is that it makes the front triangle strong. Without a strong pivot joint, the whole assembly will flex with the torque generated by the pedals, and that torque will cause the tube to twist and the chain might slip off.

Forthcoming..
The seat, and putting it all together.

Choosing a donor bike for a cruzbike.

Currently, bike manufacturers (atleast in India) seem to believe in unusual bike frames. The traditional diamond frame seems to have given way to many versions of the y-frame . I believe the reason for that might be, kids (or even women ) can easily straddle the top tube of a y-frame bike, and they would not need to keep changing frames as they grow older. However most bikes are too heavy .

The cruzbike manufacturers have a recommendation page for the donor bike. There are also a few pages that talk about Tom Traylor's recommendations (Tom is the original designer and patent holder for moving bottom bracket front wheel drive bikes, from which the cruzbike has evolved) However, some of the things dont really translate well into indian conditions:

• Hardly any bikes are available in multiple frame sizes.
• Which means that one needs to choose a bike with as low a top tube as possible, regardless of frame size.

While I started out with a hercules wow , I believe the best donor would be the old Hero ranger. (I cant seem to find pics on the net). It had a low top tube which was a straight bar, which makes it easier to attach the seat. The head angle is also more forgiving than the hercules wow. Although the bike is not in production any more, it should be easy to buy it second hand from a local bike shop.

So to evaluate a potential donor bike, take a tape measure (to measure the top tube height, anything below 26 inches is great ) , protractor ( to measure the head angle, close to 60 degrees is optimal ) , and a weighing scale ( to measure the weight of the bike ). My Hercules Wow weighed about 16 kilos , I expect that the additional kit would be between 5-10 kilos, so its important to choose a donor bike that is as light as possible.

Cruzbike in Bangalore: work in progress

I've been toying with the idea of recumbents ever since the day long rides from Bangalore to Savandurga would leave me sore in all parts. Surfing the net led me to recumbents. And I have been dreaming ever since of owning one. Done everything from write to bicycle manufacturers about them (well, ye, its hard to contain a giggle hearing that, considering how good our indian bicycle manufacturers are at actually communicating, for the record, i've never got a reply from *any* manufacturer), to start building a Short wheelbase (SWB) recumbent. But the attendant problems (Find a good fabricator, chain management and many others), meant that the bike never saw light of day.

Until now.

Yep, in may I surfed across to cruzbike. Never mind all the features , but what struck me first was that this is probably the easiest recumbent to home build. Cruzbike actually sells a kit that can convert a y-frame bike into a cruzbike, but at 400$ plus shipping and customs, I wonder how much that will turn out to be. Hence the decision to build.

In the next few posts I'll try to lay out what it takes to build a cruzbike.