Off Belay

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.