Tuesday, March 11, 2008
Drive Train In Vain
The time came for one of the most meaty parts of building the trike, the drive train.
We cut a bottom bracket from an old bike with as much connected tube as we could so we have plenty to work with (it can always be shortened). Tabs are welded to the bottom bracket with tube at a precise angle, and holes drilled in the tabs so the whole apparatus can by bolted to the main boom of the trike. This approach has the advantage of making the trike adjustable for different lengths of rider. We fudged a little on the above photo as it is more recent. We forgot to take any pictures of certain parts of the build including this crankset assemblage. Processing photographs for this blog has taught me how useful photography is at spotting things that may have gone unnoticed. Observe the shiny new red synthetic axle grease visible inside the bottom bracket, the brass horn, and the mud. While we're at it, shouldn't that horizontal line drawn on the bottom bracket tabs be parallel with the boom? Pip. -_0
An axle for a pulley with bearing is welded to the side of the main boom to guide the drive side of the chain underneath the cross boom to which the front wheels are attached. Otherwise the chain would rub against the cross boom and that would be unpleasant as well as inefficient.
We've had a number of problems with the drive train, not least with the pulley. Within ten feet of the maiden test ride of the newly trike-like trike the pulley was sheered upward breaking the apparently not so great weld as you can see in these images:
Know, good fellows, we record our foibles as well as our triumphs.
A stronger axle was masterfully welded into place. Another problem we were having was the chain would leave the pulley in hard turns at slow speeds (In first gear). With some help from the Atomic Zombie forums, we affected a cunning solution. A pliable ribbon of steel is affixed around the pulley to act as a chain guard so the chain cannot escape. We added our own extra touch- a little wriggle room is left on the axle between pulley and securing nuts, and a spring inserted so the pulley remains taught but can move wherever the chain wishes it. The new guide pulley looks thus:
Continuing with the drive train, part of a rear derailleur is attached to the back of the main boom behind the seat to pick up slack and help guide the return side of the chain.
The chain was far too long, as you can see in the photograph below, so it was shortened. The chain no longer droops on the ground.
Handlebars and goosenecks were hastily hacked and welded to serve as temporary steerage. The seat long since bent and secured.
The gears and such still need some fine tuning over time, but the drive train is essentially finished. The tadpole trike is now ready for field tests!