Monday, June 11, 2007

Final drive - well for now anyway

Building this boat seems to be a continual process of design and redesign.
The last couple of days I've been focusing on the drive, gettoi the power
from my feet on the pedals to the propeller. I thought I'd found the ideal
with Rick Willoughby's swing-arm double roller clutch mechanism till he
pointed out that the prop freewheels when you're not pedalling, and that
means you can't back-pedal. Back-pedalling could be important for
manoeuvring and also for unwinding any weed so I had to think of another
idea. So then I thought of some form of belt drive using steel cable, but
how do you join it?

Yesterday though I had the breakthrough (well I hope it is). I got to
thinking about the flat belt drives of the old cotton mills. They'd twist
and turn around the place so why couldn't I do the same? But what to use for
the belt that wouldn't stretch or slip? Nylon webbing seemed to be the
answer to the stretching, but the slipping? Then it hit me, Velcro! It's
very flat so easy to join, it can be stitched even, and if I used the hooked
side as the belt I could put the fuzzy side on the pulleys. I can even melt
stripes into it so that it becomes a fuzzy cog. That means that the peeling
off part as the belt comes off the pulley will be easier too. And it's easy
enough to make up my own pulley wheels to get just the gearing I want.

No doubt there's downsides I've not thought of. Possibly it's not the most
efficient system in the world, but as I'm not worried about 100% efficiency
that's not a problem. Perhaps it'll stretch or slip too much, well it's easy
enough to make up a test rig to find out. For now though I'm happy.

Now on to the next problem.

PS I've blogged this from my mobile, so excuse the typos, please.