Friday, 31 January 2014, 9am
Took the beast out for its first test run yesterday. Had to
do quite a bit of work before that momentous occasion. First up was building a
geared steering mechanism –
The radius of the fulcrum slides along the bolt, increasing
from 41mm to 56mm radius and increasing the turning gearing by about 2.5 times
at full lock. This enables fine control at small amounts of steering and
maximal turning near full lock. The spring, which was installed to assist
return from full lock, was later removed, as the gravitational return provided
by the wheels themselves proved an adequate assist. Steering at centre –
Left turn –
Right turn –
Not that the pivots are set up to mirror the movement of the
steering arm, resulting in very little rotation in the rod end link.
Handlebar arrangement, as in a tracked vehicle, handlebars
made from a piece of a walking frame –
One handlebar rotates back as the other moves forward. Both
are linked to the same mounting point via two adjustable track rods –
Mounting detail –
The mount holes are ‘twisted’ about 30 degrees, so that I
could get the mounts as close to the outside of the seat frame as possible,
maximising rigidity. Handlebar bearings are made from polypropylene chopping
board.
A mount for the speedo sender was fitted to the chain
tensioner mounting –
This was a bit tricky. You’d think the magnet would be set
up to run between the cable ties, allowing you to get it as close to the sender
as possible. It wasn’t, and I finally found it worked when running next to the
top tie.
A full-length chain guard was installed between the seats,
made from a half section of that wonderful hang glider tubing of Eddie’s.
The last problem I had to overcome was that the leverage on
the back shocks was too great. The shocks were compressing too much, even at
the maximum pressure of 300psi. So I bodged up some steel mounts to move the
shock fulcrum further away from the centre of the swing arm pivot. I also took
the opportunity to move the shock mount directly under the swing arm. This
brought the shock pressure down to a more reasonable 200psi, though it had the
unfortunate side effect of reducing the travel from 4” to 3”. A project for the
distant future will be to tidy up this end of the swing arm with some carbon.
Two views of the mount –
It’s a bit messy,
and I haven’t painted it, but at least it works. The lower shock mounts were
reversed and trimmed down to keep the shock ends working in as direct a line as
possible.
The test run went
well, only attempted a short run (1km), with no passenger to assist, but still
managed to get it up to 35kph on the flat. Then I bought it home and checked it
over, but there was no need to adjust or tighten anything up.
As it looks at the
moment, still a bit blunt at the front end without any fairing –
Note drink bottle
holders at the rear, mirror and horn. It’s a bit on the chunky side, weighing
in at 47kg. Magura ‘Big’ disc brakes are awesome, chassis is very rigid and
ride is nice and smooth, as is the gear shifting. As is usual with cycle
gearing, reverse is engaged Flintstone style. Hope to post a video of it in
action sometime soon.