The compressor used on HanoiSolver is a version of the improved double-acting
Hempel design. The motor's stub-axle carries a 24t gear which
engages two, subsidiary 24t gears. The subsidiary gears
share an axle with Technic cams which drive the small
pneumatic pistons round. (You can also use Technic medium pulleys
rather than the cams -- the distance provided is the same).
The original Hempel double-acting design connected the pumps directly
to the subsidiary 24ts, but this gave them a slightly short stroke. My
own conviction is that a LEGO pneumatic pump must end its stroke
bottomed out in the fully closed position to get decent pressure. The cams
(or medium pulleys) fully open and close the pump to give a bigger
turning radius and better efficiency.
To activate the pneumatic valve, the axle of one of the subsidiary 24t gears runs to the
rear of the compressor and terminates in another 24t gear.
This gear engages yet another 24t attached to the arm
of the pneumatic switch (adapted from a design by Mindstorms
forums user Blaze2).
What happens is that the 24t on the switch arm is just
in contact with the 24t on the drive train. The 24t on
the drive train spins fairly freely (there is a very slight
clicking noise of the tips of the teeth of 24t-drive knocking
against the tips of the teeth on the 24t-switch).
When the motor reverses direction, there's enough
contact for the 24t-drive to catch the 24t on the switch arm and
throw the switch lever the other way.
I've used this pump-switch combination a lot in the last few
months and I've found that it works very well so long as the two 24t gears
are absolutely parallel; it doesn't work well
if the switch is not securely anchored.
The air pressure is monitored by a large pneumatic cylinder which is
connected between the pumps and switch. The cylinder is held
normally closed by four yellow rubber bands. As air pressure
increases, the cylinder arm extends until it hits a touch sensor
(SENSOR_1) connected to the RCX. The photo opposite shows
the system fully charged (piston extended). The beauty part is
that, for the small quantity of air used by the small cylinder on
the claw, the piston also provides enough reserve air that I
didn't need one of blue air tanks.
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