The helicopter's drive
motors. The Y motor is
on the left, the X motor
is on the right.
The pot is a 10-turn wire-wound pot that is connected by gears to the “X” motor. The gears make it so that
the pot turns no more than its maximum 10 turns during the trolley’s travel. The “Y” Stamp can know where
the trolley is with an RC circuit, and do the right thing with getting the copter home in the vertical direction.
This is especially important near the top of the arc-shaped flight path, where “Y” may have to go up before
it starts going down. I calibrated it by guessing some numbers for RC time, and having an LED flash
different number of times for different positions. I then moved the trolley by hand and marked the positions
where the number of flashes changed. It only took a few tries to get a scale of numbers corresponding to the
Limit switches tell me if the copter is at the ends of travel in the “X” direction, and if it is landed at its home
landing pad. I did not use a limit switch at the upper landing, and instead used the precision of the stepper
motors counting steps to determine the final position at the top landing. This works just fine, but if I had it
to do again I would have a switch there, too, as it would make programming the flight path much easier.
Another switch detects if a ball has loaded into the helicopter. Leverage is needed to convert the tiny
movement of a microswitch into a larger movement that a marble can easily trigger.
The flight path of the helicopter can be calculated and worked out before ever flying it, but it turns out that doesn’t help much.
One needs to see it working to evaluate the speed and smoothness of the movements. You can get an idea by turning the
winches by hand and counting the turns. Make an educated guess, and watch it fly. It becomes immediately obvious how to
tweak the numbers to get on the right path. Getting it close is not too tough. Getting it just right is an art. The easy
reprogrammability of the Basic Stamp comes to the rescue.
The stamp controlling the “Y” direction also controls the rescue device. When it is involved in a rescue, it signals the “X”
stamp that it is busy, so that both stamps will be able to start together when flying the copter. The “X” stamp tells the “Y”
stamp to start, but will not tell it until the “Y” stamp no longer gives a busy signal. If one motor is trying to fly the copter while
the other one is unavailable, all kinds of bad flying can happen.
I also made a hidden test button, which could be used to start partial flights. A quick push gives one flight path, and a longer
push gives a different path. This was really useful when programming the flight path. In the final version, I use it to fly the
copter only one way: to land on the top and stay there, which is useful for transporting the RBS.
When the helicopter lands at its temporary upper landing or at its home landing pad, there is some sway to it. Since it is
important that it land predictably in the right place, there are guide rails to assist it. At the base of the copter is a “V” shaped
guide rail on each side, and the bottom skids of the copter also assist in guiding. On the landing pads are vertical rails that guide
it into position, one at the top pad and three at the bottom. They are made of 1/16” brass rod, and painted black to make them
The elevator at the
top, about to release a
marble. The blue post
in the center dumps
the marble cradle.
Slide for the elevator or the rescue
device. The brass rectangular rod
and the shim with it are removed
right before soldering.
The elevator has a similar operation to the helicopter. A stepper motor winches the
elevator up, while at the same time lowering a counterweight down. A guide pulley
separates the elevator and counterweight far enough from each other so that they
don’t hit each other during travel. Limit switches at the top and bottom tell the stamp
where the elevator is, and an “elevator loaded” switch tells when there is a marble in
the elevator waiting to go up.
The elevator is attached to a slide that rides on the same kind of rail (rectangular
brass rod) as the helicopter. The slide is soldered together out of pieces of brass.
On one side some pieces of .003” brass shim are soldered in to give clearance. The
whole thing is clamped together with it around the rail and another piece of shim.
Then the rail and one shim are slid out, and it is soldered. It is important that the
solder is flowed in from the outside, and in sparing quantities so that it doesn’t get
inside of the slide. This gives a slide that is .003” bigger than the rail. When the
motor lifts from the center of gravity of the elevator, and two coats of car paste wax
are on the rail, it slides up and down easily.