How it Works - The P.A.L
In case you were wondering, heres how the technical aspect of this works. I built a P.A.L. Paw Activated Launch mechanism for him. It simply allows him to press on a 4 x 4 pad that sets things in motion. The P.A.L. essentially converts Stetsons frenetic paw slap into the 3 second press that is required to fire off a rocket.
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Behind the Curtain
The first step in its development was to fit it with a low-pressure micro switch and a light spring. It does not take much force to activate it. This worked fine but when we test fired an igniter (Stetson thought the smoke was cool) I realized that he was not going to hold it down long enough to completely burn the igniter. So I fitted the PAL with a relay and latched it with a diode. This required another switch to re-set the latch condition. I used a magnetic security switch to accomplish this. You can see it between the buzzer and battery. I also use this as an arming switch. The magnet for this is in the flip up paw pad that he presses on, so when it is down it arms the circuit as well as the pulsing continuity buzzer. This lets Stetson know visually and audibly that system is ready when it is flipped down. The second problem I realized was that after the rocket was launched the leads were latched into a hot status. I launched a couple of rockets by accident this way. The way I solved this was to add a capacitor to supply power for the relay. The capacitor is tied to the common terminal and is charged through the normally closed relay terminal that is tied to constant 12 volts. When the relay is latched open by applying power to the coil the relay swings over and connects the capacitor to the normally open contacts which is tied back to the coil and supplies power until the capacitor drains at which point the relay returns to the at rest status. The magnetic switch now serves strictly as a security measure as it is no longer need to re-set the latch condition. There is also a constant buzzer that sounds in the latched (Ignition) condition. This gives Stetson audible feedback so he will know that he has depressed it. This was done primarily for training purposes to give him instant feedback. Another training feature is the optional continuity buzzer kill switch. I generally leave the PAL on the floor so I can give Stetson sporadic launch drills. Since I hook up a light bulb for visual feedback the buzzer kill switch is a very useful addition.
So this is how the launch sequence goes; the igniter is hooked up with the PAL in the flipped up position (Disarmed), after connecting the rockets igniter to the system, I only need to flip it down (Armed). This not only arms the system but also activates the continuity buzzer. The buzzer warns everyone, including Stetson that a launch is imminent. Once Stetson presses on the paw pad it activates the relay, which latches for 3 seconds and burns the igniter and then shuts off. I then disarm the system before connecting the next rocket by simply flipping back the paw pad. If I forget to disarm it the continuity buzzer will remind me when I connect the leads to the next igniter. By the way, the 9-volt battery is for training only as it does not pack enough oomph to activate the relay and get a good burn on the igniter. I hook up a 12-volt external source for launching.
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