Model Rocket Launchers

  Model 2 Model 1
I designed and built this model rocket launcher as I was learning digital circuits back when I was a Junior in high school.

I was very privileged to know John P. Robinson, who was a Professor of Electrical Engineering at the University of Iowa, who put up with my endless stream of questions.

It may now seem crazy to build something this complex with discreet circuitry, but I had not yet heard of a microprocessor and knew nothing about programming. In fact, the Intel 8080 was released later that very same year.

The construction was a bit rough, but hey, I was only 16.



Operation

When the launcher was powered on with the key, you first had to enter the hard wired 5 digit password. Then you entered the count down time in hours, minutes, seconds. Next you entered the pad firing order of up to 9 pads which was displayed on the single digit under the count down time. All pads used the same count down time. The four LEDs to the left of the keypad indicated the input steps.

Later I realized you might want to launch more than one rocket at a time. So to support this, just before the next launch you could enter the extra pad numbers to be launched which lit the LED for each pad on the left. How was that for a hack.

The green lights indicated the pad was programmed into the launch sequence. The yellow lights indicated the igniter clips were touching the metal blast deflector which would also stop the count. The red lights indicated the igniter was connected.

I don't remember what the buttons and switches on the lower front do, or were going to do. There is no reference to them in my construction notebook.

Yes, this launcher was over-kill, but it wasn't really about launching rockets.

Science Fair

When this project was almost complete someone suggested that I should enter it into the science fair. When my chemistry teacher gave me the entry form he told me he didn't believe in science fairs because they were just a bunch of gadgetry, and he didn't know anyone that had ever won.

So I entered it into the Eastern Iowa Science Fair and won first place in 1974. This meant I was entered into the International Science Fair, which later became the Intel Science Fair, where I won third place in the engineering category.
On the Monday after I won the Eastern Iowa Science Fair my chemistry teacher came looking for me in study hall. He sang a completely different tune, and he said he would be happy to go with me to the International Fair at Notre Dame as my "advisor".  Not a chance Mr. Gore, not a chance!





Construction

All logic was 7400 series TTL. The 74LS parts did not become available until two years later.

The only test equipment I had was a volt/ohm meter and an LED. Signals had to be slow enough so I could see they were happening.

All boards were hand soldered point-to-point with 24awg wire. The edge connectors were "stick-on" which were very unreliable and caused me no end of grief.

I had a lot to learn about reliable construction techniques. It was not as easy to find parts back in the days before the Internet either.

Countdown timer board
I designed and built this model rocket launcher when I was in 9th grade. This was my first scratch-built project as I was learning digital circuits.

This launcher was very basic and did a simple count down from 9, then launched the rocket.



Operation

The green light indicated the power was connected. The yellow light indicated the igniter clips were touching the metal blast deflector which would also stop the count. The red light indicated the igniter was connected.

The rotary switch allowed for one of three pads to be selected for launch.

The jack just under the count was used as a "key". The count would not proceed until the key was inserted.

The right switch, when flipped on, would set the count from blank to nine. When the switch was flipped off the count would begin. When the count reached zero it would launch the rocket, then once second later the display would blank.

I believe the left switch turned on the igniter power, but I don't remember at this point.

The three connectors on the top went to each of the three pad igniters. The top jack on the right side connected to the metal blast deflectors on each pad. The bottom side jack was the primary car battery power.

The jack on the left connected to secondary power which kept the unit operating when the igniter was heated.

Issues

Before adding the secondary power supply, the unit would get confused when the igniter was heated. I didn't know why at the time, so I added a second small battery for the digital circuits that was isolated from the igniter. In hindsight, the real issue was the small 18 awg wire I used for the primary power. When the igniter was heated it would draw so much current the voltage would drop too low. The correct solution would have been to simply use much heavier gauge wire.

In the photo above, the primary power jack no longer worked. The seconary power still powered the digital circuits so the display lit up, but it would no longer count down. Not surprising considering how old this launcher is.