Rocketry Planet

Programmin' by Pete (PbP) offers a variety of electronic devices for high power rocketry. The programmable (low power) timer and switch selected (high power) timers (Fig-2) are the focus of this review. Both units are single event timers designed to fire an ejection charge, or ignite motors in flight. All PbP products are available in kit form or assembled and ready to use.

During the July 1998 TRA launch at Bong Recreation Area in Wisconsin, I launched my VB “Wild Thing”, a 5.5” nicely finished model. The motor ejection charge from the I-284 motor failed completely and the rocket performed a tumble recovery.

The onboard beeper was sealed inside and only audible from a few feet away; we knew where the rocket landed, but it took us over an hour to find it.

The “Wild Thing” incurred only minor damage, but it could have been destroyed had it gone ballistic. It was this day that I decided my bigger rockets (5.5” and larger) would begin to carry backups for recovery.

We have three PbP timers, a low power programmable timer and two high power switch select timers, both of which were assembled from kits.

Building the kit version is a rewarding way to spend a couple of hours. A quality 15 to 25 watt soldering iron with a fine tip, rosin core solder, magnifying glass and wire cutters are all you need.

If soldering is new to you, purchase a generic PC board and a few resistors from Radio Shack and practice first.

Avoid using too much heat by removing the iron just after the solder melts and flows smoothly.

Take care not to create any solder bridges (connections that shouldn’t be) by not using too much solder and keeping the surrounding foils on the PC board as cool as possible.

The instructions are very well done and even give you a break or two during assembly.

Before beginning assembly, I cut about 40% off one end of the PC board. (Fig-1). There are no parts mounted there on the high power version of the timer and only one jumper wire is required.

When possible, plan your backup before you start building your project. If you are building a kit, you might need an extra centering ring or tube coupler. My first projects incorporating timer-activated backups were less than perfect.

While they did function, the process of pre-flight setup and arming was difficult. I install two .5” PVC fittings (Fig-5) in the bulkheads at the parachute side of the electronics bay of my rockets. Notice one of the fittings has a plug which I utilize when only one ejection charge will be used.

You want to plan your installation so you can connect the ejection charge(s) while at the pad; it’s very embarrassing to blow your nose at the RSO table. I find the best setup incorporates a small hatch (Fig-4) which can be opened while the rocket is on the pad; where you can give the timer a final check, connect the ejection charge wires, and arm the timer.

The programmable timer and switch select timers both perform the same function, they fire a flash bulb or electric match after the time you programmed or set elapses.

All PbP timers are started at launch by opening a circuit. This can be accomplished by a pull pin attached to the pad, a wire placed under the motor exhaust which will burn up, or a microswitch which will open as the rocket clears the rod or rail.

I used the pull pin method for a few launches, but now prefer to use the microswitch for activation.

The programmable timer can be set for any time from 1 to 255 seconds. It is programmed by pressing a small button; you would press and hold it for 15 seconds to achieve a 15 second delay. It can be difficult to get it set exactly to the number you want.

The switch select timers only allow 15 possible settings but are easier to select your time by setting four dip switches. I have one timer which can be set from 1 to 15 seconds (standard) and the other can be set from 3 to 45 seconds in 3 second increments.

PbP will program the main chip for any set-up you need, at no extra cost. All PbP timers are available in low or high power versions. The high power uses a more powerful 9V battery, and can supply a lot more current to the flash bulb or electric match, which is recommended by PbP.

Take some time to try out the timer on your workbench. Use a 9-12 volt light bulb to simulate the flashbulb; Practice setting, connecting the simulated flashbulb, arming and triggering the timer until you understand the operation completely.

It’s also a good idea to also ground test the unit in your rocket to make sure your ejection charge fires and has the correct amount of black power.

I use a short length of .5” PVC pipe to make disposable charges (Fig-5). A small piece of round foam insulation suspends an electric match while the epoxy sets, and it’s ready to add the black power.

When my motor also has an ejection charge I use a longer delay than recommended and this functions as the backup. The timer which is much more accurate, fires the primary ejection charge. A simulation program like WRASP will report the elapsed seconds from liftoff to apogee; set your timer to that number.

We have had good results with all our timers. At the last launch I attended, (Fig-3) my switch select high power timer performed flawlessly in two different rockets, both deployments fired at or very close to apogee.

If you are launching rockets over 4” in diameter without backup deployment, I would recommend that you consider adding a backup system using a PbP timer.