Issue 98, September 1998
Smart Rockets - Data Acquisition in Model Rocketry

LAUNCH BOX CONTROL

The launch control box shown in Figure 3 has many of the features of the standard Estes Electron Beam launch controller. Between the batteries and the nichrome igniter are the safety key and the armed indicator (LED D1). The launch switch is in parallel with the LED.

The igniter is connected with the safety key removed, so the clips to the igniter are not hot. Inserting the safety key applies the battery voltage across the series combination of the armed indicator and the igniter, which enables enough current to flow to light the indicator but not enough to ignite the igniter’s black powder coating. A nice feature of this design is that any break in the wiring prevents the armed indicator from lighting.

Our major modification to the Estes design was to replace their SPST launch switch with a DPDT momentary push-button switch (SW2). The second channel of this switch shorts together the two contacts brought out to the fins of the rocket. A 20? four-conductor cable brings the igniter current and the payload-trigger signal to the launch pad.

Three small blocks of wood epoxied to the blast deflector of the launch pad (see Photo 1a) support the rocket, while electrically isolating the fins from the steel blast deflector.

Copper plates are attached to each block of wood, and two of the plates are connected by leads to the trigger signal lines of the launch cable. The two rocket fins with conductive-paint contacts are positioned over these blocks, and the third fin rests on the unconnected block to balance the model on the pad.