What is CPR?
CPR is an altimeter based, two step parachute deployment system incorporated into our latest line of high altitude rocket kits. Using an altimeter, a small drogue chute is deployed at apogee allowing for a fast decent. At a user-selectable altitude, the altimeter fires a second charge, deploying the main chute allowing for a soft landing. The altimeter is centrally located in a special compartment within the main airframe. The drogue chute is ejected from a split-point in the airframe just above the fin/motor section while the main is ejected at the nose cone. Both chutes are deployed using our exclusive Piston Ejection System. Click the CPR System button in the webstore for more details.
DEPLOYMENT IGNITER SELECTION
Electric matches or igniters have a higher degree of reliability due to their more consistent current requirements. The altimeters and staging timers that PML offers can be used with most low-current igniters, including flashbulbs. The resistance reading of what you intend to use is important. Here`s why:
E = I x R, where E is Voltage, I is Amperage, and R is resistance. We know the Voltage involved depending on the onboard battery. We also know from the specifications of the unit that the ignition device must fire with a certain amperage range. So, we need to find R, the Resistance, to determine which ignition device can work successfully with the device we intend to use.
Battery = 9 volts
Current = 1.25 amps
E = I x R, 9 = 1.25 x R; rearranging, we get R = 9/1.25 or 7.2 ohms. Your ignition device must be 7.2 ohms or more to work properly with the altimeter using a 9v. alkaline battery.
Igniter manufacturers will specify the electrical usability (ohms & volts) range for their devices; contact the igniter manufacturer for their specifications. We strongly recommend that you check each igniter you intend to use before flight to determine that it is good and within the ohm range needed. We also strongly recommend that you ground-test the electronic device you intend to use with the ignition device you intend to use before committing that combination for use in an actual flight. Ground testing instructions are included in our detailed instruction package provided with each of the Electronic Deployment Devices we sell.
Ematches vs. Igniters The difference between ematches and igniters is that ematches are intended to ignite an easy-to-burn substance quickly, such as the BP used in rocket ejection charges. However, an igniter is intended and constructed to produce a large, hot ball of flame for an extended period (say, 0.5-0.75 seconds) to ignite a rocket motor. Ematches typically will not ignite motors unaided as they do not produce a hot enough flame for long enough, whereas igniters certainly could ignite BP. Another significant difference between them, which is critically important for onboard rocket electronic use, is their current requirements. Igniters typically require much more current than an ematch; the current requirements are usually more than altimeters can provide. Therefore, for onboard altimeters, which need to ignite deployment charges, ematches are needed. For staging timers, which need to ignite motors, igniters are needed. Be sure to always check using the equations to be sure an ematch or igniter will work with your onboard electronic device.
E-MATCH / IGNITER RECOMMENDATIONS
PML recommends the M-Tek or J-Tek series e-matches from MJG Technologies (www.electricmatch.com) for both the original Co-Pilot and the Co-Pilot v.2.0.
We prefer the M-Tek series for use with the AccuFire, though the J-Tek series will also work well provided you use a fresh, new alkaline battery.
Click here for a "white paper" by Robert Briody of G-Wiz Partners (makers of the PML AccuFire) on the current consumption of various igniters. In PDF format.
Also available below are Fore and Aft mounts for the PML AccuFire Timer to allow scratchbuilders the simplicity of mounting the AccuFire in a 38mm tube as shown on the Staging page.