Dual Deploy Recovery
Why do dual deploy?
What you need Mandatory Optional/Configuration-dependent • Altimeter • Redundant systems • Wiring • Charge wells • Battery and holder • Shear pins • Switch • Parachute management devices • Black powder/pressurant • Wire nuts • Recovery devices • Miscellaneous hardware
Popular Altimeters • Cost-effective • Extra Features – ADEPT products – Raven 3 – MissileWorks products (RRC – Altus Metrum products line, etc) • DIY – PerfectFlite products – Eggtimer, Eggtimer TRS (StratoLogger, etc) – Recording-only (no deployment capabilities)
ADEPT22 • Cost: $45 • Dimensions: 2.8”x0.9”x0.6” • Max Altitude: 25,000 ft • Weight: 12 g • Programming: 7 presets • Outputs: 2 • Data: Altitude buzzer tone • Memory: 1 flight • Sensors: Barometric
DDC22 • Cost: $35 • Dimensions: 2.8”x0.9”x0.6” • Max Altitude: 100,000 ft • Weight: 12 g • Programming: 7 presets • Outputs: 2 • Data: None • Memory: 1 flight • Sensors: Barometric
MissileWorks RRC3 • Cost: $70 • Dimensions: 3.9”x0.93”x0.5” • Max Altitude: 40,000 ft • Weight: 17 g • Programming: USB • Outputs: 3 • Data: Buzzer tone, USB • Memory: 15 flights • Sensors: Barometric
PerfectFlite StratoLoggerCF • Cost: $55 • Dimensions: 2”x0.84”x0.5” • Max Altitude: 100,000 ft • Weight: 11 g • Programming: FTDI • Outputs: 2 • Data: Buzzer tone, FTDI • Memory: 16 flights • Sensors: Barometric
Eggtimer • Cost: $35 • Dimensions: 3.9”x1” • Max Altitude: 30,000 ft • Weight: 20 g • Programming: USB or LCD • Outputs: 2 • Data: Buzzer tone, LCD, USB • Memory: 32 flights • Sensors: Barometric
Featherweight Raven 3 • Cost: $155 • Dimensions: 1.8”x0.8”x0.55” • Max Altitude: 100,000 ft • Weight: 7 g • Programming: USB • Outputs: 4 • Data: Buzzer tone, USB • Memory: 5 flights • Sensors: Barometric, accel
Altus Metrum TeleMetrum • Cost: $300* • Dimensions: 2.75”x1”x0.56” • Max Altitude: 100,000 ft • Weight: 18 g • Programming: USB • Outputs: 2 • Data: Buzzer tone, USB • Memory: 8 flights • Sensors: Barometric, accel
Altus Metrum TeleMega • Cost: $400* • Dimensions: 3.25”x1.25”x0.56” • Max Altitude: 100,000 ft • Weight: 25 g • Programming: USB • Outputs: 6 • Data: Buzzer tone, USB • Memory: 4 flights • Sensors: Barometric, accel
Mach Delay • Sharp rise in pressure across a shock wave falsely simulates rocket descent (pressure increasing as altitude drops) • Modern altimeters have built in filters to prevent accidental ejection at supersonic/locally supersonic speeds • Old altimeters would have timers that could prevent ejection in these scenarios
Switches • Any electronics must be armed at the pad with the rocket in a vertical position on the rail (HPR Safety Code) – Precaution in case charges go off prematurely • Switches prevent disassembly and reassembly at pad • Avionics must be turned on and verified as armed before installing an igniter into the motor • At least one switch per system required • Should be rated for current (~2 A) and voltage (~9 VDC)
Key Switches • Vary in prices, but expect to spend $5 or more each • Externally accessed, mounted by the wall of the airframe • Some have traditional keys; others have flathead “key” • Note voltage and current ratings • May require soldering
Screw Switches • Relatively cheap • Small form factor, weight • Easy to mount internally • May be difficult to access to turn avionics on/off – Multiple revolutions may be required to actuate • Any screwdriver acts as a key • Rated for voltages, currents
Magnetic Switches • Tend to be moderately expensive • Turn on and off by waving a magnet over switch • Does not require any protruding switch – Minimizes drag of vehicle – Easy to use since no key needs to be inserted • Soldering may be required
Twisted Wires • Simplest, cheapest method of arming electronics • Two wires protrude from the airframe, but are not shorted until ready to arm electronics • Exposed ends of wires twisted together and taped to complete the circuit • Tape to external airframe – Prevents wires from coming undone – Allows easy access to disarm electronics safely
Pressurization Systems • Just like motor ejection charge in traditional rocketry deployment • Black powder (or black powder substitute such as Pyrodex) is most common • Cold gases can be used, and there are commercially available solutions • Mechanical systems theoretically possible, though generally infeasible for HPR
How much powder? m "# (grams) = C , D . , L • C: coefficient based on pressure – 0.002 = 5 psi – 0.004 = 10 psi – 0.006 = 15 psi – 0.0072 = 18 psi – 0.008 = 20 psi • D: airframe diameter (in) • L: length of parachute bay (in)
Black Powder – Wrapped Charges • Simple implementation, but cannot be directed • Create 5”x5” sheet of tape (non-static) sticky side up • Place igniter head in center of the tape sheet with leads extending out • Measure correct amount of powder and pour into center of the tape sheet (onto igniter head)
Black Powder – Charge Wells • Containment system for black powder charges and igniters • Can use PVC caps or commercially available charge wells – Commercial solutions are sized to fit specific powder mass • Relatively cheap • Easy to mount on a bulkhead • Directs ejection charge
CO2 Systems • No hot gases, residues – Good for altimeters and electronics – Does not burn parachutes and cords • Significantly more expensive than black powder systems • CO 2 bottle pre-measured • Bulky, heavy, and requires small amount of black powder
Parachute Sizing Drogue Main Parachute • Size parachute for descent rate of • Size as you normally would for 50-100 ft/s optimal landing speed • Too slow of a descent eliminates • Generally 2-4 times larger than the benefit of dual deploy drogue parachute • Too fast risks rocket damage (zippering, etc) at main parachute 2 2W Diameter = deployment v 5678 ρπC < • Typically drogue chutes are 18” (lightweight rockets) to 36” (heavy)
Parachute Management • Easiest way to manage parachutes is to keep in separate compartments (classical approach) • Sometimes advantageous or necessary to keep parachutes in same compartment, but still use dual deploy • Devices exist to prevent main parachute inflation until prescribed time/altitude
Deployment Bags • Protects the parachute from the ejection charge • Prevents large “jerk” when the parachute inflates • Allows the parachute to move away from the rocket before it opens • Bag must be appropriately sized for parachute • Utilizes a pilot parachute
Tender Descender • Allows both parachutes to be packed in same compartment, but allows for delay in deployment of main parachute • Ties down main until ejection charge releases the restraint • Moderately expensive ($59+) • Comes in three sizes based on weight/forces
Cable Cutters • Allows both parachutes to be packed in same compartment, but allows for delay in deployment of main parachute • Ties down main until ejection charge releases the restraint • Moderately expensive ($30) • Very small body • Relies on expendable cables
Implementation of Dual Deploy • Set drogue parachute to be deployed at apogee – Detected barometrically, with accelerometer, or with timer • Set main parachute to be deployed at specific altitude or time – Detected barometrically or with timer – Popular settings are between 500 ft and 1000 ft • Parachutes that take longer to inflate may be set to deploy at higher altitudes for safety/reliability • Deploy at lower altitudes on small fields
Avionics Bays • Popular implementation is to convert a coupler into a sealed avionics bay – Add 1”+ of airframe as a key band and shoulder • Should be easily accessible from both sides – Do not glue into airframe! • May want to use threaded rods as structural stiffener
Avionics Bays Bulkheads Interior components • All altimeters, batteries, • At least one bulkhead should be miscellaneous electronics mounted removable so electronics can be on sled removed – May use threaded rods or puzzle locks • Mount charge wells and U-bolts/eye to hold sled in position throughout flight bolts to each bulkhead • For externally mounted switches, use wire nuts to connect switches • To accommodate igniters, install to electronics (for easier installation terminal blocks or small holes to and removal) thread igniters through • Use screws, tape, and zip ties to – No large holes so gases don’t affect hold components in place electronics
Venting • Barometric sensors must be exposed to outside environment • No obstacles above vent • Can use almost any number – Never use just two – One possible, not recommended • One 1/4 inch diameter vent hole (or equivalent area) per 100 in 3 of volume in the altimeter bay • Between 1/32” and 1/2” • At least four body diameters below nosecone junction • Evenly spaced around key band
Basic Wiring Guide
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