Robotics and Rockets

Quantum  Access codes:  62581768 Tested good to 12000 and 13000 feet. Drogue at apogee and Main at 800 feet.  Armed signal:  Series of single beeps spaced roughly 1/2 second apart.  Photon  Access code:  41738105 Tested good to 14000 feet.  Channels 1, 2 and 3.  Channel 1 setup as airstart 3 seconds, Channel 2 drogue and channel 3 main 1000 feet. Armed signal:  Series of single beeps spaced roughly 1/2 second apart.  Notes:  The photon MUST be mounted vertically with the ARROW point upward on the board.  This restricts ebay design.  The accelerometer must be still for ~5 minutes in order to allow calibration.   Final accelerometer calibration must be done on pad with the rocket vertical.  Quark Eggtimer Quark setup for Drogue at Apogee and Main at 800 feet Armed signal: continuous chirping Quark quick jumper settings.   Jumper 1 closest to buzzer Jumper 1:  (On) + 1 second (OFF)  + 0...

A 2" ANCP experimental PVC motor was fabricated according to the posts here:  The following physical parameters describe the motor: Casting Tube outer diameter:  1.55 inch Bore diameter:  .75 inch Grain length 3.875 inch Number of Grains: 4 Nozzle Throat:  0.375 inch The propellant has been previously characterized with the following parameters: a = 0.0048 in / sec n = 0.543  C* = 4565 ft/s Density = 0.0527 lb / in^3 Based on the composition of the propellant the following predictions were made: Max Pressure:  352 PSI Burn Time 3.75 s Average Thrust 35.5 lb Propellant Weight 1.18 lb Predicted Pressure vs Time curve Predicted Thrust vs Time curve After burning the motor, the following data was obtained:  Pressure(psi) vs. Time(s) curve obtained from the pressure transducer Thrust(lbs) vs Time(s) obtained from S type Load Cell  Unfortunately, there is no access to the theoretical raw curve data, so only the following comparisons can be made: Max pre...

A total of 5 ANCP motors were produced and tested.  A full test video is available here:   These are all conventional Ammonium Nitrate composite propellants that use Magnesium to increase temperature and HTPB as a binder.   The 5 motors manufactured are as follows: Motor 1:  250 PSI regressive (5.5 s burn time) Motor 2: 350 PSI regressive (5.0 s burn time) Motor 3: 350 PSI progressive (4.5 s burn time) Motor 4: 400 PSI regressive (4.5 s burn time) Motor 5: 400 PSI progressive (4s burn time) The chart show below shows safety factors for PVC motors (at 70 degrees F) with Pressure shown vertically and burn time shown horizontally.  There is  low overall confidence in this model. The case failure as a function of pressure based on the tensile strength of the PVC is well understood, but PVC changes strength rapidly with temperature.  As the burn time increases, there is heat transported to the PVC case which causes its strength to drop rapidly.  An exp...

Input Data: Burn rate exponent (n) Burn rate Coefficient (a) Throat diameter (inch) Propellant grain OD (inch) Bore diameter (inch) Combustion efficiency (%) C* characteristic velocity Thrust Coefficient Cf n, a, efficiency C* and Cf are determined empirically by burning propellant in motors with a constant nozzle area.   For the design of any motor the propellant needs to be reasonably well characterized to determine both the burn rate exponent (n) and the burn rate coefficient (a).   The theoretical Characteristic velocity (C* of the propellant can be calculated from chemistry (not my area!). There is software to do this.   When the propellant is characterized, the ratio of the theoretical C* to the measured C* gives the Combustion efficiency.   The Thrust coefficient is determined empirically from the Force and pressure graphs assuming that the nozzle area is constant.  A future post will discuss empirical techniques for measuring these two parameters from pr...

A single use rocket nozzle can be made using Water Putty and a graphite plate in a 2" PVC Pipe fitting.  Durhams water putty is a gypsum based putty that exhibits very little shrinkage while drying and is effective as a single use nozzle for motors up to 4" in diameter.  Supplies: 2" PVC Coupling 2" PVC to 3/4" threaded female reducer Water putty 1/4" thick graphite plate ~1"x 1" ( 3/8" ID fender washer can be substituted, but it adds additional complexity) Screwdriver or chopstick for mixing 2 spoons duct tape mixing cup Safety glasses nitrile gloves or equivalent Wear safety glasses and nitrile gloves  Use PVC primer to coat the surface of the reducer and the PVC coupling up to the ridge joint. Use PVC glue to coat the surfaces and then press the PVC reducer into the coupling.  Hold for at least 20 seconds so that the reducer doesn't float out of the coupling.  Cover the small hole in the bottom with duct tape to retain the putty, it i...

In February 2020, I obtained a 26' section of 8" ID commercial filament wound fiberglass pipe rated to 600 PSI continuous, 1200 peak rated from my favorite aerospace surplus yard.  I designed two 7 grain motors and a 4 grain motor and with the assistance of the Mt. SAC rocket team, cut the pipe into the appropriate sections.  The 4 grain case was to be used for static testing to prove that the pipe could serve as an effective motor casing for ~550 PSI KNSb motors.  After a lengthy break due to COVID-19 work commenced on the static test motor in Mid June.  While I have made numerous 4" and 5" KNSb motors, 8" is a larger scale.  The motor was designed to use a standard Bates grain configuration.  Sono tube was sourced that fit loosely in the motor tube which would allow for a Kevlar liner to be bonded to the casting tube.   This technique had been under development since 2017 and tested with repeated success with 4" and 5" motors in 2019-2020. In this ne...

The 4 grains had been poured 7 days previously so had setup well in the warm dry Mojave heat of the FAR motor fabrication facility.  The process commenced with the removal of the core mandrels used for the bates grains.   The motor consists of 4 grains made from 14.5" sections of 7.5" ID x 7.625 OD Sono tube.  The following cores were used: 2" hollow UHMW cylinder 2.25" Solid UHMW cylinder 2.25 to 2.625" tapered hollow aluminum core 2.625" to 3" tapered hollow aluminum core The 2.25" core and smaller tapered core removed easily.  The larger tapered core had propellant that had migrated up the inside of the mandrel.  The 2" hollow UHMW cylinder seemed to have gone slightly hour glass shaped.  The UHMW hollow core was removed by drilling a hole in the top, passing a piece of rebar through the hole and then pressing a long rod against the rebar to pull the core out of the grain using a 20 ton press.  This was done to keep the grain in tension i...