Medusa Characterization Motor Design

Responsible Engineers: Justin, Aimee, Tamara, Alex, Lee, Luke

Week 3 Assignments:

  • Figure out nozzle ranges (in openmotor)- Justin
  • Refining FC & nozzle design (dimensions)- Alex/Jeff 
    • Looking at o-rings for inner lip
  • How to seal igniter - Tamara  
    • RTV the heck out of it??
    • Firebolts?

Week 2 Assignments:

  • How to manufacture the case - Luke
  • Getting everything on Grabcad by Saturday - Justin
  • Bolt calcs - Justin, Tamara
  • Test stand CAD - Aimee, Jeff, Lee
  • Tube-Liner matching - Elizabeth

Week 1 Assignments:

Week 3 Meeting Notes:

  • How to manufacture the case (Luke)
    • cap tube is a bad idea
    • use spring loaded retaining rings
      • would need accurate liner dimensions
      • might be easier to disassemble
      • no camera sink issue
    • doing a regular forward closure plug
  • Bolt Calcs (Justin, Tamara)
    • made matlab script
    • margin of safety in all areas 
      • minimum is 1.5 (add 1 to margin of safety)
      • thickness of case is 3/16
  • Test Stand
    • made cad
  • General Meeting Notes
    • figure out remaining dimensions
    • next meeting will be doing cad w/3d experience
    • Have all the hardware CADed up by meeting next week (not necessary for CoDR but good to have)
    • Need to get dimensions to prop formulation team
    • bolt calcs suggest 2.5"OD, 1.75" ID is good for 8 bolts
      • OD of liner is 1.75", 1/8" thick
      • 1.75" OD +/- 2 thou
      • 2.25 too thin, 2.75 overkill
    • dimension overviews
      • bolts: 0.19 major diameter 
        • space for bolt needs to be 0.5"
      • O-ring section is 0.25"
      • Pressure transducer goes through liner and case
        • port for igniter and pressure transducer
        • nozzle diameter will be too small to shove something through it
        • 0.1 inch diameter nozzle yields 500 psi so need smaller
          • use a smaller bore to machine
        • 0.057" diameter needed for 1500 psi
          • 3/64 or #55 drill
        • use gauge pins to get actual ID
        • need tiny boring tool
    • might tweak formula after 5-7 characterization fires
    • start at low pressures and go from there
    • 1" nozzle, 6" case w/ 4" long liner --> 3.5" propellor length
      • needs to be long enough to be able to notice differences in burn time

Week 2 Meeting Notes:

  • Calculating yield strength in a thread/maximum load on a thread & cases with screw on forward closures - Alex My name jeff
    • Screwed on forward closure done for small rockets
    • Pretty viable
    • Big tap/chonky threads
  • Work with Cruz to figure out 3d experience - Aimee
    • No emails yet
    • Grabcad for now
  • How thick does case need to be to reach pressure - Elizabeth
    • Did calculations on case thickness
    • Borderline on thin vs thick case so using both equations
    • Choose the one that gives thicker case
    • Around 2 inches OD
  • Reach out to Kelly - Elizabeth
    • Found yellow tubes on Mcmaster
    • Need to find one that fits with the casting tube
    • Find casting tube that fits in liner
  • Integrated forward closure case design - Justin
    • Used liner type that is same size as Kelly
      • has been updated to remove steel ring
    • Can do no forward closure design with tube machined in
    • Bolt calcs
    • Liner needs to be cut to size
      • installation disk on one side
    • End burner w/cylinder propellant for constant burn rate
      • Air could get compressed 
      • Have steel bolt on bottom for venting
  • Test stand - Aimee & Tamara
    • Three prts
      • Base plate
        • weld to ring holding motor
        • use aluminum plate to be able to weld
      • Motor case
      • Thick ring to hold motor
        • hole in bottom
        • Machine out half an inch to make a nub and thread it to screw on
        • radial bolts that interface w motor
        • if bottom fails what happens to top?
          • have another ring on top that surround motor case
          • top layer holding onto top of case
          • hole in the center
          • keep in place w/ eye bolts and ratchet straps
  • Other
    • 3 propellant formulas
      • Boron
    • 10 characterization fires
    • Pressure Transducer
      • hole drilled and threaded through side of motor
      • sealed using teflon tape
      • not threading phenalic, just hole for access

Week 1 Meeting Notes:

  • New characterization motor design
    • propellant casting tube & liner
    • case can be reused
      • maybe make 2 in case one breaks
    • very thick case to accommodate a range of pressures
      • 300 psi to 2000/2500 psi
      • case should be rated for 3000 psi
    • need to test at pressures expected during flight
    • drill hole in liner to read pressure transducer
    • make forward closure part of the case
      • disassembly is harder
      • saves on O-rings
      • test with blue thunder ring 
    • adding o-ring on nozzle side
    • glue disk to bottom
    • Put steel ring on top w/small hole and clock accordingly
  • Pour propellant in layers into liner
  • Propose changing nozzle size to change pressure
  • Smaller setup (less propellant) than large motors tested for Phoenix
    • Scaling issues?
    • No mandril
    • Could 3d print casting hardware
    • Plug and Play 
    • Easier to do in blast chamber
      • Cheaper
      • Less travel
    • Data collection is easier (each fire is one data point w/one burn rate)
    • Need to keep length of motor constant (affects burn rate)
    • Pressure transducer on bottom
  • RTV use
    • very time consuming waiting to dry
    • need to use RTV on nozzles
    • to minimize time make nozzle integration faster
    • all phenalic and graphite must be replaced
  • Clocking
    • also time consuming
    • less of an issue if tolerancing is better
  • Nozzles
    • on the order of 2 inches
    • will be machining lots of nozzles
    • need to figure out nozzle range to get desired pressure values

Segmented Motors

  • Done on Hermes
  • Scale back on erosive burning
    • Have a less complex grain geometry
  • Separate layers using RTV

Phoenix Issues

  • Experienced leakage
    • No seal (tolerancing issues with O-rings)
  • Data analysis was done badly

 

 

 

 

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