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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:

Calculating yield strength in a thread/maximum load on a thread & cases with screw on forward closures - Alex My name jeff
Work with Cruz to figure out 3d experience - Aimee
How thick does case need to be to reach pressure - Elizabeth
Reach out to Kelly - Elizabeth
Integrated forward closure case design - Justin
Test stand - Aimee & Tamara

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
  - how to get around?
  - 38mm or 54mm liner (contact Kelly)
    - can make about 10 motors
  - thicker phenolic liner that Kelly used https://www.mcmaster.com/8527K244/?SrchEntryWebPart_InpBox=garolite+xx+phenolic
- 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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