BuoyancySubsystem Design

Overall Weight &Volume35 lbs

1034 cu3

Ascent/Decent Rate0.5 ft/s

Operational Depth20 m

System Volume500 mL

Cylinder Length5 in

Inner Diameter2 in

Overall Size8.5" x 2.25"

Mass Flow Raterequired Mdot = 1.57 kg/s

@max rpm 11.64 kg/s

Pressure Force onPiston @20 m

139 lbf

Motor SelectionSmall Johnson Motor

Stall Torque = 78.7 oz-inForce Produced on Piston Head = 141 lbf

Buoyancy Analysis

Inputs:

Buoyancy Mechanical Design• Johnson Electric Motor (12V)

– High rpm (16,000 rpm@12V)– Lightweight (7.50 oz per motor)

• Alexander Engel Gear Set– Proven for piston systems

• Threaded Piston Rod– 6 mm

• Piston Head– Aluminum– Machined in-house

• Cylinder– Aluminum– Machined in-house– ID x OD x thickness:

2” x 2.25” x 0.125”• Batteries

– 4 DuraTrax Receiver NiCd Flat Pack 6 Volt – 2200mAh (600mAh required per motor) – Length x Width x Height:

3-1/4“ x 1-3/4“ x 5/8"– Weight: 4.8 oz

• Sealing– Precision Associates Inc.– Piston Head Seal

• 75-1.840 1.84” ID x 0.075” C/S x 2.0” OD

– End Cap Seal• 25-237 0.237” ID x 0.025” C/S

x .287” OD

Buoyancy Electrical Design

• Ballast Tank switch (BTS-II)– Proven system for remote

submarines– Electronic (no servos)– Connects directly to Receiver

• Stop-full micro switch• Stop-empty micro switch• Trim switch

Buoyancy Test Plan• Static Motor Strength Test (Feb 7th)

• Verify System Produces force to operate at a depth of 20m– Horizontal Load Cell

• Resolution: 1 lb• Range: 50 lb – 400 lb• Accuracy: +/- 1 lb

– Expected Results: 141 lb force– Results: 11 lb force (Error due to incorrect moment arm calculation)

• Buoyancy Subsystem Test (Never Achieved)

• Verify descent and ascent rate– Antenna Marking w/ Stopwatch

• Range: 0 – 6 ft• Resolution: 0.5 ft

– Expected Results: 3.0 ft/sec– Minimum Requirement: 0.5 ft/sec

• Overall System Test (Never Achieved)• Verify system remains neutrally buoyant at given depth

– PX236 Pressure Transducer • Range: 0 – 60 psi• Bandwidth: 2 Hz• Resolution: 0.1 psi• Accuracy: +/- 1.5%

– Expected Results: 3.0 ft/sec with neutral buoyancy (< 0.2 psi change)– Minimum Requirement: 0.5 ft/sec with 1 minute neutral buoyancy

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Weight Comparison(Pounds)

Section Model Actual Difference

Payload Tray 6.3 7.25 +0.95

Tail Assembly 11.5 11.6 +0.10

LSM Assembly 4.0 3.125 -0.88

Hull Assembly 7.0 7.5 +0.50

Nose Assembly 5.0 5.4 +0.40

TOTALTOTAL 33.833.8 34.934.9 +1.10+1.10

Neutral Buoyant Weight: 36.93 lbs