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USS SHARK SSN-591: Engineering is Fun! (1:48 DeBoer Skipjack)

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  • USS SHARK SSN-591: Engineering is Fun! (1:48 DeBoer Skipjack)

    This past weekend I finally had a chance to perform a test on the boat that I've been wanting to do for a while.
    I want an honest assessment of my current draw while underway. So I set up a static test stand and
    operated the model at various bells to define the power use curve.

    As a static test, the aft end was lowered into a pool and the model remains in place. Since she is NOT moving forward
    as in a dynamic test, the data I recorded should be "worse case scenario".

    Some stats on the boat:
    LOA: 63" (1600 mm) Beam: 8" (203 mm)
    Draft: 6.5" (165 mm) Weight: 26 lbs (11.8 Kg)
    Battery(s): 2x (in parallel) 12V 7.5Ah SLA
    Drive train: JOMAR Nautical Throttle, 10A fuse inline w/Redmond PE20270 12VDC Motor (RV HVAC Blower), Direct Drive, 7 Bladed 3 1/2" RH Scimitar Prop (Prop Shop UK)

    FWIW, the model at rest, no throttle or servo command draws .18A @ 12.51V (2.2W).

    My standard bell, surfaced or Persicope Depth is at 50% throttle. So you can see from the curve below,
    the numbers came in at 12.3V 0.98A here. Cycling several servos brought it to 1.18A. All things being equal I should theoretically run
    for 14 hours at this speed.

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    Burn 'n Churn!!

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    Test setup

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    I'm fortunate enough to work with EE's at a company known for Power as well as Data Distribution in both Military and Aerospace applications.
    So I have quite a few folks to leverage for help when the fuses pop.

    They told me that jump in he graph regarding current and Voltage drop it due to "Back EMF"

    Granted, the easy way to do this is to just run your model at your favorite speed until you need to swim to get it's run time.
    But that's why they call me "Special Ed". I'm happy with the results giving me a warm and fuzzy on what I draw as well as what I should and should not do.

    FWIW, Bob was correct in stating we really run at the low end regarding amp draw when we cruise. Even this "baby"
    v/r "Sub" Ed

    Silent Service "Cold War" Veteran (The good years!)
    NEVER underestimate the power of a Sailor who served aboard a submarine.
    USS ULYSSES S GRANT-USS SHARK-USS NAUTILUS-USS KEY WEST-SSRN SEAVIEW-PROTEUS-NAUTILUS

  • #2
    Most informative, Ed. You've contributed to the knowledge base.

    David
    "... well, that takes care of Jorgenson's theory!"

    Comment


    • #3
      Ed,
      I really like the test setup. Would you walk me through your setup?
      peace,
      tom
      If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

      Comment


      • #4
        Originally posted by He Who Shall Not Be Named View Post
        Most informative, Ed. You've contributed to the knowledge base.

        David
        Dave,

        While I understand readings will be different of course for different drivetrain setups, but at least I know exactly where MY sweet post is on this boat. She holds PD very well at 50% throttle with minimal input, and it seems to be the point where I lose efficiency. It also happens to be good walking speed for me, a tad fast but I can use the exercise as I follow it around the pond. I love circumnavigating ponds lol.

        If I crank it beyond 80%, the telemetry alarm for Low Voltage starts beeping (11.7V,) and I just throttle back and the voltage pops back up.. Thatís what prompted these shenanigans. SO Iím good with cruising speed, but enough reserve to get out of a jam.

        Hereís the interesting part, the prop is slightly larger than the body of the motor, which seems to agree with the German Rule of thumb you previously mentioned. Pulling 1.18A all day? Iíll take that!!

        Next year weíll repeat this test in Groton, but with that DeBoer 688 I got from Bob. I know that YOU know that screw personally!! 7Ē or so Blade Diameter. Iíll be using the same exact Redmond motor I got off Ray, but I think Iíll be using 3:1 gear reduction.

        Heck Iíll bring the tester this year toGroton if you want to test anything, weíll just have to connect it in line the boats power source and the connections to boats power feed. Stick the aft end in the water and test various bells on the TX. Any voltage up to 100V

        Originally posted by trout View Post
        Ed,
        I really like the test setup. Would you walk me through your setup?
        peace,
        tom
        Tom

        Basically I swapped the Main Power Feed from the onboard SLAís and hooked up two 6V 7Ah SLAís in series. I placed my homebrew Servo/Volt/Amp Test Meter in line and ran the boat at several common speeds I use. FWIW, the motor starts singing at 20% or so, and only starts to rotate at 30% (~⅓ fwd). I did take a video of the test and plan to add it into a complete systemís walk through of SHARK over the winter. My ďTest MeterĒ can be seen online in various videos here: ESMM Undersea Warfare Group: Kraken Division

        The Meter itself can be had on EBAY: 100A DC LCD Digital Volt KWh Watt Current Power Meter Ammeter Voltmeter w/ Shunt

        I knocked it all together and included a simple ESC and servo tester for Other motor testing, servoís etc.
        Servo Testing with RC Engineering Test System
        v/r "Sub" Ed

        Silent Service "Cold War" Veteran (The good years!)
        NEVER underestimate the power of a Sailor who served aboard a submarine.
        USS ULYSSES S GRANT-USS SHARK-USS NAUTILUS-USS KEY WEST-SSRN SEAVIEW-PROTEUS-NAUTILUS

        Comment


        • #5
          Just a shout out to Ed for building a gorgeous boat with bulletproof performance all day yesterday here in Groton. This boat is a poster-child for thoughtful engineering and clean installation.

          Nice job, Ed!

          Comment

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