motor position

Discussion in 'Propulsion' started by The Texan, Apr 18, 2013.

  1. The Texan

    The Texan Member

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    when i was looking at the arangement of the turrets with the power plant on my Scharnhorst i noticed that the after barbette would hit the center motor, if i moved the motor back by shortening the propeller shatf and putting the mount aft of the barbette, would it cause any proplems?
     
  2. SnipeHunter

    SnipeHunter Well-Known Member

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    It shouldn't, try to keep the prop shaft as level as possible but the overall length really isn't that important. Are you planning on driving all three propeller or just the center propeller?
     
  3. The Texan

    The Texan Member

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    all three props, i want the extra water movement over the rudders
     
  4. mike5334

    mike5334 Well-Known Member

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    Frankly, it would be better to power only the center shaft to get the best turning. A single driving prop would have to run at a higher rpm to push the ship to speed than using three driven props. Also, the twin rudders will act as a nozzle to redirect that extra thrust from the single prop to increase turning. The only thing gained from running three props is more acceleration at the cost of turning radius.

    Measuring my Sharny, the face of the gearbox is 4.25" forward of the D turret barbette. That leaves plenty of room for cannons in both C and D turrets if needed. The pump is placed just forward of the drive motor. Just forward of the pump comes the batteries.

    The prop shaft runs level within the ship's keel. There isn't much room under the ship for a large prop, but with some patience the prop shaft can be lowered enough to put a 5 bladed 1.75" prop without the prop projecting barely under the keel.
     
  5. The Texan

    The Texan Member

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    RiclelieuBB, i'm building the 1939 Scharnhorst, not the predread, however what you're saying does make sense, what if you had the motor on the inside of the turn switch off when you made the turn, would that help with turn radius
     
  6. SnipeHunter

    SnipeHunter Well-Known Member

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    That would work, it is outlawed in most/all clubs but if you aren't planning on joining a club to battle with no reason not to do it if you want to.
     
  7. mike5334

    mike5334 Well-Known Member

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    Actually, I was talking about the Sharnhorst battle cruiser, not the predread. :) I do not have the predread.
    And yeah, I miscounted turrets on the BC. It only has three. The gearbox is 4.25 inches forward of the C turret barbette.

    If not battling in an established format, the inside motor could be taken even further and reversed during the turn to add extra drag on that side of the ship. :)
     
  8. The Texan

    The Texan Member

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    reversing the inboard propeller would be better for turning so i apresiate the idea, also the Scharnhorst i intend to build is far larger than the 1/144 scale you guys battle, it's going to be 1/72, so the ship being just under eleven feet long will need the extra drag to turn. thank you for the clarification, i assumed you were talking about the predred Scharnhorst,
     
  9. mike5334

    mike5334 Well-Known Member

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    11'! That is going to be an awsome sight on the water. Keep us all posted on the building progress please. :)
     
  10. Tugboat

    Tugboat Facilitator RCWC Staff Admiral (Supporter)

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    I don't think that there's ever been a predread SMS Scharnhorst. Might've been an armoured cruiser, though, built in 1905, famed in song and legend, feared by Allied captains worldwide :) Even with the rudder jammed and the guns being iffy :)
     
  11. The Texan

    The Texan Member

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    RichelieuBB, yes sir it sure would be an impressive sight. Tugboat, i hadn't realized there was a armored cruiser Scharnorst.
     
  12. The Texan

    The Texan Member

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    Scharnhorst's propellers were 4.8 meters in diameter, what would that equate to in 1/72?
     
  13. mike5334

    mike5334 Well-Known Member

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    About 2.61 inches
     
  14. The Texan

    The Texan Member

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    thank you
     
  15. The Texan

    The Texan Member

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    what size motors would you guys recomend for power on this ship?
     
  16. SnipeHunter

    SnipeHunter Well-Known Member

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    Big...

    I'd probably start with something like this.

    http://www.hobbyking.com/hobbyking/store/__8492__Turnigy_4258_Brushless_Motor_400kv.html

    Those will drive a 2.6" prop without issue.
     
  17. mike5334

    mike5334 Well-Known Member

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    That is a good choice for a direct drive setup on 12 volts. In fact, it is exactly the same motor going into my next ship. Heh.

    If looking at brushed motors, one of the big 700 or 900 size mabuchi's would work nicely. I'm not familier with those motors, so couldn't tell you what voltage they like to run at.
     
  18. SnipeHunter

    SnipeHunter Well-Known Member

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    It would probably do better geared than direct. 1:1 is rarely the optimal ratio.

    A lot of this really depends on how fast you want this behemoth to go and if you're running all the props or only the center one.
     
  19. The Texan

    The Texan Member

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    scale speed, on all three propellers, gearing would help considering it would take a lot of power to drive the ship at speed from what i've read and some of the experiments i've done with smaller plastic models
     
  20. SnipeHunter

    SnipeHunter Well-Known Member

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    How do you scale the speed then, as there are multiple "correct" scale speeds depending on how you scale. Some are better than others depending on what you're going for. For instance if you were to scale the speed linearly like you do with the physical dimensions at 1/72 the speed of the real ship you'd only be going about 0.36 ft/s (~278 sec over 100ft), which would be boring and not very fun, but you wouldn't need much power to do that. If you scale hydrodynamical you'll get about 15.1 ft/s (6.6 sec over 100 ft) which would be pretty darn quick(and probably pretty fun) but would take a ton of power. Both can be said to be "scale speed".(hydrodynamic scale is probably a "better" answer since you are only changing the size of ship and not the water.)