Fast Build Scale Model

Discussion in 'Projects & Proposals' started by rwatson, Dec 11, 2011.

  1. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

  2. El_Guero

    El_Guero Previous Member

    You can call it a banana boat .....
     
  3. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    My missus reckons it looks like woody woodpecker with the red top.

    Yellow was purely to make the photos easier to see, and the black on the bow is to stop glare for the camera.

    You have no idea what a pain it was to paint the boat yellow. I tried a few 'budget' yellow aerosol paint brands, that were just terrible.

    Then I found a brand from a range of auto shops that gave good results. I bought the last three cans from one branch. It wasn't enough. I bought the last three cans from the main city branch. I made the mistake of spraying in the outdoors on a fine, calm day- and every black winged bug spread themselves all over the coats.

    So I went to the third and final branch, and they had only three cans left also. I made sure I did the job right, and had one half a can left. There are still some bad runs on the side, but the hull is good enough for testing now.

    The Red top was so I didnt waste any of the scarce yellow paint :( Next time I will bring my compressor and invest in a touch up spraygun.
     
    Last edited: Aug 12, 2013
  4. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

  5. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    For any followers, success with ordering props from China - they arrived in 2 weeks, and all the right dimensions from

    http://www.hobbyking.com/hobbyking/store/__255__254__Boats_Parts-Props.html

    I have decided to substantially remodel the outboard motor to allow tilt adjustment with the help of animation
    http://www.boatdesign.net/forums/design-software/enjoying-animation-48176.html

    The leg needs to be longer, and I will try to achieve this without the expense of a more lifelike motor

    http://www.cornwallmodelboats.co.uk/acatalog/outboard_motors.html

    or

    http://www.hobbyking.co.uk/hobbykin...Sprint_F3_Tunnel_Hull_Racing_Boat_630mm_.html




    Note to self : Small gears at

    http://www.smallparts.com.au/about/
     
    Last edited: Sep 10, 2013
  6. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Adding this invaluable link

    http://www.modelboats.co.uk/news/article/but-i-don-t-understand-electronics/18054
    including, but not limited to -
    "Fuses

    My friend and mentor, the late Craig Talbot, wouldn’t hear of fitting fuses into a model boat as: 'They don’t prevent anything from being destroyed by a determined idiot'! I admit that I followed this until I witnessed a fire in a model which could so easily have been prevented had a fuse been fitted.

    The purpose of a fuse is primarily safety. A fuse probably won’t stop a stalled motor from blowing the output FET's in a speed controller, but it will blow fast enough to stop cables and contacts from overheating and catching fire. Choose a value which is just a little above that at which you get nuisance blowing of the fuse, e.g. try a 5A fuse in circuit with a 10A ESC (electronic speed controller) and if it continually blows when the motor is at full load, replace it with a 7.5A one or even higher rating if required, but don’t exceed the maximum rating of the ESC with the fuse value. For those who want to know whether to fit a fuse between the battery and ESC or between the ESC and the motor, there’s no harm in doing both, but you must ALWAYS fit one in the positive line between the battery and the ESC somewhere. This is also the place for the main On/Off power switch.
    "

    Curently, I am facing configuration challenges
    http://www.boatdesign.net/forums/on...pressure-diffferences-47511-2.html#post704590

    as well as prop testing and outboard modifications

    http://schoolroad.weebly.com/rpgmodel_12.html
     
    Last edited: Sep 12, 2014
  7. Jim Caldwell
    Joined: Aug 2013
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    Several problems here with the outboard.
    1 high rpm per volt motor, run it on 7.2 volts to keep rpm down.
    2 small diameter prop with too much pitch for 19 kg???

    Suggestions, cut the cav. plate off even with the front part of the prop boss to allow for a larger diameter prop with lower pitch for more thrust with out cavitation.

    Model props have typically 1.4 pitch to diameter ratio which is too high with that rpm per volt, at 7.2 volts at 2500 kv LOADED per volt that would be 18,000 rpm at the shaft.
    Octura makes a .90 pitch ratio prop at 55 mm dia. with 3 blades for high thrust that might work. Other wise you will need to a reduction gear of at least 2 to one. Maybe a right angle box since you have room in the cowling for that?
    What dia. prop was on it in the video?
    Then maybe I can narrow it down for you.
     
  8. Jim Caldwell
    Joined: Aug 2013
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

  9. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Some good suggestions there Jim, thanks.

    I did end up getting a selection of alternate props for trial, but have yet to apply them.

    From my brief observation, it appeared I had two separate problems. One was the prop of course. It actually sounded like it was under a lot of load, but because the tilt angle was wrong, it pushed the stern up until the prop was too high out of the water, and cavitated of course.

    Since power performance is a big part of the equation, tilt angle will be critical, and I am concentrating on putting a trim control in first, because I expect it to be very important to the overall importance.

    The crazy shape of the outboard, designed for lightweight electric models, has me seriously looking at building a custom built geared outboard, as you suggested. I think I can knock one together with simple aluminium sections and some off the shelf components.

    Work is on hold for a bit at this stage, with other considerations - but in the next few months, I will be able to resurrect the project fully.

    One recent win - I have been having trouble with a method of cooling the ESC and Motor. I got a cheap car windscreen washer pump to push water around, but it wasn't self priming, and spun uselessly.

    I had done a lot of inquiring about small, self priming pumps without any luck, until I found this one.

    http://www.aliexpress.com/item/NEW-...ow-2-3L-min-Micro-circulation/1111352608.html

    It seems to be a general purpose pump, maybe for aquariums. I am looking forward to testing it out.
     

    Attached Files:

  10. Jim Caldwell
    Joined: Aug 2013
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    I checked your motor with the Octura prop on a speed calc program I use for the electric racers and got 37 km/h.

    The 1200kv motor is 16km/h or = to a 2.31 gearbox.
     
  11. rwatson
    Joined: Aug 2007
    Posts: 5,852
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    Location: Tasmania,Australia

    rwatson Senior Member

    Just to quantify the information -

    XK3665-B-1200KV Brushless Inrunner
    Specs.
    # of poles: 4
    Max Amps: 42A
    Max Volt: 22.2V
    Max Watts: 930W
    Rpm/V: 1200kv
    Resistance: 0.0285 ohms
    No-load Current: 1.3A

    Versus

    Quick 540 outboard
    2858B brushless motor
    Voltage: 7.2-12V
    Output: 2800KV
    http://www.szfvt.com/eproducts/112.html

    It looks like the motor I have 540 is a 2 pole motor, and the XK3665 is a 4 pole, hence the lower rpm per volt. ( I wonder what Rpm/V: 1200kv means ? )

    I presume that the torque increases with the lower RPM - is this what you would expect too ?
     
  12. Jim Caldwell
    Joined: Aug 2013
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    Torque increases with amps or the number of poles.
     
  13. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Excellent - as you say, easier than going with gears
     
  14. Jim Caldwell
    Joined: Aug 2013
    Posts: 266
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    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    Ant progress on your project?
     

  15. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Life - and scarcity of money has put the brakes on. On the plus side, I did find the source for an essential part of the scale model outboard motor build - some decent small right angle gears. I may well gear down and run a bigger prop. I have attached a useful guide for prop sizes and speeds.


    I'll put the link in here in case I lose it - and also if someone else is in the same position.

    http://www.aliexpress.com/item/2pcs...-Bore-4mm-transmission-parts/32313244669.html
     

    Attached Files:

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