Thread: 55" Dumas Scarab

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    dude, heal up & get back at it. I don't care if it takes another year or two, this thread is good.

    Looking great!! After seeing this Scarab take shape i've been searching for one of my own I don't think it will ever look as good as your unit. Very clean. I've been running nitro cars for awhile I think speed shouldn't be a problem it just might take awhile too reach with the 4 strokes but that baby should pull the nose good on take off lots of low end. Can't wait too see it on the water. Get those eyes healed up and get back at it you know all of us are pulling for yah.


    Just realized it's been a few months since you had some retooling done on the eyes hope too see some updates soon then. take it easy


    Join Date
    NSW Australia
    G'day, mate!

    how's the peepers getting along?
    I'm curious to know if the boat has had any attention of late....
    no problem if it hasn't, hell, mine was restored and bench run, but hasn't seen the water, either!
    just gotta "get around to it" you know!

    best wishes from Down Under

    Hey Guys!!!

    I'll have to admit I lost interest on the scarab project. I was very discouraged / unhappy trying to figure out the best servo layout and setup for the boat. (Too many servos....not enough space to put it all!) I've tried a few ideas, also mentally thought many more ideas out....but just wasn't happy with any of the results over my absence period. I haven't posted anything on the site, because of the lack of progress....or backwards progress to be honest!)

    That's the MAIN reason I put the project aside (sometimes you just need time away from things) other reasons (excuses) are as follows:

    1. My eyes...they have never been better! Not one problem since the day of surgery!! (Well worth the money...even if it was double the cost)

    2. My wife and I also decided to sell and upgrade houses a few months ago....we were running out of room in our other house (my son has too many toys!haha) Hopefully I can set up a real nice workshop now.

    3. I spent a lot of the summer flying R/C and gathering up parts and pieces for my next build (Giant Scale P-47 Razorback 85" wingspan) I promised myself I would NOT start on that project until the Scarab is finished!!

    Now for the renewed interest in the Scarab build: I was searching around the web a week or so ago and ran across some photos of an International Hobbies boat with a twin outdrive setup (sounds similar to what I'm doing!) I studied the steering servo, trim servo etc....and decided I might have been falsely led thinking I would NEED (2) 1/4 scale servos for steering and (2) 1/4 scale servos for trim as well. See the attached pictures of the I.H. boat and you'll see (1) regular servo for each function. Which would save me a LOT of hassle and much needed space!

    If this will do away with my overcomplicated "bell-crank" setup seen several posts above this one.

    I'll keep everyone posted on the potential progress! I'm so enthused that I found (realized) there was an easy solution to all the problems.

    Note: These pictures are of the International Hobbies (AMPS) boat I found online....they are NOT of my Scarab project (yet)
    Attached Images

    Paintboy, good to see you back. We all need to get our priorities in order and sometimes put down a project and come back later with fresh ideas.

    My job forced me to a location where boats are not that accepted putting the nearest running spot at over an hours drive. However, there are many flying fields/clubs within 15 minutes and I've joined one. Having not flown in over 15 years, I started back with a basic 40 sized electro trainer and realized the skills have came back after some stick time.

    Now most of the boats are gone to use the cash for planes. There's always that love for them, but you do what makes you happy. When the winter kicks off, maybe I'll mill out a few little goodies here & there for good detailed hydro.

    Werd up.

    Hey DD also nice to hear from you. That's too bad for your loss of "boating" but I'm glad you were able to take interest (again) in another portion of the hobby. Flying has been my main interest always. The Scarab will be my first boat!

    I went to bed last night actually thinking in my head about the Scarab and the "new found" ideas....that means I'm excited to get back to work on it. I honestly feel that I.H. boat put me back on the right track.....and vastly increased my chances of completing this project!!

    Awsome!!! Good too see things back in swing I know how discouraging it can be too have things come to a hold either from personal issues or just plain planning setbacks. Anyway good too see you back at it. I picked up a shorter Turbo style scarab I need too get busy in it but I think it's going too be sitting for along time before I can afford too power it and find the time too put my hands in the hull. Once again good too see things rolling again I'll keep tuned for sure.


    Opinions wanted..

    I sent a note off to my cousin (who fab'd up the grease / bearing tubes for the flex shafts) We decided to chat out my questions over the phone this weekend. Before that happens I would like some input from others as well.

    The Plan

    Would there be any concerns moving the engines to the rear (which will give me much needed weight back there as well) In doing so I would eliminate the flex shafts and instead connect the collet to the "hex slip joints" (the item that I have for attaching the threaded end of the flex shaft to the AMPS input shaft) I would plan to have about 1" of solid shaft making the connection.

    The Question:

    Would a "solid" connection like this cause any problems with vibrations or ???? I would think with proper alignment this would not be an issue. (Especially since the I.H. boat in the above post has a "solid" connection between the engines and drives as well)

    Mainly I'm just looking for other's thoughts on this issue as well.

    I've attached a couple shots to help visualize the question.
    Attached Images

    I started the day out yesterday by ripping out and removing everything from inside the hull (Engine rails, old servo mounts, engine mounting plate, etc) I wanted to start over with a clean slate as I decided to mount the engines as far reward as I could (needed weight in the rear for proper c.g. point)

    I tossed the previous engine mounting plate (Aluminum plate), and made a new one (slightly different dimensions) I have yet drill out the "lightning" holes....even though I wouldn't need to as I need all the weight I can in the rear, but it looks so much better drilled out!

    Then I roughed out a new set of engine rails, and started framing up for the fuel tank area. (There will be twin tanks side by side) I added plenty of lighting holes in this structure (along with a few in the forward part of the engine rails) All the wooden structure is only tack glued at this point. The tanks will mount in foam to take up some vibration and I plan to have a strap (rubber band) or such hold the tanks down.

    The new servo placement (with far fewer servos) will be between the engines and the fuel tanks. Not in the picture are the (2) standard servos for throttle, battery packs and receiver. I just set the steering and trim servos in place to get an idea of space.
    Attached Images

    Hey guys,

    Just wanted to stop in to mention I was able to get a fair amount of work done on the scarab last weekend, but I didn't get a chance to take / upload pics yet this week.

    I plan to work on it again this weekend so I'll just post all the progress at that time.

    I promised I would update my progress at the end of the weekend:

    Since I've last posted (pictures) I've built the servo / electronics compartment. In this box I've got the 1/4 scale steering servo, 1/4 scale trim servo (yet to hook up) two standard servos for throttle, two battery packs, receiver, charge jack, battery "volt watch" (yet to be mounted)

    The batteries are in the furthest forward compartment (wrapped and hidden under they gray foam) The throttle servos are "mixed" on my radios....but operating on one channel. This way I can fine tune and adjust each engine separately. The cover will have a gasket around the edge and I will inset a plastic viewing window when finished.

    I used large sliding controls rods for the steering and am very pleased with the results and torque. I hung some weight (chain hooks) on the drives so there would be a load / stress while testing them as well. I also held them with my hands while operating them....they are very strong. Eventually I will also add rubber boots where the steering controls come in through the transom.

    As a side note: All the slide tubes (outer) are just slid in place, nothing is glued or mounted permanently. I would like to add a brace or bracket between the engines to help hold the steering control tubes even more.

    I've uploaded a couple videos to YouTube of the outdrives and servos working.

    Video Link 1:

    Video Link 2:
    Attached Images
    Last edited by paint-boy; 11-23-2008 at 07:51 PM.

    Join Date
    Pittsburgh, PA
    i can't wait for the maiden voyage!

    Well, what ever became of this project? I was anxious to see it in it's final form. Beautiful work so far.

    Man that's lookin good bud I'm also curious as too what happened with the Scarab? I haven't started building mine $$$$ is tight. Hope everything is alright.


    This project isn't just put it on the way far back burner (really really far back) When I halted work on this project I was getting to the point of final mounting the engines and figuring out the water cooling* for the engines

    *Water cooling: I planned to wrap aluminum tubing from bottom to top of the cylinder heads and cycle water through from the pickups on the outdrives

    The only other "mechanical" item to figure out was/is the power trim. I've designed several ideas in my head, but have never built a working concept yet.

    The main reason for the project going "on hold" was the YS-63s 4 stroke engines. Many are / were concerned about the use of those engines because:

    1. 4 strokes not 2 strokes
    2. Airplane air cooled not watercooled
    3. A twin (my concern)

    I thought it would be best to use these engines, so I purchased and built a couple airplanes (my main r/c hobby) so I could break in, tune, and generally use the engines and get the feel for them. I hope that once the engines are "used" they will run better and hopefully cooler in the water (haven't had a lick of trouble with the engines in the planes. BUT one of the planes met it's demise a week ago (I wasn't flying it) for loosing the plane (no biggy) for gaining 1 of my engines back for the boat build (broken in, and running great) I might retire the other airplane after this flying season, or just purchase another engine and pull the used one out to finish the boat build.

    I don't plan on doing anything with the boat till this flying season is over and winter is upon us.

  17. aluminum tubing water cooling 
    Join Date
    Missoula, MT
    How well does this work? I have been wondering about it for years. I was thinking about doing it to my homelite engine. I was thinking about cutting groves in my cooling fins and threading the tube between the fins. Or would it just be better to lathe the fins off and wrap it then? I think I am having problems with the engine losing power due to excess heat inside the engine bay.

    Join Date
    Akron Ohio USA
    paint boy ??????? Long time No hear..How's it going ?

    Hay paint boy any updates?

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