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Old Jun 28, 2012, 03:41 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
Build Log
Have no clue what I'm doing... EPP Air/Swamp Boat

Want a 3DHS 71" AJ Slick real bad and they are now back in stock but I don't have the funds for one at the moment...

So I thought I would finish up my 80's vintage pattern ship that I stole back out of my dads basement a few months ago. Needs new servos and if I want to do it right, a couple of hundred dollars worth of paint, so that ain't cheap either...

So I finally get caught up on work enough that I feel like I can have some time for ME. Going to my folks' house next week for the 4th and they have a pond. Have a Hacker A10-9L motor laying around with a 9A Castle TB ESC, some servos, RXs, 2S Lipos, some sheets of 9mm EPP, misc carbon fiber, Welders, Uhu Por, and some Ultracoat. So what the hell, why not try to make a boat!
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Old Jun 28, 2012, 08:57 PM
made of fire and pop rocks
bgnome's Avatar
Richmond Virginia
Joined Oct 2009
1,708 Posts
I like it so far sir! my only issue is the material looks a little.... Squishy to me. though I can't say im fully familiar with the material either.

let see some more progression pics!
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Old Jun 29, 2012, 03:03 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
Quote:
Originally Posted by bgnome View Post
I like it so far sir! my only issue is the material looks a little.... Squishy to me. though I can't say im fully familiar with the material either.

let see some more progression pics!
EPP foam is most certainly "Squishy"!!!

It is commonly used on smaller "profile" airplanes (and that is why I have some of it laying around).

I'm using 9mm EPP. It gains a lot of strength and rigidity when glued at angles, and even more when reinforced with carbon fiber. This will be a very light weight power system and it won't be going very fast so the hull won't need to be all that "rigid". I have no clue if it is going to make a good material for a boat, but like I said, I have no clue what I'm doing. Just throwing some stuff together to see how it works out! I'm teaching my 6 year old how to fly an EPP foamie, and I think this will help her get orientation and left/right down.
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Old Jun 29, 2012, 03:17 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
So I spend a couple more hours on the air boat or swamp boat or swamp buggy... Whatever it is supposed to be called...

Coming together nicely. Worried that I may have made the hull too deep (should help it handle rougher water however). Also worried that I didn't make it wide enough to resist tip over.

I also realized that I truly don't know what I'm doing cause I made the main motor/rudder mount strut long enough to hold the motor, but I didn't make it long enough to hold the top half of a rudder! I don't know if I need a full length rudder (same height as the prop) or not. She may turn fine with a half rudder and that may actually help keep her from tipping over. Thinking that if you are adjusting the airflow high above the deck then you have more of a moment arm and it may be more likely to tip when turning. But with a shorter rudder located more towards the bottom of the prop wash, it might make it more maneuverable. Again, don't know what I'm doing so we will see...
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Old Jul 01, 2012, 12:22 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
So I got this thing covered... I leached off others knowledge and they said that if you sprayed your EPP with 3M 77 first, then Ultracoat/Oracoat would stick to it pretty good. They were right and I'm pleased with the covering job. Don't care that you can see the "bumpy" EPP thru the covering...

I got the motor installed and rudder and electronics and took it for a spin out on at the swimming beach at the local lake and then again in a buddy's pool.

First impressions:

1) The Hacker A10-9L on a GWS 8x4.3 SF on 2 cell LiPo is PLENTY of power.
2) As a civil engineer who knows all about fluid statics and dynamics, I should have run some calcs on the displacement this thing would make. It makes next to nothing. While it will absolutely SCREAM across the top of the water, it doesn't sit down in the water enough to behave like a boat.
3) Continuation from #2, if the boat catches a little bit of wake or a wave when screaming across the water, it can all of the sudden swerve left or right REALLY abruptly! I should have made the hull have a smoother transition toward the front of the boat from flat up to the nose of the boat.

I will have to do some more testing, but I think this hull will work out pretty good if I add some weight to it in the right place. When I ran it the first time I had a single 2 cell 800 mAh LiPo in there. Almost uncontrollable it was so light. So I put two more of those same packs in there to weigh the boat down a little and it was a LOT better, but still not easy enough to handle that I could hand it over to my 6 year old and let her hammer on it.

I've got a 1800 mAh 2S pack that I can try out. And I think if I add some weight to the back of the boat to get it to sit down in the water a little I will have something that you can hammer on.

The rudder seems to work just fine and I did notice that having the rudder on the bottom half of the prop did seem to help keep the thing from wanting to tip over when feeding in large rudder deflections. It will do donuts just fine. Straight line at speed is sketchy at best.

I'll have more time to play around with different amounts of weight and see if I can't make it easier/enjoyable to drive coming up here over the 4th. So I'll report back after I've got some more empirical data.

Fun little experiment to slap together in a few evenings with parts I had laying around! Hope I can tweak it a little and Grace can get some pulls on the sticks!
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Old Jul 01, 2012, 12:40 AM
Registered User
Ladysmith Vancouver Island
Joined Feb 2008
571 Posts
the beauty of "not knowing" what your doing... and not following a set plan...

you can't really screw up... you just tweak more then others "in the know"
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Old Jul 01, 2012, 01:08 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
Heck yea! My JOB is to figure things out ahead of time so they work right the first time. Way more fun to "wing it" and throw some stuff together and see what happens. In reality you learn more that way. I know plenty of engineers that suck cause they have no practical hands on experience with any of the things they are designing (I call them "nose pickers").

I am grateful that my dad (also an engineer) exposed me to RC cars/planes/boats, motorcycles, cars, engines, electronics, and all that good stuff what I was a kid. It made me a far better engineer than I could have ever been with just a bachelors and most of a masters degree from the university.
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Old Jul 01, 2012, 02:36 AM
Registered User
Ladysmith Vancouver Island
Joined Feb 2008
571 Posts
I'm a mechanic... you don't have to tell me about engineers that have no real world or practical knowledge....

I spend my days looking at parts I have to get too to fix/replace going "who the hell through THIS was a good idea????"

you did good either way.... hell your slap together airboat works better then mine built from a kit! (by the plans... the motor/prop is at the wrong angle and shoves the nose INTO the water)
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Old Jul 01, 2012, 11:16 PM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
Quote:
Originally Posted by Reckless View Post
I'm a mechanic... you don't have to tell me about engineers that have no real world or practical knowledge....

I spend my days looking at parts I have to get too to fix/replace going "who the hell through THIS was a good idea????"

you did good either way.... hell your slap together airboat works better then mine built from a kit! (by the plans... the motor/prop is at the wrong angle and shoves the nose INTO the water)
HAHA! I'm right there with ya man!

Just replaced all the injectors in my Duramax and I couldn't stop thinking about how idiotic some of the engineering design was that went into that thing. The most annoying was that there were a couple of different and very simple things that they could have done to make it easy to pop the injectors out, but they hadn't done any of them!

You just brought up a good point on the prop/motor angle... I was thinking about it before but hadn't mentioned it. It might help to put some spacers in there to change the thrust angle to help the nose come up out of the water a little further. Another thing I can tweak on and see if I can't get this thing figured out.
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Old Jul 02, 2012, 12:51 AM
Taking care of the pond.
MILLERTIME's Avatar
USA, CA, Fresno
Joined Apr 2004
7,177 Posts
looks good. I made mine out of a boogie board.
Borrowed a barbie from the kids, don't tell her.
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Old Jul 02, 2012, 01:22 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
That thing is WAY cooler than mine! I think you have a video posted of this thing and I saw it. Boogie board looks like it works real well, I just didn't have easy access to one here in the midwest. (Remember, I did this on a total whim cause I had enough materials laying around to make it happen)

The prop cage is a work of art. Don't know what it is made of but no matter what it is, looks like a ton of work.

So are those lights functional? Get it out on the water at night?

There is NO WAY I could get away with borrowing/stealing a Barbie from my 6 year old. First off she would know it was missing (Not sure how many of them she has but its a lot, and she would still know). Second off she is always checking on what I'm working on in the garage and wants to check it all out. There is no way in hell I could hide the thing from her...

I told her I wanted to cut one of her Barbie heads off and put it in one of my planes and she was totally against that idea. Won't stop me from continuing to work her on the idea...
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Old Jul 02, 2012, 11:52 AM
1/2 a bubble off
Apismelifera's Avatar
United States, NY, Schenectady
Joined Mar 2011
843 Posts
You're just going to have to go out and buy your own Barbie Doll.
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Old Jul 09, 2012, 01:29 AM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
Quote:
Originally Posted by Apismelifera View Post
You're just going to have to go out and buy your own Barbie Doll.
That would be too easy.

Well, I played with this thing a little more over the 4th. With a little weight in it it is a lot better. But it was still light enough and the hull is tall enough (or it was top heavy enough) that a gust of wind flipped the thing over while I was tweaking down the throttle curve so my 6 year old could try the thing out.

I don't know yet if I did any permanent damage to the motor or ESC. Wanted that stuff to dry out REAL good before I tried it again to see if everything still works. BTW, I also had to get the ESC out of the nice water resistant enclosure cause it was getting too hot in there. So I mounted it on the rudder vertical.

Anyway, if all the electronics still work, then I think I'm going to make a new hull. I think the same dimensions would work well, I just need to make the hull "thinner" (not as tall). In the process, the bottom width will increase from about 5" to more like 7 or 8". I think this is what the boat needs to be more stable and easier to throw around. Just thought I would throw in some more of my "trial and error" info in case it is helpful to anyone else!
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Old Jul 13, 2012, 08:22 PM
If it floats....sail it!
FoamCrusher's Avatar
Elk Grove, CA
Joined Sep 2002
3,959 Posts
There are at least two commercial products that are what you are trying to build; the Waterboard by Stevens Aeromodel (http://www.stevensaero.com/StevensAe...t-p-20119.html and the Drifter by Model Aero (http://modelaero.com/Merchant5/merch...tegory_Code=AM)

The Waterboard is a plywood and balsa jigsaw type construction that goes together very quickly with just CA. The Drifter is Depron; much lighter but prone to becoming an uncontrolled airplane when hit by a gust of wind.

Some weight, as with the heaver Waterboard, is your friend here, as are properly rounded chines. Too sharp and the boat trips over itself in corners and rolls over. Too rounded and it skids forever and won't turn well. Stevens has done lots of testing and has found the best combination. A corner template comes with the kit so the builder gets it right.

If you just want to fool around scratch building, by all means do it, but understand that your chances of getting a well performing boat are slim. However, if you want a working boat that is easy to build and fun to drive, get a Waterboard.

There are also some free plans for an airboat at http://api.viglink.com/api/click?for...13422271394404 (Clicking this link downloads a zip file that you will have to "unzip" in order to see the jpg plans.)

My completed Waterboard is pictured below. Runs great on 2S packs with the recommended motor and 3-blade prop. Be sure to waterproof all of your electronics, either by putting them in a balloon or by dunking them in CorrosionX (http://www.amazon.com/CorrosionX-Avi...2227478&sr=1-7 and if the boat inverts, do not try and use the motor as an underwater propeller...it will fry the ESC in a blink. (Don't ask ) Airplane ESC's are rated with air flowing over them for cooling. When tucked inside a hull you need to go way up in amp rating to keep the magic smoke inside them.

FC
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Old Jul 15, 2012, 11:14 PM
When in doubt, gas it!
KTMRacr's Avatar
United States, KS, Spring Hill
Joined Dec 2010
933 Posts
Those are two really nice looking kits you pointed out there! Hadn't seen those before.

I think I'm still in the mood to "tinker" with my own design for the time being. I can certainly appreciate that it takes lots of trial and error and testing to get a really "good" hull design!

Back in my college days we built and raced a concrete canoe in an annual competition. The first year I did it we used an exact copy of a racing canoe hull. It worked pretty good but you couldn't turn it for nothing. Over the next couple of years we tinkered with the hull design and there was always something wrong with everyone of them we came up with. Really hard to test, cause the only way you could really test it was to make one and try it out (at the expense of many many many man hours)! A couple of hours to make modifications and slap some EPP together and cover it is certainly way easier.
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