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Old Aug 23, 2014, 12:03 AM
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Cool
Lets design an open source 3D printed micro Outrigger Race boat

Hey guys, first off let me start by saying that I have little knowledge in boat dynamics and design. I do however have a vast knowledge of aircraft design and aerodynamics, as well as a very thorough understanding of fluid dynamics of all types.

This being said I have really wanted to build a quick little boat, preferably sponson, and I would like to 3d print it. I would like to run some of the more common "micro" components as seen in other "pool racers" etc.

I am looking for someone to bounce some ideas off of, and in general have a fun little adventure designing printing and building a mini sponson style race boat!



To start off, I would like the main hull no larger than 40mm x 220mm, and the sponsons can be any size. I have a few hydro dynamic idea I would like to try out, such as hydro foiled "steerable" sponsons. not hydrofoiled in the sense that they "climb" but more so in the sense that when deflected at an angle, similar to caster on a car, it will suck the inside sponson down helping "track" around a corner... Again, just ideas that would be easy to rapidly prototype and try out!

Anyways, If you would like to help out you are more than welcome. I will be working primarily in Sketchup due to the ease of exproting to STL for 3d printing. I do have quite a bit of solidworks expertise, but would prefer to keep this as open as possible, and sketchup is easier to do this with.

In general the parts I am looking for help with are general dynamics, such as center of gravity, a "plane" step (not sure the correct nomenclature, placement, use, or lack of). However in the mean time I would like to utilize the benefits of 3d printing and print something much better looking such as this instead of something easily buildable such as this

The long term goal is to provide all variations of the boat on thingiverse for individuals to print ,as well as supply the files here on RCG if you wanted them printed by a 3rd party printer such as Shapeways. Thoe boat could be specifically designed for a power system, or even a variation of easily accesable power systems for the end user to utilize.

Please post! Any and all ideas welcome!
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Old Aug 23, 2014, 02:27 AM
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Just to get it rolling... Here are some preliminary ideas.

Not really sure if this whole front steer thing will even work, but I am very interesting in trying... If this current design doesnt work, or skips off the water then I am planning on adding hydrofoils at about 60 degrees down and inwards from the outside of each sponson. Doing so (when turning) will allow the inside to go to a negative angle of attack (down force) and the outer to become slightly positive.... Again, no idea if this will even work, just wanting to give it a shot!

Note that the "bridge" is not incorporated yet, connecting sponsons to the main hull.
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Old Aug 23, 2014, 01:12 PM
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Boats don't do front steer very well, it causes the nose to plunge and go down... Not good. The rudder needs to be in the rear, and on this type of hydroplane, since the hull runs mostly out of the water you will need some sort of a skid fin so the boat will have bite in the water to make the turn. The skid fin also prevents flipping when turned at high speeds. This type od boat is called an outrigger, they are usually a minimalist design made for one thing... Going fast. Good luck with your project and I hope this helps your design process.
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Old Aug 23, 2014, 04:55 PM
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Massey! Thank you very much for your input.

I will most likely resort to rear steer, however being that 3d printing allows for fairly rapid re-design, I would like to at least give front steer a try. The idea is at some point to do hydrofoiled skid fins, mounted to the outriggers, as it turns, the outer outrigger will essentially produce "lift" and the inner would be down force. This was my idea for avoide the dive... But we'll see if it works.

In the mean time, I would like to design a few different iterations and models. This will give people the flexibility to mix and match for their intended purpose.

Any suggestions on hull and outrigger design? Currently The deep cut/edge in the outriggers is meant to act similarly to a skid fin, and is mounted.

I would really like to make this thing easy to build with readily available parts. Any Idea for motors, flex shaft, prop, etc?

The inside of the main hull will have a printed motor mount, and flex shaft guide tube.
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Old Aug 23, 2014, 05:14 PM
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For reference, this is my idea for front steer.

As you can see when the outriggers are turned, the outboard fin will try to "lift" the front end, meanwhile the inboard will try to do the opposite. Not proven, but worth a try....
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Old Aug 23, 2014, 08:14 PM
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8 gram Outrunner on 3S Original Outrigger Hydroplane Test Vid 2.AVI (6 min 37 sec)


Hi Justin, I recieved your message so to confirm you have seen this vid running with a 8g motor on 3S from this thread:

http://www.rcgroups.com/forums/showthread.php?t=1289898

I see your mainly into aircraft I started with planes and still design them here is a micro 5.3oz racer flying on TD .020
TD .020 3ch Lil Speedy - Flying On a Rare Cox 4x2.5 Prop (4 min 29 sec)


Design build thread here:
http://www.rcuniverse.com/forum/1-2-...h-speeder.html
You will note my name as Pond Skipper there I post in the 1/2A boat thread at RCU more details can be sourced for small boat componets.
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Old Aug 23, 2014, 08:37 PM
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Both vids are all about micro speed on stock engines so design is everything to get the most out of the power selection.

I see you don't want to exceed 8.7in for tub size and 1.6in wide
Thus far a outrunner motor would be a good none water cooled solution
If you wish to watercool then an inrunner. You must base size on battery and motor selection 2S or 3S or room for either etc.

Let me read and see whats been shown and will respond then.
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Old Aug 23, 2014, 10:02 PM
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Okay, so after a big of reading, and a test print, Things have changed a bit.

First off, the test print showed me my original design would be really tight to work in (more than necessary....) and wouldn't be user friendly. Its buoyancy wasn't fantastic, however a quick push in the pull and it skipped along fantastic! Just to try it, I flipped it upside down to simulat a deeper V hull of the same weight, and it lost its energy in less than half the distance of the upright hull.

Back to the drawing board.

I am not working on a boat that can easily fit a motor at least 25x25mm with a max width of 50mm where the motor mount would be. It will also incorporate a flex shaft guide tube that is currently 4mm in diameter and has no ID as of yet.

AA, Thanks for posting! After looking at your build I see these guys really are much faster when getting up on plane. The last two tub designs were design with a minimalistic bottom, however surely not like the one you built. I also see that yours is entirely DD and does not use a flex shaft at all... This also has me thinking about another change.

I am focusing more on a base concept/design, with a conventional rudder, etc... And will simply adapt it to my experiments later (hydrofoil front steer, etc...)

On a standard 3d printer you usually have a 200mm x 200mm x 200 mm build surface. If you build at a 45* angle (corner to corner) you effectively increase your surface to 280mm, width of the object dependent.

Uploaded is the current tub, it can fit a fairly large motor, and has plenty of room to work or install batteries and servo. Also if you look closely you can see the design lines to fit a 25mm square motor mount, not sure how necessary this is, but it can surely provide options..... However after seeing AA's rigger, this will probably be changes drastically once again.

It seems as if these riggers don't really mind if the hull and sponsons are flat bottom, as long as it gets up on plane... Question is, can you gain turning performance (IE, lose less energy in the turn) by a more engineered bottom?

Any input on hull design for the sponsons and tub? Does it really matter? On top of this, what is the ideal CG when compared to the "step?"
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Old Aug 23, 2014, 11:32 PM
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Is your aplication of design towards having a fast water drone?
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Old Aug 23, 2014, 11:36 PM
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Nope simply a fun pond skimmer that is accessible and fun for many.

Tried to increase the tub size to make it easier to fit install equipment....

Here is a question... Why aren't any of the tubs tapered? In my own pool experiments, every hull I make that tapers (tear drop style) retains energy significantly more.

PS, the reason for the odd shapes and lines is simply designing out side of the box. Since we are designing for use with a 3d printer, in my opinion we might as well take advantage of the benefits. I know flat wood sheet is plenty efficient, but at that point we might as well build a thin ply hull.
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Old Aug 24, 2014, 12:27 AM
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Odd shapes should be for aerodynamic reasons with the bottom of the sponsons suited best for a mix of control and speed or speed only.
In turns the rounded surface help to reduce drag. Winds from whatever direction are pushing on the hull and sponsons as it zips around.
At speed the sponson are floating on the surface just touching but not planted if the cg is correct in the rear the rigger is riding on the hub of the prop is the minimal goal or further down the lower blade (one in the water) if it is really going fast.

Note in my running pic the sponsons leave no wake, surface tension is at a minimum.
Higher unloaded rpm is achieved once up on step running down the prop blade rather than a full bite running on the hub. I have approx 25% of blade in the water - it takes great power to weight to achieve this high rpm. CG needs not to be perfect but +\- 10% from the sweet spot.
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Old Aug 24, 2014, 12:49 AM
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In 2009 most folks that ran larger riggers stated no way can you make a surface prop function so small, there will not be enough blade surface in the water to produce enough thrust to motivate the water craft. I did it with just a 20mm 2 blade hand made star tipped, cupped, no tongue brass sheet prop and some metric 2 mm ID tubing. To this day no one has gone faster on a 8g motor pushing a 4.5oz rigger - least not publicly posted via video. I could have gone faster the run time is excessive with the heavy Rhino 3S 460mah cells -250mah would be enough for nice 3.5min run with an additional gain from 24mph (radar reading) approx 4 to 6ish mph gain.
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Old Aug 24, 2014, 12:52 AM
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Makes sense. So in reality, as long as the craft can get up on plane and it is trully lifting by the prop, and just barely skimming with the sponsons, than hydrodynamic shape should have little to do with it, in straight and forward motion. However, once a turn is initiated then you rely heavily on sponson lift.

This being said, the hull shape shouldn't matter much as long as you can get it up on plane. However, sponson shape can have a huge effect. As I understand it, a sponson with a flat (left to right) surface, or even a bit of a convex curve, are ideal for straight line speed as it allows it to lift out of the water, with minimal surface friction. However, when designing for cornering sponson shape should have more "bite" and/or larger skid fins.
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Old Aug 24, 2014, 12:54 AM
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What are your thoughts on the abuses put into a prop. Would it be 3d printable at this size? I know many have had success with EDF's from 20-70mm (I saw a very low powered 90mm.), however it is exactly beating at water either... not to mention the stresses on a surface prop.
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Old Aug 24, 2014, 01:57 AM
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Hydrodynamics to get it out of the water aerodynamics to keep it there. Hull shape matters very much so my scale speeds are off the chart if I had a 14ft version of my lil ply rigger with me sitting in it I would be a world recorder holder in its class.
The prop problem has been solved I will show you a source for glass filled nylon 20mm surface props when I get a chance. Remember everything that is posted online teaches others to move forward who wish to. As we know China likes to keep an eye on western development to sell new products so others who didn't put in the trial / error and expense time to buy later lol it is now 2014 look at all the micro with surface prop driven boats trickling out made cheap enough to sell world wide. As I understand they can do printable metal now and some of the new plastics are stronger?
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