Design issues

[madmic]

A lot of people know about the Dumas Swamp Buggy kits. I, myself, had two Little Swamp Buggies about 10 years ago and enjoyed them--well, the first one, yes, the second one, not so much. The variance in kit quality was astounding: My second kit's contents were warped and didn't live up to the first kit. Perhaps that was just rotten luck. I don't know. I never built a Dumas boat before then and I haven't built a Dumas boat since then.

Now, over a decade since I've built a watercraft, and with many airplane models beneath my belt, I wanted to return to this area of the RC hobby by building upon the Swamp Buggy design, but with a twist: I wanted to design a micro buggy.

So here she is: Ten inches long with a 5.00" beam, to be built with spruce stringers and laminated 1/32" balsa and 1/32" ply (may go 1/16" for the balsa, not sure yet). The ply will be exposed, not the balsa. And it will be laser cut.

Right now, my main issue lies with what power plant to use. A little 0.010 TD would be great, but I don't have one off hand (not to mention they're awfully expensive now). So I was thinking of using an electric micro ducted fan assembly. For simplicities sake, I'd like to have the duct/motor assembly (i.e., no linkages) above deck. Is this possible? If I run only in fresh water, can the motor tolerate getting splashed a bit? All of the electronics would be stowed away, but would a running wet motor be damaging to itself, to the ESC, to anything? Any input would be greatly appreciated.


Also, below are some pictures of the framed buggy. Please point out any design flaws or possible improvements. Thanks for reading and looking.

http://i74.photobucket.com/albums/i278/oside_james/boat_01.jpg
http://i74.photobucket.com/albums/i278/oside_james/boat_02.jpg
http://i74.photobucket.com/albums/i278/oside_james/boat_03.jpg

[LtDoc]

madmic,
Most motors don't really 'enjoy' getting wet, but they do tend to live over it. The 'trick' is to not let them stay wet. Sort of like giving a cat a bath. If you live over it, they will too. The 'cleanliness' of the water also plays a part with anything electrical/electronic. Using the extremes, distiled water is an insulator. Salt water is a good electrical conductor. Everything in between is... in between. It's better not to get things wet is possible. Cleaning and drying afterwards usually means survival.
- 'Doc

[madmic]

I've been searching for info about planes that rise off water (ROW), and it turns out that both brushed and brushless motors on these ROW planes have taken a dip at some time or another and they keep on going. Thoroughly cleaning after a few runs appears to be the key to continued use on the water. It seems the only true hazard is a wet ESC.

Also, don't some RC car gurus brake in their motor's brushes by running them underwater for a few hours. I thought I read this somewhere....

[der kapitan]

Madmic, LtDoc is right about the motors, and yes, they can survive getting a bit wet. :)

It doesn't take a rocket scientist to figure out a thorough drying-out and some WD-40 will keep a motor in good running order. ;)

However, an ESC should be kept completely dry. If one gets wet, you may not be so lucky that it'll ever work again---. :eek:

[Kmot]

der kap: many esc's today are 100% waterproof.

[der kapitan]

der kap: many esc's today are 100% waterproof.
Tom, I've noticed the ads on several of the newer ESC's being waterproof. :)

However all of the ones I own aren't, these dating back to the Reagan Administration---. :eek:

[Kmot]

Yeah, those tube type esc's are a little sketchy around water. :p

[AndyKunz]

Madmic - you want to keep the receiver dry if you don't want to waterproof it. I have been using 3M epoxy (buy it from www.OffshoreElectrics.com). Servos can handle getting splashed but if they get soaked you need to wash them in alcohol and dry them out before re-assembling. Water in gear train isn't a problem with plastic gears, just in the electronics section below.

Motors don't care if they get wet. Both brushed and brushless will run fully submerged, but it will waste power and in the case of the brushed, cause a LOT of brush wear very quickly. I used to soak my brushed motors in IPA after a day of racing and re-lube the bearings. Quick, easy, and effective. (BTW, I did the same thing to the servos).

I have made several swamp buggies with both DF and prop. The DF ones were nice because you didn't have to be quite so careful about fingers, but they really were bad as far as getting on the pipe. You would do much better with a prop because you spend so much time at low forward speed with these critters. Also, a prop does better when then airflow isn't straight into it vs. the DF which just loses all kinds of thrust.

What's the reason to not have any exposed linkages? A boot does a great job of keeping the water out. And it's easier mechanically than trying to pivot the whole fan.

Kap - Tom's right. You should upgrade to the mid-1990's technology at least to get a waterproof ESC. Mine have been since the early 1990's but we weren't selling them commercially until about 1995/96. Even the BL controls are pretty much not a problem nowadays.

Andy

[der kapitan]

Yeah, those tube type esc's are a little sketchy around water. :p
Tube type? Never saw one of those, but I have a few close to it---. ;)

I have one ESC that was built by a young guy in our club years ago, and it still works fine. :)

He's older now, and is presently the owner of Loyalhanna Dockyard---. :D

[madmic]

What's the reason to not have any exposed linkages? A boot does a great job of keeping the water out. And it's easier mechanically than trying to pivot the whole fan.

I was never thinking of pivoting the whole unit. I meant exposed linkages in regards to a drive shaft powering a DF unit while the motor is hidden in the hull. But after reading quite a bit on these boards, and based on what others have done, I'll just run the whole EDF unit--motor and all--above deck. I'll still have linkages for the rudder.

Does anyone know what a good thrust-to-weight ratio is with regards to watercraft? I figure the AUW of the buggy will be around 100.00g, but the best thrust off an EDF unit is about 97.00g max (GWS EDF-50). Best thrust meaning the thrust provided by the largest brushed motor I think the buggy can handle (in terms of weight).

Thanks for the comments...keep 'em coming....

[AndyKunz]

You don't need anything NEAR 1:1 to be ballistic!

Andy

[Shaun Hendricks]

Water isn't a problem for DC motors. What matters is that you need to dry the motor afterwards and re-lube it. When my motors get wet, they get an alcohol dip (to displace the water) then they get blow dried, followed up by motor cleaner and re-lubed. I've submerged motors in water, mud and muck. They all still run.