Water Skimming Robot

Hopelessatengineering

Hey guys,
I'm relatively new to the Parallax community as well as engineering and I was wondering if you would be so kind as to help me with a project of mine. My problems are mainly with hardware. I am making a water-proof robot that propels itself across the surface of water using two motors (I don't know what to get!) on either side. Also, the shape of the robot would be cylindrical and its encasing will be a heavy-duty plastic that I'm getting custom-made. However, I am running into problems in the formative process of this project. First of all, I need to know if standard servos can cut it when it comes to the water! I'm going to make some sort of propeller that will attach to the servos that will keep it moving at a steady, moderately fast rate. I will probably water-proof the servos with Plasti-dip so that if water does get inside my robot, the servos will be okay. Second of all, I happened to notice that Parallax has released a lovely new 9-volt solar panel that would be fantastic for my project Would these work as the only source of power for my robot? Another concern for me is keeping my Board of Education and Basic Stamp II happy and dry. As I said, my robot is made for going on top of (rather than under) water. Do any of you have experience with water-proofing micro-controllers? My last issue is sonar. I'm using the ping)) sonar sensor for the robot to avoid objects and it has worked marvelously for me in the past. Would it function with a layer of plastic in front of it.

Thanks for listening to my long-winded topic!!

-Matt

Mike Green

Servos are not made for immersion in water. You'll eventually ruin them. The problem is that water will leak in around the opening for the shaft. You will need some kind of water-proof bushing for the propeller shaft where it goes through the hull. You might do better buying a water-proof dc motor with a bushing built into the motor. You'd mount the motor up against the hull with the shaft going through it. You'd also use a motor controller designed for a dc motor. Parallax carries some of these and there are other good ones on the market.

The current PING))) is not designed for use underwater. It's designed to produce its ultrasonic pulse in air. Water with or without a layer of plastic would act as an obstacle and produce an echo with little if any energy coupled into the water. You'd be better off hacking a fishing sonar.

Regarding solar energy. You need storage. The panel you mentioned puts out about 100mA under ideal conditions. You might be able to get a small plastic model motor to run off 100mA, but there'd be little left over for anything else. You could use the solar panel for a charger if the robot is going to run only part of a day, but sit out in the sun for most of the time. The Stamp can sleep for periods of time reducing its power requirements. The Board of Education is not a good choice for this sort of solar powered setup in that it's wasteful of power. You would need to design (or buy) a voltage regulator designed for solar use, charging batteries efficiently, and producing +5V for the Stamp efficiently using some kind of switching regulator.

These are all doable, but you'll need to spend some more time designing, planning, and researching.

bdickens

As a bit of a jump start - http://www.rcgroups.com/forums has a forum on Water ROVs and the folks there can help you out.

Based on a suggestion there, I recently ran some brushless motors in the water directly and low and behold, they work pretty reliably. Servos however do not. Done that, got the dead cases to show for it. Brushless are simple, easy to control using RC technology (use the Servo interface) and as long as you build a critter case, reliable.

Ping))) did not work underwater (yeah, everyone told me it wouldn't but experience is useful sometimes). But what you describe sounds like a boat and on the surface, you could make it at least do above water detection. I was going to try to interface a transducer from a boat but around here, my wife can preempt my projects (so I am currently in furniture mode). If you really want object avoidance, it's a bit dicey. If you want just "stall" then the GPS + Speed combination would work.

Solar power - check out http://www.bizjournals.com/southflorida/blog/2010/11/giant-solar-catamaran-heads-to-miami.html. It was a bit out of my price range personally (more than a bit actually) but you can see the surface area they needed to make this work. But the design is pretty innovative and something that you can do in work and fiberglass in very short order. You can design, lasercut and assemble pretty easily. Takes us about 2 weeks per boat. Treat it like stitch and glue or traditional, just remember to fiberglass one side and epoxy the other. I can't speak to the effectiveness of solar charging. Ours would sit for days without moving on the dock, then when we went it would run down and spend a few more days charging. For us, that was fine.

Keeping your board dry is not that big a deal. Most of mine live in PVC pipe, with standard ends. That same ROV thread will give you some ideas. Boards have been relatively trouble free. The interface cable has been the source of most of the leaks and if you strip insulation, then pass it through the plastic, then seal, it seems to be pretty solid. If you use one of the carrier boards that bring out euro-style connectors ( I use Prop platform modules) then you should be able to do this pretty quick. Just run the programming interface out also and you don't need to get into the case as much.

Hope this helps. You should get some better info from the links.

Duane Degn

Matt,

Sounds like a fun project. I've never purchased any of their boat stuff, but I've purchased airplane stuff from Hobby Lobby many times.

I don't know if you know about Crust Crawler's High Flow thrusters or not. There are two kinds. The 600HF and 400HFS. I think Ken is working on a project using these thrusters.

I think the Hobby Lobby route would probably be less expensive.

@bdickens, I've heard of running electric motors directly in water before. That's pretty cool. Doesn't the water have to be very clean? I can't imagine it would work in salt water.

Duane

The "Preview Post" isn't showing the links. Here they are again in case they didn't work above.

http://www.hobby-lobby.com/rc_boat_accessories_452_ctg.htm

http://www.crustcrawler.com/products/urov/index.php?prod=300

http://www.crustcrawler.com/products/urov2/index.php

bdickens

"Shocking" as it sounds, they work perfectly in fresh or salt. You need to rinse them off after use and let them dry, but so far, I've been running them for a while. I did get some trouble the first time with some vegetation and a crab but I put them in a simple case and it's run great. And this only works brushless. It did not occur to me either, saw it on the forum, tried it and it worked. If I ever get back to the ROV, I even have a better platform (propeller) to try.

Thanks

Hopelessatengineering

Thanks for all of the help guys! I will take all of this into consideration and keep you posted.

-Matt

P!-Ro

If you want to use servos in your project I've heard of waterproofing them by filling up the inside with oil (mineral oil specifically) then sealing off the cracks on the outside with glue. Just as long as the oil doesn't leak out so that the water can't get in the servo will be protected from corrosion.

Duane Degn

P!-Ro,

Have you ever seen this done (filling a servo with mineral oil)? I'd be very interested (and surprised) if anyone has got a servo to work like this for very long.

Okay, I'll do a Google search.

Yep, you're right. Society of Robots has a web page explaining how to water proof servos. They use mineral oil.

I still don't think the servos would survive long periods of time underwater. But I'd think a couple of hours is the most, many users of these would need.

Dang it! Now I'm going to have to try this.

Duane

P!-Ro

I was just thinking the same, I want to try it too. I was thinking of using WD-40 though instead, since it is easy to get ones hands on, it has low viscosity, and it is formulated to dissipate water. The only thing I don't like about it however is I believe it is somewhat toxic, but I'm not certain.

rhugg

We are also building a water-borne robot, but are using two fishing motors from minnkota. It is a little bigger than what i think you are envisioning, due to the beefy power requirement. But the shape you have chosen is well suited to a buoyancy glider (google it), Very, very low power, but submersible by nature. I would be happy to correspond regarding mission goals if you are interested off line, then we can decide what might be useful to post.