This is a cheap and easy to build ROV (Remotely Operated Vehicle). I came up with it because I wanted to create a minimalist aquatic robot that avoided the traditional annoyance of needing to get / make waterproof motors for ROVs. This ROV uses a new form of aquatic propulsion that works via the creation of multiple standing vortices around the ROV's asymmetrical hull (if this isn't new please let me know). The propulsion system doesn't require contact of any actuator with the surrounding water, and is very easy to build and is very robust.
Previous bio-inspired ROVs have used flapping fish-like fins to move through the water. Although these fins work by creating vortices along their surfaces, the ROVVor creates constantly maintained, standing vortices around its hull. These standing vortices are maintained by a high frequency vibration of the vehicle, induced by an internal pager motor. The vortices seem propel the vehicle through the water due to the vehicle's asymmetrical hull shape which must create some imbalance in the vortice's forces applied to different sides of the vehicle.
Due to its ease of implementation and robustness, this propulsion mechanism could potentially be useful for creating nano-scale ROVs (would need some way to vibrate the 'actuator molecule'), although at the molecular scale vortices might not work in the same way. Due to the ROVVor vortex-drive's minimal actuator displacement (compared to spinning propellers of flapping fins) it could also be useful for military applications to avoid detection. On a lighter note, the cheapness and ease with which the ROVVor can be created, and the interesting-ness of the way in which it works would make it very conducive to introducing kids to robotics in general and specifically to ROVs.
Step 1: Vortex-Drive Design Evolution
So I put a pager motor into a centrifuge tube (see figure I), and put it into a pool of water. It vibrated and I could see standing waves created all around it, but it didn't translocate (it didn't move through the water).
So then I tried adding little bristles to its sides (see figure II) and still nothing happened.
Finally, I starting thinking about adding a 'wave-sail' to the robot (see figure III) to take advantage of the waves created by the vibrations. I based this idea on the fact that one can use a fan on a sailboat to push the sailboat (see this great video: http://www.youtube.com/watch?v=0CrXvOKPymk). When I added this 'wave-sail' the robot started moving through the water.
However, when I trimmed the 'wave-sail' down a bunch (see figure IV) the robot still moved through the water, even faster than it had before. That's when I realized that the trimmed down 'wave-sail' was not acting as a wave sail at all. So I added sawdust to the water and saw a bunch of standing vortices all around the sides of the vehicle. I drew the vortices as I saw them as can be seen in figure IV). I then added some weights into the tube (little pebbles) and saw that the ROVVor could move even when completely submerged.
Then I thought that maybe if I put the same bendy straw on both sides of the vehicle that it would move even more powerfully through the water (see figure V) ,but when I did that it didn't trans-locate anymore! So it seems like the ability to move through the water is dependent on the vehicle's asymmetry and on the standing vortices created around it.
In the future I'm planning on trying a design in which multiple ROVVors are attached to each other (see figure VI) via a semi-flexible connection. In this way, by selecting which ROVVors to activate or deactivate one could selectively steer the whole structure in a desired direction. Because the connections are semi-flexible they would not propagate the vibrations from one vortex-drive subunit to another.
I haven't yet created a fully self contained version of the ROVVor because I couldn't find batteries small enough to fit into my centrifuge tube, and it's hard finding a water-tight tube that would fit a battery and the motor. I'll update this instructable if I find a right-sized tube and am able to implement a fully self contained version.
Step 2: How to Build It
= Centrifuge Tube
= Pager Motor
= Power Supply (Wall Transformer or Battery)
= Tissue Paper
= Thin, flexible wire
= Soldering iron
1) Get a small tube with a water-tight lid (I used a centrifuge tube) that your pager motor can fit inside of. It's best if the tube has a water-tight cap that can be easily removed because that will allow you to remove the pager motor for debugging, and for drying it off in case water gets in.
2) Solder some long, very thin wires to the pager motor's leads. Using alligator clips or hook-clips connect the other end of these thin wires to the two cut leads of a wall transformer (with ~5 volt DC output). It's best not to solder the wire-to-transformer connection because you may want to swap the polarity to the motor to see if that has any effect on the direction/speed of the vehicles movement (I noticed changes dependent on the polarity/direction of motor spin).
3) Shove some tissue paper into the tip of the tube. This tissue will help absorb any water that happens to get into the tube.
4) Cut a bendy straw so that you have about 1 inch of straight straw on one side of the bend and about 1/2 inch straight on the other side of the bend. Using a piece of scotch tape, attach one of the straight parts to the side of the centrifuge tube. You can test out different directions of bends and see how that effect the direction of travel (it did for me).
5) Secure the pager motor's body into the tube, make sure the part that spins won't touch the walls of the tube. If you need to you can wrap tape around the motor's body to make it a tight fit.
6) Now close the tube's cap. I just closed the tube's cap over the motor wires, it still maintains a pretty tight seal but not as tight as it would be if I could find a battery small enough to fit in (eliminating the need for the wires).
7) Now put your tube into a body of water and check to make sure that it doesn't fill with water.
8) Now connect your motors wires to your power source (~5 volts should be fine, depending on the size of your motor)
9) Watch it go! Yay!!
Step 3: Video
In the video you'll see that it follows a curved trajectory due to its wire 'leash' being held stationary from above, so the ROVVor is trying to go forward but it's being pulled in a circle. In other tests when I positioned the suspended wires closer to one of the bowl walls I observed that the ROVVor keeps moving towards the bowl walls even when quite close, so the ROVVor's movement does not seem to be much effected by, or in any way due to reflections of waves off the bowl walls.
Theoretically, by attaching a couple ROVVors together facing different directions, one could make the assembly move in any direction by varying which motors are active at any point in time (See step 1, Figure VI). I haven't done that yet but I'll update this if I do or if someone else tried it and lets me know.