Need help with water propulsion

[Murari]

This is one of my first robots and i really havent been able to come up with a water propulsion system to suit my requirements. I was hoping someone could help..

Most of the propulsion systems i thought about like propellers seemed to either disturb the water too much or draw too much power.
Another problem with propellers was that the water is very shallow, only about 3 inches deep.

[gamefreak]

heres a random idea that went into my head a few days back  , try some sort of pulse system, like the bass of a sound system maybe.

But since i know nothing about the physics of sound other then it travels in waves and bounces off of stuff, and i know nothing about water except that it is H2O and is wet, i dont know if this would work, it would probably use a lot of electricity

[Murari]

Sound waves wouldnt nearly be enough to propel a robot boat, especially one running on an onboard NiCad battery

I was thinking of someway other than propellers to expel water and push the bot forward, something like a jet engine, only much smaller and one that uses water.

[Admin]

How about this?
http://www.cnse.caltech.edu/Research/reports/polsenberg-full.html

or this?
http://images.google.com/images?q=robotuna&ie=UTF-8&oe=UTF-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&sa=N&tab=wi

[ed1380]

Will it be in fresh or salt water? If salt water is possible, then you could dry using a magnetohydrodynamic drive. Here is an example. http://www.evilmadscientist.com/article.php/MHDCraft

[wolfy_9005]

Just a thought. Use a tube with 2 propellors and 1 dynamo thingy to recharge the batteries. Could also use a windscreen washer pump and/or a water feature pump(small one with ~1000L/hr cost like $20). Could modify it to suck in large volumes of water, and release it from a smaller hole(ie, from this O, to this o). Never tried it but thought it might work(think jetskis).

[gamefreak]

Who said my idea had to be sound waves.... Myth busters tried to make a car give off a huge amount of Bass by hooking up a speaker to an oscillator, the speaker part moved in and out causing sound waves and overall destroying there homemade giant speaker, but see my idea would be water proof because all of the mechanics are on the inside there should be little to no leakage, unless the speaker breaks.

But you see, it doesnt only create sound waves, it would displace water eqaul to the volume of the cone of the speaker, thus creating thrusr every time that the cone got pushed out

[Brandon121233]

can ypu give us a general idea of how fast you want it to go?

[gamefreak]

Also just for the fun of it, If you wanted to murder the enviroment, set a record, and probably destory what you are building you could use Nuclear Pulse Propulsuion, http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion.

Now noone can say we didnt cover all bases

Also dont forget : Nuclear marine propulsion • Nuclear navy Aircraft Nuclear aircraft

All are propulsion ideas, but i think some might be dangerous to the enviroment
 

[Murari]

I'll need it to be slow enough to steer with an adaptation of differential drive but fast enough for something of a boat race in a small tank... maybe about 1 metre per second or so.. sorry but just a little too slow for NPP
I also have a voltage constraint of about 25 Volts

[Admin]

whoa 1 metre per second?! thats fast . . .

you might want to try buying a cheap $20 drill at homedepot, hacking out the motor, wires, and batteries (keep the motor in the casing for protection), and attaching a prop to the motor . . . and use a servo'd rudder for steering . . .

one day ill write a tutorial with pics on how i did this . . .

[JonHylands]

My AUV MicroSeeker doesn't even go one meter per second. With a 6" diameter model airplane prop turning at 600 RPM (wth 4" pitch), it goes about 2 feet per second.

http://www.huv.com/uSeeker

- Jon

[Brandon121233]

I would suggest bilge pumps ( I think thats how its spelled) for pumpung water out of a real boat. Two of those would be able to displace a large ammount of water very quickly and would make a pretty nice propulsion system. Wheather that would get you to 1 m/s I dont know never tried it. This looked interesting http://www.rollette.com/rovrev2/

[Murari]

Sorry guys... I meant a maximum of 1 metre per second, something close to 2 feet per second would do..
Jon your gear motor seems quite interesting though id like to know if there would be any performance issues if i used a DC motor instead. How would the RPM count translate into thrust?

[JonHylands]

The gearmotor I am using is simply a DC motor with a gearhead on it.

Specifically, this one:

http://www.robotshop.ca/home/products/robot-parts/motors/gear-motors/gear-motors-4mm-shaft/lynxmotion-ghm-07-gear-head-motor.html

In order to use a model airplane prop, you need to gear the motor down. If you're going to use a non-geared motor, you must use something closer to a model boat prop, which are designed to run at thousands of RPMs.

Since you're running in 3" of water, you have to use a higher-RPM motor with a smaller diameter prop, which is of course going to make a lot of disturbance in the water.

How big is this vehicle you are pushing? (diameter and length)

- Jon

[Admin]

another advantage of the bilge pump that Brandon mentioned is that they are already waterproof