How Can I Create Rotating ROV Thrusters for Precise Movements?

[madacho]

Hey, I'm in charge of the propulsion component of our school's ROV team, and I was thinking of having just two thrusters on the entire ROV that are able to rotate (preferably) a full 360 degrees, so that it can turn, strafe, move up and down, etc... all with only two thrusters.

My first idea involved using waterproof stepper motors, but finding reliable but waterproof motors ended up being more trouble than it was worth. The only US ones I could find were industrial-grade ones that were a few thousand dollars each, and the only other ones were all based from China.

My thrusters are powered by already-waterproof bilge pumps, and I was thinking I could just use smaller bilge pumps to provide the rotating capability. But since they aren't meant for precise movements, any suggestions as to how I should do this? I was thinking some kind of gearbox to gear down the smaller motor a bit, but there is the issue of I want to have the thruster point straight up, or at 90 degree angles, etc...

Anyone ever do something like this or seen something like this? Any help would be extremely useful.

Thanks!

 

[mooktank]

How about steppers inside the pressure housing with their shafts protruding through seals? That way you don't need water proof motors and you can still have precise control of the thrusters' angles.

 

[madacho]

hmmm that could work... any ideas as to how to make a waterproof seal though? or what stepper motors to use?

thanks

 

[mooktank]

Download the parker O-ring handbook for designing a rotating shaft seal. That's the easy part. Choosing stepper motors shouldn't be hard either. I'd try to model your system and at least come up with a close value for holding torque, etc.

 

[madacho]

ok ill try to find that, and order some reliable stepper motors too. our school mainly has solidworks, but I've more or less used the stress test feature before so hopefully i can figure it out.

the project is due by the end of March, so hopefully I can pull this together quickly.

thanks!