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sconisbee
06-01-2008, 06:59 PM
Ok so im working on a little personal project on the side and im looking at designing a coupling to connect a motor shaft to a propellor with design and/or connecting a motorshaft to an impellor with two caveats its gotta work at upto 100ft underwater, so pressure is a slight issue and low voltage no more than 24v. Think along the lines of miniture underwater propulsion, I'm thinking one possibility would be similar to the mag-drives on fountain pumps, aquarium powerheads etc.

So any of you guys had any experiance with magnetic couplings?

I could use traditional shaft seal tech but at pressure at small sizes its gunna be a big headache.

One idea i had was something along the lines of this.
http://www.micropump.com/tech_tips/magnetic_drives.asp

Mark McGrath
06-01-2008, 07:51 PM
Look for Andantex magnetic particle clutches.Not cheap but if the application demands it they will do it.
You could also look at Crane mechanical seals,again not cheap.

Mark.

Evan
06-01-2008, 09:09 PM
You could also pressurize the inside of the vehicle. It's only 3 bar.

sconisbee
06-01-2008, 09:43 PM
You could also pressurize the inside of the vehicle. It's only 3 bar.

Now thats not such a bad idea, didnt think of that, although that would mean running an extra tether to the vehicle to maintain pressure and then use Labyrinth seals on the shafts. I would only need to pressurise the drive system as the electronics module will be seperate and have multiple seals to the tether and payload modules.

Although on second thoughts... having some physical disconect between shaft and impellor/propellor wouldnt be such a bad thing anyway so ill still be requiring an overload clutch of some description.


Thanks mark, ill shoot Andantex and email in the morning and find a local distributer and some tech specs, for the prototype they might be a touch expensive but the final product will more than warrant it.

a sneak peak of the project is below, and it might be more than enough to guess the final purpose.

http://i59.photobucket.com/albums/g290/synoguy/Frame.jpg

macona
06-02-2008, 12:48 AM
No, you just pressurize it before and let it go. Or you could install a little nitrogen cylinder with a regulator on the craft. Like the lecture bottles.

rdfeil
06-02-2008, 01:56 AM
Hi,
For the pressure regulator you could use a differential regulator on a small nitrogen / high pressure air cylinder. Reference the differential regulator to the outside of the drive unit and set it for a small (1-2 psi) positive pressure. As the unit goes down the pressure inside goes up automatically. Install a low pressure pop-off to relieve the pressure as you bring the unit to the surface.

Just a thought.

Robin

Swarf&Sparks
06-02-2008, 03:11 AM
Some useful links here
http://www.homebuiltrovs.com/

Evan
06-02-2008, 09:03 AM
Having a pressure bottle on the vehicle also allows you to fit an emergency recovery balloon that activates automatically if communication is lost (or other criteria). Either nitrogen or helium is a good choice. Helium, while more expensive, has the advantage of being able to put many more liters in the same size bottle.

sconisbee
06-02-2008, 03:25 PM
Having a pressure bottle on the vehicle also allows you to fit an emergency recovery balloon that activates automatically if communication is lost (or other criteria). Either nitrogen or helium is a good choice. Helium, while more expensive, has the advantage of being able to put many more liters in the same size bottle.


Now that is a real smart idea, infact a bloody good idea!, well depth parameters have just been increased to a service depth of 200 ft (i dont even want to think of the tether cost yet:o )

So say the tether was severed i could have it so it deploys said balloon and it pops to the surface, not such a bad idea considering cost of some of the stuff that might be going onboard.

rdfeil
06-02-2008, 03:51 PM
Way to think Evan :D Outstanding idea. Put on 2 or 3 for backup, add a small check valve on each so that if one bursts the others still hold gas. Again a small purge valve to relieve pressure as the thing rises to the surface. A small normally open solenoid valve with power looped through the tether to the surface, if the tether breaks power to the solenoid goes away and the valve opens. Relatively inexpensive compared to the cost of the equipment. An appropriate sized bladder rolled up in a break away pouch, Velcro closure possibly?

Good luck,
Robin