ROV: 3. Thrusters
NB: I ended up using bought thrusters! This article is archived. Head over to the new article:
First off I went full out on using bilge pumps. Then after a while I heard that they did not cut it at my depth requirement. Then I though maybe just run the “OpenROV’s Don’t Caring” method. But then again it would require me to have an extra 6 motors every time i fly. And I would rather do a great job the first time than do a good job lots of times.
So after a while searching and asking on RCGroups (Best RC community ever) I’ve come to the conclusion to use Magnetic Coupling. Using magnetic couplers I’ll be able to seal off the motor completely from the propeller.
So to quickly explain the concept of the magnetic couplers. I’ll have a motor, on the motor shaft I’ll attach a series of magnets (8 magnets) alternating the poles on it North, South, North, South. The magnets are put into a piece of plastic (fig.1) fastened to the shaft. In the middle there will be a 6mm ball for spacing and better friction.
The driven and drive magnet will have 8 magnets 4 which is switched north to south and a stainless steel ball in the middle (for it to have something to spin against. There will be mounted on on each side of the mechanical divider. Hopefully those 8x8mm magnets are strong enough to go trough water without slipping too much. This will give minimum strain to the motor.
The setup will be as shown on fig.2 below, having a driven and drive magnet with a mechanical seperator. The balls will rest on it making the spacing perfect and when the drive magnet goes around the north will attract the south of the driven magnet and drag it around.
Using this setup I’ll also have a “slip clutch”, so if anything gets tangled in the propeller the motor will not notice any difference. Thats the upside, the downside is that if anything gets tangled its not a strong way to break it. So probably I’ll have to pull the flight and drag it back up.
Hopefully this design will be cheap to make and easy. Will look for parts on monday since my vacation starts then 🙂
Here you see a sidecut of the housing for the magnetic coupler. The motor will be standing on the bottom part and then the mechanical separator will go inside before the cap with an o-ring on the edge. Then the cap will come on and press down on the separator which will seal the motor from the outside pressure / environment.
See how the separator comes in as a mechanical seal between the driven and drive magnet.
The only question i have is what materials i can use which is not affected by the magnets in any way? Any tips please comment below! 🙂
Hopefully this will be the finished design!
Here is my work area! Hehe, all materials are free so simple to prototype inside here. The problem is getting it real! 😉