Magnetic coupled grabber / first working prototype




Since I am involved with Openrov and follow the forum, I have seen a lot of speculations about grabbers or manipulators. Also for me this has always been a goal. Now that I have finished my rov and made a couple of modifications I turned my interest to this. I imagined a lot of different designs using servos, but then I need to be able to program these and deal with electrical connections. When I redisigned my endcaps, I already potted some extra wires for this. On the other hand I had a magnetic option in mind, which I did now first. The idea behind it was to use the camera-servo pins to plug in the servo for the magnetic actuator. I thought, I don't use the camera-tilt, when I use the grabber, because I want to see the grabber!

so I made an actuator with a servo inside (to save space) and magnets on one end.

here are the plastic-parts I milled prototypes and made molds to cast a number of copies, so I can play and modify, witout always having to start from the beginning.

My central rod (see my other posts) acts as a hinge. The position of the servo arm was chosen so that towards the end of the movement (grabber closed) the maximum of force is generated and the force is almost parallel to the servo-horn, so it is sort of self-blocking without consuming to much current at the "closed"-position:

The magnets outside of the tube are glued in another plastic part that has little weels that ride on the tube to reduce the friction generated by the manets (without the weels the magnets needs 150g to be moved, with the weels almost nothing!). This plastic part is then connected with the grabber by a pushrod.

Here are the pieces in and outside the tube to demonstrate their position:

Below you can see the grabber with all pieces. It takes less than 10 seconds to mount or dismount it!! It just snaps on the rov's threaded rod and is secured with one screw. Some of the plastic parts are made from self casted syntactic foam(resin with microballoons), to make the whole grabber neutral bouyant, so it doesn't mather, of it's on or not. The claw itself is also secured on the carbon rod with one screw, which allows to rotate it (I have already a modification for the rotation by a second magnetic coupled actuator, but there again I would need to program more servos)

the claw opens and closes nicely when I use the camera buttons.

the closing force at the tip is appr. 200gr, at the inside 300gr. This should be enough, because the rov can not lift a lot.

I am sure, this approach can still be modified a lot.

I think there can be a lot of different designs and improvements. I consider it just as some sort of "proof of concept"

So I am happy to see what others do with these ideas and look forward the your feedback!




It is amazing how people think of ways to overcome a challenge and thinking outside of the box well done! This concept also has other benefits such as dropping weights to add buoyancy to the ROV.


WHOA!! A magnetically coupled servo! I've never seen anyone actually pull this off. Well done!

This is very cool. I'm very eager to hear how this performs. I want one!!


Now this is soo COOL!


Been working on something similar!


Looks great!


The power of imagination ¡¡




Very nice build.


I just want to add.... this is brilliant! It's simple and clean.

Have you had the opportunity to use it underwater yet Hub?


Hi Charles
Yes, I put it on all the time when I dive and have collected some items from the bottom of the lake. Once I also used it to free my tether that was wrapped around a piece of wood. I am still hoping for someone to program more servos, so I can add more functions. I think I have room for two more couplers, wich could be used to turn the grabber or for others functions such as an “elevator”-flap or some sort of ailerons.


Im waiting for the same. I do not think that Im able to do it my selves.


Hello Hub,

I am assuming you are needing help on the electronics/software side to add servos right?

Disclaimer: I have been lurking the forums for just a few days and do not yet have a solid understanding of the existing OROV hardware and software. I am likely commenting prematurely here and hopefully someone will set me straight.

Having said that, could an I2C servo driver (here is one example be used to add multiple servos? This particular one offers 16 channels; I'm certain there must be smaller ones out there.

As far as the software side goes, I imagine there would be work needed on both the Topside Cockpit software as well as on the Arduino side. Perhaps those capabilities are already there?

Swing over to and give our expedition a follow. I would LOVE to get my hands on this ROV and start playing with some of these concepts. I am also trying to recruit a solid and experienced OROV hardware guy for the team. :)


502-Adafruiti2cservo.JPG (155 KB)


There is two extra servo ports that are wired on the PCB. The ones on the right hand side of the servo that controls the tilt on the camera. As I see it, we only need to figure out the software to control the two extra ports.


Sorry, on the left hand side of the servo. D9 and D10


Already an opened Issue request (#262) for the two AUX servo outputs.

GitHub OpenROV Issue #262

I tried experimenting by writing some code last month to get these to work, but I never could get the Arduino firmware to upload correctly. I'll leave it to the professionals, but I can't wait to get a 2-axis arm mounted on mine.



Awesome project! I will eventually be using my ROV for collecting benthic algae samples, and your concept is promising. Very inventive, yet relatively simple. Bravo.

One question. Is there a difference in power use between closed and open positions? I did not quite understand how the servo arm position relates to power use difference between the two positions.




You can imagine the grabber directly attached to the servo. So if you grab something, it draws some power to overcome the resistance or elasticity of the grabbed object. Due to the geometrics of the inside part of the coupler and the pin on the servo arm it needs only little power to keep it closed. It is almost self-locking in the close-position.



So excited to see this! Making the ROV's into little trash grabbing machines for kids so they can help me clean up Puget Sound is fantastic!


Did you ever end up posting the 3d printer files?


Hi Brian
I don’t have files. My prototype was handmade. I did send a “kit” to David Lang, but don’t know wether that ever arrived at Openrov -HQ
Best regards from Switzerland