Is this payload going to work?



Hi all, so I have a desire to attach a grappling hook to the trident via a payload encased in this.

The idea is to use an Adafruit ESPY8266 Feather and Wing to drive an electromagnet attached to the side of the enclosure. I am hopeing to use the ESPY8266 Wifi module to connect to the onboard Wifi, then build a simple webserver on the Feather to control the electromagnet to dynamically attach and detatch the grapplehook when I am over the target. I read in other posts, that the wifi signal under water can go to 10-15 cm. Is this true in the production trident? Also is the SSID and password for the wifi, the same as the TopSide buoy?

Thoughts on this approach? I am about to drop $100 on the project, and I just want a little assurance that this is NOT a non starter.

Thanks in advance,


Immediate thoughts are weight and buoyancy. Positioning on the ROV is another consideration. It’s ok to drop the CG from ROV center, but you want to ensure you don’t drop the CB or you’ll flip the ROV over as soon as you drop it in the water. There’s a righting moment that you will create when you start moving CG and CB around.

Software wise, sounds totally doable. I played a little with the NODEMCU using Lua.

However, electromagnets could cause adverse interference with the on-board electronics. I don’t know for sure but it’s something you’ll want to test. I used electro magnets for payloads on quad rotors a few years ago and though cool, played havoc with the INS. We had to add metal shielding…awful idea, lol. Didn’t want to spend money on a Mil spec shielded INS at the time.

I Can’t give you assurance, but it would be a good experiment for the community. I’ve seen people drop a lot more on physical science impossibilities, so 100 bucks for an education is pretty good.

Breaking it down:

  • Check electro magnet interference. So look at the static field characteristics of the actuator. I suspect that it won’t be too bad, may not even be a problem at all if you keep far off the surface of the ROV.
  • Check your ideal placement. Ensure you drop CG below CB and keep it aligned with the ROVs CM, or you’l have to add weights, etc to keep it from tilting and being un-flyable.
  • Check weight of hook and consider if your in fresh or salt water. you’ll need to address this.
  • There’s no current API available for payload interfacing. OpenROV is working towards getting this out, from what has been written in other posts. I do not know when this will happen. But hook to the RTI DDS impl exist. I’ll be looking into this over the next week.

One thing I haven’t had a chance to do yet is analyze the wifi and start digging into what’s there. One thing that has been absent is Trident API and hierarchy documentation. But, I have full faith it will be out soon.

Interested to hear how it goes!



Ok, so you got me invested in this.

Do you really need a 25Kg lifting force magnet? One thing that just hit me is that aside from the weight you are going to add to the ROV from the magnet, power board, power supply, and the communications widget, you have payload housing to consider, and THEN you need to consider how much added mass to lift and bring to the surface.

You selected a 25kg magnet. Not only is that big, it’s going to have a significant static field when engaged, so you need to characterize this.

How much is all this going to weigh? and How are you going to hand the buoyancy? The last thin you want o do is add weight to the ROV and not increase the buoyant force. Now you’re talking foam. And even more foam with you really want to bring 2.5Kg up from the dark depths of the underworld. (what it can lift is the lifting force divided by 10)

I think we can make some good engineering design decisions by first looking at the requirements of what you would like to do, then how much it’s going to weigh and size, power (SWAPC - Size Wieght Power cost analysis). It’s not hard, but trust me, do this first before you drop money.

Let’s think about it.


Final question for the evening, How do you plan to ensure that when you drop the hook, you’ll hit your mark?


Awesome questions Jim. So I am working in Freshwater. I was thinking of attaching a secondary tether to the hook, so when it was detached, I would move the ROV away, and retrieve the object by hand. I was going to position the payload and hook off the front of the ROV, but now that you mention Center of Gravity, I am having second thoughts about it. Perhaps I can add a clear enclosure like this: and put in a secondary camera at lower res pointing down, to help with positioning. Would the air contained in the enclosure help with the buoyancy issue. I guess I need to break out the University Engineering Textbooks :). I was thinking the 25kg, since the adafruit link mentions a pickup force of 5-10 times less. I was hoping to dual purpose the EM to attract any small metal items on the floor by positioning the trident over them and activating the EM.

I am working in super low visibility, and 3M of depth. This side project is in response to the video here :slight_smile: I want my chair back and that jerk’s fishing rod :slight_smile:



Ah, now I understand. I think it would work once you dealt with the new buoyancy characteristics. What’s the weight of the hook?

That visibility isn’t too bad. Some places here in the Chesapeake during summer are far worse…talking 2 maybe 3 inches if it’s rained north of us here in Hampton Roads area. I love seeing stuff like this, there’s a story to every man made thing under the water, and it fascinates me, lol.


Just made a post about a line threading mechanism for Trident that I thought you guys might find useful for this sort of thing. Here’s a link.

Excited to see how this all works out!