Finally got my grabber arm working…on the bench at least. Have went through a few trial and error iterations and design changes since I started with the idea. So now that it’s working I’ll post it up here and hopefully someone smarter than me can tell me how to make it even better.
Basic concept was the servo mechanism inside a waterproof enclosure, coupled to the grabber by magnets.
I wanted simple…I don’t have access to fancy 3d printing or even much in the way of materials locally, so the build itself was really a concept on paper and then a “figure it out as I went”, along with “what do I have here that could work for that?” methods. So naturally it’s not a well documented build process.
Not the cheapest setup, the servo alone was about $100. I used an actuonix linear servo with a VERY strong magnet attached to the head (under the blue balloon “bellows”). I went with the L16 RC version because it can run on 3-5v. For specs I chose 50mm stroke (seemed like a good length…) and 63:1 gear ratio. I wanted to make sure the servo wouldn’t stall before the spring was fully extended.
That whole assembly sits inside a modified OpenROV battery tube, and attached to the threaded rods under the bot.
It’s attached to the claw on the outside by another magnet (plastic coated), aluminum rod and a spring (inside the grey aluminum tube)
I wanted a spring so the servo wouldn’t stall once the claw closed on something. Getting the right spring was a bit of trial and error, I wanted a least 10lbs of force at full extension, but less than 15 (the magnets would separate at about 15lbs of pull). The one I’m using gives me 12 (measured with a luggage scale)
For the claw itself, I’m just using a cut-off “pick up wand” from a dollar store. Simple design, all plastic, pretty strong.
So it works! Now to get in the water and see what I need to do in terms of buoyancy and handling. While it’s not hard to remove, the idea is to just leave it on there all the time.
I also plan to drill a couple holes in each claw “finger” so that I can attach box-cutter blades and see if it works for line cutting.