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Robotic Arm for BlueROV


(Roy Petter Dyrdahl Torgersen) #1

Hi there, thought I’d share with y’all one of the things we are currently working on @ Nido Robotics.

We have several clients who have indicated they could have good use for a basic robotic arm to accomplish simple tasks. After consulting the great oracle we found that most available solutions where really expensive (20k and upwards), and too heavy for the BlueROV2 or similar systems anyway.

Talking with a member in our Maker community who was already working on a robotic arm, we decided to jump on on the challenge and start designing a small 3 or 4 function arm, specifically designed for the BlueROV2.

Everything is in a very basic prototyping phase yet, but you can get an jist of what we want to achieve:

As you can see, the arm will have a telescopic main arm, with a vertical joint at the end to lower and raise the grippers. The grippers are being designed in such a way that thye reach up to the onboard camera and can be stowed in upright position with the grippers at each side of the dome. We’re also considering putting the gripper on a swiwel joint.

What do you guys think?


(Jacob) #2

Too cool, what do you plan to use for actuators?


(Rusty) #3

@roy - Awesome! Thanks for sharing. I’m also curious about what type of actuators you will use.

I know (from our experience) that just making a single function gripper has a lot of challenges. I’m sure that a multifunction gripper will be a huge challenge.


(Roy Petter Dyrdahl Torgersen) #4

well, I really want to use brushless motors because they could go unprotected (M100 or M200 maybe).
But it’s difficult to get the necessary par to achieve any real lifting, so we are still looking at options.


(Kevin) #5

Awesome work so far! If you do manage to build a few I’ll definitely buy one. I agree, using the M100/200 in some sort of linear actuator or a worm gear is probably the way to go. Something that will give you lifting power without seizing.

I have a few of these kits, just never got around to putting an M100 on them: https://www.seeedstudio.com/Strong-Robot-Gripper-p-1691.html


(Enrique) #6

@kevink :slight_smile:That gripper looks great! Seems that it is discontinued…

We are thinking in actuators with encoders inside a small watertight enclosure. It will be necessary to control the pitch from the ROV, so it will be placed into a vectored-6DOF or something similar


(Roy Petter Dyrdahl Torgersen) #7

@kevink that looks fantastic! Did you ever put it to any testing?

@QuiGon2 the main problems with encoders is how to make them watertight. Maybe we could use a similar approach as Atlas is using for their boards, encasing in epoxy?

I’ll see if I can get Alvaro to register here.


(Kevin) #8

@QuiGon2 Yeah I think it got discontinued 2 years ago, so I snatched up 4 of the kits from the last place I could find them. These are apparently the replacements: http://www.robotshop.com/en/makeblock-robot-gripper.html I still preferred the 4 fingers though. I tri-finger is preferred.

@roy I built one kit, but never tested it with a motor or or anything. Something like that would need limit switches, which I never figured out.


(Tim Pierce) #9

I’m going to try the quick and cheap Servo route. It has the advantage of being light and theoretically easy to implement.


(Tim Pierce) #10

The starting point. The joint is going to get reinforced for the back servo, and it may get changed to a “karate chop” style .


(Enrique) #11

@piercet What is the depth rating of that servo? I didn’t find anyone for reaching up to 100m


(Kevin) #12

These are the only pressure proof servos I know of: http://www.volz-servos.com/English/DA22SUB/

I have no idea how much they cost or where to get them off the shelf.


(Tim Pierce) #13

The servos shown there are just standard servos for testing. I plan to pot the servo motherboard, and fill the servo housing with gear lube (possibly a mineral oil and more viscous gear lube combination) and switch to bushings from bearings. That will eliminate any potential air voids and pressure differentials. I think it will probably be a case of “if it works to 40m, it will work to 400m” after that, since the water isn’t going to tend to displace the denser noncompressable lubricants anyways. Some of the homebuiltrov forum users have reported dives down to a couple hundred feet with a similar servo modification, though long term survivability of the servo remains a complete unknown. They are cheap enough that I figure it won’t hurt to try it. Plan b is going to be a mineral oil flooded enclosure with a shaft penetrator for the servo arm. The main thing I am worried about is the housing of the servo, and deflection of the outer wall if there is any differential that the internal lubricant I add won’t compensate for. I plan on taking a pile of the modified servos in several configurations, and dumping them in the deepest water I can access on a retrieval line for a couple hours before I try using them operationally to see how it goes.


(Tim Pierce) #14

Just sent them an inquiry about buying some of those or the DA26. We’ll let you know if I find anything out.


#15

This looks great, I’m working on a similar design but the extender is driven with an SS lead screw driven by a T100 motor. For gripping, I’m looking at a water filled hydraulic system based around another T100 pushing a piston.

Just another thing, if you’re going to pot electronics for subsea use, it’s advisable to vacuum cure the epoxy, getting any air bubbles out is essential. Even at 12 bar any air pockets close to the PCB can cause delamination of the board itself. (Been there!)


(Tim Pierce) #16

The plan right now is to use my vacuum chamber to do that. I’m working on a 3d printable stand for the bolt passthroughs I need to pot as well, though I think that will have to be a two stage operation


(Tim Pierce) #17

Inside view of one of the Hitec waterproof servos similar or identical to what Blue Robotics sells here


I’m thinking the bottom section with the motor gets flooded with mineral oil ans sealed, then the top section gets a replacement for the upper bearing, filled with thick servo gear oil, Ran for a bit, then filled with mineral oil to address any voids, possibly with a rubber boot at the top. I’ll mostly be diving in freshwater initially anyways so i’m less concerned about corrosion than i could be. but I don’t see any components other than potentially the motor in there that wouldn’t take pressure aside from the bearing, and thats an easy swap for a bushing from mcmaster carr.


(John Griffiths) #18

Count me in as a buyer when you get an arm and gripper working. I thought I might share a couple images of various Bluerov2 versions I am working on where an arm would be on great benefit.

the first image is of a scoop for scollops,sea cucumber and crabs.

the second (still plenty of work to do on it), I will see if anybody can guess what it is.

the last image is of a relay board I have had developed that plugs directly into the pxihawk serial port and drives solenoids and 12 volts motors with button pushes on a logitech f310.

cheers

John


(undersearobotics.com) #19

That’s some nice fabrication / welding work John!

Hard to guess what the second ROV is, perhaps for inspecting smaller diameter pipelines?


(Tim Pierce) #20

Speargunbot? Looks like it has a launcher.