The grabber mechanism is made to adjust to the various cargo containers I've built, which makes it wider than I would have liked.
I also couldn't sort a way to make it entirely collapsible and still retain strength (again, my habit of over-engineering.)
The end plates ride on 8mm rods with linear bearings and each is moved by one of the big Actuonix actuators with location feedback. These two are NOT synchronized, the way the lift arms are, so that you can shift the end plates to one side or the other. This makes it easier to pick up a container if it's off center, or unevenly loaded, you can line up the grabber on its center of gravity and not the physical center.
Too many wires? Never!
Rather than try and run wires up and down the arm for all the various functions, it was easier to run just power and data from the RX. (There is one extra wire from the lighting Arduino for the rotating beacon light up there.) This worked out really nicely when I had the idea to make the end removable, just put plugs on the wires and pop.
The crane head we saw up above, just has an Arduino to drive the coupla LED's and the winch servo and then some interconnect wiring. For this one, the grabber head, it's more complicated. There's an Arduino that handles the various movement functions, and then the two red boards with the heatsinks are motor controllers. Two run the actuators that slide the grabber end plates, and two drive the center knuckle motors. Those are the silver gear motors on the right and forward sides.
These are geared WAAAAY down, to like .5RPM (yeah, like 30 revs per HOUR), so they can directly drive the knuckle mechanism. That knuckle is M8 rod welded in a cross, riding in 608 skateboard bearings, and then coupled to the motor output (left side, blue aluminum behind the wires.)
The side motor pitches the whole thing fore and aft, and the front motor rolls side-to-side. The entire mechanism also yaws, rotates around a vertical axis, using a smaller actuator in the back (upper right of that last pic.)
Also, note the little blue circuit board with four wires between the arm end (aluminum tube, top center) and the beacon. We'll get to him in a minute.
The net result of all of this is that the container under load can be shifted in all three axes:
Now, obviously you wouldn't actually want to tilt it that much, it goes to like 30*, but the pitch is relative to the arm angle. That means that as the arm rises, the pitch angle changes. You can just keep shifting the one control up and the other down to level it yourself ... or the Arduino can do it for you. I had some digital gyroscope/accelerometer chips left over from my wildly unsuccessful attempts to do a self-levelling quadcopter; that's the little blue circuit board above.
I've no idea how it works inside with no moving parts, but the chip spits out a signal as to how far off level it is in degrees. The Arduino can read that, and then carefully adjust the pitch and roll motors to bring the load back to level. This way you're level when you pick up the load, lift the arm, and it stays level through the whole process.
Now there's no guarantee that the load will be truly level when you go to pick it up, so one switch on the TX turns the auto-level on and off so you still have manual control. Also, while in motion the auto-level wants to over-correct, so it should be turned off while driving. Finally, I coded t\he auto-level so it won't kick in if it reads more than so many degrees off, under the assumption that either it's getting bogus data (which I never found to happen, but, you know, Just In Case), or that you intentionally are way off level. Once you get less than about 10 degrees of level, you can enable the auto-level and it will wiggle the load into place.