Arm assembly

The robot arm is made out of what is generally called the servo construction kit components. You will note that there are several standard parts used over and over. There is what I call the universal servo bracket, which is the U-shaped bracket with all of the holes. Most of the arm servos will fit into these brackets. There are three C-shaped brackets with rounded corners. We have one right angle bracket, one robot hand (which is pretty obvious), the five remaining servo motors, and a plastic bag with the servo couplers, which are aluminum disks with four holes around the outside and one hole in the middle. We also have three bearings in that same bag.

Our first step in the arm assembly is to take two of the large C brackets and fasten them back to back to make one long bracket with the curved sections on either end. I used four screws for this, but there are six holes. I picked the two outer and inner holes:

Now, all of the servos that attach to the C-shaped arms will go together the same way. We grab one of the small bearings and a short screw and fasten the bearing into the side of the rounded part of the C bracket away from the side of the servo. Now attach the bearing and the screw to the universal servo bracket (which I will just call a US bracket from now on) and fasten with a nut. If you think about how the servo goes in, you will see which side to attach the bracket. You now install the servo in the US bracket with four screws. Now, you have two pivot points on either side of the servo. Install the servo coupler (silver disk) to the servo and attach the servo coupler to the C bracket to complete the shoulder elevate joint.

Now for the elbow joint: we take one of the loose US brackets and also get the L-shaped bracket. We want to fasten these two together at right angles which is how the servo goes in. The image should explain how this works. Now, we repeat the technique we used to assemble the shoulder joint – we mount the bearing in the other end of the long C bracket, attach the universal bracket to it with a nut, and then install the servo. That completes the elbow, so now we work our way to the wrist. We attach the other C bracket to the end of the L bracket that we just attached to the elbow joint:

This next bit is a bit tricky. We need to fasten two of the US brackets together in the middle and at right angles to one another. We will be making a wrist joint that can both tilt and rotate, and that takes two servo motors perpendicular to each other. Once that is done, we can grab our remaining bearing and mount it in the C bracket that we attached to the elbow. Now use a screw and nut to attach one of the universal brackets to the C bracket, just as we did before, and then install the servo and servo coupler to the wrist tilt joint:

This is as good a time as any to take a break and think through the next steps. Grab the robot hand, and you can directly attach one of your servos. Make sure you first put the servo in the middle, and then incorporate the hand grip into the middle of its travel as well. Then, line things up and install the servo. That was not too bad. Now install the wrist rotate servo to the US bracket on top of the wrist joint. Our final assembly step should be pretty obvious. We put the servo coupler on the wrist with a screw in the center hole, then line up the hand, and put two screws into the matching holes in the hand and the wrist. 

Our erector-set construction is complete and we have the mechanical form of the robot.

Take some time now and tidy up all of the servo cables. There are four sets of servo extension cables in the kit, so attach these to the four top servos in the arm. I used cable ties to attach the cables to the side of the arm. There is also a spiral cable organizer – at least I think that is what it is called – in the kit. You can use this to also clean up the arm cables, and it makes everything all the same color.