Arm base assembly (turntable)

The turntable is the rotating assembly that forms the base of the robot arm, and will create the robot shoulder rotate axis. This is a fairly involved part that I approached with a great deal of skepticism. However, we will see that the result is most satisfactory and appears to be a very solid design. We start with two critical steps. You must do the following first, or you will have to disassemble everything and start over. You can guess how I know this. First, pick one of the two smaller circular plates with the small holes in their center. Into one of these, you will attach one of the servo couplers, the aluminum disks that attach to the servos. To the other one you will bolt one of the "universal servo brackets", the U-shaped arm part that has two small arms and one large arm, along with a large number of holes. This will form the shoulder elevate joint later. You have to bolt these on first because you can't do it later:

Now we sandwich the large bearing between the two small circular plates and attach them with four long screws and nuts. The servo attaches to the bottom (silver disk) and the arm servo bracket is on the top. The screws must go down so that we don't have anything poking up to interfere with the arm. After taking a moment to admire our work, we now attach to two larger circles with the big cutouts. These are secured with four of the very long screws. Next, we grab the large circle with the servo-shaped hole in the middle, and install one of our servos in that rectangular spot with four screws and nuts. Then, we need to secure the bottom of the larger turntable assembly by putting four of the brass spacers all the way down on the very long screws until they touch the bottom of the metal plate. Now, mate the servo's spline output to the silver disk-shaped servo adapter you placed on the bottom of the turntable. We can now add four nuts to the long screws to secure the bottom plate. Be sure to get them all even and do not tilt the plate with the servo to one side or the other. Our turntable is done, and you can mount it to the robot mobile base if you wish, or keep the arm assembly all together and mount the turntable later after you have assembled the entire arm: