The arm is made up of four moving parts. Each of these parts has a moving joint controlled by a servo. The construction of each part is described in detail in the sections below.
The claw hand can be opened and closed to pick up small objects, once the arm has been moved into position.
It's made up of two hinged "fingers" that have rubber tips made from lego tyres to allow it to grip.
The two fingers are connected by levers to a single moving linkage, that is pulled back by the servo to open the claw.
The servo arm is just tied to the lego linkage with a piece of cotton thread. This works ok because it only needs to pull in one direction.
The fingers are also connected by an elastic band, which pulls them together to grip when the servo is not pulling back the linkage to open the claw.
Below are a series of images showing the construction steps for the claw section, including the servo mount.
The upper joint allows the upper part of the arm with the claw to be extended away from the body.
It is a simple lever that can be extended by pulling the end by moving the servo.
The end of the lever is again connected to the servo arm by a piece of thread, like the claw.
When the tension in the thread is released, the upper arm falls back towards the body under the weight of the claw.
So again the servo only needs to pull the lever in one direction.
The upper joint lever attaches to the claw arm via a parallelogram linkage, which I found made it a bit more stable.
The lower joint lifts and lowers the arm.
The white servo arm is wired to the grey lego piece on one side.
The grey lego piece is attached on the other side to a pivot to allow it to move up and down and lift the rest of the upper arm..
The base of the arm has a rotating top piece which allows the arm to turn from side to side.
The servo is mounted vertically inside the base with the rotating arm on top.
The servo arm is wired to the grey lego wheel which turns the center of the top platform via the red connector in the center.
