To build a computer controller robotic arm capable of moving with at least three degrees of freedom. It would seem attractive to re-use a mechanical assembly like an extendable desklamp arm, as the basis for this:

The original payload of light fitting and bulb is about 256 grams (including bulb), this is partially counterbalanced by the springs, so the arm will tend to maintain whatever position it is move to. The springs would be unnecessary if using servos to drive the joints, as the servos would maintain position, in fact the springs would just add extra resistance to movement. There are 5 joints that you would motorise - swivel at the base, up-down of lower arm, up-down of second arm, up-down of hand, swivel of rist. But these are not entirely independent - the angle the second arm can bend to depends upon the angle of the lower arm (and visa-versa), if you have actuators driving these arms independently there would be positions where one was working against the other and something would break.

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