So, only the head is still missing, here’s my lamp so far:
Sorry, not yet standing proudly upright in front of a camera …
Constraints: I constrained the lower arm such that, going backwards, there is always a rotation to be found for the upper arm such that it does not go through the ground (the hinge is almost on the ground, but not entirely). Going forwards, it cannot bend all the way. For the upper arm, it can bend slightly backwards, but it can bend all the way forwards until it reaches the lower hinge. Here are my limits seen from the rest pose:
Lower arm, limit 1:
Lower arm, limit 2:
Upper arm, limit 1:
Upper arm, limit 2:
