Arm rigging:
After finishing the constrain on the small objects. I simply create a parent constrain between the controller for the elbow and forearm. Then I create parent constrain between the shoulder and upper arm.
Tips for rigging:
1.Rigging 1_elbow ctrl-forearm-parent constrain
2. Use point ctrl to centre the control curve
3. Shoulder/upper arm–parent constrain
4. Set driven key-crtl/shoulder pad-key
5. Modify constrain-limit information
Modelling process:
Rigging: