There are two common robot joints.

The joint of 1 is a carpenter's tenon-mortise structure with a shaft and hinge in the middle, such as the elbow joint, knee joint and knuckles of the robot in the picture.

2 ball head, this is not easy to do. The feasible method is BB bullets, which are the bullets in children's toy guns. First, punch a hole (blind hole, not all through) in the BB bullet, and put the shaft through. Then apply a layer of vaseline (paste oil or something) on the BB bomb. Finally, cover the oiled ball head with two brothers, dry, shape and polish, and the joint connected with the ball head is completed. Bitu robot's shoulder joint and ankle joint.

The ball joint is recommended for wrist joint.

Old-fashioned: There are many ways to solve this problem, such as:

Color difference: after the main color is painted, add a little white to the main color to draw highlights; Add some black and shaded parts.

Pickling and washing: dilute the black or brown pigment in the oil painting with ZIPOO oil, apply it to the model with a cotton swab, dry it for a while and then wipe it off, so that gaps and things will be highlighted.

Dry sweeping: Dip the flat-headed pen in silver, and apply it to the frequently worn parts of the model when the paint is dry.

That's usually all. There are many ways. You can buy some magazines like Model World to read.