Visible crew/equipment: When Newton is playing with the robot arm and the piano you can clearly see wires attached to the top of it controlled by the puppeteers.
Visible crew/equipment: You can see a wire attached to the back of Stephanie's truck in this scene, which obviously stops it from really falling over the edge of the cliff. (00:43:20)
Visible crew/equipment: When number 5 falls off the bridge you can see a thin rope attached to him, either used to activate the parachute, or used as a guide wire to keep the robot stable while falling.
Visible crew/equipment: When Number 5 plays with the light switches on the way to the disarming section, a coffee serving robot comes through the corridor, and the reflection of the camera is visible in the coffee pot. (00:12:15)
Visible crew/equipment: When we see a wide shot of Stephanie's truck driving through the town, look closely to the left of Johnny when we see the truck start to go up the hill. You can see one of the puppeteers hiding beside the robot. (00:21:35)
Visible crew/equipment: Look REALLY closely at the mirror in the background when Stephanie is trying to control Number 5 from destroying her house. You can see a man leaning over in its reflection. Possibly the director or other crew member. (00:32:15)
Visible crew/equipment: When Johnny is blocking Frank's gunshots with pieces of Frank's car, you can see the wires attached to Johnny's arms for the puppeteers to control him. In the last one, you can even see one of the puppeteers' hands. (01:06:25 - 01:12:21)
Answer: There were always 5. You see the 5 during the demonstration. Then, before the lightning hits, we see 4 of them in line, but number 5 was still attached to the generator and not in line. When they go inside, there's a weird cut that makes it look like only 3 made the turn, but if you watch closely you can see there's 4 followed by number 5.
Bishop73