Very interesting concept you got there.
Pretty sure you've got more work ahead of you, but is there an area in which the player could see everything at their disposal, control wise? Maybe a pause menu or environmental suggestions, like you have with the magnet gun and text pop-ups.
Also I see that when finishing up the creation of the robot, either by putting it together entirely or pulling the switch, it often takes away the swingable pipe. Not until I pick up something else (like the blocks) and drop it does it show back up.
(EDIT) I see the problem, it seems that when you put the robot pieces into the designated areas, it takes away the pipe. It may have something to do when pressing E to pick up stuff AND pressing E again to assign the robot parts. Maybe you already know this, but it's something to help.
Other than that, you've got a fun little game right here. I hope to see more of it when you finish it up.