The Arm Is Too Heavy

We are build a robot to do multiple things in one lap around the track. We are trying to use this arm, however it is too heavy for use. When we try to use this attachment it will go and then stop at it’s designated location then continue to drop down after it’s rotations and it’s actions are over.

Consider more elastic assistance (rubber bands), additional gearing, so the motor or motors have more torque to counter act the additional weight, and add additional motor to the arm.

Also investigate the motor holding mode which will make the motor try to hold it’s position after the movement has completed. What programming language are you using?
Edit: Also, it would help if you could post a picture of your robot.