Last time I have made a dynamometer using friction force with a metal plate. Today I will make a modification for more simple and easy use. It is the simplest dynamometer in the world using a 3D printer as I knew.
The friction force can be adjusted easily with the double thread screw. Use the clockwise and counterclockwise thread, the adjusting process becomes very simple. You only need to rotate the screw the upper and bottom parts will move at the same speed but in different directions. They will keep the balance and make the friction force change smooth and homogeneous.
The speed can be measured using a tachometer. You will only use several M3 balls and 4 M2X8 screws and 2 M2 screws and nuts. One long M3 screw can be changed to another long stick.