LEGO Punchers (4 bar linkage warm-up)

LEGO Punchers

A 4-Bar Linkage Optimized for Punching

Battling is fun, and guarantees that students will innovate to win

Note: Students should wear eye protection when battling with punchers

These punchers can also be motorized, but this requires converting the circular motion of the motor to oscillation. This can be done by programming a servo motor to do a partial rotation, or by adding a crank and a 6th bar to the mechanism as done in the following video:

If you build a motorized puncher like the one above you'll notice the strong inertial forces generated by the oscillating arm, which could cause vibration problems if mounted on a robot - especially at scale since vibration problems tend to be proportional to scale raised to the 4th power. You can greatly reduce inertial forces and associated vibration by building a pair of punching arms 180 degrees out of phase of each other.

Also, "Boxing Bots" may be a better application for an EV3 build, since the weight of the brick would help to absorb the inertial forces generated by the punching action.

Racing to Build the Champion Puncher

These punchers use a basic 4-bar linkage that students can easily modify to improve performance, which is easiest to do before adding the 2nd side of both the handle and the 4th bar. Alternatively, you can test changes with the simulator below - but remember that when determining the length of LEGO beams to enter into the simulator, the first hole is always counted as zero as shown in the image above.

4-Bar Linkage Simulator for Optimizing LEGO Punchers

Below is the embedded simulator. After changing a bar's length, click somewhere other than a slider bar and then press the space bar to see the new linkage, and use your keyboard's left/right arrows to rotate the crank.