A Pendulum at Last Feb. 27

Today we finally got to make a platform out of Lego's and see a pendulum in action. Up to this point our circuit did three things: measure speed by making the voltage proportional to the speed, integrate for position (voltage is proportional to position), and exert a force (voltage is proportional to torque).

In a perfect pendulum, the position vs. speed graph would look like a spiral spinning toward the center (zero). This is because as the pendulum moves back and forth it starts slowing down until it comes to a complete stop at the resting position. Our circuit, however, is flawed. A force is applied as it swings back and forth which makes our pendulum continue to swing without slowing down (unless you adjust the speed on the potentiometer).

As you can see, the position vs. speed graph of the pendulum does not form a perfect spiral, spinning to the center. Our imperfect circuit exerts a force which creates a duck shaped graph that does not appear to slow down.

The abstraction for our pendulum would be voltage entering the current driver as proportional to position and coming out as voltage proportional to speed. The voltage then goes through the integrator and makes it voltage proportional to torque which is proportional to position. This is how the circuit comes to a full circle. Since there is a resistor within the motor the voltage proportional to speed can be voltage proportional to speed and torque.

Before activating our pendulum, we practiced circuit hygiene (circuits are messy objects); we shortened the wires and made our connections easier to be seen.  The only thing I wished I would have done at the beginning of circuit building is having a clean circuit. This would have reduced my confusion and frustration.  Observing and building the pendulum was the final topic we will cover on circuits.

Our circuit after we "cleaned" it up to increase circuit hygiene.

Picture of our pendulum. You are not able to see the pendulum because it is moving quickly back and forth.