Over the past few days in class we have been experimenting with the Lego Mindstorm robots once more. This time, we used the robots to better help us understand Newton’s 2^nd Law, the law of conservation of energy, velocity and acceleration, and power. We used the Lego Mindstorn motor to operate a pulley system. As you can see in the image below, the Mindstorm motor is connected to the computer via a USB cable, and a telephone cable connects port A of the motor to the port on the back of the Mindstorm “arm” piece. A piece of string then wraps around the round part of the Mindstorm robot “arm”, and up around the pulley, where it then comes back down and is connected to some weights.

Below is the VI on LabView that we used for this experimenter.

The image below is a bit blurry, but you can see that this is where we plugged in the commands for the robot; i.e. the level of power we wished to use, and the mass of the weights at the base of the pulley system in kilograms. What we did, is we changed the power level each time we had the robot start, as well as changing the amount of weights at the end (mass). The control panel below also displays the milivolts, rotations, battery discharge, speed (RPM), time (seconds), and acceleration (RPM/s). Each time we changed either the weight or the power, this was recorded on an excel spreadsheet. The power level was our “force” in this experiment, the motor of the pulley, F=ma. Work was being done on the weight when they were lifted up by the pulley. We changed the amount of potential energy by applying work on the weights, work = F(distance the weights moved), which is equal to the change in energy of the weights (gravitational potential energy). Battery Discharge is directly proportional to the energy used; all of the energy does not go into lifting up the weights, because there is a frictional loss when the wheel needs to be turned (heat). The battery has chemical potential energy, and it gets changed into gravitational potential energy when you lift up masses. Power = work/time, if you have something done in a minimal amount of time, you have a higher power level.

We changed the weight on our pulley a few times to: 05 kg, .1 kg, .15 kg, .2 kg, and .25 kg. We then left the power level on 75, we could see that the acceleration decreased. The less weight there was with a higher level of power made the pulley go faster. The more weight we had on the bottom meant that there was going to be a higher level of battery discharge. This is shown in the graph below.

We also changed the power level a few times to: 50, 60, 70, 80, and 90, and left the mass at .1 kg. In doing this, we observed that the acceleration increased. This is shown in the graph below.