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[MUSIC PLAYING] The purpose of this lab is to interface the motors to the LaunchPad. For this lab, you're going to need the TI RSLK Max robot. Now the TI RSLK chassis board contains two DRV8838 motor drivers, which are connected to your motors. You will also need a current meter and an oscilloscope.

In this particular portion of the lab, we're going to see that the software adjust power to the motors using the duty cycle of the PWM outputs. Here's the robot, and notice we're measuring the current to the robot. Loaded on the software is the starter code for lab 12. In particular, running program 12.2.

The way this works is when I push the buttons, it'll start and stop. But notice while the motors are not spinning it's drawing about 70 milliamps. OK, let's turn on the motors. All right. Let's see what happened, OK.

Now over on the oscilloscope, we see that the frequency is 100 Hertz, and the duty cycle is 20%. Now the motor's spinning slowly, and we can see it's drawing about 300 milliamps.

All right, let's go faster. All right, and I push the button again. Now it's spinning at 40% duty cycle. Notice the frequency's still 100 Hertz, and the current has gone up to about 400 milliamps.

All right, faster. All right, now we're going at 60% duty cycle. Again the frequency is fixed at 100 Hertz, and notice that the current is still at 400 milliamps.

All right, one more. Stop the motors. Run the motors. Now we're running at 80% duty cycle, and notice the current has gone down now, but the power has gone up, because power is voltage times current times duty cycle.

Because of friction, there is no direct relationship between the delivered power and the resulting speed of the motor. The power in this lab is the voltage times current times duty cycle.

Now the voltage was constant, about 7.2 volts, and the current meter measured the current. And the oscilloscope or the software set the duty cycle. In this lab, you see that the software uses duty cycle to adjust power to the motors. Understanding duty cycle, voltage, and current and how they combine to affect power is required when building your own robot. Have fun.

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