WEBVTT 00:00.110 --> 00:05.360 In this lesson, we will see how to control a servo motor with Arduino and Ros to. 00:06.280 --> 00:11.530 We will use the knowledge acquired in the previous lesson to publish a certain position command for 00:11.530 --> 00:14.530 a servo motor within a ros2 topic. 00:15.210 --> 00:21.600 This command will be received and serialized by the transmitter node implemented in the previous lesson 00:21.600 --> 00:25.140 and then will be sent to the Arduino through the serial port. 00:26.760 --> 00:33.840 Upon receiving this command instead of turning on or off a Led as we did in the previous lesson, Arduino 00:33.840 --> 00:38.250 will instead actuate a servo motor to our desired position. 00:38.610 --> 00:43.890 So let's open the Arduino IDE and here let's create a new sketch. 00:43.890 --> 00:45.360 So a new project. 00:46.500 --> 00:52.350 And within this new sketch still we have the setup function, which is executed once at the startup 00:52.350 --> 00:56.850 of the Arduino and the loop function, which is repeatedly executed. 00:57.630 --> 01:01.440 To interact with the servo motor and to send commands to control it. 01:01.620 --> 01:04.710 Arduino as a nice library called Servo. 01:05.010 --> 01:07.950 So let's start by importing this library. 01:09.990 --> 01:16.530 So let's include the library server dot age. 01:18.000 --> 01:21.330 And let's use this library to create a new variable. 01:21.330 --> 01:24.390 So a new object of type server. 01:24.510 --> 01:27.000 And let's call this one motor. 01:27.790 --> 01:28.630 This class. 01:28.630 --> 01:34.990 So the server class contains a series of functions and tools that make it very easy to send commands 01:34.990 --> 01:37.090 and so to operate a servo motor. 01:37.840 --> 01:40.030 To initialize the communication with the servo motor. 01:40.060 --> 01:41.140 So let's go. 01:41.140 --> 01:46.750 Here in the setup function, we need to use the motor object that we have just created. 01:46.750 --> 01:51.130 And on this one let's use the function attach. 01:52.220 --> 01:58.200 So with this function, we can pass the number of the pin to each servo motor is connected. 01:58.220 --> 02:04.940 For example, let's assume that we want to connect the servo motor to the PIN number eight of our board. 02:05.300 --> 02:11.240 And now still using the servo library, we can move our servo motor to a certain angle. 02:11.240 --> 02:18.350 And this is as simple as calling the function right on the object motor. 02:18.350 --> 02:25.310 And to this function we need to pass the angle in degrees to which we want to rotate the servo motor. 02:25.430 --> 02:33.980 For example, at the start up, let's make the motor to be in the position 90 degrees so in the middle 02:34.010 --> 02:35.150 of its range. 02:35.450 --> 02:41.240 Now still in the setup function after initializing the communication with the motor and after moving 02:41.240 --> 02:43.430 it to the position 90 degrees. 02:43.460 --> 02:50.330 Let's also initialize the serial communication between the Arduino and our PC on which Ros two is running. 02:50.810 --> 02:59.610 So let's use the function begin and then let's set the about rate that we want to use for this communication 02:59.610 --> 03:03.120 to 115 200. 03:03.610 --> 03:08.450 And then let's also, as usual, use a timeout. 03:08.470 --> 03:14.560 So with the function set timeout and let's set a timeout of one. 03:14.770 --> 03:17.250 With this, the setup function is completed. 03:17.260 --> 03:19.720 And now regarding the loop function. 03:19.720 --> 03:24.880 So regarding this function here, in this case, we want the microcontroller. 03:24.880 --> 03:31.870 So at each iteration of the loop function, we want to check if there is any new message available on 03:31.870 --> 03:32.830 the serial port. 03:32.830 --> 03:36.040 So if there is any new message coming from Ros two. 03:36.430 --> 03:43.480 So let's check this one with the serial available function. 03:43.600 --> 03:47.950 So with this one, we are checking if there is any new message. 03:47.950 --> 03:57.010 And in this case, so if there is a new message available, let's read it with the function read String. 03:57.400 --> 04:04.430 And since we know that we are going to receive an integer, let's also convert this one to an integer. 04:04.610 --> 04:10.910 Let's store this integer here within a new variable and let's call this one angle. 04:10.910 --> 04:12.680 And now we can use this variable. 04:12.680 --> 04:17.900 So the angle variable in order to move the servo motor in the desired position. 04:17.900 --> 04:29.390 And so we can do this by using the function motor dot write and so we can write the angle position that 04:29.390 --> 04:30.380 we just set. 04:31.120 --> 04:40.300 Finally, let's also add a delay in the loop function here of 0.1 so that there is so that there is 04:40.300 --> 04:43.960 a small interval between two execution of the loop function. 04:44.720 --> 04:46.520 We can save this code. 04:46.970 --> 04:54.350 So let's save it within the Arduino workspace, within the Arduino board firmware, and within the firmware 04:54.350 --> 04:55.070 folder. 04:55.340 --> 05:03.420 And let's call this one simple servo control. 05:03.440 --> 05:04.820 So let's save it. 05:06.920 --> 05:12.830 Now before actually uploading this code on the Arduino board, let's verify that it compiles so that 05:12.830 --> 05:14.360 we have no errors. 05:14.360 --> 05:16.060 So it compiles properly. 05:16.070 --> 05:21.410 So now, before uploading the code into the Arduino board, let's first connect the servo motor to the 05:21.410 --> 05:22.070 board. 05:22.190 --> 05:27.530 And we are going to need three jumper wires to connect the servo motor pins to the board. 05:34.870 --> 05:40.330 And let's connect the brown wire to the GMD pin of the Arduino. 05:46.910 --> 05:52.940 Then let's connect the red wire to the board's power, which is the five volt pin. 05:56.780 --> 05:58.060 And the last wire. 05:58.070 --> 06:02.750 So the orange one is the one that transmits the signal to move the robot. 06:02.750 --> 06:08.960 And so we are going to connect it to the PIN eight of the Arduino, as we said in the setup function 06:08.960 --> 06:10.010 of our script. 06:15.080 --> 06:18.530 Now that's the Servomotor is connected to the PIN eight of the Arduino. 06:18.560 --> 06:21.380 We can proceed to connect the Arduino to the PC. 06:29.930 --> 06:37.460 And once we do so, the Arduino IDE should be able to automatically detect the port to which it is connected. 06:37.550 --> 06:44.490 So if we go to the board now, we can see that in my case it is connected to the port ACM zero. 06:44.510 --> 06:48.410 So let's click on this one and let's upload the code on the Arduino. 06:50.100 --> 06:55.830 Now, as soon as we upload the code, we can see that the servo motor moves to its initial position, 06:55.830 --> 06:59.820 which is 90 degrees, as we indicated in the setup function. 07:00.390 --> 07:06.450 Now we can finally send movements to the motor and to do so, let's open a new terminal. 07:07.470 --> 07:10.650 And here let's go to our workspace. 07:10.650 --> 07:11.790 Let's source it. 07:12.390 --> 07:15.570 So let's source the setup dot bash. 07:15.570 --> 07:21.420 And now let's see how we can send command to our servo motor using our ros2 topic. 07:21.840 --> 07:30.000 So as a first thing, let's run a Ros two node that is in the Arduino bot firmware package and that 07:30.000 --> 07:32.070 we have implemented in the previous lesson. 07:32.100 --> 07:37.590 That is the simple serial transmitter here. 07:37.590 --> 07:42.990 I'm using the Cplusplus implementation, but if you want you can use the Pi implementation by adding 07:42.990 --> 07:46.080 the suffix dot pi to this node. 07:46.110 --> 07:51.690 We need to pass a Ros argument, so we need to pass a parameter. 07:52.020 --> 07:55.110 So a value to the parameter port. 07:55.260 --> 07:58.710 And in my case this is connected to the port. 07:59.910 --> 08:02.910 ACM, ACM zero. 08:03.090 --> 08:10.510 So let's press enter and upon starting this node does nothing but initializing the communication with 08:10.510 --> 08:11.020 the Arduino. 08:11.020 --> 08:17.830 So the serial communication with the Arduino and this node is listening on a topic on a Ros two topic 08:17.830 --> 08:23.680 for any new message that is sent through that topic in order to forward it to the Arduino through the 08:23.680 --> 08:24.580 serial port. 08:25.330 --> 08:30.970 So let's open a new terminal and let's use the command Ros two topic list. 08:31.850 --> 08:35.630 To see that actually there is the serial transmitter topic. 08:35.810 --> 08:39.200 So now let's use this topic to move our servo motor. 08:39.530 --> 08:48.090 So with the command Ros2 topic pub and let's publish a message within the serial transmitter. 08:48.110 --> 08:52.130 Here the message type that is accepted is string. 08:52.460 --> 08:55.040 So let's insert a standard message string. 08:55.070 --> 08:56.580 Then let's use double quote. 08:56.600 --> 09:02.680 Let's type D and press tab, and this will insert an empty prototype of the string message. 09:02.690 --> 09:05.420 And for example, let's publish the message zero. 09:05.420 --> 09:06.960 So the angle zero. 09:06.980 --> 09:11.950 So with this, we are asking the Arduino to move the servo motor to the position zero. 09:11.960 --> 09:13.580 So let's press enter. 09:14.420 --> 09:20.330 And indeed we can see that as soon as we publish this message, it is serialized and sent to the Arduino, 09:20.330 --> 09:22.640 which then moves the motor accordingly. 09:22.850 --> 09:25.220 Let's send another message. 09:25.250 --> 09:30.920 This time let's make the servo motor reach the position 180 degrees. 09:30.920 --> 09:32.630 So let's press enter. 09:33.270 --> 09:36.600 And again the servomotor is moved as requested. 09:36.600 --> 09:38.400 So in the desired position. 09:38.610 --> 09:45.120 Building upon this code, in the next lesson, we are going to extend this control to all the four servo 09:45.120 --> 09:46.280 motors of the robot. 09:46.290 --> 09:49.860 And so we are going to control all the servo motors of our robot.