WEBVTT 00:00.110 --> 00:01.640 This is the step number three. 00:01.670 --> 00:03.740 And it's going to be the last step for this activity. 00:03.770 --> 00:07.610 Number four in this step we are going to create a new node for the battery. 00:07.640 --> 00:12.020 We're going to kind of simulate the behavior of the battery to say that it's full or empty. 00:12.020 --> 00:14.450 And when it's full or empty we are going to change. 00:14.960 --> 00:18.650 So we are going to set an LED with the set led service. 00:18.650 --> 00:24.110 And that's why I've created first the LED panel node, so that we have the service that is already working 00:24.110 --> 00:24.920 and tested. 00:24.950 --> 00:29.030 So now when we create a client we know the service is already working. 00:29.060 --> 00:29.300 Okay. 00:29.330 --> 00:32.240 So it's going to be easier for us to test the client. 00:32.270 --> 00:32.690 Great. 00:32.690 --> 00:36.530 So let's go again in our Python package. 00:37.220 --> 00:47.420 So my pi pkg and let's create here another file that's going to be battery dot pi. 00:47.450 --> 00:53.900 Let's also make it executable with plus x. 00:54.080 --> 00:54.980 Okay. 00:55.490 --> 01:00.180 And let's edit it in the code. 01:00.690 --> 01:07.020 So let's get the templates here in battery dot pi. 01:07.680 --> 01:09.750 So that's going to be the battery node. 01:14.280 --> 01:15.120 Okay. 01:15.210 --> 01:17.010 Battery here. 01:18.210 --> 01:19.710 Let's keep things simple. 01:22.500 --> 01:25.560 And I'm going to do this step actually in two steps. 01:25.560 --> 01:28.230 First we are going to kind of simulate. 01:28.260 --> 01:34.230 We are going to fake the mechanism of the battery to say when it's full or when it's empty. 01:34.230 --> 01:38.730 And when that is working we are going to call the service. 01:38.760 --> 01:39.870 So let's get started. 01:39.870 --> 01:42.570 And how can we monitor the battery state? 01:42.600 --> 01:49.230 How can we say that the battery state is empty after four seconds and then full again after six seconds 01:49.290 --> 01:50.370 repeatedly? 01:50.400 --> 01:55.830 Well, first what I'm going to do is I'm going to create a timer and say that we check the battery state 01:55.860 --> 01:57.330 ten times per second. 01:57.360 --> 02:04.160 So usually if you had a real battery, you would probably create something like a timer and then check 02:04.160 --> 02:06.890 the battery state every X amount of time. 02:06.890 --> 02:08.330 Maybe you don't need that much. 02:08.330 --> 02:11.390 Maybe every one minute, every 10s. 02:11.420 --> 02:14.000 Well, here we're going to do it ten times per second. 02:14.000 --> 02:20.360 So let's create a timer first here self dot. 02:20.390 --> 02:21.890 Let's call it battery. 02:22.400 --> 02:31.580 Timer is equal to self create create timer. 02:31.580 --> 02:33.440 And I set 0.1. 02:33.440 --> 02:35.990 So ten times per second self. 02:35.990 --> 02:44.570 And let's create a function here check battery state. 02:47.330 --> 02:47.810 Okay. 02:47.840 --> 02:50.600 And let's provide the callback here. 02:51.290 --> 02:52.820 Check battery state. 02:53.330 --> 02:53.690 All right. 02:53.690 --> 03:00.720 So here you would in a real application directly check the battery state and from that you can know 03:00.720 --> 03:03.930 if maybe the battery is full or empty and call the service. 03:03.930 --> 03:05.970 But now we don't have a real battery. 03:05.970 --> 03:08.370 So I'm going to fake the behavior. 03:08.370 --> 03:14.400 And like I gave you in the activity, we're going to say that let's say the battery is full and then 03:14.400 --> 03:16.410 after four seconds is going to be empty. 03:16.440 --> 03:18.510 And then six seconds later it's full again. 03:18.510 --> 03:20.430 So we have a ten second cycle. 03:20.430 --> 03:28.470 And how can I check this duration of four seconds and six seconds from the callback here so I could 03:28.470 --> 03:29.220 save the time? 03:29.220 --> 03:32.310 For example, I could save the time when the last time. 03:32.310 --> 03:37.080 So the actual the last time that the battery state was changed, and then I could compare with the current 03:37.110 --> 03:41.730 time and see if we have spent at least 4 seconds or 6 seconds. 03:41.730 --> 03:44.850 So here I could start with creating a variable. 03:44.880 --> 03:48.750 Time now is equal to the current time. 03:48.750 --> 03:50.130 How to get the current time. 03:50.130 --> 03:56.360 There is actually something you can use in Ros two, and I'm going to create a new function for that. 03:56.390 --> 03:59.240 Diff get current time. 03:59.240 --> 04:02.150 You will see why in a second. 04:02.180 --> 04:04.430 I want the time in seconds to make it simple. 04:04.430 --> 04:06.110 You can use the self. 04:06.110 --> 04:18.170 So from the node you have get clock and then dot know and then dot sequence nanoseconds. 04:18.200 --> 04:23.270 This will give you a tuple of seconds and nanoseconds two integers. 04:23.270 --> 04:33.410 So for example seconds nano seconds is equal to self get clock now seconds nanoseconds. 04:33.740 --> 04:34.370 All right. 04:34.400 --> 04:37.430 And well we don't really want a tuple like this. 04:37.460 --> 04:39.920 We want a float number. 04:39.920 --> 04:47.720 So let's just do a return seconds plus nano seconds divided by. 04:47.750 --> 04:49.760 And then we need nine zeros. 04:49.760 --> 04:53.670 So Eight nine. 04:53.790 --> 04:55.830 And let's put dot zero. 04:55.920 --> 04:56.190 Okay. 04:56.220 --> 05:00.540 So make sure you have nine zeros 123456789. 05:00.570 --> 05:00.930 All right. 05:00.960 --> 05:05.010 So now we have the current time with a comma with a decimal point. 05:05.010 --> 05:09.210 And I've created a function so that we don't need to do that in the code. 05:09.210 --> 05:10.890 We just get the current time sequence. 05:10.890 --> 05:12.060 And that's going to be easier. 05:12.090 --> 05:17.880 So self dot get current time sequence. 05:17.910 --> 05:18.390 All right. 05:18.390 --> 05:25.350 So every time we get to this callback timer here which is ten times per second, we get the current 05:25.380 --> 05:25.650 time. 05:25.650 --> 05:28.950 And we're going to check with the last time. 05:28.950 --> 05:30.600 The last time what actually. 05:30.600 --> 05:33.390 Well the last time that the battery state changed. 05:33.390 --> 05:47.580 So I'm going to add here self last time battery state changed for example I can initialize it to the 05:47.580 --> 05:52.700 current time get current time sequence. 05:52.730 --> 05:53.450 Okay. 05:53.540 --> 06:00.170 And so I will do if time now minus the last. 06:00.830 --> 06:07.010 So last time the battery state change is greater than 4 seconds or 6 seconds. 06:07.040 --> 06:07.430 Okay. 06:07.460 --> 06:10.310 And how to know which one we want to check. 06:10.340 --> 06:17.960 Well we could create here I'm just going to create a string self dot battery. 06:18.350 --> 06:21.770 Battery state. 06:22.010 --> 06:25.910 Here I'm just going to say full. 06:26.300 --> 06:26.750 Okay. 06:26.780 --> 06:33.380 You could create a number for example that goes between 0 and 100 something like that. 06:33.410 --> 06:36.230 Well here we don't have a battery. 06:36.230 --> 06:38.390 So I'm just going to make a very simple example. 06:38.390 --> 06:41.930 So it's going to be full or it's going to be empty with a string. 06:41.930 --> 06:50.610 And I can say if the self battery state is full. 06:52.080 --> 07:00.240 Then inside this if I add this other if I check the time now minus the last time the battery state change. 07:00.240 --> 07:03.510 So time minus time gives us a duration. 07:03.660 --> 07:14.130 If this is greater than four seconds, then I can say that the battery state is empty. 07:14.970 --> 07:18.660 And then maybe add a log get logger. 07:18.690 --> 07:22.350 That's going to help us to do debug what's happening in the code. 07:23.250 --> 07:30.090 Let's say battery is empty, um, charging. 07:31.170 --> 07:36.390 And there's one more thing we need to do in this case is that, uh, well, we have changed the battery 07:36.390 --> 07:40.590 state, so we need to update the last time the battery state changed. 07:40.590 --> 07:45.810 So self dot last time battery state changed. 07:45.960 --> 07:48.690 This is going to be time now. 07:48.720 --> 07:53.410 So Now that's the time we have right now when we execute this specific callback. 07:53.440 --> 07:53.950 Okay. 07:53.980 --> 07:58.270 So this structure is quite common in programming and in robotics in general. 07:58.300 --> 07:58.660 Okay. 07:58.690 --> 08:03.250 You have a function that you call quite often here ten times per second. 08:03.250 --> 08:05.470 Or it could be much, much faster. 08:05.470 --> 08:09.580 You save the time of an event that you want to monitor. 08:09.580 --> 08:14.680 And if you want to check a duration, then you get the current time and you just do current time minus 08:14.680 --> 08:15.460 last time. 08:15.460 --> 08:20.530 If this is greater than the duration you want, then you can well, you can do an action, change a 08:20.530 --> 08:21.490 state, whatever. 08:21.490 --> 08:26.140 And you keep basically the last time becomes the current time. 08:26.170 --> 08:26.680 Okay. 08:26.710 --> 08:32.080 And we have done half of the code here because the battery. 08:32.080 --> 08:34.450 So it's full and then it's going to be empty. 08:34.450 --> 08:37.150 But then we also need to check else. 08:37.150 --> 08:46.360 So we could do else if uh self dot battery state is empty. 08:46.390 --> 08:48.690 Actually I'm going to keep it like that. 08:48.720 --> 08:53.550 We could just do an else because we will have only two states, but it's probably more explicit like 08:53.550 --> 08:54.030 this. 08:54.030 --> 08:56.160 So if it's empty, I do. 08:56.190 --> 09:03.660 If time now minus self last time battery state change. 09:03.660 --> 09:15.780 And this time we are going to wait for six seconds, then I can do self battery state is full and let's 09:15.810 --> 09:17.070 add another log. 09:17.670 --> 09:21.150 Get logger info. 09:21.660 --> 09:33.180 Let's say the battery is now full and we also do self dot last time battery state change. 09:33.240 --> 09:39.330 This is time now and that's how we're going to fake the battery state. 09:39.330 --> 09:41.850 So this is just my implementation okay. 09:41.880 --> 09:43.320 This is my solution. 09:43.320 --> 09:46.120 Maybe you have come up with a different solution Okay. 09:46.150 --> 09:52.060 I didn't give you so many information about using those functions here and this mechanism. 09:52.090 --> 09:52.300 Okay. 09:52.330 --> 09:54.310 That was to make you think more. 09:54.340 --> 09:54.550 Okay. 09:54.730 --> 09:56.050 That's a real challenge. 09:56.080 --> 09:59.800 You're not going to have the solution to everything you do when you program with Ros2 and when you do 09:59.830 --> 10:00.370 robotics. 10:00.370 --> 10:03.580 So you might have come up with a complete different solution. 10:03.580 --> 10:05.980 But if it still works the same, it's fine. 10:06.010 --> 10:06.340 Okay. 10:06.370 --> 10:09.460 So we have let's make sure we have the timer. 10:09.460 --> 10:12.160 So that's going to get called ten times per second. 10:12.160 --> 10:14.410 And just a quick recap of what's going to happen. 10:14.410 --> 10:16.000 So the battery state is full. 10:16.000 --> 10:19.240 The last time the state changed is right now. 10:19.240 --> 10:22.420 So we're going to save it in the constructor. 10:22.450 --> 10:24.850 Then we call that and then we check. 10:24.850 --> 10:27.610 So we have if the battery is full that's the case. 10:27.610 --> 10:32.500 We're going to check if the time to the current time minus the last time is greater than four seconds. 10:32.500 --> 10:39.640 So we're not going to go inside this until four seconds have passed since basically the constructor 10:39.640 --> 10:40.690 was executed. 10:40.690 --> 10:42.940 And then we change the battery state. 10:43.030 --> 10:47.100 We print a log and we save the current time as the last time. 10:47.100 --> 10:52.830 So then the next time that we enter this check battery state method, we're going to also get the current 10:52.860 --> 10:55.680 time and the battery state is going to be empty. 10:55.680 --> 10:58.290 So we're going to go inside this Elif. 10:58.290 --> 11:02.730 And then we can only enter this if after six seconds. 11:02.730 --> 11:09.480 And when we enter this if we change the battery state to full, we also save the last time. 11:09.480 --> 11:12.420 So basically the current time becomes the last time. 11:12.420 --> 11:20.370 And then again we will go back to this first if okay etc. etc.. 11:20.370 --> 11:21.390 So let's try that. 11:21.390 --> 11:22.530 Let's see if it works. 11:22.530 --> 11:24.930 We have some logs that's going to be very useful. 11:24.960 --> 11:28.020 I'm going to save and let's go to setup.py. 11:28.020 --> 11:30.540 And let's add yet another executable here. 11:30.540 --> 11:39.930 Battery is equal to my Python package dot battery because it's battery.py and the main function. 11:39.960 --> 11:52.300 Okay let's build Built that Qualcomm build packages select let's build a Python package and let's also 11:52.300 --> 11:54.400 add Simulink install. 11:56.320 --> 11:56.830 Great. 11:56.830 --> 11:59.080 And let's run the battery node here. 11:59.080 --> 12:07.330 Source workspace and Ros to run my Pi PG with battery. 12:08.290 --> 12:09.790 And let's see what we have. 12:09.820 --> 12:12.520 I didn't have any log in the constructor. 12:12.550 --> 12:13.750 Maybe I'm going to add one. 12:13.750 --> 12:15.970 And you see battery is empty. 12:16.930 --> 12:18.340 Let's wait a bit more. 12:19.360 --> 12:22.570 Battery is now full and you can see the difference of time. 12:22.570 --> 12:24.970 Here is six seconds. 12:24.970 --> 12:29.890 And now we have four seconds okay so let's wait a bit more okay. 12:29.920 --> 12:33.370 And you see we have two full cycle now. 12:35.710 --> 12:40.060 So when we look at the logs you see we have a cycle here 10s. 12:40.090 --> 12:41.400 And then 10s. 12:41.430 --> 12:46.800 We have six seconds between empty and full and four seconds between full and empty. 12:46.830 --> 12:47.310 All right. 12:47.310 --> 12:53.700 So that was the probably the main challenge of this step is to come up with a solution to fake this 12:53.700 --> 12:54.390 behavior. 12:54.390 --> 12:57.480 And now what's left is quite straightforward. 12:57.480 --> 13:03.720 We need to call the set led service that we have created in the LED panel node. 13:03.720 --> 13:07.230 When the battery is empty, we want to turn on the third LED. 13:07.590 --> 13:10.650 And when the battery is full we want to turn it off. 13:10.650 --> 13:15.660 And so we're going to use the basically the same thing we did for the add to insert client. 13:15.690 --> 13:16.230 Okay. 13:16.260 --> 13:19.620 We're going to create a client inside the constructor. 13:19.620 --> 13:28.800 So let's create a client here I'm first going to add a log actually self dot get logger. 13:29.580 --> 13:37.470 Battery node has been started okay. 13:37.500 --> 13:42.400 And here I'm going to create a client self dot set. 13:42.430 --> 13:50.290 LED client is equal to Self-create client and I need to provide a service type. 13:50.290 --> 14:01.780 So I need to do from my robot interfaces dot srv import set LED okay. 14:01.810 --> 14:04.480 And I'm already using my robot interfaces in this package. 14:04.480 --> 14:08.350 I've already set up the package dot XML with the dependency. 14:08.560 --> 14:12.640 So let's put set LED and the name. 14:12.640 --> 14:18.700 So let's make sure we use the same name here set LED. 14:19.210 --> 14:19.600 All right. 14:19.600 --> 14:21.940 So we have our client here. 14:22.240 --> 14:27.580 Then what we can do is we can create a function to call the service. 14:27.820 --> 14:29.470 So let's do that here. 14:29.470 --> 14:34.720 For example the order doesn't matter call set LED. 14:34.870 --> 14:39.960 And I'm going to put self and then led number state. 14:40.620 --> 14:41.040 All right. 14:41.040 --> 14:42.750 And what do I need to do? 14:42.780 --> 14:47.760 Once again, if I come back to this example, I'm going to first wait for the service. 14:47.850 --> 14:51.330 Then I'm going to create a request and send that request. 14:51.330 --> 14:56.670 So let's do that while not self. 14:57.690 --> 15:02.940 And let's set LED client dot wait for service. 15:03.150 --> 15:15.660 With one second we could say self dot get logger one waiting for set LED service. 15:16.050 --> 15:19.050 And you might want to handle that differently. 15:19.050 --> 15:23.550 Maybe because here it's going to block here in this function. 15:23.550 --> 15:31.170 But because this service is quite important for this node, you could also decide to do the while not 15:31.200 --> 15:37.750 here directly in the constructor for example, to check that the service is up before you finish the 15:37.750 --> 15:39.880 initialization of the node. 15:39.910 --> 15:40.480 Okay. 15:40.510 --> 15:46.840 Or here, instead of doing a while loop, you could just return an error if the service is not found. 15:46.840 --> 15:48.760 So there are different ways of handling that. 15:48.790 --> 15:50.470 It's going to depend on your application. 15:50.470 --> 15:50.980 Here. 15:50.980 --> 15:54.040 We just wait for the service to be up and that's it. 15:54.340 --> 16:03.250 Now we can create our requests which is going to be set LED dot request. 16:03.370 --> 16:11.980 And then we do request dot led number, which is the LED number we got from the parameter here. 16:11.980 --> 16:17.950 And request dot state which is the state. 16:17.950 --> 16:30.220 And then we can do so we're going to get a future out of that self set LED client dot call async with 16:30.220 --> 16:31.810 the request. 16:32.020 --> 16:32.740 All right. 16:32.740 --> 16:35.050 So same thing what we did here. 16:35.050 --> 16:37.760 and we can add a Dawn callback. 16:37.910 --> 16:40.340 So let's create a callback actually. 16:41.180 --> 16:47.570 So def callback set led. 16:47.570 --> 16:50.300 So maybe callback call set led. 16:50.600 --> 16:54.140 That's the callback for this method self. 16:54.140 --> 16:56.210 And we get a future. 16:57.320 --> 16:57.560 Okay. 16:57.590 --> 17:00.200 So here let's do pass here. 17:00.200 --> 17:01.700 So we don't have the error. 17:02.720 --> 17:11.960 And we can do future dot add dawn callback self callback call set LED okay. 17:11.960 --> 17:13.010 Just like we did here. 17:13.010 --> 17:16.550 And note that I didn't provide the request. 17:16.550 --> 17:21.170 You could pass the request as well, or you could pass any other parameter. 17:21.170 --> 17:26.570 In this case you would have to use the partial keyword here with the Functools functionality. 17:26.600 --> 17:28.010 I'm not going to do it here. 17:28.040 --> 17:30.530 It's not necessarily useful for this application. 17:30.530 --> 17:36.790 So I'm just going to provide the callback here with We've had done callback and we just receive a future. 17:36.790 --> 17:44.020 So it's a bit simplified and then we can just do future dot result to get the response. 17:44.320 --> 17:50.590 So response is equal to future dot result. 17:50.590 --> 17:53.260 And let's just print this. 17:53.260 --> 17:56.620 So actually this is going to be a boolean. 17:56.620 --> 18:00.970 We can say if response dot okay. 18:01.000 --> 18:09.520 And here maybe I can also provide the type I can say that's going to be set LED um response. 18:09.850 --> 18:15.580 So then I have the auto completion response dot success. 18:15.580 --> 18:22.720 If success self get logger and then info. 18:23.710 --> 18:39.110 And we can say led turned on for example else self get logger info led not changed. 18:39.140 --> 18:43.550 Okay, that's probably not going to happen because we're going to give something that's valid. 18:43.550 --> 18:49.520 But well you can handle the response here if needed and monitor the different errors. 18:49.550 --> 18:49.850 Great. 18:49.850 --> 18:51.770 So let's do a quick recap here. 18:51.770 --> 18:59.540 Once again we have so we have our client here that we have created with the interface and the name. 18:59.540 --> 19:00.740 Then we have a function. 19:00.740 --> 19:01.880 We wait for the service. 19:01.910 --> 19:06.710 We create a request and we call asynchronously the service. 19:06.740 --> 19:12.110 We register a callback that's going to be called when the server replies to the client. 19:12.110 --> 19:15.680 And then we get the response and we just print a log here. 19:15.710 --> 19:19.070 Now the only thing left is to actually call this method. 19:19.070 --> 19:20.690 And where do we call this method. 19:20.690 --> 19:25.370 Well, after we just change the state where we print a log. 19:25.400 --> 19:29.630 And I'm going to do here self dot call set LED. 19:29.960 --> 19:31.600 So what's the LED number? 19:31.630 --> 19:33.490 I start to count at zero. 19:33.490 --> 19:34.960 So that's zero one and two. 19:34.990 --> 19:35.890 For the third LED. 19:36.100 --> 19:38.770 And the state is going to be one. 19:38.830 --> 19:39.040 Okay. 19:39.040 --> 19:41.860 When the battery is empty I want to notify the user. 19:41.860 --> 19:50.140 And then when the battery is full I'm going to do call set LED with also the same index. 19:50.140 --> 19:53.350 And then it's going to be zero for the state zero. 19:53.380 --> 19:53.950 All right. 19:53.950 --> 19:55.630 And let's save. 19:55.630 --> 19:57.370 And that's going to be it for the code. 19:57.370 --> 19:59.530 So we've already tested the behavior here. 19:59.560 --> 20:04.240 Now let's test if the client call is going to work successfully. 20:04.240 --> 20:06.310 So let's go here. 20:06.310 --> 20:10.090 And well I have run with Simulink install. 20:10.090 --> 20:12.970 So it should work. 20:13.960 --> 20:20.590 I'm just going to well I'm just going to run it here and let's do a source bash SC just in case. 20:21.520 --> 20:31.640 Bash SC I'm going to run here the LED panel node which is needed first because, well, we need the 20:31.640 --> 20:33.230 service for the battery. 20:34.220 --> 20:34.550 Okay. 20:34.580 --> 20:40.610 LED panel and I'm going to run my battery node. 20:41.840 --> 20:47.870 So just run my Pi PG with battery. 20:47.870 --> 20:57.170 And actually before that I'm just going to do a Ros two topic eco led panel state to see what's happening 20:57.290 --> 20:58.460 on those LEDs. 20:58.460 --> 21:00.500 So for now they are powered off. 21:00.530 --> 21:02.900 Okay, let's run the battery. 21:04.070 --> 21:05.750 And you see battery has been started. 21:05.750 --> 21:10.610 We need to wait six seconds and you see battery is empty turned on. 21:10.610 --> 21:13.910 And we see that LED is one still one. 21:13.910 --> 21:17.840 And then LED turned uh, on what? 21:17.870 --> 21:20.060 Actually, I probably need to change the log. 21:20.780 --> 21:22.100 Let's go back here. 21:24.170 --> 21:28.370 Well, you could pass the request and know what you have decided to do. 21:28.940 --> 21:35.090 Let's say led state was changed. 21:37.160 --> 21:38.870 And let's run it again. 21:40.310 --> 21:41.600 So we start again. 21:41.600 --> 21:43.220 But reload has been started. 21:43.250 --> 21:44.630 Let's wait for six seconds. 21:44.660 --> 21:46.550 You see, battery is empty. 21:46.580 --> 21:51.440 Charging LED state was changed and then is no fool. 21:51.440 --> 21:53.000 We go back to zero. 21:53.450 --> 21:54.740 Let's wait another. 21:55.190 --> 22:00.740 You see empty is one and then full. 22:00.770 --> 22:02.390 It goes back to zero. 22:02.390 --> 22:04.250 And again and again and again. 22:04.280 --> 22:08.360 That's going to be infinitely repeating the same cycle. 22:11.390 --> 22:11.810 All right. 22:11.810 --> 22:13.700 And that's the end of this activity. 22:13.700 --> 22:16.250 So you have practice here with everything. 22:16.250 --> 22:17.540 You have created nodes. 22:17.540 --> 22:19.970 You have created topics services. 22:19.970 --> 22:26.480 You have run those communications between two nodes and all of that also using custom interfaces.