FLL 2021: Keep a straight line and push - How to accomplish the Unload Cargo Ship mission Pro Preview

WEBVTT 1 00:00:01.280 --> 00:00:02.860 In this video tutorial, 2 00:00:02.890 --> 00:00:10.740 we accomplish a push poll mission where we must push or pull on the mission, though, 3 00:00:10.770 --> 00:00:18.520 and we use the FIRST LEGO League cargo connect unload cargo mission as a demonstration. 4 00:00:18.840 --> 00:00:21.380 We use a LEGO Education SPIKE Prime robot 5 00:00:21.400 --> 00:00:25.980 to accomplish the mission with an interesting attachment. 6 00:00:26.010 --> 00:00:29.260 Let's see how we accomplish the mission. 7 00:00:29.290 --> 00:00:36.140 This here is the robot and it's from move forward and we push on the mission model. 8 00:00:36.170 --> 00:00:42.460 Now, this mission seems quite simple and it might be, 9 00:00:42.490 --> 00:00:46.420 but don't forget that this mission is on the other end of the field. 10 00:00:46.450 --> 00:00:51.860 So getting here and pushing it forward is a difficult part. 11 00:00:51.890 --> 00:00:55.860 Now, when you want to get to this part of 12 00:00:55.890 --> 00:01:02.260 the field, we can align first to this black line, then we can turn back 13 00:01:02.290 --> 00:01:07.920 and align to this black line in order to compensate for the error that the robot 14 00:01:07.950 --> 00:01:12.460 is making, then move back into align to this black line. 15 00:01:12.490 --> 00:01:16.540 And in this way we autcorrect, we 16 00:01:16.570 --> 00:01:20.700 compensate for the errors that the robot is making. 17 00:01:20.730 --> 00:01:23.420 On its way from the base to this side 18 00:01:23.450 --> 00:01:27.100 of the field, the robot will make some errors. 19 00:01:27.130 --> 00:01:31.660 As you can see, we have a rather large attachment at the front. 20 00:01:31.690 --> 00:01:35.140 So you should think about a good strategy 21 00:01:35.170 --> 00:01:38.180 when turning when the robot has large attachments. 22 00:01:38.210 --> 00:01:42.290 And for this specific mission, it's better to move backward 23 00:01:42.320 --> 00:01:49.490 with the robot. At the end, we reach this line and for this recording 24 00:01:49.520 --> 00:01:55.180 we start from this line because we want to also discuss how do we move forward. 25 00:01:55.210 --> 00:01:58.380 And we keep a straight line with the motion sensor. 26 00:01:58.410 --> 00:02:01.740 And we see this when we discuss the program. 27 00:02:01.770 --> 00:02:06.380 And our goal is to show you the algorithm of how do we move forward. 28 00:02:06.410 --> 00:02:11.020 Now, do we need to use this algorithm for this specific mission? 29 00:02:11.050 --> 00:02:14.340 Probably not. We can just move forward with the robot 30 00:02:14.370 --> 00:02:18.340 when we reach the line, but we take the opportunity. 31 00:02:18.370 --> 00:02:22.220 So again, we align to different lines. 32 00:02:22.250 --> 00:02:26.020 We reach one of these lines and then we 33 00:02:26.050 --> 00:02:28.660 move forward and we accomplish the mission. 34 00:02:28.690 --> 00:02:31.730 And when moving forward, we use the motion sensor. 35 00:02:31.760 --> 00:02:34.500 And an interesting algorithm for keeping 36 00:02:34.530 --> 00:02:40.520 a straight line. Right here when we move, we want to keep a straight line. 37 00:02:41.880 --> 00:02:46.960 Let's see the programming and discuss the algorithm. 38 00:02:47.520 --> 00:02:50.380 This here is the program for our robot. 39 00:02:50.410 --> 00:02:53.820 Again, we don't need to implement the program in this way. 40 00:02:53.850 --> 00:03:00.340 For this particular mission, we can always just move forward with the motors. 41 00:03:00.370 --> 00:03:04.380 But what we've learned, and I hope you've learned with this course 42 00:03:04.410 --> 00:03:09.100 and with the demonstration with all the other courses, is that we cannot rely 43 00:03:09.130 --> 00:03:16.020 on the robots on the motors to move the robot in a straight line. 44 00:03:16.040 --> 00:03:16.540 Why? 45 00:03:16.570 --> 00:03:20.340 Because they will slip on the field, they will make some mistakes. 46 00:03:20.370 --> 00:03:23.900 There will always be some errors, errors that are occurring. 47 00:03:23.930 --> 00:03:28.420 So what we must do is try to use different algorithms. 48 00:03:28.450 --> 00:03:30.580 And in our case, we'll use an algorithm 49 00:03:30.610 --> 00:03:35.500 for keeping the robot moving straight in a straight line. 50 00:03:35.530 --> 00:03:39.700 And this here is our LEGO Education SPIKE Prime robot program. 51 00:03:39.730 --> 00:03:46.220 Here is when the program starts, we set movement speed to 50%. 52 00:03:46.250 --> 00:03:52.420 And what we can see is that there are two variables right here. 53 00:03:52.450 --> 00:03:56.340 If I open this window, I can see that there are two variables. 54 00:03:56.370 --> 00:04:03.220 One of the variables says movement speed, which is 50, and the other is ten yaw. 55 00:04:03.250 --> 00:04:04.580 But we'll get to there. 56 00:04:04.610 --> 00:04:08.500 So, movement speed, this is the speed with which we want to move the road. 57 00:04:08.530 --> 00:04:13.940 And we set movement motors to A and B, and we set the movement speed 58 00:04:13.970 --> 00:04:20.980 for the two motors to the value of the variable movement speed. 59 00:04:21.010 --> 00:04:25.380 And the reason why we do this is because further down in the program, 60 00:04:25.410 --> 00:04:29.700 we might want to change the value of this movement speed. 61 00:04:29.720 --> 00:04:34.620 And it's easier as a configuration to have all the variables on the right, 62 00:04:34.650 --> 00:04:39.460 and when you want to change something, to just change it at one place. 63 00:04:39.480 --> 00:04:42.180 Otherwise it gets a little tricky. 64 00:04:42.210 --> 00:04:44.500 Because if we want to change the speed 65 00:04:44.530 --> 00:04:50.260 of the robot, we must go to this set movement speed. 66 00:04:50.280 --> 00:04:54.740 And we then have to go to 67 00:04:54.770 --> 00:05:01.780 probably there is some other movement speed block down the program. 68 00:05:01.800 --> 00:05:07.860 And if we want to change the speed of the robot, we have to change on two places. 69 00:05:07.890 --> 00:05:12.380 When we have the variable on the right, we change on a single place. 70 00:05:12.410 --> 00:05:14.460 But that's not the main point here. 71 00:05:14.480 --> 00:05:18.780 The main point is how do we make the robot move forward? 72 00:05:18.800 --> 00:05:20.460 Here it is. 73 00:05:20.480 --> 00:05:22.940 Set movement motors to A and B. 74 00:05:22.970 --> 00:05:25.740 Set movement speed to movement speed. 75 00:05:25.770 --> 00:05:29.780 Then we reset the motion sensor. 76 00:05:29.800 --> 00:05:31.940 We set yaw angle to zero. 77 00:05:31.970 --> 00:05:34.220 This is our starting position. 78 00:05:34.250 --> 00:05:39.780 And we detect the rotation with Motor A, 79 00:05:39.800 --> 00:05:46.180 and we wait until Motor A has reached a relative position of -520. 80 00:05:46.200 --> 00:05:48.820 Degrees. So motor A is moving forward. 81 00:05:48.850 --> 00:05:53.060 And this is how we know that we moved forward long enough. 82 00:05:53.090 --> 00:05:55.260 Now, should we use a sensor here? 83 00:05:55.290 --> 00:05:58.500 Yes, we should definitely use the sensor 84 00:05:58.530 --> 00:06:04.500 and not a fixed repeat until with a value 85 00:06:04.530 --> 00:06:11.100 for the rotation. We should use this black line here to understand whether to stop. 86 00:06:11.130 --> 00:06:14.180 But this would have made the program way too complex. 87 00:06:14.210 --> 00:06:19.460 And in some of the previous programs we've demonstrated how you can stop there. 88 00:06:19.480 --> 00:06:25.020 So don't use hard coded values for angles. 89 00:06:25.040 --> 00:06:30.980 The moment you use hard coded values for angles and for rotations like this, 90 00:06:31.010 --> 00:06:36.340 you get a robot that's not consistent and it's not reliable. 91 00:06:36.360 --> 00:06:39.620 If you see such a value, always try to remove it. 92 00:06:39.640 --> 00:06:41.020 How are we going to remove it? 93 00:06:41.040 --> 00:06:47.420 In our case, we can always move forward until we reach this black line here. 94 00:06:47.450 --> 00:06:50.980 So just move forward until we reach this black line. 95 00:06:51.010 --> 00:06:55.780 In our case, for the recording, we hard coded it to make the program 96 00:06:55.800 --> 00:07:01.420 simpler and to be able to explain it in like two to three minutes. 97 00:07:01.450 --> 00:07:04.940 Then what we are doing is while we are 98 00:07:04.970 --> 00:07:10.140 waiting for the robot to move forward, we are repeating two actions. 99 00:07:10.170 --> 00:07:16.500 First, we set the angle. 100 00:07:16.530 --> 00:07:19.700 We take the Yaw angle from the motion 101 00:07:19.730 --> 00:07:24.020 sensor and we set it to this variable tempYaw. 102 00:07:24.040 --> 00:07:31.580 So if the robot moves slightly to the right, tempYaw will be positive integer. 103 00:07:31.600 --> 00:07:36.180 If it moves slightly to the left, tempYaw would be a negative integer. 104 00:07:36.210 --> 00:07:38.340 And that's the important part here. 105 00:07:38.360 --> 00:07:40.980 Move right, it will be positive. 106 00:07:41.010 --> 00:07:44.140 Move left, it will be negative. 107 00:07:44.170 --> 00:07:50.900 And as we take this value from the Yo angle, this here is the interesting block. 108 00:07:50.920 --> 00:07:55.020 This is the block that's helping us keep a straight line. 109 00:07:55.040 --> 00:07:57.580 What we do with this block we have right 110 00:07:57.600 --> 00:08:03.780 here in the pallet on the left, we have more movement motor or blocks. 111 00:08:03.800 --> 00:08:07.540 And in these more movement blocks, we have this. 112 00:08:07.570 --> 00:08:16.900 Start moving at 50 50% of power, which practically means set this 113 00:08:16.920 --> 00:08:21.780 value to one of the motors and set this value to the other motor. 114 00:08:21.800 --> 00:08:26.020 And this will be our A motor and this will be our B motor. 115 00:08:26.040 --> 00:08:29.180 So what do we want to happen with the robot? 116 00:08:29.210 --> 00:08:32.980 If the robot goes slightly to the right, 117 00:08:33.010 --> 00:08:39.500 what we want to do is for the right motor to move faster than the left motor. 118 00:08:39.530 --> 00:08:44.420 So if the robot goes up, it makes a mistake and it goes up. 119 00:08:44.440 --> 00:08:46.580 We want to compensate for this mistake 120 00:08:46.610 --> 00:08:52.140 by moving faster with the right motor and slower with the left motor. 121 00:08:52.170 --> 00:08:54.980 And this is how we want to compensate for the error. 122 00:08:55.010 --> 00:08:58.820 And this is what this block here is doing. 123 00:08:58.850 --> 00:09:06.980 If we set moving at two different values, values for A and values for B. 124 00:09:07.010 --> 00:09:14.660 So if the Yaw angle is positive, which means the robot has turned slightly 125 00:09:14.690 --> 00:09:20.660 to the right, we want the left motor to be slower. 126 00:09:20.690 --> 00:09:27.820 So we set movement speed, which is 50 minus, let's say five, because 127 00:09:27.850 --> 00:09:32.220 this is the angle that the robot has turned. 128 00:09:32.250 --> 00:09:35.420 And this gives us 45. 129 00:09:35.440 --> 00:09:38.140 And for the other motor, for the B motor, 130 00:09:38.170 --> 00:09:41.820 which is on the right of our robot, 131 00:09:41.850 --> 00:09:48.380 we set the speed to 55 50 plus five. 132 00:09:48.410 --> 00:09:52.980 So in this way, we start moving at 45 55, 133 00:09:53.010 --> 00:09:59.620 which makes the left motor turns slower than the right motor. 134 00:09:59.650 --> 00:10:02.900 And in this way, we compensate for that error. 135 00:10:02.930 --> 00:10:06.820 Now, if there is no error, if the robot is moving perfectly straight, 136 00:10:06.850 --> 00:10:13.500 and yaw angle says that we are at zero degrees, what we are doing then is we are 137 00:10:13.530 --> 00:10:22.220 moving at 50 minus zero, which is 50, and 50 plus zero, which is 50. 138 00:10:22.250 --> 00:10:29.020 And this way we make the robot keep a straight line. 139 00:10:29.050 --> 00:10:31.820 And if we want to change the speed of the robot, 140 00:10:31.850 --> 00:10:37.420 we can change only at a single place, right here, at the variables. 141 00:10:37.440 --> 00:10:40.940 We don't have to change it in three different places. 142 00:10:40.970 --> 00:10:47.380 We don't have to change it here and here and here, we change it at a single place. 143 00:10:47.410 --> 00:10:51.060 So it's easy for us to configure the behavior of the robot. 144 00:10:51.080 --> 00:10:58.820 These are the principles - extract such constants into variables that we can 145 00:10:58.850 --> 00:11:03.580 configure at a single place that's for the variables and 146 00:11:03.610 --> 00:11:10.780 for moving straight, we try to compensate for the error that the robot is making. 147 00:11:10.810 --> 00:11:13.040 Now, if we move forward here is 148 00:11:13.070 --> 00:11:21.140 the program move forward and show how the robot it went slightly 149 00:11:21.170 --> 00:11:28.500 to the left, slightly to the left, and here it is to the right. 150 00:11:28.530 --> 00:11:30.820 Sorry. When the robot starts, 151 00:11:30.850 --> 00:11:35.940 it goes slightly to the right, and then we start compensating. 152 00:11:35.970 --> 00:11:39.140 We see AHA, the robot is to the right, 153 00:11:39.170 --> 00:11:42.580 probably around three, four, five degrees to the right. 154 00:11:42.610 --> 00:11:50.500 So we start compensating and the robot turns and it's now moving straight. 155 00:11:50.530 --> 00:11:56.380 It corrected the error, which is perfect. 156 00:11:56.410 --> 00:11:58.740 This is exactly what we need if the robot 157 00:11:58.770 --> 00:12:04.820 makes a mistake, always correct for the Error, and then we start moving back. 158 00:12:04.850 --> 00:12:08.920 When moving back, we want to do the same thing. 159 00:12:10.040 --> 00:12:11.860 We set the angle to zero, 160 00:12:11.890 --> 00:12:15.860 we set the relative position of eight to zero and we move back again. 161 00:12:15.890 --> 00:12:21.060 Don't hardcode such values always try to detect something with the light sensors. 162 00:12:21.080 --> 00:12:22.900 We do it here to make the robot, 163 00:12:22.930 --> 00:12:29.340 the program simpler, and to focus on one specific thing, which is moving straight. 164 00:12:29.370 --> 00:12:36.940 When we are moving straight, the opposite should happen we move with 165 00:12:36.970 --> 00:12:41.100 motors A and B, but we move back and that's why we 166 00:12:41.130 --> 00:12:46.900 multiply this movement speed by -50 minus one. 167 00:12:46.930 --> 00:12:51.300 So if it was 50, it is now -50 168 00:12:51.330 --> 00:12:58.900 if it was 50 it is now -50 and if the robot is slightly to the right. 169 00:12:58.930 --> 00:13:02.620 This means that tempYaw will be A positive integer. 170 00:13:02.650 --> 00:13:06.540 Let's say five and we'll start moving 171 00:13:06.570 --> 00:13:14.780 with -50 minus five which is -55 and when we are moving back. 172 00:13:14.810 --> 00:13:21.540 If the robot is slightly to the right, we set the speed of the left motor to be 173 00:13:21.570 --> 00:13:27.180 -55 and the speed of the right motor to be 174 00:13:27.210 --> 00:13:33.340 -45 and in this way the left motor moves 175 00:13:33.370 --> 00:13:39.060 faster than the right, and the robot compensates for the Error. 176 00:13:39.080 --> 00:13:42.040 Let's see it in action. 177 00:13:42.840 --> 00:13:51.220 You see how the robot when it starts, it is slightly to the right, right here. 178 00:13:51.250 --> 00:13:54.860 And now we move back and it compensates. 179 00:13:54.890 --> 00:14:03.260 And it is again at an exact angle. 180 00:14:03.290 --> 00:14:11.300 It makes the Error when it starts right here it is slightly to the right. 181 00:14:11.330 --> 00:14:12.700 We compensate. 182 00:14:12.730 --> 00:14:15.820 Now it makes a second Mistake, second Error. 183 00:14:15.850 --> 00:14:17.460 It is slightly to the right. 184 00:14:17.490 --> 00:14:22.120 You see it right here, how it is slightly to the right. 185 00:14:25.480 --> 00:14:32.900 And we compensate and we turn it to the left. 186 00:14:32.930 --> 00:14:34.860 Because of this algorithm, 187 00:14:34.890 --> 00:14:39.700 and this is how we use the motion sensor to keep a straight line. 188 00:14:39.730 --> 00:14:41.620 This is how we use the motion Sensor 189 00:14:41.650 --> 00:14:45.140 to auto correct and to compensate for the Error. 190 00:14:45.170 --> 00:14:53.860 I know I've been repeating this more than enough, but it's important. 191 00:14:53.880 --> 00:14:54.540 It's important. 192 00:14:54.570 --> 00:15:00.580 It's a very simple way in which we can use the motion sensor to keep a straight Line. 193 00:15:00.610 --> 00:15:06.380 I hope this is helpful, and I hope that you can use it in your programs. 194 00:15:06.400 --> 00:15:07.960 And I'll see you in the next tutorial.