WEBVTT 00:00:00.000 --> 00:00:05.760 Proportional control multiplies error by kP. Let's follow one update from target to output. 00:00:05.760 --> 00:00:10.440 Watch the correction shrink as the measurement approaches the target. 00:00:10.440 --> 00:00:16.260 The target is 1,000 ticks, and the measurement is 600 ticks. 00:00:16.260 --> 00:00:20.220 Target minus measurement gives us an error of 400 ticks. 00:00:20.220 --> 00:00:28.380 For this calculation, kP is 0.0005, so the raw output is 0.2. 00:00:28.380 --> 00:00:38.520 Keep the units and sign visible. If the target is above the measurement, the correction is positive. 00:00:38.520 --> 00:00:44.220 This gain is only sample data. It is not a value to put on your robot. 00:00:44.220 --> 00:00:53.760 This software fixture performs the exact sequence once per loop. 00:00:53.760 --> 00:01:02.760 It reads the encoder, calculates target minus measurement, and multiplies by kP. 00:01:02.760 --> 00:01:09.240 It keeps the output between -0.25 and 0.25, then writes every stage to telemetry. 00:01:09.300 --> 00:01:18.900 At 600 ticks, the error is 400, and the output is 0.2. 00:01:18.900 --> 00:01:26.220 At 900 ticks, the error is 100, and the output is 0.05. 00:01:26.220 --> 00:01:37.860 At 990 ticks, the error is 10, and the output is 0.005. 00:01:37.860 --> 00:01:44.040 That shrinking correction is the basic behavior of P control. 00:01:44.040 --> 00:01:54.300 Friction or gravity can leave a small steady error when the correction becomes too small to move or hold. 00:01:54.540 --> 00:02:05.520 If we calculate measurement minus target, the same point produces -400 and -0.2. 00:02:05.520 --> 00:02:08.400 The controller pushes away from the target. 00:02:08.400 --> 00:02:15.060 Do not try to tune a sign mistake with a smaller gain. 00:02:15.060 --> 00:02:23.220 Inspect the target, measurement, coordinate convention, encoder direction, motor direction, and error equation. 00:02:23.220 --> 00:02:35.400 Once those agree, use a low-power environment and choose a small gain and output limit just to test. 00:02:36.240 --> 00:02:43.020 Direction errors can be among the most dangerous things to test. 00:02:43.020 --> 00:02:46.020 Especially with larger mechanisms, take all the proper precautions.