Dev/dc motor transmission (#25)

* Add translated transmission class

* Add docs and unit tests

* Update build.gradle

Author: andycate

build.gradle

@@ -32,7 +32,7 @@ dependencies {
 }
 
 group = 'org.team5499'
-version = '2.1.2'
+version = '2.2.0'
 
 task sourcesJar(type: Jar) {
     from sourceSets.main.allJava

src/main/kotlin/org/team5499/monkeyLib/math/physics/DCMotorTransmission.kt

@@ -0,0 +1,90 @@
+package org.team5499.monkeyLib.math.physics
+
+/**
+ * Model of a DC motor rotating a shaft.  All parameters refer to the output (e.g. should already consider gearing
+ * and efficiency losses).  The motor is assumed to be symmetric forward/reverse.
+ *
+ * @property speedPerVolt kV, or rad/s per V (no load)
+ * @property torquePerVolt N•m per V (stall)
+ * @property frictionVoltage the voltage needed to overcome static
+ */
+class DCMotorTransmission(
+    val speedPerVolt: Double,
+    val torquePerVolt: Double,
+    val frictionVoltage: Double
+) {
+    // TODO add electrical constants?  (e.g. current)
+
+    /**
+     * Returns the idle speed of the motor at this voltage
+     *
+     * @param voltage The voltage across the motor
+     * @return The theoretical speed in rad/s
+     */
+    @Suppress("ReturnCount")
+    fun freeSpeedAtVoltage(voltage: Double): Double {
+        if (voltage > 0.0) {
+            return Math.max(0.0, voltage - frictionVoltage) * speedPerVolt
+        } else if (0.0 > voltage) {
+            return Math.min(0.0, voltage + frictionVoltage) * speedPerVolt
+        } else {
+            return 0.0
+        }
+    }
+
+    /**
+     * Get the theoretical torque applied by the motor at a given speed and voltage
+     *
+     * @param outputSpeed The speed of the motor in rad/s
+     * @param voltage The voltage across the motor
+     * @return The theoretical torque in N•m
+     */
+    fun getTorqueForVoltage(outputSpeed: Double, voltage: Double): Double {
+        var effectiveVoltage = voltage
+        if (outputSpeed > 0.0) {
+            // Forward motion, rolling friction.
+            effectiveVoltage -= frictionVoltage
+        } else if (0.0 > outputSpeed) {
+            // Reverse motion, rolling friction.
+            effectiveVoltage += frictionVoltage
+        } else if (voltage > 0.0) {
+            // System is static, forward torque.
+            effectiveVoltage = Math.max(0.0, voltage - frictionVoltage)
+        } else if (0.0 > voltage) {
+            // System is static, reverse torque.
+            effectiveVoltage = Math.min(0.0, voltage + frictionVoltage)
+        } else {
+            // System is idle.
+            return 0.0
+        }
+        return torquePerVolt * (-outputSpeed / speedPerVolt + effectiveVoltage)
+    }
+
+    /**
+     * Get the required voltage for the requested torque at a speed.
+     *
+     * @param outputSpeed The output speed of the motor in rad/s
+     * @param torque The output torque of the motor in N•m
+     * @return The theoretical voltage for the requested torque and speed
+     */
+    fun getVoltageForTorque(outputSpeed: Double, torque: Double): Double {
+        var modifiedFrictionVoltage: Double = 0.0
+        if (outputSpeed > 0.0) {
+            // Forward motion, rolling friction.
+            modifiedFrictionVoltage = frictionVoltage
+        } else if (0.0 > outputSpeed) {
+            // Reverse motion, rolling friction.
+            modifiedFrictionVoltage = -frictionVoltage
+        } else if (torque > 0.0) {
+            // System is static, forward torque.
+            modifiedFrictionVoltage = frictionVoltage
+        } else if (0.0 > torque) {
+            // System is static, reverse torque.
+            modifiedFrictionVoltage = -frictionVoltage
+        } else {
+            // System is idle.
+            return 0.0
+        }
+        return torque / torquePerVolt + outputSpeed / speedPerVolt + modifiedFrictionVoltage
+    }
+}

src/test/kotlin/tests/math/physics/DCMotorTransmissionTest.kt

@@ -0,0 +1,34 @@
+package tests.math.physics
+
+import org.junit.Test
+import org.junit.Assert.assertEquals
+
+import org.team5499.monkeyLib.math.physics.DCMotorTransmission
+
+class DCMotorTransmissionTest {
+    val motor = DCMotorTransmission(1000.0, 0.5, 1.0)
+    val stallTorque = 5.5 // N•m
+    val freeSpeed = 11000.0 // rad/s
+    val epsilon = 0.1
+
+    @Test
+    fun stallTorqueTest() {
+        val calculatedStallTorque = motor.getTorqueForVoltage(0.0, 12.0)
+        println("Expected $stallTorque, but got $calculatedStallTorque.")
+        assertEquals(stallTorque, calculatedStallTorque, epsilon)
+    }
+
+    @Test
+    fun freeSpeedTest() {
+        val calculatedFreeSpeed = motor.freeSpeedAtVoltage(12.0)
+        println("Expected $freeSpeed, but got $calculatedFreeSpeed.")
+        assertEquals(freeSpeed, calculatedFreeSpeed, epsilon)
+    }
+
+    @Test
+    fun constantsTest() {
+        assertEquals(1000.0, motor.speedPerVolt, 0.0)
+        assertEquals(0.5, motor.torquePerVolt, 0.0)
+        assertEquals(1.0, motor.frictionVoltage, 0.0)
+    }
+}