diff --git a/wpilibc/src/main/native/cpp/controller/ArmFeedforward.cpp b/wpilibc/src/main/native/cpp/controller/ArmFeedforward.cpp
deleted file mode 100644
index 25e72b37d5..0000000000
--- a/wpilibc/src/main/native/cpp/controller/ArmFeedforward.cpp
+++ /dev/null
@@ -1,33 +0,0 @@
-/*----------------------------------------------------------------------------*/
-/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
-/* Open Source Software - may be modified and shared by FRC teams. The code   */
-/* must be accompanied by the FIRST BSD license file in the root directory of */
-/* the project.                                                               */
-/*----------------------------------------------------------------------------*/
-
-#include "frc/controller/ArmFeedforward.h"
-
-#include <wpi/MathExtras.h>
-
-using namespace frc;
-
-using Angle = units::radians;
-using Velocity = units::radians_per_second;
-using Acceleration = units::compound_unit<units::radians_per_second,
-                                          units::inverse<units::second>>;
-using kv_unit = units::compound_unit<units::volts,
-                                     units::inverse<units::radians_per_second>>;
-using ka_unit =
-    units::compound_unit<units::volts, units::inverse<Acceleration>>;
-
-ArmFeedforward::ArmFeedforward(units::volt_t kS, units::volt_t kCos,
-                               units::unit_t<kv_unit> kV,
-                               units::unit_t<ka_unit> kA)
-    : m_kS(kS), m_kCos(kCos), m_kV(kV), m_kA(kA) {}
-
-units::volt_t ArmFeedforward::Calculate(
-    units::unit_t<Angle> angle, units::unit_t<Velocity> velocity,
-    units::unit_t<Acceleration> acceleration) {
-  return m_kS * wpi::sgn(velocity) + m_kCos * units::math::cos(angle) +
-         m_kV * velocity + m_kA * acceleration;
-}
diff --git a/wpilibc/src/main/native/include/frc/controller/ArmFeedforward.h b/wpilibc/src/main/native/include/frc/controller/ArmFeedforward.h
index 75bcd216b2..d1a8ceac9b 100644
--- a/wpilibc/src/main/native/include/frc/controller/ArmFeedforward.h
+++ b/wpilibc/src/main/native/include/frc/controller/ArmFeedforward.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <units/units.h>
+#include <wpi/MathExtras.h>
 
 namespace frc {
 /**
@@ -26,7 +27,7 @@ class ArmFeedforward {
       units::compound_unit<units::volts, units::inverse<Acceleration>>;
 
  public:
-  ArmFeedforward() = default;
+  constexpr ArmFeedforward() = default;
 
   /**
    * Creates a new ArmFeedforward with the specified gains.
@@ -36,9 +37,10 @@ class ArmFeedforward {
    * @param kV   The velocity gain, in volt seconds per radian.
    * @param kA   The acceleration gain, in volt seconds^2 per radian.
    */
-  ArmFeedforward(units::volt_t kS, units::volt_t kCos,
-                 units::unit_t<kv_unit> kV,
-                 units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0));
+  constexpr ArmFeedforward(
+      units::volt_t kS, units::volt_t kCos, units::unit_t<kv_unit> kV,
+      units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0))
+      : m_kS(kS), m_kCos(kCos), m_kV(kV), m_kA(kA) {}
 
   /**
    * Calculates the feedforward from the gains and setpoints.
@@ -51,7 +53,10 @@ class ArmFeedforward {
   units::volt_t Calculate(units::unit_t<Angle> angle,
                           units::unit_t<Velocity> velocity,
                           units::unit_t<Acceleration> acceleration =
-                              units::unit_t<Acceleration>(0));
+                              units::unit_t<Acceleration>(0)) const {
+    return m_kS * wpi::sgn(velocity) + m_kCos * units::math::cos(angle) +
+           m_kV * velocity + m_kA * acceleration;
+  }
 
  private:
   units::volt_t m_kS{0};
diff --git a/wpilibc/src/main/native/include/frc/controller/ElevatorFeedforward.h b/wpilibc/src/main/native/include/frc/controller/ElevatorFeedforward.h
index 2c1e9e12c0..9938b7b46c 100644
--- a/wpilibc/src/main/native/include/frc/controller/ElevatorFeedforward.h
+++ b/wpilibc/src/main/native/include/frc/controller/ElevatorFeedforward.h
@@ -26,7 +26,7 @@ class ElevatorFeedforward {
       units::compound_unit<units::volts, units::inverse<Acceleration>>;
 
  public:
-  ElevatorFeedforward() = default;
+  constexpr ElevatorFeedforward() = default;
 
   /**
    * Creates a new ElevatorFeedforward with the specified gains.
@@ -36,9 +36,9 @@ class ElevatorFeedforward {
    * @param kV The velocity gain, in volt seconds per distance.
    * @param kA The acceleration gain, in volt seconds^2 per distance.
    */
-  ElevatorFeedforward(units::volt_t kS, units::volt_t kG,
-                      units::unit_t<kv_unit> kV,
-                      units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0))
+  constexpr ElevatorFeedforward(
+      units::volt_t kS, units::volt_t kG, units::unit_t<kv_unit> kV,
+      units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0))
       : m_kS(kS), m_kG(kG), m_kV(kV), m_kA(kA) {}
 
   /**
@@ -48,9 +48,9 @@ class ElevatorFeedforward {
    * @param acceleration The acceleration setpoint, in distance per second^2.
    * @return The computed feedforward, in volts.
    */
-  units::volt_t Calculate(units::unit_t<Velocity> velocity,
-                          units::unit_t<Acceleration> acceleration =
-                              units::unit_t<Acceleration>(0)) {
+  constexpr units::volt_t Calculate(units::unit_t<Velocity> velocity,
+                                    units::unit_t<Acceleration> acceleration =
+                                        units::unit_t<Acceleration>(0)) const {
     return m_kS * wpi::sgn(velocity) + m_kG + m_kV * velocity +
            m_kA * acceleration;
   }
diff --git a/wpilibc/src/main/native/include/frc/controller/SimpleMotorFeedforward.h b/wpilibc/src/main/native/include/frc/controller/SimpleMotorFeedforward.h
index 8293fc9e91..03aebf2c07 100644
--- a/wpilibc/src/main/native/include/frc/controller/SimpleMotorFeedforward.h
+++ b/wpilibc/src/main/native/include/frc/controller/SimpleMotorFeedforward.h
@@ -26,7 +26,7 @@ class SimpleMotorFeedforward {
       units::compound_unit<units::volts, units::inverse<Acceleration>>;
 
  public:
-  SimpleMotorFeedforward() = default;
+  constexpr SimpleMotorFeedforward() = default;
 
   /**
    * Creates a new SimpleMotorFeedforward with the specified gains.
@@ -35,8 +35,9 @@ class SimpleMotorFeedforward {
    * @param kV The velocity gain, in volt seconds per distance.
    * @param kA The acceleration gain, in volt seconds^2 per distance.
    */
-  SimpleMotorFeedforward(units::volt_t kS, units::unit_t<kv_unit> kV,
-                         units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0))
+  constexpr SimpleMotorFeedforward(
+      units::volt_t kS, units::unit_t<kv_unit> kV,
+      units::unit_t<ka_unit> kA = units::unit_t<ka_unit>(0))
       : m_kS(kS), m_kV(kV), m_kA(kA) {}
 
   /**
@@ -46,9 +47,9 @@ class SimpleMotorFeedforward {
    * @param acceleration The acceleration setpoint, in distance per second^2.
    * @return The computed feedforward, in volts.
    */
-  units::volt_t Calculate(units::unit_t<Velocity> velocity,
-                          units::unit_t<Acceleration> acceleration =
-                              units::unit_t<Acceleration>(0)) {
+  constexpr units::volt_t Calculate(units::unit_t<Velocity> velocity,
+                                    units::unit_t<Acceleration> acceleration =
+                                        units::unit_t<Acceleration>(0)) const {
     return m_kS * wpi::sgn(velocity) + m_kV * velocity + m_kA * acceleration;
   }
 
diff --git a/wpiutil/src/main/native/include/wpi/MathExtras.h b/wpiutil/src/main/native/include/wpi/MathExtras.h
index 8d5fec490c..52a56a1ae5 100644
--- a/wpiutil/src/main/native/include/wpi/MathExtras.h
+++ b/wpiutil/src/main/native/include/wpi/MathExtras.h
@@ -838,9 +838,10 @@ SaturatingMultiplyAdd(T X, T Y, T A, bool *ResultOverflowed = nullptr) {
   return SaturatingAdd(A, Product, &Overflowed);
 }
 
-// Typesafe implementation of the signum function.  Returns -1 if negative, 1 if positive, 0 if 0.
+// Typesafe implementation of the signum function.
+// Returns -1 if negative, 1 if positive, 0 if 0.
 template <typename T>
-int sgn(T val) {
+constexpr int sgn(T val) {
   return (T(0) < val) - (val < T(0));
 }