Servo Motors

The collection now has a Multi-Mode Smart Servo included. The new servo will replace the old servos and provide more functionality than before. The multi-mode servo allows for continuous and standard operation of the servo motor. In continuous mode, the servo will spin proportionally based on input in the CW or CCW direction. The max speed the servo will spin is 50rpm. In standard mode, the servo will act as a regular servo and have a range of motion of 300°. That is 150° CW and 150° CCW.

Servo Specs

Mechanical Specs

Function	Range
Size	40mm x 20.1mm x 38.3mm x 54mm
Weight	64g
Gear Type	Steel
Bearing	Dual Ball Bearings
Spline	25T
Case	Nylon & Fiberglass
Connector Wire	750mm ± 5mm (White, Red, Black)
Motor	Metal Brush Motor
Water Resistance	No

Electrical Specs

Function	4.8V	6.0V
Idle Current	5mA	7mA
No Load Speed	0.25sec/60°	0.2sec/60°
Running Current	130mA	150mA
Stall Torque	180.85oz-in	300oz-in
Stall Current	1500mA	1800mA

Control Specs

Function	Spec
Command Signal	Pulse Width Modulation
Amplifier Type	Digital Comparator
Pulse Width Range	500μS ~ 2500μS
Neutral Position	1500μS
Range of Motion	300° ± 5°
Dead band width	4μS
Rotating Direction	CW

Enviromental Conditions

Function	Range
Storage Temperature	-30°C ~ 80°C
Operating Temperature	-15°C ~ 70°C

Standard Enviroment

Function	Range
Temperature	25°C ± 5°C
Humidity	65% ± 10%

Programming

Standard Servo

Java

C++

Roscpp

//import the Servo Library
import com.studica.frc.Servo;

//Create the Servo Object
private Servo servo;

//Constuct a new instance
servo = new Servo(port);

//Can then use this mutator to set the servo angle
servo.setAngle(degrees); //Range 0° - 300°

The mutator method will allow you to set the angle of the servo

//Include the Servo Library
#include "studica/Servo.h"

//Constructor
studica::Servo servo{port};

//Use this function to set the servo angle
servo.SetAngle(degrees); //Range 0° - 300°

The function will allow you to set the angle of the servo

//Include the Servo Library
#include "Servo_ros.h"


double servo_angle;

// Returns the angle value set by the Servo motor
void servo_angle_callback(const std_msgs::Float32::ConstPtr& msg)
{
   servo_angle = msg->data;
}

int main(int argc, char **argv)
{
   system("/usr/local/frc/bin/frcKillRobot.sh"); //Terminal call to kill the robot manager used for WPILib before running the executable.
   ros::init(argc, argv, "servo_node");

   /**
    * Constructor
    * Servo's ros threads (publishers and services) will run asynchronously in the background
    */

   ros::NodeHandle nh; //internal reference to the ROS node that the program will use to interact with the ROS system
   VMXPi vmx(true, (uint8_t)50); //realtime bool and the update rate to use for the VMXPi AHRS/IMU interface, default is 50hz within a valid range of 4-200Hz

   ros::ServiceClient setAngle;
   ros::Subscriber servo_angle_sub;

   ServoROS servo(&nh, &vmx, channel);

   // Use these to directly access data
   servo.GetAngle(); //returns a double;
   servo.GetMinAngle(); //returns a double
   servo.GetMaxAngle(); //returns a double

   // Using the set_angle service, channel index is declared in the constructor
   setAngle = nh.serviceClient<vmxpi_ros::Float>("channel/channel_index/servo/set_angle");

   // Declaring message type
   vmxpi_ros::Float msg;

   // Setting the servo angle
   float angle = 45.0; //Range -150° - 150°
   msg.request.data = angle;
   setAngle.call(msg);

   // Subscribing to Servo angle topic to access the angle data
   servo_angle_sub = nh.subscribe("channel/channel_index/servo/angle", 1, servo_angle_callback); //channel_index is the input channel set in the constructor

   ros::spin(); //ros::spin() will enter a loop, pumping callbacks to obtain the latest sensor data

   return 0;
}

Important

Subscribe to Servo topics to access the data being published and write callbacks to pass messages between various processes.

Note

Calling the frcKillRobot.sh script is necessary since the VMXPi HAL uses the pigpio library, which unfortunately can only be used in one process. Thus, everything that interfaces with the VMXPi must be run on the same executable. For more information on programming with ROS, refer to: ROS Tutorials.

Continuous Servo

Java

C++

//import the Servo Continuous Library
import com.studica.frc.ServoContinous;

//Create the Servo Continuous Object
private ServoContinous servo;

//Constuct a new instance
servo = new ServoContinuous(port);

//Can then use this mutator to set the servo speed
servo.set(speed); //Range -1 - 1 (0 Stop)

The mutator method will allow you to set the speed of the servo

//Include the Servo Library
#include "studica/ServoContinuous.h"

//Constructor
studica::ServoContinuous servo{port};

//Use this function to set the servo angle
servo.Set(speed); //Range -1 - 1 (0 Stop)

The function will allow you to set the speed of the servo