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Synchronous_ServoKit

Project Description

An extension library for Adafruit_CircuitPython_ServoKit that allows users to control the velocity of multiple positional servos in a synchronized fashion. The project aims to provide users more sophisticated levels of servo control without needing to develop the low level code. The package acts as a stand alone interpertuer providing execution and automatic handling of the following.

  • Sending velocity arguments in units of deg/sec to positional servos
  • Move multiple positional servos in a synchronized fashion over a fixed time interval
  • enforce upper and lower limits for servo actuation range

Examples

Sending incrementally increasing (periodic) velocity arguments (in rads/sec) to positional servos and having them execute the prescribed velocities over a fixed time interval (in this case 1 sec) in a synchronous fashion. Notice in the second video (non-symmetrical case), the head joint rotates at half the rate of the tail joint.

Hardware Requrments

  • Rasberry Pi 3B+
  • adafruit 16channel servo sheild
  • 1 or more positional servos

Installation Software Dependencies

  - pip install r.requirments.txt
  - pip install Synchronous_ServoKit

Usage Example

 import Synchronous_ServoKit

 # Define channel servo is connected to, accutation range, reset position, and desired units you would like to use 
 servo_one = Synchronous_ServoKit.configure(channel = 1, lower_servo_limit = 35, upper_servo_limit = 145, reset_position = 90, units='rads')
 servo_two = Synchronous_ServoKit.configure(channel = 2, lower_servo_limit = 35, upper_servo_limit = 145, reset_position = 90, units='rads')

 # Reset servo to there "home" reset positions
 positions = Synchronous_ServoKit.reset(servo_one,servo_two) 

  # Define control arguments 
  speed_servo_one = 30; speed_servo_two = 30; execution_time = 1 
  arguments = speed_servo_one,speed_servo_two,execution_time

  # Send arugments to be executed and get back new position 
  new_positions = Synchronous_ServoKit.execute(servo_one,servo_two,arguments)

Setup Instructions

After complettign installation and configuring your hardware import the package into your python script

    import import Synchronous_ServoKit

Next, create an instance for each servo in your system and configure the following parameters for each of them.

  • Reference number

    • This will determine what order your arguments need to be in

  • Channel Number

    • This will assostate what channel the servo is connected

  • Joint Limits

    • This will ensure that the servo stays within a given positonal range

  • Reset position

    • The position you would like the servo to return to if the system is reset

  • Speed constant

    • Obtained from specs on servo, speed constant = t/60deg, used to approximate the delay between 1deg steps
    # Define channel servo is connected to, accutation range, reset position, ect
servo_one = Synchronous_ServoKit.configure(channel = 1, lower_servo_limit = 35, upper_servo_limit = 145, reset_position = 90, units='rads')
servo_two = Synchronous_ServoKit.configure(channel = 2, lower_servo_limit = 35, upper_servo_limit = 145, reset_position = 90, units='rads')
servo_three = ....
servo_four = ....
ect ...

Now constuct your system by defining a variable, in this case I will define it is "system", which is an array contained each servo instance

  system = [servo_one,servo_two,servo_three, ... ]

You can inspect the current system configuration by simply calling the get_info method. This will return a list of the parapemeters assosistaed with each servo defined in your system.

  system_info = Synchronous_ServoKit.get_info(system)
  print(system_info)

You will notice that the current_positions of the servos will be listed as None, this will update after initating a system reset by simply writing

   # move all servos in system to there reset_positions
   Synchronous_ServoKit.reset(system)
   
   # re-check system info 
   system_info = Synchronous_ServoKit.get_info(system)
   print(system_info)

The current_positions of each servo should now be equal to the reset_positions you defined. You can also check the info or position of an indivdual servo by writing

   servo_one_info = servo_one.info
   print(servo_one_info)
   
   servo_one_position = servo_one.position
   print(servo_one_position)

If you want to save the current system configuration to a file just use

   Synchronous_ServoKit.save(system,file_name = 'Name of your system')

Now to reload this configuration

   system = Synchronous_ServoKit.load(file_name = 'name of your system')

After completeting the steps above, you can now control your system using velosity arguments in a syrncounous fashion by simply writing

  # Get current positions of servos
  print(system.positions)
  
  # Define speeds for each servo (units deg/sec) and an execution time (units = sec) 
  speed_servo_one = 30; speed_servo_two = -30; execution_time = 1 
  arguments = [speed_servo_one,speed_servo_two,speed_servo_three,.....] 

  # Send arugments to be executed and get back new position 
  Synchronous_ServoKit.execute(system,arguments,execution_time)
  
  # Get new positions of servos
  print(system.positions)

You should verify the new positions agree with the arguments. It is recommend that you calibrate the system

  system.calibrate(min_speed,max_speed,execution_time)