examples: added servo control example

Author: tridge

examples/servo_control.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+'''
+demonstrate servo monitoring and servo control
+the selected servo will be given sinisoidal control while printing position
+'''
+
+import dronecan
+import time
+import math
+from dronecan import uavcan
+
+# get command line arguments
+from argparse import ArgumentParser
+parser = ArgumentParser(description='test servo actuators')
+parser.add_argument("port", default=None, help="CAN URI")
+parser.add_argument("--bitrate", default=1000000, type=int, help="CAN bit rate")
+parser.add_argument("--node-id", default=125, type=int, help="CAN node ID")
+parser.add_argument("--target-node-id", default=100, type=int, help="target CAN node ID")
+parser.add_argument("--rate", default=20, type=float, help="servo update rate")
+parser.add_argument("--freq", default=1, type=float, help="servo sinisoid frequency")
+parser.add_argument("--actuator-min", default=-1, type=float, help="actuator min")
+parser.add_argument("--actuator-max", default=1, type=float, help="actuator max")
+parser.add_argument("--actuator-id", default=1, type=float, help="actuator ID")
+
+args = parser.parse_args()
+
+port = args.port
+
+# Initializing a DroneCAN node instance.
+node = dronecan.make_node(port, node_id=args.node_id, bitrate=args.bitrate)
+
+def handle_actuator_status(msg):
+    '''handle actuator status message'''
+    print(dronecan.to_yaml(msg))
+
+def control_actuator():
+    '''control for actuator, called at rate Hz'''
+    t = time.time()
+    sint = math.sin(t * args.freq * math.pi * 2)
+    amplitude = 0.5 * (args.actuator_max-args.actuator_min)
+    mid = args.actuator_min + amplitude
+    v = mid + sint * amplitude
+
+    req = uavcan.equipment.actuator.ArrayCommand()
+    cmd = uavcan.equipment.actuator.Command()
+    cmd.actuator_id = args.actuator_id
+    cmd.command_type = cmd.COMMAND_TYPE_UNITLESS
+    cmd.command_value = v
+    req.commands = [ cmd ]
+
+    node.broadcast(req)
+    
+
+# Subscribe only to actuator status messages
+node.add_handler(uavcan.equipment.actuator.Status, handle_actuator_status)
+
+node.periodic(1.0/args.rate, control_actuator)
+
+while True:
+    node.spin()