ESC throttle control
This example script demonstrates how to control ESC throttle setpoint using the PyDroneCAN library. Before running the script, make sure that no other node on the bus issues contradictory ESC commands concurrently.
Writing the script
One code sample is worth 1024 words:
#!/usr/bin/env python3
import dronecan, time, math
# get command line arguments
from argparse import ArgumentParser
parser = ArgumentParser(description='ESC throttle control example')
parser.add_argument("--bitrate", default=1000000, type=int, help="CAN bit rate")
parser.add_argument("--node-id", default=100, type=int, help="CAN node ID")
parser.add_argument("--dna-server", action='store_true', default=False, help="run DNA server")
parser.add_argument("--send-safety", action='store_true', default=False, help="send safety off messages")
parser.add_argument("port", default=None, type=str, help="serial port")
args = parser.parse_args()
# Publishing setpoint values from this function; it is invoked periodically from the node thread.
def publish_throttle_setpoint():
if args.send_safety:
# optionally send safety off messages. These are needed for some ESCs
message = dronecan.ardupilot.indication.SafetyState()
message.status = message.STATUS_SAFETY_OFF
node.broadcast(message)
print(dronecan.to_yaml(message))
# Generating a sine wave
setpoint = int(512 * (math.sin(time.time()) + 2))
# Commanding ESC with indices 0, 1, 2, 3 only
commands = [setpoint, setpoint, setpoint, setpoint]
message = dronecan.uavcan.equipment.esc.RawCommand(cmd=commands)
node.broadcast(message)
# display the message on the console in human readable format
print(dronecan.to_yaml(message))
# Initializing a DroneCAN node instance.
node = dronecan.make_node(args.port, node_id=args.node_id, bitrate=args.bitrate)
# Initializing a node monitor, so we can see what nodes are online
node_monitor = dronecan.app.node_monitor.NodeMonitor(node)
if args.dna_server:
# optionally start a DNA server
dynamic_node_id_allocator = dronecan.app.dynamic_node_id.CentralizedServer(node, node_monitor)
# Waiting for at least one other node to appear online
while len(node_monitor.get_all_node_id()) <= 1:
print('Waiting for other nodes to become online...')
node.spin(timeout=1)
print("There are %u nodes online" % len(node_monitor.get_all_node_id()))
# setup to publish ESC RawCommand at 20Hz
node.periodic(0.05, publish_throttle_setpoint)
# callback for printing ESC status message to stdout in human-readable YAML format.
node.add_handler(dronecan.uavcan.equipment.esc.Status, lambda msg: print(dronecan.to_yaml(msg)))
# Running the node until the application is terminated or until first error.
try:
node.spin()
except KeyboardInterrupt:
pass
Running the script
Save the above code somewhere and run it. The connected ESC will be changing their RPM in a sine pattern, slowly accelerating and decelerating. The script will periodically print output similar to this:
### Message from 124 to All ts_mono=19376.645693 ts_real=1470440665.872391
error_count: 0
voltage: 13.2812
current: 1.3379
temperature: 313.15
rpm: 1514
power_rating_pct: 13
esc_index: 3
Using the DroneCAN GUI Tool
It is also possible to run the above script (with minor modifications) directly from the interactive console of the DroneCAN GUI Tool, because the DroneCAN GUI Tool is built on top of PyDroneCAN. In that case you won’t need to create a new node yourself in the script - just use the application’s own node, it is accessible from the interactive console. For details, please read the documentation of the DroneCAN GUI Tool.
