What is a Part
A part Python class that wraps a functional component of a vehicle.
These include:
- Sensors - Cameras, Lidar, Odometers, GPS ...
- Actuators - Motor Controllers
- Pilots - Lane Detectors, Behavioral Cloning models, ...
- Controllers - Web based or Bluetooth.
- Stores - Tub, or a way to save data.
Here is an example how to use the PiCamera part to publish an image in the 'cam/img' channel on every drive loop.
V = dk.Vehicle()
#initialize the camera part
cam = PiCamera()
#add the part to the vehicle.
V.add(cam, outputs=['cam/img'])
V.start()
Anatomy of a Part
All parts share a common structure so that they can all be run by the vehicles drive loop. Here is an example of a part that will accept a number, multiply it by a random number and return the result.
import random
class RandPercent:
def run(self, x):
return x * random.random()
Now to add this to a vehicle:
V = dk.Vehicle()
# initialize the channel value
V.mem['const'] = 4
# add the part to read and write to the same channel.
V.add(RandPercent, inputs=['const'], outputs=['const'])
V.start(max_loops=5)
Threaded Parts
For a vehicle to perform well the drive loop must execute 10-30 times per second so slow parts should be threaded to avoid holding up the drive loop.
A threaded part needs to define the function that runs in the separate thread and the function to call that will return the most recent values quickly.
Here's an example how to make the RandPercent part threaded if the run
function takes a second to complete.
import random
import time
class RandPercent:
self.in = 0.0
self.out = 0.0
def run(self, x):
return x * random.random()
time.sleep(1)
def update(self):
# the function run in it's own thread
while True:
self.out = self.run(self.in)
def run_threaded(self, x):
self.in = x
return self.out
part.run: function used to run the partpart.run_threaded: drive loop function run if part is threaded.part.update: threaded functionpart.shutdown