42099-off-roader: Add basic driving demo.

sets/technic/42099-off-roader/README.md

@@ -0,0 +1,9 @@
+---
+permalink: /projects/sets/technic/42099-off-roader/
+title: "42099: 4X4 X-treme Off-Roader"
+image:
+    local: "42099-off-roader.jpg"
+    credit: "LEGO"
+layout: set
+description: "Add set description"
+---

sets/technic/42099-off-roader/driving/README.md

@@ -0,0 +1,25 @@
+---
+permalink: /projects/sets/technic/42099-off-roader/driving/
+title: "42099: Technic Off-Roader: Driving"
+maintainer:
+    user: "pybricks"
+    name: "The Pybricks Authors"
+image:
+    local: "../42099-off-roader.jpg"
+    credit: "LEGO"
+description:
+    "This project shows how to make the car drive and steer. You can also
+    remote control it with a keyboard."
+building_instructions:
+    external: https://www.lego.com/cdn/product-assets/product.bi.core.pdf/6314518.pdf
+---
+
+# Basic driving and steering
+
+This program centers the steering motor, and defines a function called
+``drive`` which can be used to control the vehicle. Further details
+are given as comments in the program.
+
+```python
+{% include_relative main.py %}
+```

sets/technic/42099-off-roader/driving/main.py

@@ -0,0 +1,55 @@
+from pybricks.pupdevices import Motor, ColorDistanceSensor
+from pybricks.parameters import Port, Direction, Stop
+from pybricks.tools import wait
+
+# Initialize the motors
+steer = Motor(Port.C)
+front = Motor(Port.A, Direction.COUNTERCLOCKWISE)
+rear = Motor(Port.B, Direction.COUNTERCLOCKWISE)
+
+# Lower the acceleration so the car starts and stops realistically.
+front.control.limits(acceleration=1000)
+rear.control.limits(acceleration=1000)
+
+# Find the steering endpoint on the left and right. The difference between them
+# is the total angle it takes to go from left to right. The middle is in between.
+left_end = steer.run_until_stalled(-200, then=Stop.HOLD)
+right_end = steer.run_until_stalled(200, then=Stop.HOLD)
+
+# We are now at the right limit. We reset the motor angle to the limit value,
+# so that the angle is 0 when the steering mechanism is centered.
+limit = (right_end - left_end)//2
+steer.reset_angle(limit)
+steer.run_target(speed=200, target_angle=0, then=Stop.COAST)
+
+# Given a motor speed (deg/s) and a steering motor angle (deg), this function
+# makes the car move at the desired speed and turn angle. The car keeps moving
+# until you give another drive command.
+def drive(drive_motor_speed, steer_angle):
+    # Start running the drive motors
+    front.run(drive_motor_speed)
+    rear.run(drive_motor_speed)
+    
+    # Limit the steering value for safety, and then start the steer motor.
+    limited_angle = max(-limit, min(steer_angle, limit))
+    steer.run_target(200, limited_angle, wait=False)
+    
+# Drive forward for 5 seconds.
+drive(800, 0)
+wait(5000)
+
+# Drive backward for 5 seconds.
+drive(-800, 0)
+wait(5000)
+
+# Drive forward to the right for 5 seconds.
+drive(800, 90)
+wait(5000)
+
+# Drive backward to the left for 5 seconds.
+drive(-800, -90)
+wait(5000)
+
+# Stop smoothly and center the steer.
+drive(0, 0)
+wait(2000)