Tutorial 4.3: Driver Practice¶
Time: ~10 minutes Prerequisites: Tutorial 4.2: Arcade Drive
Why Practice Matters¶
The best robot in the world is useless with an unpracticed driver. Driver skill can be the difference between winning and losing!
Beginner Driver Practiced Driver
~~~~zigzag~~~~> ━━━━━━━━━━━━━━━>
Overshoots turns Hits targets precisely
Bumps into walls Smooth movements
Slow reactions Quick reflexes
Practice Patterns¶
Pattern 1: The Straight Line¶
Goal: Drive in a perfectly straight line
START END
●━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━●
Set up two markers and drive between them
without veering left or right.
Tips: - Look ahead, not at your robot - Small corrections, not jerky movements - Use tank drive for best straight-line control
Pattern 2: The Square¶
Goal: Drive in a perfect square
●━━━━━━━━━━●
│ │
│ │
│ │
●━━━━━━━━━━●
Drive forward, turn 90°, repeat 4 times.
End exactly where you started!
Challenge: Can you make the square with no gaps or overlaps?
Practice Pattern Specifications¶
Here are the exact dimensions to set up each pattern:
PATTERN 1 - THE STRAIGHT LINE:
●━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━●
START END
Distance: 6 feet (1.8 meters)
Goal: End within 3 inches of the centerline
Setup: Use tape or cones to mark start and end
────────────────────────────────────────
PATTERN 2 - THE SQUARE:
●━━━━━━━━━━●
│ │ Side length: 3 feet (90 cm)
│ │ Total distance: 12 feet
│ │ Goal: End within 6 inches of start
●━━━━━━━━━━●
Setup: Mark 4 corners with tape or small objects
────────────────────────────────────────
PATTERN 3 - THE SLALOM:
● ● ●
╱ ╲ ╱ ╲ ╱ ╲
━━●━━━━━●━━━━━●━━━━━●━━━━━●━━━━━●━━>
╲ ╱ ╲ ╱
● ●
Cone spacing: 2 feet (60 cm) apart
Lane width: 2 feet (60 cm) total
Number of cones: 5-7
Goal: Don't touch any cones!
────────────────────────────────────────
PATTERN 4 - THE FIGURE-8:
╭───╮
╱ ╲ Circle radius: 18 inches (45 cm)
│ │ Total distance: ~9 feet
╲ ╱ Goal: Smooth curves, no jerky turns
╳───╳ Setup: Mark center crossover point
╱ ╲
│ │
╲ ╱
╰───╯
Pattern 3: The Figure-8¶
Goal: Continuous smooth curves
Tips: - Arcade drive works well here - Keep constant speed - Smooth joystick movements
Pattern 4: The Slalom¶
Goal: Weave between obstacles
Tips: - Plan your path ahead - Look at the NEXT obstacle, not the current one - Smooth steering inputs
Fine Control with curve_input()¶
For precise driving, we can apply a curve to joystick input:
def curve_input(value, exponent=2.0):
"""Apply exponential curve for finer control at low speeds."""
sign = 1 if value >= 0 else -1
normalized = abs(value) / 100.0
curved = (normalized ** exponent) * 100.0
return sign * curved
How It Helps¶
LINEAR INPUT CURVED INPUT (exponent=2)
Joystick Motor Joystick Motor
25% → 25% 25% → 6.25% ← More precision!
50% → 50% 50% → 25%
75% → 75% 75% → 56.25%
100% → 100% 100% → 100%
The middle range is Small movements
equally sensitive are much finer
Understanding curve_input() Math (Complete Breakdown)¶
The formula might look intimidating, but let's break it down step by step:
def curve_input(value, exponent=2.0):
sign = 1 if value >= 0 else -1 # Step 1: Remember direction
normalized = abs(value) / 100.0 # Step 2: Convert to 0-1 scale
curved = (normalized ** exponent) * 100.0 # Step 3: Apply curve
return sign * curved # Step 4: Restore direction
COMPLETE TRACE: curve_input(50, exponent=2)
flowchart TD
A["INPUT: value = 50, exponent = 2"] --> B["STEP 1: GET THE SIGN"]
B --> C{"Is 50 >= 0?"}
C -->|YES| D["sign = 1 (positive, forward)"]
D --> E["STEP 2: NORMALIZE"]
E --> F["abs(50) = 50"]
F --> G["normalized = 50 / 100.0 = 0.5"]
G --> H["STEP 3: APPLY THE CURVE"]
H --> I["curved = (0.5 ** 2) * 100.0"]
I --> J["= 0.5 × 0.5 × 100.0 = 25.0"]
J --> K["STEP 4: RESTORE THE SIGN"]
K --> L["result = sign × curved = 1 × 25.0 = 25.0"]
L --> M["FINAL: 50 → 25 (50% input becomes 25% motor speed)"]Why each step matters: - Step 1: Remember if joystick was pushed forward (+) or backward (-) before using absolute value - Step 2: Convert joystick range (-100 to +100) to 0-1 scale for easy math - Step 3: Squaring a number less than 1 makes it SMALLER (0.5 × 0.5 = 0.25) - this gives more precision at low speeds - Step 4: Restore the original direction (positive or negative)
COMPLETE TRACE: curve_input(-40, exponent=2)
INPUT: value = -40, exponent = 2
STEP 1: GET THE SIGN
Is -40 >= 0? NO!
sign = -1 (negative, meaning "backward")
STEP 2: NORMALIZE
abs(-40) = 40
normalized = 40 / 100.0 = 0.4
STEP 3: APPLY THE CURVE
curved = (0.4 ** 2) * 100.0
= (0.4 × 0.4) * 100.0
= 0.16 * 100.0
= 16.0
STEP 4: RESTORE THE SIGN
result = -1 * 16.0
= -16.0
FINAL ANSWER: -40 → -16
(40% backward becomes 16% backward)
WHY PRESERVING SIGN MATTERS
WITHOUT preserving sign:
(-40)^2 = 1600 ← WRONG! (positive and way too big)
WITH preserving sign:
abs(-40) = 40
(0.4)^2 = 0.16
0.16 × 100 = 16
-1 × 16 = -16 ← CORRECT! (negative and right size)
Visual Comparison: Linear vs Curved¶
WITHOUT CURVE (exponent = 1):
Output
100% │ ●
│ ●
│ ●
│ ●
│ ●
0 └────●────────────────────── Input
0 25 50 75 100%
Everything is proportional: 50% → 50%
WITH CURVE (exponent = 2):
Output
100% │ ●
│ ●
│ ●
│ ●
│ ●
0 └────●────────────────────── Input
0 25 50 75 100%
↓ ↓ ↓
6% 25% 56%
Low inputs are "squished" down for finer control!
Adding Curve to Drive Code¶
def driver_control_with_curve():
while True:
left_speed = controller.axis3.position()
right_speed = controller.axis2.position()
# Apply deadband
left_speed = deadband(left_speed)
right_speed = deadband(right_speed)
# Apply curve for finer control
left_speed = curve_input(left_speed, exponent=2.0)
right_speed = curve_input(right_speed, exponent=2.0)
left_motors.spin(FORWARD, left_speed, PERCENT)
right_motors.spin(FORWARD, right_speed, PERCENT)
wait(20, MSEC)
Competition Driving Tips¶
Before the Match¶
- Check controller battery - Dead controller = dead robot
- Test all buttons - Make sure everything works
- Warm up your hands - Cold fingers are slow fingers
- Watch your opponents - Know their robot's capabilities
During Driver Control¶
- Know your field - Where are the goals? Where are the blocks?
- Communicate - Your partner is your teammate!
- Don't panic - Smooth is fast, jerky is slow
- Watch the clock - Know when to rush, when to be careful
Push Back Specific Tips¶
SCORING PRIORITY:
1. Blocks in goals (3 pts each)
2. Zone control (6-10 pts)
3. PARKING (8 or 30 pts!) ← Don't forget!
In the last 10 seconds:
- Stop scoring blocks
- Get to the parking zone!
- Two robots parked = 30 points!
Push Back Driving Scenarios¶
Let's walk through specific situations you'll face in competition:
SCENARIO 1: Approaching a Goal to Score
You're 3 feet from the goal with a block.
WRONG APPROACH:
┌─────────────────────────────────────────────┐
│ Full speed ahead → overshoot! │
│ Block falls out of robot or misses goal │
└─────────────────────────────────────────────┘
RIGHT APPROACH (with curve_input):
┌─────────────────────────────────────────────┐
│ 1. Start at 50% stick → 25% motor speed │
│ (smooth acceleration) │
│ │
│ 2. Slow to 25% stick → 6% motor speed │
│ (precision placement) │
│ │
│ 3. Gently push block into goal │
│ │
│ 4. Back away slowly │
└─────────────────────────────────────────────┘
The curve gives you fine control when it matters most!
SCENARIO 2: Defending Your Zone
Opponent is trying to descore your blocks.
TANK DRIVE ADVANTAGE:
┌─────────────────────────────────────────────┐
│ Pivot turns are FAST with tank drive! │
│ │
│ Left stick UP + Right stick DOWN: │
│ │
│ ↻ │
│ ╱ ╲ │
│ │ ● │ ← You spin to block opponent │
│ ╲ ╱ │
│ ↺ │
│ │
│ You can react to their movement instantly! │
└─────────────────────────────────────────────┘
This is why many teams use tank for defense.
SCENARIO 3: Parking with 10 Seconds Left
The clock shows 0:10 remaining!
PRIORITY ORDER:
┌─────────────────────────────────────────────┐
│ 1. COMMUNICATE: Yell "PARKING NOW!" to │
│ your partner │
│ │
│ 2. ABANDON current task - don't finish │
│ that block you were scoring │
│ │
│ 3. DRIVE DIRECTLY to park zone │
│ (shortest path, ignore everything) │
│ │
│ 4. FIT BOTH ROBOTS: │
│ │
│ ┌───────────────┐ │
│ │ ┌───┐ ┌───┐ │ ← Park zone │
│ │ │ R1│ │ R2│ │ (18" × 16") │
│ │ └───┘ └───┘ │ │
│ └───────────────┘ │
│ │
│ 5. STOP MOVING before buzzer! │
│ (movement at buzzer = NOT parked) │
└─────────────────────────────────────────────┘
POINTS COMPARISON:
- 0 robots parked: 0 points
- 1 robot parked: 8 points
- 2 robots parked: 30 points (!!)
The 30-point bonus is HUGE - it can win matches!
SCENARIO 4: Recovering from a Tip
Your robot has tipped onto its side!
DON'T PANIC:
┌─────────────────────────────────────────────┐
│ 1. Check if your wheels can touch ground │
│ │
│ 2. If wheels touch: Try driving to │
│ flip yourself back over │
│ │
│ 3. If wheels don't touch: Signal partner │
│ for help (they can push you back up) │
│ │
│ 4. If you're stuck: Focus on PARKING │
│ at match end - even a tipped robot │
│ in the zone counts! │
└─────────────────────────────────────────────┘
Controller Button Layout¶
Plan your button assignments:
SUGGESTED LAYOUT:
[L1] = Intake In [R1] = Turbo Mode
[L2] = Intake Out [R2] = Slow Mode
+------+ +------+
| LEFT | | RIGHT|
| STICK| [A] Unused | STICK|
| Drive| [B] Unused | (Tank)|
+------+ [X] Reverse +------+
[Y] Toggle Mode
Document your layout in a comment:
# BUTTON ASSIGNMENTS:
# L1 = Intake forward
# L2 = Intake reverse
# R1 = Turbo mode (1.5x speed)
# R2 = Slow mode (0.5x speed)
# X = Reverse direction
Exercise: Tune Your Drive Feel¶
Goal: Experiment with curve exponent to find your preference
Step 1: Add curve_input() to your driver control:
left_speed = curve_input(left_speed, exponent=2.0)
right_speed = curve_input(right_speed, exponent=2.0)
Step 2: Try different exponent values:
- 1.0 = Linear (no curve)
- 2.0 = Squared (default, good for most)
- 3.0 = Cubed (very fine control at low speed)
- 1.5 = Mild curve
Step 3: Test with the slalom pattern
Question: What exponent gives you the best control?
Timed Challenges¶
Set up these challenges and time yourself:
Challenge 1: Speed Run¶
- Set up two cones 3 meters apart
- Drive from one to the other and back
- Best time wins!
Challenge 2: Precision Park¶
- Set up a small box (slightly larger than your robot)
- Park inside the box as fast as possible
- Touching the walls = 5 second penalty
Challenge 3: Block Push¶
- Place a block on the field
- Push it into a goal
- Don't let it fall out!
Ready to test your knowledge? Check out the Drive Control Q&A Review!