Fig. 13 · Robotics Lab · ROS 2 brain

Raspberry Pi 5

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Bench

No reading yet

Supply (5 V rail)

No reading yet

Current draw

0 mA

Build and break

1BuildNext up
Strip it to the bare PCB
Unplug the supply, then take every part off. The Pi 5 is built like any modern board: surface-mount parts first, then the through-hole connectors from low to tall, and the microSD card and the Active Cooler last.
2
Pick and place the SMD parts, then reflow
3
Place the low through-hole parts
4
Place the tall connectors
5
Solder the through-hole joints
6
Push in the microSD card
7
Fit the Active Cooler
8
Plug in the 27 W USB-C supply
9
Run the ROS 2 drive node
10
Check power and heat
11
Break it: power it from a 5 V 2 A phone chargerBreak it
12
Break it: run it without the Active CoolerBreak it
13
Break it: a cold joint on the fan headerBreak it
14
Break it: drive motors on the Pi's 5 VBreak it
15
Break it: the robot's 5 V wired backwardsBreak it
16
Break it: 12 V into the 5 V pinsBreak it
17
Exploded view

Break it on purpose

Each fault is one that catches real builders. Trigger it, read the symptom on the bench, then fix it.

Under-voltage from a phone charger
wrong voltage
Why it happens
Symptom: The supply reads 4.6 V, the clock drops to 1.5 GHz, get_throttled shows 0x50005 and the kernel logs 'Undervoltage detected!'.
The Pi 5 flags under-voltage below 4.63 V (±5 %). A 5 V 2 A phone charger and a thin cable sag under the Pi's load, so the firmware caps the clock. Weak supplies also cause random reboots, corrupted SD cards and USB devices dropping out.
Fix: Use the official 5 V 5 A (27 W) USB-C supply.
No Active Cooler
overheating
Why it happens
Symptom: The CPU temperature climbs past 80 °C, the clock falls from 2.4 GHz toward 1.5 GHz, get_throttled shows 0x40004 and the drive node warns about the heat.
The firmware throttles the Arm cores step by step from 80 °C, and the GPU too at 85 °C. Under ROS 2 load a bare BCM2712 gets there quickly, and 1.5 GHz is only 62.5 % of full speed.
Fix: Unplug, refit the Active Cooler and plug its cable into the fan connector.
Cold joint on the fan connector
cold solder joint
Why it happens
Symptom: The fan stops and starts, its duty jumps between 0 and the curve's value, and the CPU runs hotter.
A cold joint is a dull, grainy blob that never wetted the pad, so it makes contact only some of the time. The fan's supply or PWM pin drops out with every vibration.
Fix: Reflow the joint: heat the pad and the pin together, add a little fresh solder and let it set into a shiny, concave fillet.
Brown-out: motors on the Pi's 5 V rail
brown-out
Why it happens
Symptom: The supply dips, the LED goes out and comes back, and the terminal repeats the boot log: the Pi resets every time the motors start.
A TT gear motor draws 1.2-1.5 A when it starts or stalls. Two of them plus the Pi's 0.8 A is more than the robot's 3 A buck can give, so 5 V collapses and the board resets.
Fix: Drive the motors from the battery through a motor driver controlled by the ESP32, and give the Pi its own 5 V 5 A supply.
Reverse polarity on the GPIO 5 V pins
reverse polarity
Why it happens
Symptom: Nothing boots, the supply goes into current limit and the PMIC gets hot.
USB-C is keyed and cannot be plugged in backwards, but the 5 V header pins go straight to the 5 V input rail with no protection. Reversed, current flows the wrong way through the PMIC and burns it.
Fix: Swap the leads: 5 V to pin 2 or 4, ground to pin 6. Better still, power the Pi through USB-C.
12 V into the 5 V pins
wrong voltage
Why it happens
Symptom: The PMIC burns out at once and the board stays dead.
The 5 V pins bypass every regulator: whatever you feed them reaches the PMIC input directly. A 3S battery (11.1-12.6 V) is more than twice what the PMIC is built for.
Fix: Feed the 5 V pins only from a regulated 5 V supply, such as a buck converter set to 5.1 V, or use USB-C.
No microSD card
missing part
Why it happens
Symptom: The LED stays red: the board has power, but no boot log appears.
The Pi 5 has no operating system of its own. The bootloader in its SPI flash looks for one on the card (then USB and the network, if you set the boot order) and finds nothing to load.
Fix: Unplug, push in a card written with Raspberry Pi Imager, and power up again.
PMIC left off
missing part
Why it happens
Symptom: No light at all: nothing on the board powers up.
The DA9091 makes every rail from the 5 V input. Without it no chip gets power.
Fix: Put U4 back and reflow it.
BCM2712 left off
missing part
Why it happens
Symptom: The LED stays red: the rails come up, but no boot log and no green light.
The BCM2712 is the computer: the four Arm cores, the GPU and the memory controller. The rails come up but nothing runs the bootloader.
Fix: Put U1 back and reflow it.
RAM left off
missing part
Why it happens
Symptom: The LED flashes eight short green flashes, over and over, and the boot stops.
The bootloader cannot find any SDRAM and shows the documented flash code 0L8S: zero long and eight short flashes, 'SDRAM failure'.
Fix: Put U2 back and reflow it.
RP1 left off
missing part
Why it happens
Symptom: The LED flashes four long and three short, and there is no USB, no Ethernet and no GPIO.
Every port on the Pi 5 comes from the RP1. The firmware cannot find it and shows the documented flash code 4L3S, 'RP1 not found'.
Fix: Put U3 back and reflow it.

Meet the bench

Build it, card and cooler last, then power it from a real 5 A supply

The Raspberry Pi 5 is the robot's brain, not its spinal cord: a 2.4 GHz quad-core Linux computer that runs ROS 2, SLAM Toolbox, Nav2 and the camera pipeline. Linux is not real-time, so the motor and balance loops live on an ESP32 or Nano that talks to the Pi over USB serial, the same split as Waveshare's UGV Rover. Build it up from the bare board, give it its microSD card and the Active Cooler, feed it a real 5 V 5 A supply and watch the terminal. Heat moves about ten times faster here than on a real board, so you see in seconds what takes minutes on the bench.

Sources

On the bench

Selected

Instant: switches at once, no upload

Code: Boot and check

# boot_check.py: run it after the first boot to see that the Pi is healthy
# on a fresh SD card, update first:
#   sudo apt update && sudo apt full-upgrade
from pathlib import Path
import subprocess


def vcgencmd(*args):
    out = subprocess.run(['vcgencmd', *args], capture_output=True, text=True, check=True)
    return out.stdout.strip()


model = Path('/proc/device-tree/model').read_text().rstrip('\x00')
print(model)                             # Raspberry Pi 5 Model B Rev 1.0
print(vcgencmd('get_throttled'))         # throttled=0x0: the supply has never sagged
print(vcgencmd('measure_temp'))          # CPU temperature
print(vcgencmd('measure_clock', 'arm'))  # Arm clock: 2400000000 Hz at full speed

Practice tasks

0/3 tasks

Write the code, then run the checks. The run uses a virtual clock and a scripted world, so the same code always gives the same result.

Publish /cmd_vel at 10 Hz with a timer

Python

The starter drives the robot from a while loop with time.sleep(0.1). That blocks the node, so rclpy can never run its callbacks, and the period drifts by however long each publish takes. Rewrite it the ROS 2 way: a 0.1 s timer that publishes the Twist (0.2 m/s forward, 0.5 rad/s turn) and logs what it sent, then rclpy.spin().

Checks

Not run yetUses a 0.1 s timer and rclpy.spin, with no sleep loop
Not run yetPublishes 0.20 m/s and 0.50 rad/s ten times a second
Not run yetRuns for 2 seconds without an error

Hints

self.create_timer(0.1, self.tick) calls tick every 0.1 s once the node spins.
Log each message with self.get_logger().info(f'linear.x={msg.linear.x:.2f} angular.z={msg.angular.z:.2f}').
Replace Drive().run() with node = Drive() and rclpy.spin(node).

Code for Publish /cmd_vel at 10 Hz with a timer

Turn /cmd_vel into wheel speeds

Python

The ESP32 drives two wheels, so the Pi splits every Twist into a left and a right wheel speed: left = v − ω·b/2 and right = v + ω·b/2, where b is the distance between the wheels. Finish the base node: declare a wheel_base parameter (0.16 m), subscribe to cmd_vel and log both speeds.

Checks

Not run yetDeclares wheel_base and subscribes to cmd_vel
Not run yetLogs left=0.16 right=0.24 m/s for every message

Hints

self.declare_parameter('wheel_base', 0.16), then read it with self.get_parameter('wheel_base').value.
self.create_subscription(Twist, 'cmd_vel', self.on_cmd, 10) calls on_cmd for every message.
With v = 0.2 m/s, ω = 0.5 rad/s and b = 0.16 m you get left = 0.16 m/s and right = 0.24 m/s. Log f'left={left:.2f} right={right:.2f} m/s'.

Code for Turn /cmd_vel into wheel speeds

Three nodes: sensor, filter, safety stop

Python

A multi-node system with no robot. The sensor node publishes a range that closes in on a wall (2.0 m, 1.9 m, 1.8 m … at 10 Hz). Write a filter node that averages the last window readings (a parameter, 4) and publishes range_avg, and a safety node that publishes a zero Twist on cmd_vel and warns once when the average drops below stop_m (a parameter, 0.5 m). On a real Pi, take it further: your own .msg and .srv types, a Python launch file with arguments, then ros2 bag record and replay.

Checks

Not run yetDeclares window and stop_m and subscribes to range
Not run yetThe filter logs an average for every reading
Not run yetThe safety node stops at 0.45 m within 2 seconds

Hints

Filter: keep a list, append each reading, pop(0) when it grows longer than the window, and publish sum / len.
Safety: remember that you have stopped, so the warning prints only once.
With a window of 4 the average first drops below 0.5 m at 0.45 m: log f'obstacle at {msg.data:.2f} m: stop'.
On a Pi: ros2 pkg create --build-type ament_python my_robot, a launch file with DeclareLaunchArgument, then ros2 bag record -a and ros2 bag play.

Code for Three nodes: sensor, filter, safety stop

# Task: average the range in a filter node and stop the robot in a safety node
import rclpy
from rclpy.node import Node
from rclpy.executors import SingleThreadedExecutor
from std_msgs.msg import Float32
from geometry_msgs.msg import Twist

class Sensor(Node):
    def __init__(self):
        super().__init__('sensor')
        self.pub = self.create_publisher(Float32, 'range', 10)
        self.k = 0
        self.create_timer(0.1, self.tick)

def tick(self):
        # the robot rolls toward a wall at 1 m/s: 0.1 m closer every 0.1 s
        msg = Float32()
        msg.data = max(0.2, 2.0 - 0.1 * self.k)
        self.k += 1
        self.pub.publish(msg)

class Filter(Node):
    def __init__(self):
        super().__init__('filter')
        # declare 'window', publish the moving average on range_avg and log it

class Safety(Node):
    def __init__(self):
        super().__init__('safety')
        # declare 'stop_m', subscribe to range_avg and publish Twist() once it is below

rclpy.init()
executor = SingleThreadedExecutor()
for node in (Sensor(), Filter(), Safety()):
    executor.add_node(node)
executor.spin()

Build and break

1BuildNext up

Strip it to the bare PCB

Unplug the supply, then take every part off. The Pi 5 is built like any modern board: surface-mount parts first, then the through-hole connectors from low to tall, and the microSD card and the Active Cooler last.

Pick and place the SMD parts, then reflow

Place the low through-hole parts

Place the tall connectors

Solder the through-hole joints

Push in the microSD card

Fit the Active Cooler

Plug in the 27 W USB-C supply

Run the ROS 2 drive node

Check power and heat

Break it: power it from a 5 V 2 A phone chargerBreak it

Break it: run it without the Active CoolerBreak it

Break it: a cold joint on the fan headerBreak it

Break it: drive motors on the Pi's 5 VBreak it

Break it: the robot's 5 V wired backwardsBreak it

Break it: 12 V into the 5 V pinsBreak it

Exploded view

On the bench

Selected

Instant: switches at once, no upload

Code: Boot and check

# boot_check.py: run it after the first boot to see that the Pi is healthy
# on a fresh SD card, update first:
#   sudo apt update && sudo apt full-upgrade
from pathlib import Path
import subprocess


def vcgencmd(*args):
    out = subprocess.run(['vcgencmd', *args], capture_output=True, text=True, check=True)
    return out.stdout.strip()


model = Path('/proc/device-tree/model').read_text().rstrip('\x00')
print(model)                             # Raspberry Pi 5 Model B Rev 1.0
print(vcgencmd('get_throttled'))         # throttled=0x0: the supply has never sagged
print(vcgencmd('measure_temp'))          # CPU temperature
print(vcgencmd('measure_clock', 'arm'))  # Arm clock: 2400000000 Hz at full speed

Three nodes: sensor, filter, safety stop

Python

Checks

Not run yetDeclares window and stop_m and subscribes to range
Not run yetThe filter logs an average for every reading
Not run yetThe safety node stops at 0.45 m within 2 seconds

Hints

Filter: keep a list, append each reading, pop(0) when it grows longer than the window, and publish sum / len.
Safety: remember that you have stopped, so the warning prints only once.
With a window of 4 the average first drops below 0.5 m at 0.45 m: log f'obstacle at {msg.data:.2f} m: stop'.
On a Pi: ros2 pkg create --build-type ament_python my_robot, a launch file with DeclareLaunchArgument, then ros2 bag record -a and ros2 bag play.

Code for Three nodes: sensor, filter, safety stop

class Filter(Node):
    def __init__(self):
        super().__init__('filter')
        # declare 'window', publish the moving average on range_avg and log it

class Safety(Node):
    def __init__(self):
        super().__init__('safety')
        # declare 'stop_m', subscribe to range_avg and publish Twist() once it is below

rclpy.init()
executor = SingleThreadedExecutor()
for node in (Sensor(), Filter(), Safety()):
    executor.add_node(node)
executor.spin()

Raspberry Pi 5

The bench

Build and break

Strip it to the bare PCB

Pick and place the SMD parts, then reflow

Place the low through-hole parts

Place the tall connectors

Solder the through-hole joints

Push in the microSD card

Fit the Active Cooler

Plug in the 27 W USB-C supply

Run the ROS 2 drive node

Check power and heat

Break it: power it from a 5 V 2 A phone chargerBreak it

Break it: run it without the Active CoolerBreak it

Break it: a cold joint on the fan headerBreak it

Break it: drive motors on the Pi's 5 VBreak it

Break it: the robot's 5 V wired backwardsBreak it

Break it: 12 V into the 5 V pinsBreak it

Exploded view

Break it on purpose

Under-voltage from a phone charger

No Active Cooler

Cold joint on the fan connector

Brown-out: motors on the Pi's 5 V rail

Reverse polarity on the GPIO 5 V pins

12 V into the 5 V pins

No microSD card

PMIC left off

BCM2712 left off

RAM left off

RP1 left off

Live status

Current draw

Check yourself

After: Pick and place the SMD parts, then reflow

After: Solder the through-hole joints

After: Plug in the 27 W USB-C supply

After: Run the ROS 2 drive node

After: Break it: power it from a 5 V 2 A phone charger

After: Break it: run it without the Active Cooler

End of bench quiz

Meet the bench

Sources

On the bench

Practice tasks

Publish /cmd_vel at 10 Hz with a timer

Checks

Turn /cmd_vel into wheel speeds

Checks

Three nodes: sensor, filter, safety stop

Checks

Raspberry Pi 5

The bench

Build and break

Strip it to the bare PCB

Pick and place the SMD parts, then reflow

Place the low through-hole parts

Place the tall connectors

Solder the through-hole joints

Push in the microSD card

Fit the Active Cooler

Plug in the 27 W USB-C supply

Run the ROS 2 drive node

Check power and heat

Break it: power it from a 5 V 2 A phone chargerBreak it

Break it: run it without the Active CoolerBreak it

Break it: a cold joint on the fan headerBreak it

Break it: drive motors on the Pi's 5 VBreak it

Break it: the robot's 5 V wired backwardsBreak it

Break it: 12 V into the 5 V pinsBreak it

Exploded view

Break it on purpose

Under-voltage from a phone charger

No Active Cooler

Cold joint on the fan connector

Brown-out: motors on the Pi's 5 V rail

Reverse polarity on the GPIO 5 V pins

12 V into the 5 V pins

No microSD card