Components (BOM)
BOM for REMO Robot
Affiliate links
The Amazon links in the following lists are affiliate links. As an Amazon Associate I earn from qualifying purchases, at no extra cost to you.
The following figure shows a 3D-printed Remo robot together with its components that satisfy the requirements for the ROS Navigation Stack. These parts are introduced next:
Bill of Materials (BOM) for REMO robot:
| Part | Quantity | Cost | Store | Notes |
|---|---|---|---|---|
| Raspberry Pi 4 B (4 GB or 8 GB) | 1 | $55.0 | Sparkfun (4 GB), Amazon.com (8 GB), Amazon.de (8 GB starter set) | 4 GB is enough |
| SanDisk 64 GB SD Card Class 10 | 1 | $13.99 | Amazon.com, Amazon.de | |
| SLAMTEC RPLiDAR A2M12 (12 m) | 1 | $319.00 | Robotshop, Amazon.com, Amazon.de | Other, less expensive, LiDARs will work as well, e.g., RPLiDAR A1 |
| SLAMTEC RPLiDAR A1M8 (12 m) | 1 | $99.00 | Robotshop, Amazon.com, Amazon.de | Cheaper alternative to RPLiDAR A2M8 |
| Adafruit DC Motor (+ Stepper) FeatherWing | 1 | $19.95 | adafruit.com, Amazon.us, Amazon.de | |
| Teensy 4.0 or 3.2 | 1 | $32.29 | Amazon.com, Amazon.de, PJRC Teensy 4.0 | |
| Breadboard (half size, 400 points) | 1 | -- | Holds the Teensy, see assembly step 15 | |
| Hobby Motor with Encoder - Metal Gear (DG01D-E) | 2 | $12.50 | Amazon.com, Amazon.de, Sparkfun, RobotShop | On Amazon.de it's sold by BerryBase |
| Powerbank (e.g 15'000 mAh, or 10'000 mAh) | 1 | $23.99 | Anker 10K Amazon.com, Anker 10K Amazon.de | The Powerbank from Goobay (and Anker) is close to the maximum possible size LxWxH: 135.5 x 71 x 18 mm |
| Battery pack (for four or eight batteries) | 1 | $5.59 | Amazon.com, Amazon.de | |
| USB C to USB C cable | 1 | $6.99 | Amazon.com, Amazon.de | USB C to USB C for Powerbank to SBC |
| Remo Base | 1 | -- | Remo STL files on Gumroad | 3D printed, see 3D printing |
| Caster ball | 1 | $6.30 | Amazon.com, Amazon.de | 25.4 mm (1-inch) diameter; Alternatively any smooth, durable 3/4" ball bearing for the caster |
| Wheels | 2 | $3.50 | Amazon.com, Amazon.de, Sparkfun, exp-tech.de | Wheels are often part of a robotics kit or can be purchased separately |
| Power supply | 1 | $7.50 | Amazon.com, Amazon.de | USB C, 5V, 3.5A |
USB Wi-Fi Dongle (optional)
For improved connectivity use a Wi-Fi USB dongle.
| Part | Quantity | Cost | URL | Notes |
|---|---|---|---|---|
| WiFi Dongle - TP-Link Archer T2U Nano | 1 | $17.99 | Amazon.us, Amazon.de | RTL8811AU chipset |
| WiFi Dongle - TP-Link Archer T3U | 1 | $18.99 | Amazon.us, Amazon.de | RTL8812AU chipset |
| WiFi Dongle - TP-Link Archer T3U Plus | 1 | $19.99 | Amazon.us, Amazon.de | RTL8811AU chipset |
Camera Modules (optional)
The camera modules are currently optional. SLAM, localization and navigation is currently laser based. Get a camera in case you plan to do applications such as object detection, visual graph based SLAM methods, etc.
| Part | Quantity | Cost | Store | Notes |
|---|---|---|---|---|
| Raspi Camera Module V2, 8 MP, 1080p | 1 | $ | Amazon.com, Amazon.de | |
| OAK-1 | 1 | $149 | OpenCV.ai | |
| OAK-D | 1 | $199 | OpenCV.ai | |
| OAK-D Lite | 1 | -- | OpenCV.ai | Will be released |
Assembly Hardware
You need the following parts to build REMO. They come in packs, so order the quantity you need for the number of REMOs you are going to build.
| Part | Qty per REMO | Qty per pack | Cost per REMO | URL | Notes |
|---|---|---|---|---|---|
| Adhesive pads | 2 | 48 | $0.14 | optional | |
| Velcro strap | 2 | 48 | $0.14 | To fix the battery pack and the breadboard | |
| M2 screw (self tapping) | 22 | 100 | $1.42 | Amazon | 8mm long, self tapping; 4 more if you screw the camera into its adapter |
| M2 screw | 8 | 60 | $0.94 | Amazon | 8mm long, for the deck and the Raspberry Pi |
| M3 screw | 4 | 20 | -- | Amazon.de | 25mm long, to fix the motors to the base frame; from a 280-piece M3 set |
| M3 screw | 4 | 20 | -- | Amazon.de | 6mm long, to fix the LiDAR to its platform; same set |
| M3 nut | 4 | 100 | -- | Amazon.de | To fix the motors to the base frame; same set, which has 20 screws of each length (4–25 mm) and 100 nuts |
| M2 Brass threaded inserts | 8 | 100 | $0.48 | Amazon | 4 in the chassis posts, 4 in the deck for the Raspberry Pi |
| Jumper wires | 4 | 40 | $0.13 | Amazon | Female-female, ~20cm |
Optional parts
| Part | Quantity | Cost | Store | Notes |
|---|---|---|---|---|
| Jetson Nano | 1 | $99.00 | NVIDIA | |
| PiOLED display | 1 | $14.95 | Adafruit, Amazon | |
| PiOLED header | 1 | $5.95 | Adafruit, Amazon, Sparkfun | 2x(3+) right angle male |
Components
The following shows a more detailed part list and assembly of the robot platform and the components.
Affiliate links
The Amazon links in the following lists are affiliate links. As an Amazon Associate I earn from qualifying purchases, at no extra cost to you.
| Category | Hardware | Part Number | Data Sheet & Info |
|---|---|---|---|
| Accessories | |||
| Case for Raspberry Pi 4 B | Slim acrylic case for Raspberry Pi 4, stackable, rainbow/transparent | BerryBase | |
| Micro SD Card | SanDisk 64GB Class 10 | Amazon.com, Amazon.de; Raspberry Pi Setup for the image | |
| Robot Car Kit 2WD (plate, caster, two wheels, battery holder and mounting plate) | robot05 | Instructions manual | |
| Power bank | Intenso Powerbank S10000 | Intenso | |
| Actuator | |||
| (Deprecated) Gearbox motor | DC Gearbox motor - "TT Motor" - 200RPM - 3 to 6VDC, without encoder; DiffBot's first version | Adafruit | |
| DG01D-E Motor with encoder | DG01D-E Hobby motor with quadrature encoder, in DiffBot and Remo | Sparkfun | |
| Board | |||
| Raspberry Pi 4 B | Raspberry Pi 4 B - 4 GB | OEM Website | |
| Cables | |||
| Jumper - Female to Female | |||
| Jumper - Male to Male | |||
| Micro USB - USB Cable | |||
| Camera extension cable | |||
| I2C 4 pin cable | |||
| Electronics | |||
| Fan | Fan 30x30x7mm 5V DC with Dupont connector | BerryBase | |
| I2C motor driver | Grove - I2C Motor Driver | Seeed Studio | |
| I2C Hub | Grove - I2C Hub | Seeed Studio | |
| Human Machine Interface | |||
| OLED Display | Grove OLED Display 0.96" | Seeed Studio | |
| LED Ring | NeoPixel Ring 12x5050 RGB LED | Adafruit | |
| Sensors | |||
| Camera module | Raspberry Pi - camera module v2.1 | Raspberry Pi | |
| Ultrasonic ranger | Grove - Ultrasonic Ranger | Seeed Studio | |
| IMU | Adafruit 9-DOF Absolute Orientation IMU Fusion Breakout - BNO055 | Adafruit | |
| Odometry | The quadrature encoders in the DG01D-E motors | Motor and Wheel Encoder | |
| (Deprecated) Speed sensor | Joy-IT - LM393 Speed Sensor with H206 slot-type opto interrupter, for the TT motors without encoder | Joy-IT |
Order list
Affiliate links
The Amazon links in the following lists are affiliate links. As an Amazon Associate I earn from qualifying purchases, at no extra cost to you.
| Part | Store |
|---|---|
| Raspberry Pi 4 B (4 Gb) | Amazon.com, Amazon.de |
| SanDisk 64 GB SD Card Class 10 | Amazon.com, Amazon.de |
| Robot Smart Chassis Kit (plate, caster, two wheels and battery holder) | Amazon.com, Amazon.de |
| DG01D-E Hobby Motor with encoder (2) | Amazon.com, Amazon.de |
| SLAMTEC RPLidar A2M8 (12 m) | Amazon.com, Amazon.de |
| Grove Ultrasonic Ranger | Amazon.com |
| Raspi Camera Module V2, 8 MP, 1080p | Amazon.com, Amazon.de |
| Grove Motor Driver | seeedstudio.com, Amazon.de |
| I2C Hub | seeedstudio.com, Amazon.de |
Additional (Optional) Equipment
| Part | Store |
|---|---|
| PicoScope 3000 Series Oscilloscope 2CH | Amazon.de |
| VOLTCRAFT PPS-16005 | Amazon.de |
Board - Raspberry Pi 4 B
The main processing unit of the robot is a Raspberry Pi 4 B with 4 GB of RAM.
Accessories and Electronics
Case and Cooling
To protect the Raspberry Pi 4 B we choose a case that provides access to all its ports. The following images show a stackable acrylic case in rainbow colors.
With this case it is possible to install four heatsinks and apply a fan as cooling equipment for the electronics of the Raspberry Pi 4 B such as its ARM processor.
SD Card
The Raspberry Pi requires a medium to boot from. For this we will use a micro sd card because it is lightweight and easy to flash new operating systems.
Although a micro sd card won't last that long compared to an hard disk drive (HDD) or solid state disk (SSD) it is well suited for testing. Because sd cards are slower when reading and writing data you should make sure to choose a micro sd card with high performance ratings. For the Raspberry Pi a Class 10 micro sd card is recommended. Regarding speed, the Pi has a limited bus speed of approximately 20 MB/s (source)
Robot Base
For the robot base you have at least two options to choose from: DiffBot, built on the acrylic plate of a robot car kit, or the sturdier, 3D printed Remo.
DiffBot is built on the acrylic plate of the Robot Car Kit 2WD from Joy-IT (article no.: robot05). The kit includes two drive wheels, a caster wheel and a battery holder. The holder sits under the base plate and supplies the motors.
The acrylic plate has many holes for the kit's mounting plate, which holds the development boards, such as the Raspberry Pi 4 B. The two drive wheels and the caster wheel let the robot turn on the spot, but not move sideways: a differential drive robot is nonholonomic (Modeling a Differential Drive Robot).
DiffBot uses the same DG01D-E motors with built-in quadrature encoders as Remo, and the same nominal 65 mm wheel type. Its first version (source code from April 2020) used the kit's motors without encoders and separate optical speed sensors that count the slots of a punched disk on each motor (Alternative Optical Sensor).
Remo is a 3D printable Research Education Mobile/Modular Open robot platform. You can find more information in the following video and
on the remo_description package page.
Alternatively, you can build your own mobile robot!
Power Supplies
DiffBot's Raspberry Pi 4 B runs on a 5 V/2.1 A USB-C power bank.
DiffBot's motor supply uses the battery holder under the chassis.
I2C Hub
The Raspberry Pi provides just two I2C ports, which is why we will use a I2C hub. With the four port I2C hub from Grove it is possible to connect three I2C devices to a single I2C port of the Raspberry Pi
Breadboard and GPIO Extension Cable
Optional but helpful for testing is a breadboard and a GPIO extension cable suitable for the Raspberry Pi 4 B.
Sensors
Sensors are used to sense the environment and to collect information of the current state. For this 2WD robot the sensors are categorized into perception and localization which are explained in the following two sections.
Perception
Perception sensors of the 2WD robot will be used to avoid collisions using ultrasonic rangers. Another use case is to detect and follow objects using a camera.
Ultrasonic Ranger
To avoid obstacles the robot will carry a Grove - Ultrasonic Ranger at the front.
It is a non-contact distance measurement module which works at 40KHz and can be interfaced via a single GPIO. For example physical pin 11 of the Raspberry Pi connected to the SIG pin on the sensor can provide the PWM communication.
| Parameter | Value/Range |
|---|---|
| Operating voltage | 3.2~5.2V |
| Operating current | 8mA |
| Ultrasonic frequency | 40kHz |
| Measuring range | 2-350cm |
| Resolution | 1cm |
| Output | PWM |
| Size | 50mm X 25mm X 16mm |
| Weight | 13g |
| Measurement angle | 15 degree |
| Working temperature | -10~60 degree C |
| Trigger signal | 10uS TTL |
| Echo signal | TTL |
The code that will be used to wrap this sensor as a ROS node can be found in the Grove Raspberry Pi repository on GitHub.
As an alternative we could use the HC SR04.
Camera
Localization
Inertial Measurement Unit
An inertial measurement unit (IMU) measures the acceleration and orientation through gyroscopes directly. Other states such as the velocity can then be calculated. For this the Adafruit 9-DOF Absolute Orientation IMU Fusion Breakout - BNO055 is used.
Odometry
For the used odometry sensor see the section below Motor and Wheel Encoder
Alternative Optical Sensor
To estimate the change in position over time (odometry), DiffBot's first version, with motors without encoders, used an optical speed sensor. Specifically the Joy-IT Speed Sensor which combines a LM393 (datasheet) comperator and a H206 slot-type opto interrupter. The Wheel Encoders (LM393) page describes the optical sensors and their wiring.
Technical Specifications:
- Dimensions: 32 x 14 x 7mm
- Operating voltage: 3.3V to 5V (DiffBot's first version ran it at 3.3V)
- Two outputs: Digital (D0) and Analog (A0)
References: https://dronebotworkshop.com/robot-car-with-speed-sensors/
Actuators
Control
To drive DiffBot's two motors we use the Grove - I2C Motor Driver V1.3 from Seeed Studio. Remo uses a different driver, the Adafruit DC Motor + Stepper FeatherWing (Electronics).
Motor and Wheel Encoder
DiffBot and Remo both use the DG01D-E Hobby Motor. It has a quadrature encoder built in, which makes it easy to assemble the robot and saves space because of no additional (optical or magnetic) wheel encoders.
For more details such as the encoder pulses per revolution see the documentation on Motor and Encoder.
Alternative Brushed Gear Motor
Brushed Gearbox Motor
Human Machine Interface (HMI)
The human machine interface is the layer between the user and the robot.
OLED Display
To update the user with status messages the robot has a 0.96 inch oled (organic light emitting diode) display. The oled display used is the Grove I2C 0.96 inch OLED display from Seeed Studio.
The display is connected to the RPi via I2C on the physical pins 27 (scl) and 28 (sda), refer to the pinout.
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