Meander Bot

The goal of this project is to create a modified jetbot that can patrol or meander around my house.

Robot Hardware:

• jetson nano
• adafruit featherwing motorcontroller
• DG10D-E-PH motor with encoder
• Slamtex RPLidar A1 lidar
• Luxonis OAK-D stereo AI camera
• MPU6050 imu

CAD of Meandor Bot

Early version of Bot

First assembled version of bot with video server

Setup

Jetson Setup

note: that I don't remeber but you need to configure the I2C pins (maybe some other pin thing) on the jetson, there is some config thing here may be helpful

we will also need to set the correct permissions so our user can access GPIO. Follow instruction from Jetson GPIO to set the correct user permissions. I ran into issues where I would have to reset the rules/permissions every time the Jetson rebooted and found a fix here.

I2C

to check if a device is connected via I2C use:
i2cdetect -y -r 1 to see I2C bus 1 (pin 3 SDA and 5 SCL)
i2cdetect -y -r 0 to see I2C bus 0 (pin 27 SDA and 28 SCL)

oddly enough the i2c bussses are mislabled when using busio:

• to used bus0: i2c = busio.I2C(board.SCL_1, board.SDA_1)
• to used bus1: i2c = busio.I2C(board.SCL, board.SDA)

Setting Jetson power setting

sudo nvpmodel -q to see current power setting
sudo nvpmodel -m0 for maxn power setting (10W)
sudo nvpmodel -m1 for 5W power setting (recommended when not using barrel connector)

installing ROS melodic on Jetson

here

Info

Motor drivers info

// feather motor driving wiring

• 5v-12v input power
• 3.3v logic power (across from input power)
• communication
• output on long ends of controller

Wiring photo of the Feather motor driver

The brown and white cable in the lower left of the driver are the I2C connectors with the brown wire connecting to 3 and the white to 5. The red and black cable near the top of the feather are the logic 3.3V power. This is connected to the Jetson's 3.3V and ground. The red and black cable near the bottom of the feather is the VIN or power to the motors. In this case it is plugged into the Jetson's 5V and ground but this is not super safe for the Jetson to power motors off of its pins so instead I now plug it into an external battery (still experimenting with the voltage but it can handle up to 13V).

IMU info

blog that has some basic info on getting the sensor working.

I've decided to use the MPU6050 ROS package from Brazilian-Institute-of-Robotics (BIR) you can find the instructions on setting up their project and nodes there.

Wiring / Sensor setup

I am currently using the MPU6050 IMU. If you are looking to get an IMU I would recommend getting a more new sensor like the BNO085 has show better accuracy and has a large community base. I am using the 6050 since it is what I had around.

We will wire the 6050 directly to the Jetson nano. We connect the IMUs VCC to 3.3V and the ground to ground on the Jetson. I also connected the SDA/SCL to the Jetson's second I2C pins on pin 27 (SDA) and 28 (SCL). The 6050 also uses address 68 on i2c.

In the BIR ROS package we need to switch the mpu_settings.yaml to reflect that we are using the right I2C on the Jetson so switch to bus_uri: "/dev/i2c-0" if using pin 27/28 or leave it at bus_uri: "/dev/i2c-1" if using 3/5.

Lidar info

The Lidar uses a separate ROS package that can be found here: driver code repo (note that it is not contained in this repo).

Download/clone the ROS package into the src folder of you ROS workspace.

Before using may need to run sudo chmod 777 /dev/ttyUSB0 to allow for the lidar to communicate with the jetson.

Run rplidar node and view in the rviz:

roslaunch rplidar_ros rplidar.launch (for RPLIDAR A1/A2)

If we don't want to use rviz then we can run rplidar node and view using test application:

roslaunch rplidar_ros view_rplidar.launch (for RPLIDAR A1/A2)

then run to see the lidar output in the terminal:

rosrun rplidar_ros rplidarNodeClient

ROS

catkin build to build/compile code. You made need to install sudo apt install python3-catkin-tools to use it.

Some info about ROS can be found in MRover's wiki

Running ROS code

Before running code we need to source devel/setup.bash

to check running nodes: rosnode list

Teleop Robot

To run the robot in a teleop mode (using keyboard control):

roslaunch meanderbot teleop.launch

Video Streaming

We are currently using MJPEG ROS package to stream camera footage from the bot. You can install the package here web_video_server.

1. roslaunch usb_cam usb_cam-test.launch to start the camera node. Note that it will try to open a display window and will fail because there is no display attached to the jetson (but the camera node will still work).
2. rosrun web_video_server web_video_server to start the web server that will host the video. We can then connect to the server as long as we are on the same network and by going to (host-name).local:8080 so in my case john-jetson.local:8080

Running Individual scripts/nodes

make sure you start the main ros node before running other nodes:
roscore

running motorcontroller node:
rosrun meanderbot motor_controller.py

TODO

• begin CAD work on chassis
• IMU node
  • mostly working as of now but need to make sure TF tree is setup correctly
• lidar node
  • check if it works in rviz (drivers seems work so far)
• encoder hardware / code
• power concerns (how tf we gonna power everything)

Alternative Hardware

• Larger Motors with encoder