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ros melodic raspberry Pi 02W bittle robot, serial communication.

Hello, I am stuck with a problem with ros serial communication from a raspberry Pi zero running Raspbian Buster server image and ROS Melodic following instructions from https://www.hackster.io/dmitrywat/bittle-teleoperation-with-ros-and-raspberry-pi-22c454 By Dmitry Maslov

As far as I can tell the master Ubuntu 20.04 and slave on the raspberry Pi zero are working correctly, I have used the appropriate permissions

sudo usermod -a -G dialout,tty pi

sudo usermod -aG tty pi, and enabled serial trough raspi-config.running master and slave gives me velocity messages in terminal when I steer using rqt_robot_steering and I get a video feed from the USB cam. When a command is sent from the rqt_robot_steering GUI, I get a beep but the robot doesn’t move.

This is not a hardware problem. I used the steps from the Petoi ros page https://docs.petoi.com/apis/rosboth nodes ran perfectlyrosrun opencat_server opencat_service_nodesending command below was executed perfectly.rosrun opencat_examples opencat_examples_client_cpp

Can anyone help with the issue?Thanks!

16 comments

Comments (16)

Reid Graves

Feb 20

Best Answer

I also had issues getting the serial communication to work on ROS melodic following that article. A good place to check in his repository is his bittle_driver.py script. I had to change the baud rate to 115200 to get it to work. I have also detailed instructions on raspberry pi setup here: https://github.com/gravesreid/autonomous-bittle.git I created these instructions after many hours of trial and error to get serial communication working from the Pi to Bittle. I have tested that they work on raspberry pi zero, zero 2w, pi 4, and pi 5. A key issue that I've noticed recently is that port ttys0 does not always work, I suspect this is due to an update to the raspberry pi setup. To work around this, I disabled bluetooth and modified the scripts to use port ttyAMA0. Details for this are also in the instructions. As far as ROS goes, I have recently made a ROS2 package that has the same functionality as the tutorial you linked, with the addition of control through a generic USB controller, such as this one: https://vilros.com/collections/retro-gaming/products/vilros-snes-classic-weighted-usb-gamepad-set As well as video streaming through a USB camera or Raspberry pi camera. The repository is here: https://github.com/gravesreid/bittle_ros2.git If you want to use the usb controller functionality, you'll also need the messages package I made for it: https://github.com/gravesreid/bittle_msgs.git I'm actively working with and updating this package.

Jason

Mar 04

Replying to

I'm curious to ask: What's the frame rate like? Approximately how many frames per second?

Reid Graves

Mar 04

Replying to

I've had quite the battle with frame rate. Playing with compression and image size, I've been able to get mid 20 frames per second on the Pi zero, and low 30s with the Pi 4. I do about 50-60% compression with the 4, with 640x480, and 75% compression with 320x240 on the Pi zero. Typically it will start off with low latency, but increase and the average frame rate won't change drastically, but the maximum time for image transmission increases substantially, sometimes up to 30s. For the Pi zero the latency increases within a minute or so, while the pi 4 will stream well for about 5 minutes straight.

Jason

Mar 05

Replying to

Could you share your solutions in a new post? Thanks a lot!

Alex Fernandes

Feb 23

I want to share my rig. I used 2 brass standoff's to mount an acrylic sheet from a Pi 0 case. The USB camera is stuck to the acrylic sheet with double sided tape. Bittle can retain his head.😊

Reid Graves

Feb 23

Replying to

How is the video streaming latency with this setup? Is that a Pi Zero 2w or Zero?

Alex Fernandes

Feb 24

Replying to

It's a Pi Zero 2W. There's a great deal of lag in the video, which is why I didn't proceed with the ORB SLAM part. I did check out your github repo, and I gave autonomous Bittle a try with success. I will work on the Bittle ROS2 from your repo soon; it seems very exciting. Great work. I saw a section "set up raspberry pi camera" in the repo, and I presume that was why you asked about latency with the USB cam. I have a V1 Raspberry Pi camera with me; I will give it a shot.

Edited

Reid Graves

Feb 24

Replying to

I hope to implement ORB SLAM eventually also. I've been fighting with video latency quite a bit. It is better on a Pi 4 or 5 than the 0 2W, but still an issue eventually. It has been a challenge to find exactly where the hangup is. By adjusting compression, queue sizes, and image size I have been able to get reliable low latency for a few minutes, but typically the latency increases over time. If you try the Pi 4 or 5, you'll need a separate power source for them, or hard wire in a voltage regulator into the bittle battery. The Nyboard voltage regulator can't handle the power requirements for them.

Jason

Feb 19

You may refer to: https://www.petoi.camp/forum/software/bittle-ros2?origin=member_posts_page

Alex Fernandes

Feb 21

Replying to

Thanks Jason.

Position controller and its gains

Fixable!!

Issue connecting Bluetooth BittleX with Mac

ros melodic raspberry Pi 02W bittle robot, serial communication.