Jacob Smith, Fall 2019, Brandeis University
My project is to interface an arm to the mutant campus rover.
See the project Proposal in extras folder
using VarSpeedServo Library as background code, all my work is in examples and extras folder
Functionality so far
(provided) Sweep Controls Servo on Port 7
(provided) RobotArmScript Arduino Program to control rest of the Arm
(provided) ArmArduinoV1, lets the Arduino talk to the Pi
(provided) PiArduinoV1 lets teh Pi talk to the Arduino
Screenshot showing Message from Arduino being printed on Rasberry Pi
(provided) ArmArduinoV2*, lets the Arduino talk to the Pi
(provided) PiArduinoV2 lets the Pi talk to the Arduino
It sends a serial command to the Arduino, which reads it and moves the servo
Now that the basic premise was set up, I remounted the Servo Arm onto a robot chassis. Also, I can log into the mutant robot and execute python scripts over ssh.
ls /dev/tty* Lists available USb ports, look for USB 0
ssh mutant@mutant.dyn.brandeis.edu 'python' < '/home/robot/catkin_ws/src/arminterface/Raspi/ArmPiV4.py' Executes a python file on ssh without copying that file to the mutant rasberry Pi, 40 second time lag
These workflow improvements should allow me to test the arm much more quickly than plugging in to the mutant and and plugging in the arm etc.
Also, I am running the commands on the mutant robot, where the arm now has a port.
ArmArduinoV3, Opens the gripper if receives o character over serial, closes if c character
PiArduinoV3 Sends the open and close characters, also two way communication
This is the simplest expression of the interface required for the final project.
First, we check that the arm shows up in hte list of USB ports as USB 0
Then, we run the ArmPiV3 script over ssh, which moves the arm and displays output
Finally, the servo opens and closes!
Here is a video of this stage:
The main future goal is to interface the arm to ROS. In the short term, I want to decrease the lag, enable the arm to respond to keyboard input, and get the arm fixed
This week, I focused on the hardware of the arm, taking it apart, putting it back together, and mounting it to the Mutant Robot. Version 4 of the Arduino and Pi scripts show updated functionality, where the whole arm can be controlled.
First, I replaced the broken motors on the arm, this shows the base motor rotating after I lined it up again absolute position matters for servos):
Then, I mounted the arm on the mutant, note how there is enough clearance for the lidar because of the washers I added:
Version 4 of my scripts allow mulktiple parts of the arm to be controlled, shown here is the console output and robot motion.
A video of this week's work can be found here
Future Work:
By Next week, I will have communicated with Charlie about the battery and broken motors, and plugged the arm into a publisher/subscriber model in ROS. The deliverable will be a video of me moving the arm as I did this week but with ROS scripts.
Update: Charlie remounted the arm, I wrote the bringup and roscore script and it works over ssh, the arm moves using rostopic publisher and subscriber, subscriber has nice error handling like if usb times out.
Sssh Script problem: It seems that running roscore in ssh command doesn't work even though it works in an interactie session. i tired allowing mutant to allow user environment variables, but the problem persists. Even though i haven't figured anything out, i am learning a lot about linux and how to use vim. I also tried specifying the exact directory location of roscore file, but I go this error https://www.howtoforge.com/vim-basics
Here is a gif of the bash script working, no more opening multiple terminals to run roscore, bringup, and the nodes!
Here is the arm top mounting that Charlie did, now the arm doesn't get in the way of the lidar's field of vision.
Future work: Upload python file remotely, implement ROS actions, implement sensor control.
-
Get Charged Battery
-
Turn Mutant Robot On
-
run
cd ~/catkin_ws/src/arminterface/scripts -
run
bash runRos.shand follow instructionsFeedback from testing arm with TA
roscd
Explain what publihser subscriber do
stop unplug replug
Time took : 2:18, 2:33
Be interactive
Dont continue usb if unpluged
What threw you off the most? new terminal window
explain what that window does
Is the command line interface good?
yeah
The API is more important than the user application
better reset condition
avoid typing in password
1:10 usablity 8
Meeting with Pito :
I need to write a generic and reliable ROS node and not get sucked in to
Get to coordinate engage, write this so you could use it for a different arm
Then maybe write an action.
Add Ultrasonic Sensor
Possibly write angle information.
Main priorities: generic interface, ultrasonic sensor, and fun demo
General Interface:
The things we need to do: send commands
Goal Arduino Command Inputs other than Name Outputs Wait Comment Get Distance distancesensor.getDistance(); Distance No Type Output Sensor Set Arm Coordinates set_arm(100, 200, 90, 0 servoSpeed); 4 coordinates, speed Still Moving Yes Type 4 Coordinate Set Manipulator manipulator(true =open/false =code); open or close Still Moving Yes Type Binary Manipulator ROS outline
Node: Publish distance to topic
Action: Control arm and manipulator (one or two actions)
Then I have a node publishing Arduin commands, which keeps the Arduino code pure
https://raspberrypi.stackexchange.com/questions/13455/how-to-force-rescan-of-usb-serial-devices
https://stackoverflow.com/questions/41560818/usb-serial-data-sending-gibberish 2:15 PM: Pito says I'll have a serial Node which publishers serial data, then another ROS node which parses the data. Pito Recommends that I use a struct instead of plain text.
Another problem is that other students need to use the robot with an arm on it. I want to take off the arm so it can work on any robot anyway, but I need to fix the ssh error.
Pito agrees with this serial interface scheme : 
https://forum.arduino.cc/index.php?topic=396450
Trying to get Servo to tell my if its moving. I set the servo to run for 2 seconds at degree increments, and print whether it was moving. There would be a spike at 40 and 160 if this method actually could tell if the servo was moving.
Plotting the number of times the servo moved by different degrees shows that there is no correlation between where the servo is jammed and what the isMoving function returns.
This agrees with what Charly said about the servos having no feedback, but I thought a function named isMoving would return whether the servo is moving. In summary, the servo functions I thought would work don't really.
November 25 :
I wrote ArduinoV6, which uses a serial interface to control Arm position, manipulator, and and return the distance.
Setting up simple action example file in my program. Ran it in prrexamples, finishes prints elapsed time. Edited cmake and package.
Ismoving, atttaches limits, stop
limits dont seem to work
Reason is the limits are in microseconds not angles, here is the conversion from the cpp file of th VarSPeed Srvo class
- Get Charged Battery
- Turn Mutant Robot On
- run
roscd arminterface/scripts - run
bash runRos.shand follow instructions
Tested running einstctuions withTS< they are better
SSH Commands manual https://www.freebsd.org/cgi/man.cgi?sshd_config(5)
Edit read only file in vimhttps://www.geekyboy.com/archives/629
How to use vim https://www.howtoforge.com/vim-basics
Links http://gazebosim.org/tutorials/?tut=ros_urdf http://wiki.ros.org/joint_trajectory_controller Pito doesn;t like https://answers.ros.org/question/38694/running-ros-across-multiple-machines/
Non interactive shell information https://www.howtoforge.com/vim-basics https://www.howtoforge.com/vim-basicsS
Permit user enviornmet https://stackoverflow.com/questions/10562722/command-not-found-via-ssh-with-single-command-found-after-connecting-to-termina
Remote run ROS https://askubuntu.com/questions/1156507/cannot-perform-command-after-remote-logging-in-via-ssh
Run remote rs node https://github.com/pandora-auth-ros-pkg/pandora_docs/wiki/Remote-Machines-Running-ROS-nodes
How turtlbebot handles erial connections https://github.com/ros-drivers/rosserial/blob/melodic-devel/rosserial_python/nodes/serial_node.py
Error with running ros I got https://answers.ros.org/question/310848/run_id-on-parameter-server-does-not-match-declared-run_id/
Trying to get positon from servos, Charly convinced me there is no way to get position because there is no position wire.
Arm is Moving function eixst in varspeedservo
Error with running node remotely which I had https://answers.ros.org/question/243478/getting-rosgraph-resource-not-found-when-trying-to-get-turtlebot-local_plan/
Rosremote (didn't try) http://wiki.ros.org/ROSRemote
Ros remote machine (didn't try) https://github.com/pandora-auth-ros-pkg/pandora_docs/wiki/Remote-Machines-Running-ROS-nodes
Exception message python https://stackoverflow.com/questions/9823936/python-how-do-i-know-what-type-of-exception-occurred
Add python file to path https://askubuntu.com/questions/470982/how-to-add-a-python-module-to-syspath
ssh python finding module https://stackoverflow.com/questions/6851184/python-cannot-find-module-when-using-ssh
[1] Links fix Arduino download error https://www.arduino.cc/en/Guide/Linux
[2] Get Arduino to listen to Serial https://www.instructables.com/id/Connect-Your-Raspberry-Pi-and-Arduino-Uno/
[3]Get Pi to talk to Serial https://pyserial.readthedocs.io/en/latest/shortintro.html
[4] Run a Python File remotely https://www.shellhacks.com/ssh-execute-remote-command-script-linux/
Strings don't work in Arduino aarg post https://forum.arduino.cc/index.php?topic=387175.0
Servo min max writing https://forum.arduino.cc/index.php?topic=169501.0