Is there a method in which I can run the magni without using ros

IngeniousDoc · March 21, 2021, 9:35am

So, I was curious if there was a way where I would control the magni using basic python scripts to control it. Without having ros as the middleware?

Just something I am exploring

MoffKalast · March 21, 2021, 11:52pm

Sure, you just have to write your own motor controller script that talks to the MCB using serial.

Why would you not want to use ROS? If Python 3’s the issue then it would be easier to either wait another month or two until we have Noetic support or write a way to interface your external script with the ROS part. Websockets would be easiest most likely.

mjstn2011 · March 22, 2021, 7:30am

More specifically I point you to two existing programs that can do simple speed control.

This python ‘tool’ allows sending raw speed commands to the MCB. Look at commands for the ‘1’, ‘2’ and other 1-9 speed commands.

github.com

UbiquityRobotics/ubiquity_motor/blob/kinetic-devel/scripts/test_motor_board.py

#!/usr/bin/python -u

#
# Command control direct to Ubiquity Robotics Magni Controller Board
#
# This is diagnostic code that can be usedto directly run the motors
# without ROS and all the overhead of joysticks and so on.
# The idea started as a simple serial controller to do basic tests.
#
# Usage:
# Stop the ROS magni control using:  sudo systemctl stop magni-base
# sudo python magni_cmd.py    # OPTIONALLY add --dev /dev/ttyUSB0 for other port
# Enter single keys followed by return to change speeds.   
# Example:  enter '1' for slow speed then enter 3 and speed goes to 3
# Change speeds like this and when done enter 'e' for exit or 's' for stop.
#
# The Magni uses a binary packet and this program uses only the speed command
# Packet Structure    0x7E CC RR AU AL BU BL SS   
#   Where 0x7E starts a packet and SS is cksum (CC -> B0) truncate 8 bit
#   CC - Command   MS Nibble is 3 for protocol version and LS Nibble:

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This Arduino Nano sketch controls velocity in simple ways:

github.com

UbiquityRobotics/ubiquity_motor/blob/kinetic-devel/scripts/McbController.ino

/*
  MCB Controller That Runs On The Arduino Platform for debug or very very simple controllers

  Some basic MCB speed control for the Ubiquity Robotics Magni Robot is implemented
  This code is meant for the Arduino Nano model.

  This code could be used to build upon a far more complex robot based on the Arduino platform
  or other platform supported by the Arduino IDE libraries.

  As a minimum the Arduino 5V level TX signal goes to MCB board P508  RX pin and Arduino Ground goes to P508 ground.
  Optionally you can power the Arduino all from P508 because there is 5V VCC on P508 as well.
  (Note that to do that you must tie MCB Vcc on P508 to Arduino 5V power because the spec for VIN is for 6V or more)

  Usage Instructions
  - Ground the ENABLE_SPEED_PIN (can be used as an ESTOP)
  - Connect tow 1k to 20k pots with each of the ends on GND and Vcc.  
    Center tap of one pot to A1, center tap of other pot to A2.
    Default with no jumpers is for each pot to separately control a single wheel.
  - Optionally ground the ENABLE_JOYSTICK pin to interprit two pots as joystick if you hook up dual pot joystick
  - Optionally a normaly closed switch from ground to ENABLE_SPEED_PIN for switch that must close to run motors

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Where your question becomes complex is in reading back how fast the robot is going and a great many other control methods. That is beyond this explanation. Very involved.

Mark