Retrieve Encoder Data

The Pegasus-Mini uses the BasicMicro Roboclaw 2x7A Motor Controller in order to control each of its drive motors, each having independent encoders. The motor controller uses these encoders in order and provides rotational information such as motor ticks, as well as motor speed, in the form of ticks per a second. A tick can be described as a change in angular position of the motor. The Pegasus-Mini has 64 ticks per a rotation of its drive motors. The following describes how to obtain this data from the motor controller using Python.

Note

This documentation assumes that you have been through the Python Tutorials in order to gain an understanding of how the roboclaw.py script when importing the roboclaw module.

  1. Firstly ensure your motor controller is connected to your computer via USB.

  2. Run the following lines of code in Python in order to initialize connection with motor controller. This both points to the desired ports, opens the port and then declares the address.

import time
from roboclaw import Roboclaw
#Windows comport name
rc = Roboclaw("COM9",115200)
#Linux comport name
#rc = Roboclaw("/dev/ttyACM0",115200)
rc.Open()
address = 0x80
version = rc.ReadVersion(address)

  1. Encoder data can be obtained for either of the motors, M1 or M2. Speed and encoder data are arrays with the following format:

[status1, encoder1_value , crc1] = rc.ReadEncM1(address)
[status2, encoder2_value , crc1] = rc.ReadEncM2(address)
[status1, speed1] = ReadSpeedM1(address)
[status2, speed2] = ReadSpeedM2(address)

In order to obtain encoder data and print said data run the following line.

enc1 = rc.ReadEncM1(address)
enc2 = rc.ReadEncM2(address)
speed1 = rc.ReadSpeedM1(address)
speed2 = rc.ReadSpeedM2(address)
print("Encoder1:")
print enc1[1]
print "Encoder2:"
print enc2[1]
print format(enc2[2],'02x')
print "Speed1:"
print speed1[1]
print("Speed2:")
print speed2[1]