Phidgets Motor Encoder Low Level

Pre Req

• Phidgets Motor Encoder See High Level

Investigate

 rostopic info phidgets/encoder/351673
     Type: phidgets/encoder_params
 
     Publishers: None
 
     Subscribers: 
      * /odometry (http://hood:41705/)

 rostopic echo phidgets/encoder/351673
     header: 
       seq: 1
       stamp: 
         secs: 0
         nsecs: 0
       frame_id: base_link
     index: 0
     count: -60
     count_change: -60
     time: 5
     ---

Test Script

Just run the odometry without running the encoder publishers. The encoder publishing will be with the encode_test.sh below.

 cat test/odometry_test.launch 
     <launch>
         <node pkg="phidgets" type="odometry" name="odometry" respawn="true" output="screen">
             <param name="serialleft" value="351547" />
             <param name="serialright" value="351673" />
             <param name="wheelbase" value="283" />
             <param name="countspermmleft" value="6" />
             <param name="countspermmright" value="6" />
             <param name="verbose" value="true" />
         </node>
     </launch>

See echo encoder fields above. Format is yaml. This will publish one encoder message for each encoder. At 6 counts per mm the 60 count message below should make the while move roughly 1 cm.

 cat test/encoder_test.sh
     #!/bin/bash
 
     # left
     rostopic pub -1 /phidgets/encoder/351547 phidgets/encoder_params 
          '{header: 
               {seq: 1, 
                stamp: {secs: 0, nsecs: 0},   
                frame_id: "base_link"},
            index: 0, 
            count: 60, 
            count_change: 60, 
            time: 5} '
 
     # right
     rostopic pub -1 /phidgets/encoder/351673 phidgets/encoder_params 
          '{header: 
               {seq: 1, 
                stamp: {secs: 0, nsecs: 0}, 
                frame_id: "base_link"},
            index: 0, 
            count: -60, 
            count_change: -60, 
            time: 5} '

Test

Terminal 1

 roscore

terminal 2

 roslaunch floor_hugger odometry_test.launch 

terminal 3

rostopic echo odom

terminal 4

. encoder_test.sh

echo result

 pose: 
   pose: 
     position: 
       x: -0.00999791911171               almost 1 cm
       y: -0.000176660062442              almost 0
       z: 0.0
     orientation: 
       x: 0.0
       y: 0.0
       z: 0.0
       w: 1.0
 
 ----

Sanity Check on Wheel Rotation

Terminal 1

 roscore

Terminal 2

 roslaunch floor_hugger odometry.launch

Terminal 3

 rosbag record -a

Rotated right wheel about one revolution. Results will be approximate.

Terminal 2 and 3

 ^C

Terminal 4

 rostopic echo phidgets/encoder/351673 > ~/tmp/en73.txt

Terminal 3

 rosbag play 2016-04-21-11-27-20.bag

Wait to complete

Terminal 4

 ^C
 emacs ~/tmp/en73.txt&

Results

• see Calibrate_Phidgets_Odometry
• circumference is 330 mm
• right encoder count is 1897
• 1897 / 330 => 5.75 counts / mm
  • close to that measured value in calibaration page. Wheel rotation was approximate.