TF error

[chrismalyon]

Hi James,
Im really struggling with one last bit. When i launch the rur_navigation package on my remote workstation i get two errors "no transform from Laser to Map and no transform from Base_link to Map. Im really stuck, can you point me in the right direction?

Thanks
Chris

[XRobots]

Presumably you ran Gmapping and made the map ok?

[chrismalyon]

No as I get a No Map received error but im currently using your map. I have tried to build this robot a few times but havent been able to. I was hoping I could do it now based on your videos but it seems im still struggling :(

[XRobots]

You'll have to step back a bit. Just run the stuff on the robot and open RVIZ - can you add in the laser scan and TF and have it all line up? After that you should be able to run Gmapping and have it draw the map.

[chrismalyon]

Part of the problem i think is finding the correct distro to run. Im running a Raspberry Pi 4 and no matter what distro I use there always seems to be issues with getting ROS running properly. Right now for instance when I run your code I get an error with the serial connection to my Arduino due to a python version issue.

[chrismalyon]

Ok I figured it out and I now have the robot communicating with the remote workstation and displaying the map correctly. The last bit is driving the robot. if i echo the odom topic and manually turn the wheels im getting the encoder count so that looks good however im not using ODrive im actually using a pair of hoverboard wheels with two BLDC drivers. these are driven essentially by a pwm signal. Im having trouble converting your code to make the wheels move. Below is what i have updated in the main loop. My thinking is to take the forward0 + turn0 and convert this to a PWM value however nothing happens :( I know im taking the micky a bit asking but if you could take a look at the below and let me know what im doing wrong i would appreciate it. I think others would find it useful to see how to make the code work in this way as pwm driven controllers and wheels are a lot cheaper than an ODrive setup.

Thanks in advance
Chris

nh.spinOnce(); // make sure we listen for ROS messages and activate the callback if there is one

currentMillis = millis();
if (currentMillis - previousMillis >= loopTime) { // run a loop every 10ms
previousMillis = currentMillis; // reset the clock to time it

    float modifier_lin = 1.03;        // scaling factor because the wheels are squashy / there is wheel slip etc.
float modifier_ang = 0.92;        // scaling factor because the wheels are squashy / there is wheel slip etc.


forward0 = demandx * (83466 * modifier_lin) ; // convert m/s into counts/s
forward1 = demandx * (83466 * modifier_lin); // convert m/s into counts/s

turn0 = demandz * (15091 * modifier_ang);    // convert rads/s into counts/s
turn1 = demandz * (15091 * modifier_ang);    // convert rads/s into counts/s

//forward1 = forward1 * -1;    // one motor and encoder is mounted facing the other way

// odrive1.SetVelocity(0, forward0 + turn0);
// odrive1.SetVelocity(1, forward1 + turn1);

  analogWrite(Left_Wheel_speed, forward0 + turn0);
  digitalWrite(Left_Wheel_Direction, HIGH);
  digitalWrite(Left_Wheel_Stop, HIGH);

  analogWrite(Right_Wheel_speed, forward1 + turn1);
  digitalWrite(Right_Wheel_Direction, LOW);
  digitalWrite(Right_Wheel_Stop, HIGH);
  

// get positions and velocities from ODrive

// pos0 = (odrive1.GetPosition(1)) * -1;
// pos1 = odrive1.GetPosition(0);

pos0 = pos;
pos1 = pos2;

[XRobots]

Well it looks ok, if you try the motor driver code on its own does it drive the motors?

[chrismalyon]

It does. I have done some debugging via Serial1 on the arduino mega. It seems that the Arduino is not receiving the cmd_vel topic so there seems to be some issue with how it is subscribing. It is however publishing ok as when i rotate the wheels manually the encoder count is updated to the odom topic which i can see with rostopic echo /odom on the remote workstation. I will continue playing with it to see if I can work out whats going on.

[chrismalyon]

Hmmm I thought it could be an issue with the Arduino Libraries i was using so I recompiled but didnt work. I have added the following to the callback function on the Arduino but It doesnt seem to fire. If I rostopic echo cmd_vel on the raspberry on the robot then i can see the topic getting the data from rviz but the arduino doesnt seem to capture it :'(

void velCallback( const geometry_msgs::Twist& vel)
{

demandx = vel.linear.x;
demandz = vel.angular.z;

Serial1.print("Callback X: ");
Serial1.println(vel.linear.x);

Serial1.print("Callback Z: ");
Serial1.println(vel.linear.z);
}

[matthewjreeves]

Hi @chrismalyon

Ok I figured it out and I now have the robot communicating with the remote workstation and displaying the map correctly.

Earlier in this thread, you had exactly the same problem (above) as I am currently having. Running Rviz after launching all the nodes is throwing up the error Transform [sender=unknown_publisher]
For frame [laser]: No transform to fixed frame [map]. TF error: [Could not find a connection between 'map' and 'laser' because they are not part of the same tree.Tf has two or more unconnected trees.]

I am really stuck too! Could you shed some light on how you fixed it. I am also trying to run it all on an RPI 4b and have had a hell of a time trying to compile Realsense (which is now sorted thankfully)!