Is there a way for MoveIt2 to only output the final goal position rather than the entire path?

[proffalken]

I'm working with a robot arm of my own design and I want to use Moveit2 for the IK calculations, however I'm driving the motors via a CNC shield so all that needs is the last set of coordinates from the path, not each step along the way as the GCode I am sending dictates

For example, if I want to rotate a joint connected to the "X" by 45 degrees, I need to send the GCode G21 F250 X10 which moves the stepper 10mm clockwise and, because of the size of the gears, the joint rotates 45 degrees.

What I need to avoid is sending a GCode step for each movement between <current> and the goal, because the GCode controller will then try and move X by 1, then by 2, then by 3 etc. which means by the time Moveit thinks that the goal has been reached, it's actually several orders of magnitude away from where it needs to be!

Is there a way to tell Moveit2 to calculate the end state, and then only send that end state to the controller?

The CNC Shield isn't capable of calculating the IK, but it knows where it is and how far it needs to move in order to get to the specified location, so I'm hoping I can pair the both and get the result I need!

Here's the example output from the current code:

[move_group-5] [INFO] [1737442526.933027259] [moveit.simple_controller_manager.follow_joint_trajectory_controller_handle]: Goal request accepted!
[ros2_control_node-2] [INFO] [1737442527.031136446] [RobotarmInterface]: Message sent: G21 F250 X0 Y0
[ros2_control_node-2] [INFO] [1737442527.131038367] [RobotarmInterface]: Message sent: G21 F250 X1 Y0
[ros2_control_node-2] [INFO] [1737442527.231069318] [RobotarmInterface]: Message sent: G21 F250 X4 Y0
[ros2_control_node-2] [INFO] [1737442527.331042284] [RobotarmInterface]: Message sent: G21 F250 X7 Y0
[ros2_control_node-2] [INFO] [1737442527.431046297] [RobotarmInterface]: Message sent: G21 F250 X11 Y0
[ros2_control_node-2] [INFO] [1737442527.531081557] [RobotarmInterface]: Message sent: G21 F250 X16 Y0
[ros2_control_node-2] [INFO] [1737442527.631030429] [RobotarmInterface]: Message sent: G21 F250 X22 Y0
[ros2_control_node-2] [INFO] [1737442527.731108451] [RobotarmInterface]: Message sent: G21 F250 X28 Y0
[ros2_control_node-2] [INFO] [1737442527.831149725] [RobotarmInterface]: Message sent: G21 F250 X36 Y0
[ros2_control_node-2] [INFO] [1737442527.931033596] [RobotarmInterface]: Message sent: G21 F250 X44 Y0
[ros2_control_node-2] [INFO] [1737442528.031051090] [RobotarmInterface]: Message sent: G21 F250 X54 Y0
[ros2_control_node-2] [INFO] [1737442528.131094101] [RobotarmInterface]: Message sent: G21 F250 X64 Y0
[ros2_control_node-2] [INFO] [1737442528.231074458] [RobotarmInterface]: Message sent: G21 F250 X76 Y0
[ros2_control_node-2] [INFO] [1737442528.331041908] [RobotarmInterface]: Message sent: G21 F250 X87 Y0
[ros2_control_node-2] [INFO] [1737442528.431169820] [RobotarmInterface]: Message sent: G21 F250 X98 Y0
[ros2_control_node-2] [INFO] [1737442528.531037213] [RobotarmInterface]: Message sent: G21 F250 X108 Y0
[ros2_control_node-2] [INFO] [1737442528.631052769] [RobotarmInterface]: Message sent: G21 F250 X116 Y0
[ros2_control_node-2] [INFO] [1737442528.731035042] [RobotarmInterface]: Message sent: G21 F250 X124 Y0
[ros2_control_node-2] [INFO] [1737442528.831092386] [RobotarmInterface]: Message sent: G21 F250 X132 Y0
[ros2_control_node-2] [INFO] [1737442528.931050157] [RobotarmInterface]: Message sent: G21 F250 X138 Y0
[ros2_control_node-2] [INFO] [1737442529.031050038] [RobotarmInterface]: Message sent: G21 F250 X143 Y0
[ros2_control_node-2] [INFO] [1737442529.131110076] [RobotarmInterface]: Message sent: G21 F250 X147 Y0
[ros2_control_node-2] [INFO] [1737442529.231089128] [RobotarmInterface]: Message sent: G21 F250 X151 Y0
[ros2_control_node-2] [INFO] [1737442529.331059776] [RobotarmInterface]: Message sent: G21 F250 X153 Y0
[ros2_control_node-2] [INFO] [1737442529.431148544] [RobotarmInterface]: Message sent: G21 F250 X155 Y0
[ros2_control_node-2] [INFO] [1737442529.531038424] [RobotarmInterface]: Message sent: G21 F250 X156 Y0
[ros2_control_node-2] [INFO] [1737442529.631036660] [arm_controller]: Goal reached, success!

All I need the controller to receive is the last value G21 F250 X156 Y0

[gavanderhoorn]

Perhaps not the kind of solution you were looking for, but it sounds like your "CNC shield" is interpreting all motions as relative/incremental motions -- perhaps/probably due to using steppers.

If you have encoders on those steppers, try switching the shield to absolute mode. Provided your board / gcode interpreter / motion controller supports blending as well, that should make a 1-to-1 conversion of JointTrajectory to Gcode probably work well enough for basic motion.

If you have no encoders, or absolute mode is not supported, you could consider extending your JointTrajectory-to-gcode converter node to keep track of how many increments have been sent to your stepper and implement an absolute position controller that way. Or convert the JointTrajectory into a set of increments of course.

[proffalken]

Thanks.

The code I'm using is modified from a Udemy course and just reads whatever is sent to the topic before sending it on to the CNC controller.

I can set the controller to use absolute rather than relative mode, however it would still be passed a series of strings rather than the final result.

I was hoping there would be a flag somewhere in Moveit2 that said "don't send the entire sequence of events, because the controller you're talking to is intelligent and can work out how to get to the end goal from where it currently is, it just can't do the IK side of things", but I'm guessing that's not the case.

I'll see if switching to absolute mode works and feed back, but I don't have sensors as I'm trying to only use hardware that I already have to save money!