From 8f26f43195464b69be24757a3936f3282ed4ba33 Mon Sep 17 00:00:00 2001 From: Sutou Kouhei Date: Mon, 26 Oct 2026 16:11:22 +0900 Subject: [PATCH] website: Add FAQ entry for checking that the arm has reached the target The joint trajectory controllers don't check the goal tolerance in the default configuration of ROS 2 control, like the default of `joint_trajectory_controller`. A trajectory can succeed even if the arm stops short of the target because of the steady-state error. Add an FAQ entry that recommends checking the error at the end effector and explains that the goal tolerance (`constraints..goal`) can be set for the task and gains. Co-Authored-By: Claude Opus 5.5 --- website/docs/faq/index.md | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/website/docs/faq/index.md b/website/docs/faq/index.md index 4d7f7080..54d06ce3 100644 --- a/website/docs/faq/index.md +++ b/website/docs/faq/index.md @@ -85,6 +85,16 @@ To control the end effector accurately, use a frame at the tool center point (TC We don't define a standard TCP because the best point depends on the task. For reference, the lower end of the fingertips is 0.170 m from the origin of `openarm__ee_base_link` along its -Z axis when the gripper is closed. +## How do I check that the arm has reached the target? + +In the default configuration of [ROS 2 control](../api-reference/ros2/control.mdx), the joint trajectory controllers don't check the goal tolerance. +A trajectory can succeed even if the arm hasn't reached the target, for example because of the [steady-state error](#the-arm-doesnt-reach-the-commanded-position-or-the-end-effector-sags). +Check the error between the target and the actual position yourself. +We recommend checking the error at the end effector, not at each joint. + +You can also set the goal tolerance of each joint (`constraints..goal`) in the [controller configuration](https://github.com/enactic/openarm_ros2/tree/main/openarm_bringup/config/controllers) to make a trajectory fail when the arm doesn't reach the target. +The appropriate tolerance depends on your task and gains. + ## The cameras disconnect. In the standard configuration in the [OpenArm 2.0 BOM](https://drive.google.com/drive/folders/14RM-fIPml0HTMnt2zcTXjNxJj9s2R_mG), the head stereo camera (ZED mini) and both wrist cameras share one USB hub and one USB repeater cable.