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kou merged 1 commit into from
Oct 26, 2026
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website: Add FAQ entry for checking that the arm has reached the target #643

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10 changes: 10 additions & 0 deletions website/docs/faq/index.md
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Expand Up @@ -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_<side>_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.<joint>.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.
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