From 8f80a37d08d79fa975690303b9eaa3d17887f416 Mon Sep 17 00:00:00 2001
From: Binit Shah <bshah@hello-robot.com>
Date: Tue, 3 Sep 2024 14:55:34 -0400
Subject: [PATCH] Update jogging.md

---
 ros2/jogging.md | 62 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/ros2/jogging.md b/ros2/jogging.md
index 1dff4e9..221af25 100644
--- a/ros2/jogging.md
+++ b/ros2/jogging.md
@@ -43,3 +43,65 @@ Copy the above into a file called "example.py" and run it using:
 ```{.bash .shell-prompt .copy}
 python3 example.py
 ```
+
+## Retrieving joint limits
+
+In a terminal, echo the `/joint_limits` topic:
+
+```{.bash .shell-prompt .copy}
+ros2 topic echo /joint_limits
+```
+
+In a second terminal, request the driver publish the joint limits:
+
+```{.bash .shell-prompt .copy}
+ros2 service call /get_joint_states std_srvs/srv/Trigger {}
+```
+
+In the first terminal, you'll see a single message get published. It'll look like this:
+
+```yaml
+header:
+  stamp:
+    sec: 1725388967
+    nanosec: 818893747
+  frame_id: ''
+name:
+- joint_head_tilt
+- joint_wrist_pitch
+- joint_wrist_roll
+- joint_wrist_yaw
+- joint_head_pan
+- joint_lift
+- joint_arm
+- gripper_aperture
+- joint_gripper_finger_left
+- joint_gripper_finger_right
+position:
+- -2.0171847360696185
+- -1.5707963267948966
+- -2.9114955354069467
+- -1.3933658823294575
+- -4.035903452927122
+- 0.0
+- 0.0
+- -0.1285204486235414
+- -0.3757907854489514
+- -0.3757907854489514
+velocity:
+- 0.4908738521234052
+- 0.45099035163837853
+- 2.9176314585584895
+- 4.416586351787409
+- 1.7303303287350031
+- 1.0966833704348709
+- 0.5197662863936018
+- 0.34289112948906764
+- 1.0026056417808995
+- 1.0026056417808995
+effort: []
+```
+
+We're misusing the [sensor_msgs/JointState](https://docs.ros.org/en/noetic/api/sensor_msgs/html/msg/JointState.html) message to publish the joint limits. The `name` array lists out each ranged joint. The `position` array lists the lower bound for each joint. The `velocity` array lists the upper bound. The length of these 3 arrays will be equal, because the index of the joint in the `name` array determines which index the corresponding limits will be in the other two arrays.
+
+The revolute joints will have their limits published in radians, and the prismatic joints will have them published in meters. See the [Hardware Overview](../../getting_started/stretch_hardware_overview/) to see the ranges represented visually.