Knob
FREERotary dial control with bidirectional feedback
When to reach for it
Knob is functionally the same widget as Slider: identical min/max/step, feedback, and publish-rate behavior underneath. Reach for it when the control should feel rotary, a heading setpoint or a gain dial, rather than linear.
When the value maps more naturally to a straight throw, a throttle or a linear actuator's travel, Slider is the better fit.
Worked example: heading setpoint
Topic /heading_setpoint, schema std_msgs/msg/Float64. Min 0, Max 360, Step 1. Turn on Publish on Release Only for a one-shot heading goal; leave it off if the controller expects a continuous setpoint while the operator is dialing.
Watch out for
- Min Value, Max Value, and Step are the scale, not a safety limit. The robot does what you command: set them to match what the receiver can actually handle.
- On Pro, with Track Robot State on, if feedback never settles within Recouple Timeout (ms) the indicator auto-recouples to feedback so it does not strand at a stale command. A teleporting indicator means a slow or silent controller, not a broken widget.
Configuration fields
The topic this widget publishes to. While connected, tap to pick one the robot advertises.
The ROS message type, like sensor_msgs/msg/Image. Fills in when you pick a topic.
Send one value on release instead of streaming while you turn.
How fast the knob streams updates while the user is rotating.
WITH PRODefault 10 Hz. Raise to 20 to 50 Hz for smoother turns, lower on slow links. No effect with Publish on Release.
Show the robot's actual value as a ghost indicator alongside your command.
WITH PROSee the robot's actual value as a ghost next to your command, live as it moves.
Topic carrying the robot's actual value, drawn as a ghost alongside your command.
Field path on the feedback topic to read as the actual value.
Messages per second this widget takes from the feedback topic. Lower saves data, higher tracks closer.
0.1 to 60, step 0.1How long the indicator holds your value after release while feedback settles. Raise it for slow controllers.
500 to 10000, step 500Ease the ghost and indicator toward the robot's reported value instead of snapping to every sample.
WITH PROCalms jumpy or noisy feedback on screen. Your commanded value is unaffected.
How strongly to smooth the feedback. Heavy damps a noisy controller but adds lag.
Show a name on the widget.