Hardware & control
Control frequency
Control frequency is the rate, usually expressed in hertz, at which a robot control loop reads state, updates its controller or policy, and issues commands. A robot can contain several nested loops at different rates, so policy frequency, actuator-control frequency, sensor sampling rate, and dataset frame rate should not be assumed to be identical.
Also known as: control rate, policy update rate, action frequency
Updated
One robot can run several clocks
A motor-current loop may run much faster than a joint controller, while a large learned policy updates only a few times per second and sends targets to those lower layers. Camera, tactile and logging streams can each use another rate.
The ros2_control controller manager defines its update rate as the frequency of the loop that reads hardware state, updates controllers and writes commands. Individual asynchronous controllers can run at different rates, which is why “the robot runs at 100 Hz” is incomplete without naming the loop.
Frequency changes the meaning of a command sequence
A Cartesian delta applied at 5 Hz produces a different velocity from the same delta applied at 20 Hz. Position targets may be less directly rate-dependent, but a slower loop observes disturbances later and offers fewer opportunities to correct.
RT-1 produced closed-loop actions at 3 Hz, while DROID recorded state and actions at 15 Hz. Neither number describes every inner hardware loop. It identifies the temporal resolution of the policy or released training sequence.
Nominal rate is not measured timing
A configured 100 Hz loop has a 10 ms target period, but computation overruns, scheduling jitter or dropped samples can reduce the achieved rate. Dataset metadata should include timestamps rather than relying only on a nominal frequency.
Documentation should distinguish capture, policy, command and actuator rates; state whether streams were resampled; and report timing variation where available. Cross-dataset training must account for those differences before action chunks or deltas are treated as comparable.
Sources
Related terms
Hardware & control
Feedback control
Feedback control is a closed-loop control method that measures a system’s current output or state, compares it with a target and adjusts the command using the resulting error. In robotics, feedback can correct joint, end-effector, balance or force errors as new sensor measurements arrive.
Models & learning
Action space
An action space is the set and representation of commands that an agent or robot policy is allowed to choose. In robotics, actions may be discrete choices or continuous values such as joint targets, motor torques, end-effector pose changes, base velocities, or gripper commands. The action space defines what the policy outputs, not necessarily the motion the hardware ultimately executes.
Hardware & control
Control latency
Control latency is the elapsed time between a relevant event or observation and the physical effect of the resulting robot command. It can include sensor exposure and transport, preprocessing, policy inference, network transfer, controller scheduling, actuator response, and communication back to a human operator. The measured boundary must be stated because each component has a different latency.
Models & learning
Asynchronous inference
Asynchronous inference is a deployment pattern that overlaps robot action execution with prediction of a later action chunk. A robot client consumes queued actions while a policy process or server evaluates a newer observation, then merges or replaces the remaining queue when the new chunk arrives. The pattern reduces idle inference gaps but does not remove latency, stale observations or safety constraints.
Data & collection
Data synchronisation
Data synchronisation is the process of placing sensor, state, action, annotation, and outcome records on a common timeline so samples that describe the same physical instant or transition can be matched. It requires trustworthy timestamps or trigger relationships and an explicit rule for handling streams with different rates, delays, dropped samples, and clock offsets.