ALMotion

Overview | API | Advanced

---

See also

Control	Stiffness, Joint, Locomotion, Cartesian, Whole body.
Reflexes	Self-collision avoidance, External-collision avoidance, Fall manager, Smart Stiffness Diagnosis effect, Push Recovery, Slope compensation.
Idle	Idle.
Tools	General tools, Motion task.

What it does

The ALMotion module provides methods which facilitate making the robot move.

Control

It contains four major groups of methods for controlling the:

• joint stiffness (basically motor On-Off): see Stiffness control,
• joint position (interpolation, reactive control): see Joint control,
• walk (distance and velocity control, world position and so on): see Locomotion control,
• robot effector in the Cartesian space (inverse kinematics, whole body constraints): see Cartesian control.

Reflexes

The ALMotion module implements also some “reflexes” such as Self-collision avoidance, External-collision avoidance, Fall manager, Smart Stiffness and Diagnosis effect.

The reflexes are activated by default and modify the behavior of your robot.

More specifically, they:

• alter the motion to avoid self or external collision (see Self-collision avoidance, External-collision avoidance),
• adjust the stiffness to spare power when the robot is not moving (see Smart Stiffness),
• trigger a specific task when a fall is detected (see Fall manager), or when issues or errors are raised on a device potentially critical (see reflexes-diagnosis`).

Advanced users may need to deactivate all or part of the reflexes. For further details see: Deactivation of the safety reflexes.

Idle

The module also provides tools to define the robot behavior when no user command is sent. See Idle.

Tools

This module gives also access to useful information about the robot hardware, such as the number of joints, their name, limits, the available sensors and so on. See General tools.

How it works

ALMotion runs at 50Hz (cycle of 20ms).

In ALMotion, every time you call a public method to request a motion, a “motion task” is created to handle the job. See Motion task to learn how to manage these tasks.

Performance and Limitations

Performance

ALMotion is a core module. As it manages some reflexes and updates the model every cycle, the module consumes a constant CPU. This consumption could increase during special tasks like walk.

The table below gives you some hints of ALMotion CPU consumption.

Task \ Processor	Atom (NAO V4)
update Model	3%
walking	10.8%

Adaptation to Pepper specificities

We have tried hard to maintain a unique Motion API for both NAO and Pepper.

However, some adaptations were necessary:

Group	Main adaptations	For further details, see ...
Stiffness	Manual Stiffness control is forbidden for Pepper‘s lower part.	Stiffness control
Locomotion control	Specific stability constraints on the leg. Locomotion methods are prohibited if power hatch is open.	Locomotion control
Cartesian control	Most of the methods are unusable.	Cartesian control
Whole Body control	Do not use any Whole Body control methods.	Whole Body control
Safety reflexes	A specific safety reflex is dedicated.	Push Recovery
	A specific safety reflex is dedicated.	Slope compensation
	Frontal security distance is correlated with speed.	External-collision avoidance
	Hardware issues trigger specific Rest reflexes.	Diagnosis effect

Getting Started

Essential information to deal with ALMotion:

Axis definition

The X axis is positive toward the robot’s front, the Y from right to left and the Z is vertical.

SI - International System of Unit

The ALMotion module uses the SI - International System of Units (meters, second, radian...).

How to name joints and body parts

Depending on the method chosen, ALMotion requires to name joints, group of joints or a body part.

	called ...	are used by ...
Body parts	Effectors	Cartesian control and Whole Body control
Joint names can be called individually or by groups	Chains	Stiffness control, Joint control, General tools and Motion task.

For further details, see:

• Effector & Chain definitions,
• “Body”, chains and joint names,
• Effectors.

Advanced Users

Motion from scratch

If you are familiar with the ALMotion definition and you want to go further creating advanced behavior in C++ like a new reflex, a better object tracker or use at the same time DCM module and ALMotion, see: Motion - advanced.

Deactivation of the safety reflexes

Each reflex can be temporarily deactivated, using the relevant setNameOfReflexEnabled method.

However, deactivation of very critical reflexes will not be effective unless the owner of the robot has previously given his consent.

The list below specify whether the reflex deactivation require or not owner consent:

Method	User consent required
	NAO	Pepper
ALMotionProxy::setCollisionProtectionEnabled	No	No
ALMotionProxy::setDiagnosisEffectEnabled	No	No
ALMotionProxy::setSmartStiffnessEnabled	No	No
ALMotionProxy::setExternalCollisionProtectionEnabled	No	Yes, Arms excepted
ALMotionProxy::setFallManagerEnabled	Yes	Yes
ALMotionProxy::setPushRecoveryEnabled	NA	Yes

For further details about owner consent, see: Consent for the deactivation of safety reflexes, Consent for the deactivation of safety reflexes.