Units

Physical quantities and units are defined in the units module. The module provides a set of predefined units and unit systems. It allows to do simple conversions between the user preferred and “base” units the robot understands. The framework also provides a type checked interface that ensures that the physical domains are not mixed up (e.g., passing speed in m/s instead of percent). Numeric values with units are represented as objects of the Value[] generic class, for example Value[DistanceDomain] or Value[AngleDomain].

Supported units

The following units are provided by the framework:

Name	Domain	Represented as
millimetre	DistanceDomain	mm
metre	DistanceDomain	m
inch	DistanceDomain	inch
degree	AngleDomain	deg
radian	AngleDomain	rad
second	TimeDomain	s
minute	TimeDomain	minute
hour	TimeDomain	hour
percent	RatioDomain	percent
kilogram	WeightDomain	kg

Additionally, the following unit systems are provided:

Name	Domain	Represented as
speed	SpeedDomain	mm/s
acceleration	AccelerationDomain	mm/s ** 2
jerk	JerkDomain	mm/s ** 3
angular speed	SpeedDomain	deg/s
angular acceleration	AngularAccelerationDomain	deg/s ** 2
angular jerk	AngularJerkDomain	deg/s ** 3

Using units

Converting from number

Object representing a physical quantity can be created using the ozobot.ora.units.units function. To create the object and assign it to a variable, the following syntax is used:

speed = units(0.1, m)

Converting back to number The result of units function is not a number, but an object that represents a physical quantity. To get the value of the quantity, the default conversion function to float or int should be used. This yields the value in the base unit of the quantity. For example, to get the value of the speed in m/s, the following syntax is used:

speed = units(10, mm/s)
speed_m_s = float(speed)

Combining units

Units can be combined to create more complex units. For example, to create a speed object, the following syntax is used:

speed = units(10, mm/s)
angular_acceleration = units(100, deg/s ** 2)

Tip

How do I know what units to use?

See the function signature. For example joint() accepts speed as RatioDomain quantity. After checking the Supported Units table we can see that RatioDomain is represented as percent. Therefore, the speed should be passed as ~ozobot.ora.units.quantities.percent quantity. For example, move.joints(pose, speed=units(10, percent))