Inertia & load

A rotating load with inertia and viscous friction.

  • rotational
  • Gradara equations
  • 2 ports
  • 2 parameters
BlockInertia & loadKindinertiaLibraryRotational

Description

A rotating load with inertia and viscous friction to the housing. Both flanges are rigidly attached to the same body, so the block can sit between a motor and further drivetrain parts.

Example

Clutch, backlash, and rotational sources A clutch that locks, gear backlash, a spring-damper coupling, and a load that steps its torque.

100 rad/s at 0.1 sDriveClose at 0.5 sClutchDriven 1 kg·m²Driven speedω ref 10 sin 2πtSpeed sourceBacklash 0.1 radInertia 0.01Speed behind backlash0.5 N·mTorque sourceCouplingInertia 0.02, damping 0.05Coupled speed0.4 N·mShaft loadLoad speed
In Gradara, select a Inertia & load block and press F1, then choose Open example. It opens as a new model in My models, ready to run.

Also in this example:ConstantMechanical loadStepSpeed sensorSine waveSpring-damperBacklashInertia (ideal)ClutchTorque sourceConstant torqueSpeed sourceSpeed sensor (ideal)

Ports

Conserving terminals 2

  • shaftarotational

    Shaft flange a. Torque into the flange is positive.

  • shaftbrotational

    Shaft flange b, rigidly joined to a (same angle).

Parameters

  • InertiaJ0.02 kg·m²

    ≥ 0.00001

    Moment of inertia, in kg·m². Must be positive.

  • Viscous frictiondamping0.002 N·m·s

    ≥ 0

    Viscous friction coefficient to the housing, in N·m·s. Zero or positive.

Equations

Modelica
a.phi = b.phi = φ
ω = dφ/dt
J · dω/dt = a.tau + b.tau − damping · ω

Implementation

The block’s Modelica model
J*der(w) = tau - damping*w;

Assumptions and limitations

  • The body starts at rest at φ = 0; these initial conditions are fixed. Rigidly connecting it to another block that fixes its own initial angle or speed (another Inertia & load, a Speed source) over-determines the initial conditions.
  • Friction is purely viscous; there is no Coulomb friction or stiction.

Tips

  • For a lossless inertia without fixed initial conditions, use Inertia (ideal).

Used in

These larger examples use it too. Open them from Examples in the app.

  • Motor speed control
  • Servo position control

See also

Select a block in Gradara and press F1 to open its page offline.