Mechanical load

Shaft inertia, viscous friction and a step in opposing load torque at 0.45 s.

  • signal
  • rotational
  • Gradara equations
  • 2 ports
  • 5 parameters
BlockMechanical loadKindshaftLoadLibraryRotational

Description

A complete test load for a motor shaft: an inertia with viscous friction to the housing and a load torque that steps up at a set time. Use it to check how a speed or current controller rejects a load disturbance.

The load torque is also sent to the TL output, so you can plot it next to the motor torque.

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 Mechanical 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:ConstantStepInertia & loadSpeed sensorSine waveSpring-damperBacklashInertia (ideal)ClutchTorque sourceConstant torqueSpeed sourceSpeed sensor (ideal)

Ports

Outputs 1

  • TLloadTorquesignal · N·m

    The load torque currently applied, in N·m (signal output).

Conserving terminals 1

  • shaftflangerotational

    Shaft flange. Torque into the flange drives the load in the positive direction.

Parameters

  • InertiaJ0.002 kg·m²

    ≥ 0.00001

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

  • Viscous frictiondamping0.001 N·m·s

    ≥ 0

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

  • Initial load torqueinitialLoad0.05 N·m

    Load torque before the step, in N·m.

  • Added load torquestepLoad0.35 N·m

    Torque added to the load at loadTime, in N·m.

  • Load step timeloadTime0.45 s

    ≥ 0

    Time of the load step, in seconds.

Equations

Modelica
loadTorque = initialLoad for time < loadTime, initialLoad + stepLoad afterward
J · dω/dt = flange.tau − damping · ω − loadTorque
ω = dφ/dt, with φ(0) = 0 and ω(0) = 0

Assumptions and limitations

  • The load torque does not depend on speed or direction: it always acts in the negative direction. If the drive torque is smaller than the load, the shaft turns backward rather than stalling.
  • The initial angle and speed are fixed at zero. Driving the flange from a speed source, or rigidly joining another block that also fixes its initial speed, over-determines the initial conditions.

Tips

  • For a load with a different profile, combine Inertia (ideal) with Torque source or Torque step.

Used in

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

  • PMSM · Field-oriented control

See also

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