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DDRA - Double Differential Rheological Actuator (patent pending)


Robotic systems are increasingly moving out of factories, stepping into a dynamic world full of unknowns, where they must interact in a safe and versatile manner. Traditional actuation schemes, which rely on position control and stiff actuators, often fail in this new context. There have been many attempts to modify them by adding a full suite of force and position sensors and by using new control algorithms but, in most cases, the naturally high output inertia and the internal transmission nonlinearities such as friction and backlash remain quite burdensome.

The proposed actuation scheme addresses many of those limitations. The DDRA uses a differentials mechanism and two magnetorheological brakes coupled to, for example, an electromagnetic motor. This configuration enables the DDRA to act as a high bandwidth, very low inertia, very low friction and without backlash torque source that can be controlled to track any desired interaction dynamics. The advantages include safety and robustness due to extreme backdrivability and a lot of versatility in interactions. In a more traditional context, the actuator’s low inertia, eliminated backlash and reduced nonlinearities allow for greater accelerations and a more precise positioning, thus improving productivity and quality.

DDRA from proof-of-concept (Prototype 0) to first compact integration (Prototype 1)


Download QuickTime for these videos.


Prototype 1 Prototype 1b Prototype 2 (under construction)

Nominal power

90 W 96 W -
Nominal torque

11 Nm 12 Nm -
Maximum torque

20 Nm 12 Nm -

1.2e-4 kg.m² - -
Power Rate

1025 kW/s - -
Torque bandwidth

>40 Hz (limit of test)

33 Hz -
Maximum speed

160 RPM 68 RPM -
Reduction ratio

33:1 123.79:1 -
Dimensions ratio

90 dia X 137 mm 83 dia X 145 mm -

2.4 kg 1.65 kg -

Force control:

Torque control bode plot
Torque command following
Torque step

Position control:

Position command following (0.084 kg.m.m load, 8 Nm nominal, PIDc)

Interaction control:

Simulation of a spring

Simulation of a wall



  1. Fauteux, P., Lauria, M., Heintz, B., Michaud, F. (2010), “Dual differential rheological actuator for high performance physical robotic interaction,” IEEE Transactions on Robotics, 26(4):607-618. (pdf)
  2. Heintz, B., Fauteux, P., Létourneau, D., Michaud, F., Lauria, M. (2010), “Using a dual differential rheological actuator as a high-performance haptic interface,” IEEE/RSJ International Conference on Intelligent Robots and Systems. (pdf)
  3. Fauteux, P. (2010), Conception d'un actionneur adapté à l'interaction physique dans un contexte de robotique, Mémoire de maîtrise, Département de génie mécanique, Université de Sherbrooke. (pdf)
  4. Heintz, B. (2010), Électronique embarquée pour un actionneur adapté au contrôle d'interaction, Mémoire de maîtrise, Département de génie électrique et de génie informatique, Université de Sherbrooke. (pdf)
  5. Fauteux, P., Lauria, M., Legault, M.-A., Heintz, B., Michaud, F. (2009), "Dual differential rheologic actuator for robotic interaction tasks", Proceeedings IEEE International Conference on Advanced Intelligent Mechatronic, July. Best student paper award of the conference, and ASME Dynamic Systems and Control Division Best 2009 Student Paper Award in Mechatronics (pdf)
  6. Lauria, M., Fauteux, Ph., Legault, M.-A., Lavoie, M.-A., Michaud, F. (2008) “Differential elastic actuator for robotic interaction tasks,” Proceedings of Actuator 2008, 11th International Conference on New Actuators, Bremen, Germany.


  • Philippe Fauteux
  • Guifré Julio
  • Benoit Heintz
  • Marc-Antoine Legault
  • Dominic Létourneau
  • Michel Lauria
  • François Michaud