From IntRoLab

DDRA - Double Differential Rheological Actuator (patent pending)


  • Philippe Fauteux
  • Benoit Heintz
  • Marc-Antoine Legault
  • Matthieu Tanguay
  • Michel Lauria
  • Dominic Létourneau


Robotic systems are increasingly moving out of factories, stepping into a dynamic world full of unknowns, where they must interact in a safe, robust and versatile manner.

Traditional actuation schemes, which usually rely on position control and stiff actuators, often fail in this new context. There has been many attempts to modify classic actuators 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 all of those limitations. By using a differentials mechanism and two magnetorheological brakes, it transforms some speed source into an open loop controlled force source which can track any desired interaction dynamics.

The advantages include safety and robustness due to extreme backdrivability. In a more traditional context, the actuator’s low inertia, eliminated backlash and reduced nonlinearities allow for greater accelerations/decelerations and a more precise positioning, thus improving productivity and quality. Of course, the ability to precisely control the interaction dynamics (force-position) opens a set of new possibilities.

From proof-of-concept to first compact integration


The first compact prototype is being assembled and tested. This is an ongoing project. Preliminary results are listed below.


DR2 prototype compact 1.jpg

Power rating


Nominal torque

10 Nm

Maximum torque

20 Nm

Torque bandwidth

>40 Hz

(limit of test)

Maximum speed

160 RPM

Reduction ratio


Dimensions ratio

90 dia X 137 mm


2.4 kg


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