Legged robots: contact detection

Photo: Universal Robots
Photo: Wikipedia: Jacobian matrix and determinant
Photo: MAB Robotics
Photo: MAB Robotics co-founders student’s project made as a part of the activity in a research club — KN Mechatron, Poznan University of Technology. Inside the feet are buttons. The later foot version was equipped with a strain gauge sensor.
Photo: ANYbotics; ANYdrive sea actuator
Photo: Quasi direct drive actuator; Benjamin G. Katz, MIT, Master Thesis — A Low Cost Modular Actuator for Dynamic Robots
  • The planetary gears provide a significant increase in torque and don’t reduce the dynamics of movement. This is due to the low level of reduction — 1:10 ratio is maximum for one staged gear. The low level of reduction provides resistance to impact loads and passes them to the engine.
  • The BLDC (BrushLess Direct-Current) motor generates the torque. Because of gears’ small reduction ratio the motor has to be big to generate demanded torque. Furthermore, thanks to the control algorithm the motor can work like a shock absorber — we can precisely model spring coefficient and damping factor, and also change it at any time.
  • The control electronics is the “brain” of the actuator. It’s responsible for motor control, position measurement and communication with the robot. It must be precise, fast and reliable like the MD10.
  • The case should be compact in size, have low weight, characterized by high resistance and have convenient mounting points.


There is a range of solutions of how walking robots can detect contacts with the ground or other objects and each of them have advantages and disadvantages. Switches inside the robot foot are the cheapest and simplest solution but provide inaccurate data only from the end of the leg. Force sensors in the robot foot provide more accurate data but also only from the end of the leg. SEA are very good actuators, have very accurate torque measurement and nice parameters of move. The disadvantages are mechanical complexity and high price. QDD actuators also have accurate torque measurement and nice parameters of move. QDD are much cheaper than SEA and usually have less torque and greater speed. Choosing one depends on various factors: your objectives, budget and desired output information.



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MAB Robotics

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