How do I model a simple robot arm as a plant?block diagram. I know how to model motors but, I think, controlling individual motors may not be enough; and in order to control the the arm as a plant I need to model it as a plant. In the block diagram below my trouble is in finding the hardware model of the robot arm.


1 Answer 1


Each joint of your robot is one motor. They are coupled though kinematic relations and dynamic physics.

One straight forward way is to derive these so called 'equations of motion' using the euler-lagrange formalism. Once you obtained your equations you can create for example a Matlab function to solve them dynamically.

But back to the modelling part, check out the slides in Dynamic model of robots: Lagrangian approach, by Prof. Alessandro De Luca .

  • $\begingroup$ So the robot's mechanical model(in the block diagram) could be represented by the dynamic model you suggested? That's to say, will the dynamic model relate input voltages to the robot to output joint angles? I will check the slides of course, just want to be sure that's what I'll get at the end. Thanks for the help! $\endgroup$
    – Addis
    Dec 5, 2017 at 13:14
  • $\begingroup$ You are missing a few steps in between. It's not as easy as a fixed relation voltage --> angle An advice from my side: think about what's really going on inside of your robot if you apply some voltage to a motor. The voltage will generate a torque, the torque will accelerate the link of your robot. This whole process can be described as a dynamical system where the voltage is the input and the angle is the output. But as mentioned, first you need to think about the phyiscs, then do the modeling, then the implementation ;) $\endgroup$
    – madn
    Dec 5, 2017 at 13:29
  • $\begingroup$ Whether fixed relation or not, my concern was how to relate the input voltage to output angles. And I suppose your answer is that the dynamic model of the robot will solve that. Thanks for the help again, I will try to develop a dynamic model for the robot. $\endgroup$
    – Addis
    Dec 5, 2017 at 13:48
  • $\begingroup$ Welcome to Robotics madn, that's a nice first answer. On stack exchange, it is better to edit your question to add information requested in comments, rather than adding more comments. Comments are for helping to improve questions and answers, and are distracting, so we try to keep them to a minimum. If all of the information needed to answer the question is contained within it, the comments can be tidied up (deleted). $\endgroup$
    – Mark Booth
    Dec 5, 2017 at 16:53

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