# Transforming position to torque

first question in this forum :D

so i started creating a 2 link robotic arm in SIMULINK and made a function that builds its trajectory (cubic spline) and used it as an input for my joint. so my input was position and output was the torque etc.

Now i would like my input to be torque,how do i go about it? should i create a transfer function out of the dynamic equation OR can i use the trajectory in someway OR is there a simple way? If you have an answer i would appreciate if you can send a detailed explanation on how you can do that in SIMULINK

• Welcome to Robotics, Susanoo. As it stands, it's not quite clear what you're asking. If you want to supply a joint torque to the Joint1 block, then you need to double click the joint, go to "Z Revolute Primitive" --> "Actuation" --> "Torque" and set it to "Provided by input," then set "Motion" to "Automatically computed." If you're asking how to generate a torque reference that you could pass to the torque input port for the joint, then the answer is however you want; open loop, PID, etc. – Chuck Jan 23 '18 at 16:14
• If you have a more specific question, then please edit your question to reflect those details - what you wanted to have happen, what you tried, what you saw, and what you expected to see. – Chuck Jan 23 '18 at 16:15
• Thanks for the response :) I knew how to change the joint input, the question is how can i use my trajectory function or dynamic functions of the structure to create a torque input instead of position. i want to use torque control. – Susanoo Jan 23 '18 at 16:27
• It depends what you want to achieve, test a torque controller you can just feed the joint with a smooth torque command, follow a velocity or position profile for the joint then you need to pass through the dynamics of your assembly and use inverse dynamics and classic control theory. – N. Staub Jan 26 '18 at 17:39