# Connecting DC motor to a revolute joint

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Vicente Casanova on 20 Mar 2021
Answered: Vicente Casanova on 18 Nov 2021
Hi
I'm trying to interface the DC motor block (Simscape Electrical) to a revolute joint (Simscape Multibody). The aim is to develop a simulation model for a Pendubot.
Following several examples I think (I hope) I've made the connection properly, including the Rev-Rot interface to feedback the joint velocity into the DC motor but I have a doubt. If I want to change the friction, where is the right place to do it?. I've noticed that I can change the damping coefficient in the revolute joint (which is what I usually do) but it can be changed in the mechanical parameters of the DC block. (Rotor inertia).
Find attached a zip file with the simulink model and the stp files. Don't mind the commented blocks, just trying to model the motor non-linearity.
Best regards

Juan Sagarduy on 22 Mar 2021
Hi Vicente
It shall work in both cases, but it is more natural to do it on the Simscape side (DC actuator). This makes sense if u wanted to add friction later on.
Good luck Juan
Vicente Casanova on 24 Mar 2021
Thank you, Juan for you answer.
That's what I thought but there must be any difference. The parameter in the DC motor (rotor inertia) is mesured in Kg*m2 (momentum of inertia) and the one in the joint (damping coefficient) is measured in N*m/(deg/s) (viscous friction). I guess there must be some kind of equivalence. I mean, if the damping coefficient is e.g. 0.0001, which is the value of the rotor inertia to get the same results?.
Best regards
Thi Pham Duy on 17 Nov 2021
Edited: Thi Pham Duy on 17 Nov 2021
hello friend, if I want to add a coefficient of friction for the DC motor, how can I add it. I hope you can reply

Vicente Casanova on 18 Nov 2021
I usually adde the friction in the damping coefficient of a revolute joint (Simscape Multibody) connected to the motor. But I'm not really sure if it is the right form to do it.

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