Variation in dynamics: would I able to vary the existing dynamics on this platform??

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hi all, I need to vary the dynamics in the existing model, such as variation in the resistance of the motor , or friction coefficient of the joints.
so my question is , would I able to vary the existing dynamics on this platform?? and then use it in conjunction with al other funcitonalities? ..If so, how? ..kindly direct me towards some links. Regards, mayank