I just notice that here https://advrhumanoids.github.io/XBotInterface/classXBot_1_1KinematicChain.html#adca0efb2635f626df7c1138f188ff41b if you go in the details of the function : void XBot::KinematicChain::getEffortLimits(Eigen::VectorXd & tau_max) const you have as parameters description 'qdot_max' which should be tau_max.