[20160928] Valkyrie Stands up with Single Support

Finally, Valkyrie made a single support balance. After moving CP to the left leg, Valkyrie reduce the reaction forces of the right foot (transition phase). When the vertical direction reaction force of the right foot is smaller than 15N, Valkyrie starts to lift up the right foot. There is only position control so we can see the foot orientation is not parallel to the ground. Anyway, it sustains the posture after lifting the foot by 13 cm.

Major changes are followings:

1. Change CP control law:
   Previously, it was feedforward (current CP) + feedback (push the CP to desired location). Now, I weight down the feedforward term to push harder CP to the desired.
   
   
2. Relaxed inequality constraints for tangential reaction forces:
   Previously, tangential contact force cannot be larger than 150 N. However, I increased the limit to 350 N since optimization solver keep complaining there is no solution.
   
   
3. Change optimization solver from NLOPT_LD_SLSQP to NLOPT_LN_COBYLA :
   This is essential change since Valkyrie cannot make a single support balance before I changed solver even after did all of above. Cobyla is fully generic optimization solver, which can handle nonlinear cost and constraint. After trying several solvers, I just tested this too much generic solver, and it dis reaction force calculation although it takes much longer time. I strongly feel that we need to find another optimization solver and closely examine the current formulation. Currently, Jhanani Selvakumar is working on this problem. I look forward to see progress.