  Current engineering design trends, such as light-weight machines and
humanmachine-interaction, often lead to underactuated systems. Output
trajectory tracking of such systems is a challenging control problem. Here, we
use a twodesign-degree of freedom control approach by combining funnel feedback
control with feedforward control based on servo-constraints. We present
experimental results to verify the approach and demonstrate that the addition
of a feedforward controller mitigates drawbacks of the funnel controller. We
also present new experimental results for the real-time implementation of a
feedforward controller based on servo-constraints on a minimum phase system.
