We describe a user-centered approach to the process of designing spoken dialogues for commanding robots. Using scenarios and synthetic dialogues followed by simulated trials with real users we built a spoken language interface for commanding an office robot. Initial evaluation with the implemented system has brought interesting questions concerning the feedback necessary for interacting with a robot that has no screen. We are using a small life-like character placed upon the robot who is able of displaying conversational gestures. We have performed initial evaluations on video recorded material which have raised issues concerning low-level feedback, timing and sequencing of commands in dialogue