The drive mechanism of many robot joints are composed of an electrical actuator and a gear transmission. Besides actuator dynamics and gear elasticity, friction effects are of particular importance for accurate dynamic modeling. This paper presents the design and development of a modular testbed for experimental friction identification in modular robot drives. We have used this testbed to investigate modules that were developed at our institute for the humanoid robot Lola and an agricultural manipulator. We discovered that a friction law, similar to a law proposed in the literature, can be very accurately fitted to our measurements.