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Feet-ground interactions influence the legged robot's stability. In this paper, a high-resolution indirect force measurement for hydraulic-legged robots is presented. The use of pressure transducers placed at one or both chambers of the robot's double-effect hydraulic actuators is investigated, and conclusions are drawn regarding their capability for indirectly measuring the contact forces between the feet and the ground. Because of the nonlinear dynamic properties of hydraulic cylinders, friction modeling is essential to determine at all times the true forces of each foot against the soil. The test case is called ROBOCLIMBER, which is a bulky quadruped climbing and walking machine able to carry heavy-duty drilling equipment for landslide consolidation and monitoring works. Sensor calibration and signal filtering requirements are also taken into consideration. To end, the overall proposed approach to measure feet-ground interactions is experimentally evaluated.