## 5 Experimental Results  
### The Experimental Facility  
In this section, the test-bed used in this research is described in detail. Considering the high experimental cost of the MMMS, a tunable planar flexible base with three degrees of freedom is designed, which includes a two-dimensional motion platform carrying the linear variable stiffness module (containing X and Y directions) and one rotation (Rz direction) variable stiffness module, as shown in the right picture of Figure 11b. The stiffness can be adjusted corresponding to different configurations of macro manipulators. An inherent slight backlash is added in the three directions due to the mechanical structure, but the real-time base backlash compensation is not included. A prototypical manipulator of EMM is connected with the flexible base and is supported on the air-bearing table. The manipulator is constrained to move in the horizontal plane, only the three parallel joints of the manipulator can rotate, which is equivalent to a three-link manipulator. The configuration from 1 to 7 is \([90,-90,wrist, elbow, shoulder,-90,-90]^{T}\) deg, as shown in the sub-figure of Figure 11a. The joints are supported by the micro-gravity compensation system, the EEF (including FTS) near joint 7 (shown in left top picture of Figure 11b) is connected with the flexible base. The detail of the FTS used in the experiment has been exhibited in [33]. The EEF near joint 1 can be connected with the payload. Figure 11a shows the scenario of the empty load visual servo, where the payload is fixed on the ground. A grapple figure is mounted in the back of the payload, the VM of the HC is installed on the grapple fixture, which is shown in [9]. The left picture of Figure 11b shows the scenario of the 1500 kg load visual servo, where the EEF connected with the grapple fixture. HC is obscured by the large payload and the PC will work. The software of the manipulator system includes communication, imaging, visual measurement, active thermal control, motion, power management, fault detection and handling, software maintenance and update, and task list management. The control system of the manipulator is distributed, where the central controller is fixed on the elbow joint, as shown in Figure 11a. Controllers of the joints and central controller are all based on the BM3803 and FPGA. The console, consisting of a server, display, and monitor, is connected based on Ethernet. The primary task processing process is that the central controller parses the control commands and control parameters on the manipulator's dedicated 1553B bus, as well as the real-time calculation results, and controls the joints, effectors (including FTS), and end cameras, respectively, via the arm's internal 1553B bus to complete the specified arm system tasks. After the task is completed, the arm software system returns to a non-working state or a safe or standby mode state, as required, pending the next task. Interpolation is required between the camera, central controller, and joints due to the different performance of the processors. The frequency of the posture measurement, central controller, and joint controller is 8 Hz, 10 Hz, and 500 Hz, respectively. The posture measurements obtained from EVS are widened to 10 Hz. The desired joint angles calculated in the central controller are interpolated in the joint controller every 50 times. The joint controllers are PD-based motor control with a steady closed-loop control accuracy of better than 0.025 deg. The sensors' data are stored in the server at a frequency of 10 Hz for the fast telemetry. Two cases of experiments have been performed based on the flexible base manipulator testbed. First is the no-load visual servo based on the HC; second is the large payload visual servo based on the PC. Here, we assume no contact between payload and pallet. The visual marker is ahead of the camera, and two desired berth positions are planned to reach the final target.