Servo Test And Torque Needed
The set-up to test the servos was provided from the schematic obtained from http://www.arduino.cc . The reason from this test was to make sure that the servos are working, to know the actual voltage and current the servos consume, as well as the amount of weight the servos can lift. During the test it was noticed one of the servos did not work. After making sure that the rest of the servos were working, it was used in two tests to determine the max current of the servos consume.
First Test
The first test was adding weight to the servos and noting the current the servos consume at that amount of weight. For example, 100 grams was added the current was 236mA. The group kept adding weight until it got to 448g, because the servos could not lift the weight anymore and current was 448mA (stall).
| Weight (g) | Current (mA) |
| 100 | 236 |
| 200 | 300 |
| 321 | 372 |
| 400 | 400 |
| 448 | 448 (stall) |
Second Test
For the second test a 7 inch, 10.16 cm, length arm was attached to servo and loaded 70g to the arm (7cm away from the servo). It was noticed that the servo needs more current (256mA) to lift the weight. By increasing the weight until the servo could not lift anymore weight, which was about 148g, the maximum current was determined.
| Weight (g) | Current (mA) |
| 70 | 256 |
| 90 | 324 |
| 120 | 388 |
| 148 | 448 (stall) |
Additionally
The group tried to figure out the maximum weight or load, i.e. W1, W8, and W9 can be as shown in the picture with the given torque (1.8-kg/cm).
In order to do so, Dr. Fumio Hamano, whose major research interests include theory, computer vision, robotics and Autonomous System, recommended the use Robot Modeling And Control by Mark W. Spong. However, it became incredibly difficult to solve the problem. In order to compensate the group decided to change the current servos to MG92B instead. Because it is believed that the current servos would not be able to left the leg, especially the servo located on the hip. The current servo (MG90S) provides 1.8-kg/cm torque, but MG92B provides higher torque with 3.1kg/cm. Besides difference in torque, there is a difference in price. The MG90S cost $4.95 and the MG92B cost $7.95.
