In this example, you simply need to know L1, 元, and the weight of the servos and arm parts. It means, if you know the weight of each servo and the length of each part of your arm, it’s possible to evaluate the torque and determine which servos to use. If the weights F1 and F2 are located in the center of the mass, then you can conclude:

Suppose you need to evaluate the torque in servo A1. This is explain further in a bit.īy definition, torque must consider the perpendicular length, as shown in Figure 11-4, and not the arm length as you see in the servo specification. A second point to be considered when the vendors provide such numbers is that the measurement is the worst-case scenario when the arm is holding weight in the horizontal position. Torque is force times length, but if you search for different servos on the Internet, you will realize that vendors only mention the mass, excluding the gravitational acceleration. In other words, the servo will not be able to rotate or it might rotate backwards. That means when you use a 1-inch long arm, the servo will hang if you apply a weight equal to 100oz (M). So, when you read that a servo supports a specific amount of Kg/cm or oz/inch, it means the servo hangs if you apply the weight mentioned in a 1-cm or 1-inch arm.įor example, suppose you have a servo with a stall torque of 100 oz/inch. The letter M represents the quantity of mass (weight) attached to the end of the arm. In Figure 11-3, the length is represented by L and it’s the measurement of center of the servo’s shaft to the end of the arm. To understand what this means, consider Figure 11-3. Stall torque is usually measured in ounces per inch or kilograms per centimeter. When you order a servo motor, it comes with several items on its specification, including stall torque. Stall torque helps determine which servos you need to use in your robotic arm. In Chapter 4, you learned about servo motors, but not about stall torque, which is an important concept that you must understand. There are several factors you must consider when constructing a robot arm, including the maximum load weight, the stall torques of each one of the servos, how much weight each servo must support related to its position in the arm, and the weight each frame that constitutes the arm. Your arm, as it turns out, has seven DOF the wrist alone has an amazing three DOF.

For example, using you own arm and following Figure 11-2, try to reproduce the following movements:

Simple arduino robotic arm project