• Sajiv Shah

Bartender Arm #2 - Motion Manipulator Component selection

In Robotics, experience matters a lot.

I've seen some of the smartest people get very frustrated with robotics, mainly with dealing with electronics and software, as things do not seem to work as they are supposed to. That's why we made sure to select trusted components that we were familiar with when selecting parts. We decided we would rather engineer around components that may underperform, rather than struggle with components that we are not familiar with and spend many hours diagnosing failures. Here is a list of the things we were looking for when deciding on motors:

  1. Low Power draw (Max 100W for larger motors)

  2. Low RPM

  3. High torque

  4. Resistant

  5. Compatible with the motor controllers we are likely to use, or a common built-in motor controller

  6. No longer than 6 inches

  7. Require a gear ratio no greater than 5:1

DC Motors

We knew that the motors for the two long arms (axis 2, and axis 3) should be designed for high torque and low RPMs. We wanted to find a motor that would have a torque rating close to what we desired, which is listed in an earlier post. We aimed for a motor that wouldn't require a gear ratio of more than 5:1, as that would require more space and might create problems with aesthetics.

We chose the tetrix torquenado motor, which is a high torque brushed motor that offers multiple types of gearing ratios that are built into it. We settled for the 60:1 ratio, which meant that on our robot we would need to supply a 3:1 ratio to achieve the torque rating we desire. These motors are 5 inches long and relatively heavy, so they are not ideal for all exis, especially where lots of torque is not required. We plan to use two of these motors on axis 2, and one on axis 3. This motor operates at 12v and 8.7A, which means that our system will not have to accommodate lots of power draw. This motor matches our seven requirements listed above.

For axis 1 and axis 4, which are two rotary axes, we realized we would not need nearly as much torque. We then decided to use two Tetrix DC motors that we had sitting around in our garage. These motors appeared well suited for the project as they do not have a lot of power draw.

Stepper Motors

For Axis 5 and Axis 6, we knew that the large, heavy motors would not be ideal. After all, the torque required for these two axes to move the objects they are attached to is minimal. There are many stepper motors, each varying in their step size, number of phases, and more. We simply wanted to find the smallest, lightest one that would supply the necessary torque for our application. After all, the major purpose of these motors is to be able to move the robot. After searching, we found this one on Amazon which had good reviews. Stepper motors have a low power draw and do not require as much software for their motion, so a robotic arm is a great application for them.

Now that we have chosen motors, the next step we have identified is choosing the motor controllers. Details on our component selection will be in the next post.