Designing a Home Cleaning Robot (Part 2)

Part 2: Mechanical Design

Continuing with this four-part article series about building a home cleaning robot, Nishant and Jesudasan discuss the mechanical aspects of the design.

By Nishant Mittal and Jesudasan Moses
Cypress Semiconductor

In part one (Circuit Cellar 329, December 2017) of this home cleaning robot article series, I discussed the introduction to the concepts of cleaning robots and the crucial design elements that are part of a skeleton design. Apart from that I discussed various selection criteria of the components. In this part, with the help of my colleague Jesudasan Moses, I’ll explore the mechanical aspects of the design. This includes selecting materials, aligning all the components on base, designing the pulleys for optimal performance, selecting motors and so on. The mechanical design for such a system can be very challenging because it’s a moving system and that adds complexity to the process. While this part is focused on mechanical issues and making the base ready, all this paves the way for when we add the “brains” into the system in part three.

DESIGN ELEMENTS

Figure 1 shows the block diagram of the mechanical design for this project. The overall structure of this design requires a base that is strong, but not too heavy. Using a metal base isn’t a good option for this type of system because it would increase the overall weight. Such an increase might mean that a higher torque motor would be required. The next elements are the motors and wheels. We chose to include motors only in the back. Using a front motor would probably be an overdesign for such a system. If you examine professionally designed home cleaning robots—like those I covered in part one—all of them had only the back motors for movement.

Figure 1
Mechanical arrangement of the home cleaning robot

On the front side of the unit, only rollers are added. This gives the system a complete 360-degree freedom of movement. The most important parts of the system are the cleaner and the roller. These are placed toward the center of the system and are controlled using an arrangement of motors and pulleys. In the front of the system, side brushes are added that again are controlled using motors. Now let’s look at the selection of each of the design elements.

Selection of the base shape: The base shape selection is very important because it defines how efficiently your home cleaning robot can clean at corners. A circular base shape is the most recommended option. A circular base enables the robot to move around corners and thereby cover each and every part of the house. That said, for a hobby project like this one, a rectangular base means no advanced tools are needed to cut and shape the base. With that in mind, we chose to use an acrylic material in a square shape for the base.

Motor selection: For our design, we opted for two movement motors on the back of the unit and another motor at the back for the roller pulley. On the front, there are two more motors to move the side brushes. We’ll save the more technical discussion about motor selection in part three. Choice of motor size depends upon the total weight that the front and back need to handle. The total weight should be equalized, otherwise the system won’t remain stable when the robot is moving fast. The placement of the two movement motors should be aligned to their center of axis. That ensures that when the robot is moving straight, it won’t divert its direction. It’s also important to buy those two motors from the same vendor to make sure they share the same mechanical properties.

Wheel Selection: It’s very important to decide on the net height of the system early on. Wheel selection is the deciding factor for the net height. .

Read the full article in the January 330 issue of Circuit Cellar

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