## The Robotics Primer: Chapter 9

• Public
By Adam Kroeker July 13, 2022 - 9:57am

### Speed of sound

According to the textbook, the speed of sound is 1.12 feet per millisecond. That is equal to 1120 feet per second, since there are 1000 milliseconds in a second. There are approximately 3.28 feet in a metre, and dividing 1120 by 3.28 gives us about 341. So, the speed of sound is about 341 metres per second.

### Speed of light vs speed of sound

The speed of light is much greater than the speed of sound. According to the Speed of light Wikipedia article, the speed of light is 299 792 458 m/s. From the previous question, the speed of sound is 341 m/s. Dividing the speed of light by the speed of sound gives us about 879157, so the speed of light is 879 157 times faster than the speed of sound. This tells us that sensors that use the speed of light are much faster than sensors that use the speed of sound. A robot that uses lasers to detect objects would be able to detect them more quickly than a robot that uses sonar.

### Multiple sonar robots

When multiple robots that have sonar sensors need to work together, their sonar sensors might interfere with each other. Sonar sensors send out ultrasonic sound waves and detect them when they bounce off objects. This could be problematic if two or more sonar sensors are operating near each other, because one sonar could detect the other sonar’s sound wave and interpret it as the reflection of the wave that it sent out. This problem might be solved by programming the sonar sensors to emit sound waves at different times, so they do not all send out signals at the same time.

### Doppler shift

Robots usually do not need to know the velocity of an object. Robots only need to know the location of objects, so that they can either avoid them or interact with them. Time-of-flight sonar already provides that information, so examining the doppler shift is usually not necessary.

### Eyes

Two eyes are better than one because having two eyes allows for either stereo vision or a 360-degree view of your surroundings. Having two eyes beside each other at the front of the head allows for stereo vision which is required for depth perception and the reconstruction of 3D objects. Two eyes on either side of the head allows for a full view of your surroundings, to watch out for any predators. Adding a third eye might be useful for allowing a 360-degree view and stereo vision. If humans had an eye at the back of the head, we could have a much wider range of vision while also having stereo view in front of us. The downside to having a third eye is that it would provide a lot more information for our brains to process, which would require our brains to be more powerful and use more energy.