Ultrasonics

Hi. This is Richard Mitchell with a video explaining how we use echolocation on our robots to determine how far away they are from other objects. So if our robot is to react to its environment, it must find what else is there. How far away is the wall, say? Or how far away is another robot or some other object? And is that object on the left or on the right? Here, we can borrow some ideas from nature. For instance, bats and dolphins emit the ultrasound signals for this purpose. Let’s investigate the idea. So basic concept– an ultrasonic signal is emitted, which takes time to travel.

If it reaches an object, that signal gets reflected back, which also takes time, and the time taken for the echo to return is measured, and that gives you an idea about how far away the object. The longer the measured time, the further away the object. Works for ultrasonics. Also works for infrared. In fact, for cost reasons, for ERIC, we use infrared, whereas we’ve used ultrasounds on other robots. So here, we see a robot and a series of other objects around it. By default, the robot has a sensor which emits ultrasound straight across. Let’s see what happens. Press to Start. Here we see the signal, gets an object, gets reflected back.

There’s also a reflection here, but it’s the first one to return that we note. And we can see that it’s taken 96 units for the signal to return. If I move the object a bit closer, like so, do the same thing, comes back, and it’s only 68. That’s fine for detecting an object straight ahead, but we want to know if there’s something on the left or the right. So our robots have two sensors. First, you signal it on the left. Comes back. Then the right. Comes back. And we can see it took 40 units before the left signal returned, 52 for the right, which means that this object here is closer than that one.

But if I move that one a bit closer like so and repeat the thing, now it’s only taken 28 units, so this one is closer. So in summary, our robots have two sensors, two transmitters and associated receivers, and they first find the distance to the nearest subject to one eye, then to the other eye. Feel free to investigate this web page further. You can move the robot around. You can move the objects around and so forth. Later, you will do an exercise where you will set the robot’s speeds depending upon the information from sensors such as these.