View Full Version : [Question(s)] sensors, sensors, sensors!

11-03-2008, 12:33 AM
As I have mentioned before multiple times, I am a beginner to robotics (I'm particularly interested in humanoid). I've noticed tons of sensors used for the humanoid robots and I'm confused what their capabilities are.:confused: I know that the gyroscope is used to stabalize a robot and keep it in balance, but what do tilt sensors and accelerometers do? Are they the same? Which one makes a robot get back up when it has fallen?


11-03-2008, 03:08 AM
A tilt sensor is a sensor that senses if it is placed at an angle - be it just an indication of yes/no, or an output stating the actual angle it is at.

An accellerometer measures accelleration, but since gravity is accelleration, you can also use it to measure angles (relative to ground for example, it can be used as a tilt sensor)

A gyro is a device that resists movement, and gives an output relative to the speed with which it is moved out of balance. Say you have a gyro in your hand, and you rotate your wrist 90.
The output depends on the speed with which you rotate your hand, the harder you flick your wrist, the higher the output.

So you see, there's not really a sensor that determines whether a robot has fallen. It's the roboteer who decides what sensor he'll use, to what purpose and on which principle.

You could strap an egg to the butt of your robot and have a sensor detect if the egg is ok. When it's broken, one could decide the robot has fallen. It's all in the way you decide to use your sensors

11-03-2008, 11:42 AM
[moved to sensors forum]

11-03-2008, 09:51 PM
Thanks ScuD,
I've always wondered what all the sensors were used for...
I guess it really depends on how I use them.

11-10-2008, 02:18 PM
Now that I know what these sensors do, can anyone tell me what's the difference between sonar and distance sensors?
I know the fact that it differs by how I use them, but I just want to know their capabilities.

11-10-2008, 02:27 PM
Now that I know what these sensors do, can anyone tell me what's the difference between sonar and distance sensors?
I know the fact that it differs by how I use them, but I just want to know their capabilities.

Could you post an example of each? A link would be fine

11-10-2008, 02:36 PM
I think you are talking about the difference between sonar and IR distance sensors. They can both be used to measure distance. IR works by sending out an infra-red beam, and measuring the angle at which it bounces back. Sonar sends out audio pulses, and records how long it takes them to come back. They both measure distance, just one uses light, and the other uses sound. That said, some IR sensors can also detect the color of an object by measuring the intensity with which the IR beam is reflected.


11-11-2008, 02:43 PM
With that said,
what are some pros and cons between these sensors?

11-11-2008, 02:58 PM
They're really useful when used together. Don't trust any one sensor, no matter what it is, always err to the conservative sensor, and always keep a history of prior sensor readings to compare (a "sliding window") and correct error.

IR is confused by specular surfaces and mirrored surfaces. Wanna see something funny? Try getting a distance from your hand to a mirror at a slight angle with an IR or laser ranger. :) Specular surfaces might as well not even exist, you'll just merrily run them over. It's also frequently confused in sunlight, or at least diminished in sensitivity

Ultrasound is confused by sound deadening. Try to get the range to the duvet on your bed... They also tend to get confused in really fast changing environments - like when you're about to drive off the side of that cliff...

The best bet in my experience is to carefully experiment with your mapping system in a *controlled* environment where you won't damage property or life [or bot]. Then *carefully* make controlled runs in the environment it's intended to operate in. Just know that sometime, somewhere, the robot is gonna go bonkers for something you didn't predict. As your 'bots grow in size, make sure you have some means to kill them remotely. And yes - I'm serious... That's why the autonomous urban vehicles in the DARPA challenge have a couple humans: One with a finger always on the kill switch, another ready to wrest control of the vehicle if necessary. And even for all that, the last DARPA Urban Challenge had a fender-bender. And these are all multi-million-dollar robots with the finest sensor arrays known to man today.