Speed Sensors

[Dillon Compton]

There are really two options i am aware of: Accelerometers and gear-tooth/encoder/banner sensors.

The main advantage of an accelerometer is that it will mease the robot's net acceleration, not the wheel revolutions. Basically, it measures your actual acceleration (can be converted to velocity relatively easily). This means that in a situation (such as running into a wall/other robot) where your wheels are spinning out, you will get an accurate speed reading, whereas with an encoder-style sensor you will not!

However, encoders are certainly simpler to implement, so look at the application and decide what sort of accuracy and reliability you need, and then choose which sensor to use.

//Dillon Compton
Team 1394

[DARKAGE]

how do you connect the speed sensor???

[lukevanoort]

If you use encoders of some sort and have the weight/space I'd suggest mounting them on a non driven wheel that touches the floor to eliminate error from the robot doing spinning its wheels.

[mluckham]

Accelerometer doesn't tell you current speed, it just measures acceleration. And if you are turning at the time, you will get the forward component of acceleration plus the lateral component (2-axis accelerometer).

Using encoders, you can figure distance travelled, speed, and acceleration.
Put an IF statement in your code that executes its inner code at a known rate (eg: 10 times per second).

if (time_elapsed_100msec)
{
   Speed = CurrentEncoderCount - prev_EncoderCount;
   Acceleration = Speed - prev_Speed;

   prev_EncoderCount = CurrentEncoderCount;
   prev_Speed = Speed;
}