In Stock.     Vaccel    Acceleration & Tilt  Sensor    $59.00                 

The VAccel Sensor lets your robot measure it's acceleration.  The sensor can also be used to measure tilt.  This is a two channel device that lets you measure acceleration or tilt along two perpendicular axis. This sensor is compatible with the VEX robotic system. *

Acceleration is a change in speed.  When you push the gas pedal of a car, and the car speeds up, this is acceleration.  I.  The VEX Dual Acceleration/Tilt Sensor (VAccel) measures acceleration by it’s effect on a small mass.  The sensing mass is also affected by gravity.  Because of this, the sensor can be used to measure gravity.

Gravity is constant, and points straight down.  Since the Accel sensor can measure gravity, you can use it as a tilt sensor.  The sensor is most sensitive to tilt when it is mounted so the sensing channels are perpendicular to gravity.  (the electrical connector is horizontal)  When mounted this way, the light sensor value will be 50, indicating zero acceleration.  The value will increase or decrease depending on the direction of tilt.
 
 

Accel Sensor.
 

  Direction of sensitivity.

Programming

The Accel & Tilt Sensor is programmed like a light sensor. Use the “Light Sensor” block in EasyC to generate the statement

YourVariable = GetAnalogInput (1)

This reads the sensor on port 1 and loads the value into the variable named YourVariable. The sensor value is an integer with range 0 – 1023. (This is actually reading the 10 bit A/D converter in the VEX computer.)

Here is a programming example of using the acceleration sensor to make a robot stop at the top of a hill.

The Accel sensor must be programmed as a light sensor. With zero acceleration, it has a VEX light sensor value around 500. With one “g” (one gravity) of acceleration in the forward direction, the output will be around 900. One “g” in the reverse direction will give an output around 100. The sensor response is linear between +1g and –1g.

Specifications

•  Size 1.05 x 1.05 x 0.8 inches Mounting ears extend 0.35 inches on each side.. 

•  Two cables with 3-pin connectors for VEX

•  Range: + /- 1.1 g.  (gravity)

•  Bandwidth:  50 Hz.

The sensor element is a micromachined polysilicon structure suspended over a silicon wafer by polysilicon springs.  The structure forms a differential capacitor with the wafer below.  Acceleration causes movement of the suspended structure relative to the wafer, and thus a change in capacitance.  The capacitance is measured and converted to an output to the RCX.  The sensor achieves high reliability in a small package by using surface mount parts using a reflow solder process.  .

* VEX is a product of Innovation First, Inc