An accelerometer is a component able to measure acceleration along one or more axis (see Accelerometer on wikipedia).
To be able to dimension the accelerometer (range and sensitivity), a bit of math:
An acceleration of 1g along an horizontal axis is equivalent to an acceleration of 10m.s-2 during one second, or going from 0m/s to 10m/s in one second. The robot's maximum speed will be somewhere near 0.6m/s, so, to generate an acceleration of one gee on the sensor, it must accelerate from full stop to full speed in 60ms. This is pretty quick ! So I can (safely) assume the robot will never be able to generate by itself such an acceleration, and limit the range to +/-1.2g. Thus, the sensitivity will be greater (for the same output range, the input range is smaller, so the output sensitivity will be greater) than with a +/-2g sensor.
Of course I'll use what I can find, but +/-1.2g is enough for this application.