Realistic Velocity Calculation

[Greg McKaskle]

Integrating the acceleration to get velocity is theoretically correct and simple, but won't yield good results unless you can handle lots of pesky details.

The biggest problem is that the accelerometer is operating in the earth's gravity field. You have a big force that just doesn't go away. You can sit still and calibrate it out, but if you tilt just a tiny bit, gravity's "down" vector starts to show up in your other orthogonal dimensions you really care about. And since you are accumulating, it adds up quick and appears that your robot has been accelerating and is now traveling across the field. My understanding is that good IMUs also contain a good inclinometer ( a specialized gyro) so that they measure the tilt and correct for it.

If this were straightforward, you'd also see tons of phone apps that not only counted steps, but told you how fast you were walking/driving and didn't need GPS and cell triangulation to know your location. Cars wouldn't measure wheel speed either. They would use the same technique.

So the concept is a good one to discuss and experiment with, but a little bit of additional analysis will show the need to cancel gravity for matches in order for this to work well enough.

Greg McKaskle