Cross-Language Question ... Control Systems Practices ... Encoders/Gyros/Accels

[Ziaholic]

I've been struggling with some decisions for a while now and have finally decided to surrender to the "cloud" of knowledge & advice here on CD.

In practice, in general, do you find yourself depending on these various sensors for different reasons within your code? We have many navigational sensors at our disposal and sometimes I find it hard to decide which one to pick.

When do you choose to use the encoder values over the gyro angles? When do you trust your accels over your encoder positions?

I find myself jumping between encoder distances (but then worry if/when we lose traction), and the gyro (which drifts, but is good for short bursts), and the accels that summarize the situation (provided we haven't been recently jarred).

For you advanced control systems gurus, what sorts of advice can you offer for all of these various trade-offs.

I'm interested in general overall theories/practices ... and ... to perhaps spur some conversation, provide a simple example of the best way to "perfectly" rotate your 'bot by exactly 90-degrees (CW or CCW) with the single push of a joystick button. There may be subtle differences depending on the drive-train type, but I'd like to steer the conversation towards more "generic" theory/practice.

... I'm all ears ...