Drive drifts at higher speeds

[tfield]

Even when driving straight, as speed increases, heading compensation does not seem to prevent the drive base from turning to one direction or the other.

1. FIgure out why drive wants to turn
2. Figure out why heading correction only works at low speeds. Is this due to the fact that speed measurements are happening at the start of the periodic cycle only once? Note, on Jan 26 signal periods were updated significantly to potentially address this but this has not yet been tested.