Before #14212 the velocity control gains used in the multicopter
position controller were defined as a scale between velocity error in
one axis (or it's integral and derivative respectively) and the unit
thrust vector. The problem with this is that the normalization of the
unit thrust vector changes per vehicle or even vehicle configuration
as 0 and 100% thrust get a different physical response. That's why
the gains are now defined as scale between velocity error
(integral/derivative) and the output acceleration in m/s².
Channels belonging to a certain timer were not all grouped together.
This is required by the .first_channel_index and .last_channel_index data
members.
We introduce a new mixer geometry to solve the problem.
Beat Küng