Stage 1 of Falcon 9 uses its gimballed engines during launch to control roll, pitch, and yaw.
Only the eight peripheral engines can be used for roll control since the center engine couldn't possibly exert a significant counter torque about the rocket's length axis.
But eight engines seems overkill for roll control... Do they all participate in roll control or is it just a subset of the eight that do?
It seems four engines would suffice, or maybe even just two (in pairs of diametrically opposed engines).
Sources would be appreciated, but if you don't have them handy, a comment pointing me in the right direction would still do.
Would be curious also if all engines participate in pitch and yaw control, or if again only some of them do. Thanks!!!