A majority of the members elected to the board of commissioners shall constitute a quorum to do business, but a less number may adjourn from time to time and compel the attendance of absent members in such manner and under such penalties as may be prescribed by ordinance. The affirmative vote of a majority of the members elected to the board of commissioners shall be necessary to adopt any ordinances, resolutions, order or vote; except that a vote to adjourn, or regarding the attendance of absent members, may be adopted by a majority of the members present. No member shall be excused from voting except on matters involving the consideration of his own official conduct or when his financial interests are involved.