Sforno on Exodus 35:5/ספורנו על שמות ל״ה:ה׳

1קחו מאתכם, you shall select from amongst yourselves men to collect the donations for G’d.

2כל נדיב לבו, the donations must not be forced contributions.

3'יביאה את תרומת ה, he shall bring the voluntary donation together with the terumat Hashem which is mandatory (the half shekel). The latter is known as beka lagulgolet.