I Think, Therefore I Grow

To say that Henry Pym's evolution in size-changing amounted to a work in progress is perhaps putting it mildly--much like his cybernetic technology, which was harnessed in helmet form when he took on the identity of Ant-Man.

Good thing that schematic identified the helmet's antennae.  Those protrusions could've been anything.

And Hank's headgear would become even more crucial to him, as he went on to experiment in increasing his size and began adventuring in another identity:

(Hank doesn't seem to have grasped the fact that it's the walls, as well as the rest of his demolished house, that ended up being crushed by him.)

Hank may conduct his research using the trial-and-error method--but despite the cries of alarm no doubt being shrieked from the rest of the homes on his block, what we're seeing is Hank taking the first steps toward dispensing with using special gas to change his size, in favor of a more handy capsule form. It would certainly have advantages over battling villains on windy days, where the size-changing fumes would be in danger of dispersing before they could be inhaled, but I'll still state the obvious: Wouldn't Hank and Jan have to wait a few minutes for their capsules to dissolve and the contents released in their bloodstream? Maybe Whirlwind or the Black Knight would be sporting about it and put their attack on hold until the capsules took effect.

Eventually, Hank redesigned his headpiece to allow him to pitch those capsules altogether. I rather liked the fact that the antennae of the headpiece also let him continue to communicate with the insect world as well as other sensory functions, though stories featuring Giant-Man would understandably tend to focus more on his large size--he's not called "Cybernetic Man," after all.

The Wasp, unfortunately, received no such upgrade, though Hank was able to use his new gear to extend his mental size-changing to her, as well.

It's not really clear when Jan was able to pitch her size-changing capsules. It stood to reason that Hank wasn't always going to be in range or otherwise available to change her size for her--and when they were separated, she'd have to be able to adjust her size, er, on the fly as the situation called for it. At some point off-panel, Hank presumably gave her the ability to mentally adjust her size, even without a headpiece of some sort. As for Hank, his role as an Avenger led him back to the lab to tinker on more powerful headgear for himself--and this time, the Wasp also took the opportunity to give him a more eye-catching costume. (It was certainly that, all right.)

But, what was the new power that the helmet attachment was supposed to have? Well, you've actually already seen it, to an extent--but now it applies to all organic forms.

Giant-Man never really made any use of this power--nor was he given the time, since he and the Wasp would soon go on hiatus from both the Avengers and his feature in Tales To Astonish. The size-changing difficulties he began experiencing as his time in that title wound down would follow him when he returned to the Avengers after a ten-issue absence--and he eventually reached a point where he would make another adjustment to his headpiece, this time focusing on the possibility of a more extended career as Ant-Man.

When Hank eventually abandoned the growth aspects of his powers and settled on the identity of Yellowjacket, it seemed a good compromise that would ensure his continued health while allowing him to have a higher profile than Ant-Man.

BONUS:

By sheer coincidence, a couple of size-changing cybernetic cosplayers!