The Greeblie seen on the back of the AT-ACT Driver helmet, apparently also used on Jyn Erso's hat (flashlight accessory) and Enfys Nest's belt. I modeled it in Fusion360 using references from those costumes, as well as the Helmet replica produced by Anovos.
It's been scaled to fit the Sean Fields Shoretrooper helmet (http://www.shoretrooper.co.uk/)
It's in 3 separate parts, the main body, canister and knob, for ease of printing (less supports needed)
The Canister was reprinted on a Sparkmaker DLP printer for a cleaner result.
I haven't fully finished the painting, but I've sanded and applied filler primer. A little finer sanding the I'll use a Satin black paint over the entire surface the I'll apply a bit of light weathering with Silver Rub n Buff wax.