I tested the Titan Battlecage of Kabr helmet in the raid and in non-raid vex zones fully leveled, and it doesn't spawn orbs as it should (even after killing hundreds of vex). Either the orb drop rate is less than 1 per raid (useless), or it is broken.
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Its just random. Same as iron harvest. Sometimes i kill 200 enemies with heavy ammo and get 0 orbs. Somtimes i kill 10 enemies and get 10 orbs... i feel like the melee ability works better on the helmet but havent done enough testing to confirm. I have recieved far fewer orbs from crits though