Here is how Ultron takes the Sentinels from the Starswirl the Bearded Wing in G-Merl's Eternal Quest.
(we see The Dazzlings facing Starlight, Discord, and Shining Armour)
(we see Celestia has been injured)
Adagio Dazzle: Look, it's admiral what you're doing and all, but we'll eventually destroy the peace and harmony of Equestria.
Familiar voice: The only path to peace, is their extinction.
(KSI Robots drive up and transform while the Avengers Age of Ultron trailer music plays)
(scooters and motorcycles drive up and transform into Ultron Sentries)
Garble: Uh, what's going on here?
(Creed and Riptide jump out of a chopper with the president in hand)
Victor Creed: One more step, and I slit his throat.
(the chopper transforms into Ultron, shocking everybody)
Starlight Glimmer: Ultron!
Discord: What are you doing here, you rust bucket head?!
Ultron: I'm here for for Celestia or Luna to take me to the secret room of the Starswirl the Bearded Wing.
Shining Armour: Well you're not going to!
Princess Luna: If I take you there, will you leave Canterlot in peace?
Ultron: Yes, I'll leave peacefully.
(Luna takes him there)
Princess Luna: Now take whatever it is you want, and leave.
Ultron: So thoughtful. I'll take(pauses for effect) them.(points to fifteen pods)
(we see the Sentinels in the pods)
Ultron: Pack them up.(leaves)
(the robots pack up the pods and leave with Victor and Riptide)