The Dalek's makeshift casing was the very first in the show's history not to be driven by a human operator from inside, instead being steered by remote control. Since the casing's midsection is much skinnier than that of normal Dalek armour, this was likely done in part because it would be much more difficult for a person to fit inside.
In an attempt to prevent spoilers, the Dalek had the codename "Kevin" in the script. Read more here.
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