Animation script not animating?

I have a script... It is supposed to animate my custom model, my custom model has a HumanoidRootPart and has Motor6D's connecting all the parts... it doesn't work! Why not? Here is the script

local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/asset/?id=274560333"

local animController = Instance.new("AnimationController")
local animTrack = animController:LoadAnimation(animation)
animTrack:Play()

Please help!!! Thank you!!! P.S This is in a regular script