Help with animations?

I use ROBLOX's Animation tool, and there are no animations inside the tool, and this is the code I use to run the animations:

equipanim = Instance.new('Animation')
equipanim.AnimationId = 'rbxassetid://' .. EquipSwordAnimation
animTrack2 = char:FindFirstChild(humname):LoadAnimation(equipanim)
animTrack2:Play()

But, sometimes, when you press, the animations dont play, and the character gets stuck at the end or start of the animation, and the character has weird arms/legs that prevent the animations from looking good, and when I play another animation, its fine. When it ends, it still has the ending animation from the other one. Any help? Do I need to have the animation inside the tool before playing it?