Custom Animation Help?

How can I prevent adding to the rotation? Only prevents if I reset to the default but I dont want that, and I need help fixing.

local speed = .1
local tick = .5
local motor = script.Parent
motor.MaxVelocity = speed
if script:FindFirstChild("Default") == nil
    then
    local def = Instance.new("CFrameValue")
    def.Name = "Default"
    def.Value = motor.C0
    def.Parent = script
end
local def = script:FindFirstChild("Default")
--Rotation,Time,Direction--
local draw = {
{0, 0, 0},
{-180, .5, 30},
{-30, .5, 30}
}

--Problem Line
function play(ani)
    last = math.rad(0)
    for a = 1, #ani do
        num = a
        angle = tonumber(ani[num][1])
        motor.DesiredAngle = math.rad(angle)
        ang = math.rad(ani[num][3])-last
        motor.C0 = motor.C0*CFrame.Angles(0,ang-last,0)
        last = ang
        wait(ani[num][2])
    end
end
----

motor.C0 = script.Default.Value
play(draw)