Rotate a part around a pivot point via motor?

So, what I'm trying to do is get PartA to rotate to 180* around PartB.

    M = Instance.new("Motor", game.Workspace.A)
    M.Part0 = workspace.A
    M.Part1 = workspace.B
    --DesiredAngle = 12
    --CurrentAngle = 0
    --MaxVelocity = 43

What the Read-me told me to do

--[[1. Insert two bricks in Workspace named 'A' and 'B'
    2. Make sure they are the same size and position
    3. Copy and paste following code into command bar:]]--
    M = Instance.new("Motor", game.Workspace.A)
    M.Part0 = workspace.A
    M.Part1 = workspace.B
--[[4. Press 'Run' and begin playing with it!
    5. Tweak the MaxSpeed/DesiredAngle options to get the effects you desire.
    A suggestion would be to weld everything in your flap/gear strut/whatever to B
    and weld A to a central brick in your aircraft. Not too difficult scripting and
    I shall not ruin your fun by doing for you. Remember, DesiredAngle is in radians.
    For the motor to work, both A and B should NOT be anchored. 
--]]