Results 1 to 6 of 6
  1. #1
    Member
    Join Date
    Nov 2008
    Location
    Brooklyn, NY
    Posts
    3

    Tilting Rotation Axis

    I have what I thought was an easy problem. I want to make a small animation showing the Earth revolve around the Sun with lighting set up to show how the axial tilt causes the seasons. The Earth also rotates.

    I can almost get there. The problem I'm having is when I try to tilt the Earth's rotational axis (the Z-axis) so it is not aligned with the global Z axis. As soon as I start the animation, it realigns. Here's what I'm doing.

    I create an empty, then numpad-7 to get the x-y view. I set up two key-frames at 0 and 61 to go through a full 360-degree rotation. This rotates very nicely with a second period (targeted at NTSC). I can view the rotation using any of the 3-d views.

    I then do a numpad-1 to get the x-z view. I rotate the empty's z axis by about 20-25 degrees (just by hand). It looks fine, but as soon as it hit the play button, the empty's axis realigns with the global z axis and then it rotates.

    What I am doing wrong?

    roland



  2. #2
    Member Surt's Avatar
    Join Date
    May 2004
    Location
    Brisbane, Australia
    Posts
    313
    Try a LocRot key instead of just a Loc key perhaps? That Rot is handy for storing rotation.
    "...oppression and happiness...not necessarily mutually exclusive." - Cessen



  3. #3
    Member
    Join Date
    Nov 2008
    Location
    Brooklyn, NY
    Posts
    3
    I wasn't doing a Loc key at all, only a Rot key.

    What I really want is for the object's Z axis to point in a certain direction (other than the global Z direction, which is what I seem to be stuck with).

    I did discover part of the problem. I needed to delete the RotX and RotY parts of the key. the keeps it tilted, but it still rotates around the global Z direction, not the object Z. But it doesn't seem to matter what orientation I select: View, Normal, Local, Global, for when I tip the object Z axis, it still rotates around the global Z direction (centered on the object, so only the object is rotating).

    There has to be a way to do this, but I'm too new at Blender to figure it out....

    Help!

    roland



  4. #4
    Member Surt's Avatar
    Join Date
    May 2004
    Location
    Brisbane, Australia
    Posts
    313
    Parent the Planet to an empty (Tilt).
    Rotate Tilt for the desired amount away from Z-axis.
    Set desired RotZ or dRotZ IPOs for Tilt and Planet.
    Planet will take on the spatial transform of Tilt while rotating about its local (now tilted) axis.

    See attached blend.
    Attached Files Attached Files
    "...oppression and happiness...not necessarily mutually exclusive." - Cessen



  5. #5
    Member
    Join Date
    Apr 2007
    Location
    Richmond, BC, Canada
    Posts
    17

    Uncanny

    That is freakishly uncanny! I was just doing exactly the same thing! I too am doing an animation of a planet (for an astronomy course I'm teaching next semester) and wanted to set up the axis in exactly the same way. I log on to post my question and here it is at the top of the pile! How awesome is this forum ... they answer your question before you even ask it!



  6. #6
    Member
    Join Date
    Nov 2008
    Location
    Brooklyn, NY
    Posts
    3
    I'll have a look at your file. I found the answer also in this thread http://blenderartists.org/forum/showthread.php?t=138509

    I had parented the sphere to the empty, but was rotating and tilting the empty. I had to rotate the sphere and the tilt the empty. After playing around (and finding a couple of textures online with the Earth and Sun surfaces), I've now got a nice short animation. It needs some tuning, but my kids understand it (they're the beta testers :-)

    Thanks!

    roland



Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •