Trying to build a globe in UDK, but when I do (create a sphere), my player falls straight through it. How do I make a sphere that I can walk on? Every other shape (cube, cone...etc) work just fine.


Edit: Specifically, I want to build a CSG/Brush sphere, not a mesh sphere. It appears to work just fine if I set the "sphere exptrapolation" to 1 or 2, but if I bump it up to 3 or higher, I fall right through. I literally created 2 spheres next to each other, one set at "2" and one at "3" - I can walk from the top of the "2" sphere and jump onto the "3" sphere, but I fall right through it.

  • \$\begingroup\$ I don't want to sound discouraging. But, Official UDK forum might be a better place for your question. \$\endgroup\$ Commented Nov 30, 2011 at 9:21
  • 2
    \$\begingroup\$ I appreciate the heads up - hopefully this Game Development page starts reaching a larger audience - THIS should be the place for this type of question... just - lack of users so far I guess. I'll leave the question in hopes it comes up in Google and starts drawing UDK users here. \$\endgroup\$
    – Dave
    Commented Nov 30, 2011 at 15:03
  • \$\begingroup\$ I am a UDK user too, but not experienced enough to answer your question, to the point. :) But since there is no sphere brush, so the only solution comes in my mind is creating a sphere geometry/model and making it collidable. \$\endgroup\$ Commented Nov 30, 2011 at 15:17
  • \$\begingroup\$ Do you walk the character inside(like you are in a big spherical room, but the gravity is always downward) or outside(like earth, where center of gravity if at the center of the sphere) of the sphere? \$\endgroup\$ Commented Dec 3, 2011 at 6:44
  • \$\begingroup\$ iamcreasy: I just want to be able to stand on it - gravity still normal - always pulling straight down, but - I want to be able to stand on top of it without falling through. (I'm making a "map" where you fight on top of a globe - you can still fall off the edge though - it's just a VERY large sphere w/ normal gravity) \$\endgroup\$
    – Dave
    Commented Dec 3, 2011 at 14:39

4 Answers 4


I have had the same problem, Dave. There are two options and they both involve creating a static mesh sphere. Either, you can create a sphere object with third-party software or you can create it with UDK. To create it with UDK:

  1. Click BSP Sphere
  2. Pick optimal sphere extrapolation
  3. CSG Add
  4. Right-click the BSP sphere and go down to Convert > Convert to Static Mesh
  5. Pick package to save to and click OK
  6. Double-click the sphere static mesh in the content browser
  7. Go to Collision > Sphere Simplified Collision
  8. Go to the right-side options on the Mesh Editor
    • uncheck Simple Box Collision
    • uncheck Simple Line Collsion
    • uncheck Simple Rigid Body Collision

You can now walk on the sphere. BSP spheres, especially with high extrapolation, are hyper-slow.


This what I have found:

"If you double click on the mesh you are talking about int he Content Browser, a new window will pop up. This window is your Mesh Editor. On the mail Tool Menu Bar, you will see a Collision drop down menu. From there pick the collision you want to use, and then save you package the mesh is in. Now, that mesh, even in your scene should have collision, and you should not be able to pass through them.

Also, if you right click on your mesh in the view port, and choose properties. You will find a Check box in there named Can Stand up on. This will also help sometimes if your collision is built but you can still pass through the model."


  • \$\begingroup\$ Maybe I should have been more specific, but - by "Build a sphere in UDK" - I meant a CSG/Brush, not a mesh. \$\endgroup\$
    – Dave
    Commented Dec 6, 2011 at 20:23
  • \$\begingroup\$ (Also, I wish people wouldn't up-vote answers unless they know it to be true - now less people are likely to view/answer this question since they see an up-voted answer). Not your fault, Den, obviously you can't up-vote your own :) \$\endgroup\$
    – Dave
    Commented Dec 6, 2011 at 20:32
  • \$\begingroup\$ Is there any reason why you do not want to create sphere as a mesh? \$\endgroup\$
    – Den
    Commented Dec 6, 2011 at 21:12
  • \$\begingroup\$ Alternatively can you just convert the BSP sphere into 'Blocking Volume'? \$\endgroup\$
    – Den
    Commented Dec 6, 2011 at 21:23
  • \$\begingroup\$ Den: I don't know how to create a mesh honestly - I assume I'd need a third-party modeling software do to that, which I'd rather not get into. Plus, the question still exists - why would I need to create a mesh to just walk on a bsp sphere? I'll try to look up what you're talking about with the 'Blocking Volume'. \$\endgroup\$
    – Dave
    Commented Dec 6, 2011 at 21:38

Even without any experience on UDK, I can tell you that if you are walking over something, then gravity should not be calculated for your character: gravity should be applied ONLY to objects which are NOT standing over anything else...

Imagine a wall of bricks, where each brick is dynamic and then you calculate gravity for every brick in every frame... they won't look like a wall, but a lot of jumping bricks! Float precision makes it even worse and you'll never reach 0 vertical speed, so you have to clear the speed to 0 and remove any gravity calculations for objects standing on some kind of horizontal or not-so-steep surface (then you reactivate it when you JUMP, for example).

I've posted something in another question about something similar, maybe it also helps:: Handling collisions with ground

I don't know how UDK handles this kind of stuff, but if you can control gravity for a particular object and be told about collisions with the sphere to your character, you'll be able to prevent that behavior from happening.

  • 1
    \$\begingroup\$ That has absolutely nothing to do with my question. I want to 1) make a sphere, and 2) walk on it - that's it. Changing gravity, custom gravity, gravity per things on other things...etc etc has literally zero to do with my question. As mentioned, it works with all other shapes, just not a sphere. \$\endgroup\$
    – Dave
    Commented Dec 6, 2011 at 5:30
  • \$\begingroup\$ walk On it? Like as around the sphere as people walks on Earth? Like a clown walking on a ball? Walk in a straight line over a sphere is really creative... actually I think I never saw it (the sphere surface never goes in a straight line!) I still believe you should do this, maybe creating a sphere geometry first, and if you don't have to do anything about it is because UDK does it for you, but FYI it has EVERYTHING to do :) \$\endgroup\$ Commented Dec 6, 2011 at 15:21
  • \$\begingroup\$ Pablo Ariel: I'm specifically talking about a sphere geometry - which is why it seems strange that I'd fall through it instead of being able to walk on it. Literally - create a new/empty map, build a sphere at 3 or higher detail ('sphere extrapolation'), and try to walk on it - you'll fall right through. If you do the same thing with a square, cone, cylinder, stair...etc, you can walk on it just fine. \$\endgroup\$
    – Dave
    Commented Dec 6, 2011 at 20:31
  • \$\begingroup\$ @PabloAriel Yes, you should still apply gravity to an active, dynamic object in the world, including the character, even if it is on the ground. A collision resolution pass should be robust enough to prevent bouncing. Your wall of bricks example does not apply because said bricks should be "asleep" until woken up by a collision with an active dynamic object. While stacking is a harder problem to solve, a decent collision system will still be able to simulate it in a stable fashion (were the bricks to be awake). \$\endgroup\$ Commented Nov 4, 2013 at 23:41

Easy to do, just dont use the simple sphere collision, use the things with "Auto" and make yourself a collision box. Else you can also make your own collision box in blender or any 3D program by using an object with a name starting by "UCX_". The simple sphere collision doesn't allow player to collide at all.


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