Bug/featue. physics, moving spinning objects dont curve

Development World Creation
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1

This may be a limitation of the engine, (or i may be missing something).

Physics simulated objects that have spin and directional momentum do not travel in a curve, they travel in a strait line.

I found this bug/feature while investigating the rolling ball example. I added spin to the ball (torque in YAW axis) to see if I could make ‘trick shots’.

I understend this may be a limitation - as friction is dealt with via damping on entire objects.

2

Hi,

This actually isn’t a limitation of physics or a bug, but is instead how physics works.

Mythbusters did a whole segment on this a while back explaining this by using the movie “Wanted” as an example. If you’ve not seen the film the story involves being able able to sling your gun to get bullets to curve around corners as part of it’s story.

To better illustrate the Bernoulli and Magnus principles to explain why a curveball can be thrown with a baseball.

Even though in the Bernoulli and Magnus principles there is air that affects the curving baseball and in UE4 we do have the “Wind Directional Source” this will not currently affect physics actors.

Wind Directional Source may later on work with physics actors but at the moment it is not planned.

If you have any other questions feel free to ask!

Tim

3

thanks for the response.

Is it possible in UE4 to set up materials such that spin will generate curve. (or must this be handled in code or blueprint)

The example im thinking of is a snooker/pool table game (note this is not project relevant for me, but I am curious)

Also im curious if in UE4 2 adjacent materials can be created such that they have different friction, this would be usefull in driving games, eg grass next to tarmac.

4

I’m theorizing with this as it should be possible but I have no idea how to set this up exactly off the top of my head.

Also im curious if in UE4 2 adjacent
materials can be created such that
they have different friction, this
would be usefull in driving games, eg
grass next to tarmac.

This is possible. This would be a Physical Material. In your material for your Tarmac or your Grass you would assign this in the material itself. There are settings in your Physical Material that you can setup things like Friction.

Here is the documentation for that.

Is it possible in UE4 to set up
materials such that spin will generate
curve. (or must this be handled in
code or blueprint)

Blueprints or C++ would be a good place to start with this. In BP I would look into things like adding impulses or forces when specific events happen. This would possibly be a good place to start with to fake the effect you want. Just thinking off the top of my head this is where I would look first. There are some users on the forums (Click here for search results via Docs.Unrealengine.com and switch the Forums Tab) that have been doing some good things with the ball template and their own rolling ball games. Maybe they will have tips or you will see if they have done something similar to what you’re trying to achieve with the curve.

Tim

5

thankyou tim.