Need some physics help with a domino effect

Unity Engine
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1

This is my scene setup: phy hosted at ImgBB — ImgBB

The grey towers are made up of the column, and the base. The column and base both have a rigid body. There is a FixedJoint on the column that has the base as the connected body. The ball also has a rigid body. It’s like a cannon

I want the following to happen:

  1. When the ball hits the tower’s column, I want the column to tip and start falling without lifting the base alongside it. The base should have enough mass to stay in place

  2. I do not want the domino effect to go on forever, so the FixedJoint needs to be strong enough to resist certain forces. I want the domino effect going on for maybe 2 or 3 columns. Not more

  3. The force is applied to the cannon ball, which will always hit the column’s at the top. I want the cannon ball to always be able to topple a tower, but I don’t want the towers to be so weak that a domino effect goes on past 2-3 columns as I stated in 2

I’m sure it’s straight forward, but could I please get some physics help to know what to set as the canon’s balls Force, the FixedJoint BreakForce and the masses of both the column and base. Any physics equations should I look at?

I know I can figure it out eventually, but I’d like some guiding help

Thank you so much

2

Physics is NEVER straightforward unless you’re talking about a ball that doesn’t touch anything.

Keep in mind that computer simulations operate at a discrete level. That means every part of them moves a certain amount and distance all at once in a single frame (eg, it steps over the full distance). If that amount is too big or too fast, then you will miss collisions, contacts, etc.

Also, the physics system is most comfortable with things that are very simple in shape and similar in size and velocity. Anything too small, moving too fast, rotating too fast, weighing too much, in contact with too many other things, etc. will always be problematic.

This is because the physics system in Unity operates with single precision floating point computations.

Generally the process to get what you want is to iterate until you get close enough, trying combinations, keeping in mind the mathematical precision limitations and considerations above.

3

Thank you so much

By combinations you mean:

First list out all constraints like: x needs to always be bigger than y, but then make a matrix of all the variables. Like the mass of the tower bigger than…, mass of the base bigger than…, etc etc and go through each combination?

4

Starting with a list is a great idea because it can keep you on track as you iterate.

Any and every combination of things towards making what you want work, keeping in mind the constraints above.

I’ve been meaning to explore the whole domino-chain-falling physics space for a while so I just did a quick experiment… you’re welcome to run it yourself with this handy script:

After making the script it took about 15 minutes of iterating with spacing, numbers, frictions, etc. to get a nice steady consistent fall.

Screen Shot 2024-10-20 at 1.29.22 PM
Screen Shot 2024-10-20 at 1.29.22 PM1504×1120 32 KB

MakeGeo is presently hosted at these locations:

https://bitbucket.org/kurtdekker/makegeo

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