Can thrusters (BP) affect rocket (another BP)?


I have one actor physic blueprint for thrusters, they works, flying ok. Then I have rocket blueprint (also physic actor) which will do nothing. I want to add thrusters blueprint to the rocket to move rocket away. How to connect it together?

If I will add thrusters into rocket like a child blueprints, then the thrusters still flying alone without the rocket.

And I want to have it in two blueprints (thruster, rocket) to simply add or remove various thrusters.

Is possible to have one blueprint (thruster) that will move another physic object without collision?


One way you may be able to do it, is in the Rocket BP, have a Child Actor Component attached to the Main Rocket (which will be your thruster). You could then have as many Thruster BP’s as you want and then just use the ‘Set Child Actor Class’ node in the Rocket BP to select which ever Thruster BP you wanted. You could change the thruster many ways, via a widget, key press etc.

Jimminy_Cricket: But problem is that child thruster still not move the rocket but move only itself and the rocket is not affected at all. This will probably work ok only without physic enabled. But with physic is every component separated even in one BP, even as a child.

Why does the rocket need physics?

How about attaching the rocket mesh to a thruster with physics disabled (or extend a collision box out from the thrusters to include all attachments). Otherwise the rocket (with its own physics) may repel / fight / ignore the motion of the thruster(s). Or try adding an equal force onto the rocket mesh to match. By compartmentalizing active thrusters like this into separate actors, it may lead to more unwanted side-affects though, so why not take a look at Jacky’s Viper project and see how that was done.

BTW: What was the end result here?

Rocket without physics cannot be moved by something physical, isn’t? Anyway I tried every combinations and nothing works.
Adding same force to the rocket would not work - I could collide with thruster with something and thrusters will fly away from the rocket. I need to weld them together with rocket. Don’t know Viper project, I will check it.

I thought it will be simple - one BP is the rocket, one BP is the thruster (spawned several times), attach it together and it is done. But no and now it almost looks like it is not possible :open_mouth:

I solved it right now with very ugly and hacky and crazy solution, and does not like it at all and I have to divide the thrusters apart from a visual representation, everything is hardcoded etc. :frowning:

Result is none. Not solved. Probably nobody know how to create the AI bots with real players controllers (not just different mobs). Or it is bug in 4.18.

For sure its possible… There must be something different about your setup you haven’t mentioned yet. I have spaceships in my own projects that are separate actors powered by physics (Add Force / Set Linear Velocity / Angular Physics etc). I can attach one to the other easily, just by disabling physics and using Attach-To-Actor etc. Then mother-ships can tow sub-ships without issue. However, if physics aren’t disabled, sub-ships / mother-ships fight / repel each other. So, are there child components or other sub-components in the Thruster / Rocket BPs that have a different physics setup and so aren’t acting as a single-unit?

Can you look at this?: I just recreated the basic problem.

There is: Rocket BP actor (physics off). Thruster BP actor (physics on), GameMode BP (constantly adding force to the thruster). Gravity is 0. Thruster is added into Rocket as a Child Actor.

Result: The thruster is flying up, rocket is doing nothing. If I will enable physics on the rocket, nothing will change.

I had a quick look and added some code to the Rocket BP and it does what you want, but there must be a better way to go about it.

Sorry I couldn’t be of more help.

Thanks. Your solution works, but in a different way. There is one thruster only on the one side and the rocket is flying straight up. But in my case I need to achieve this behaviour:

Yeah my solution just makes the rocket move whatever way the thruster moves. I’ll be interested to see how you end up solving this problem. Good luck.

So you’re just after an effect of an uncontrolled roll??? Do you need to use thrusters at all for this (is it a classroom project or something)? If you’re flexible, why not just apply Physics-Angular-Velocity to the rocket to put it into a spin (break the rotation and apply -100 or -1000 to X etc). Adding a little Physics-Linear-Velocity on Z could then make the rocket rise. Can’t look at the project as I won’t be back at my rig for a while (it’d need to be 4.18 anyway as I only upgrade every 5-10 versions anymore).

ClavosTech: Uncontrolled roll? In this case yes. I want to have object realistically affected by forces from the thrusters. I have this so far:

But it is done in very ugly and complicated way. I expected that I will create several instances of the Motor BP and attach them where I want and it will work. Sadly, no. So now I have thrusters separated from their visual representation with “flames”. For my project (testing submarine) it is ok, it is only taking time to set everything up, but if I would need to create something where you can dynamically add motors to the main object (something like ) then it is impossible (or I don’t know how to do it).

If you’re trying to get realism like KSP that’s above my paygrade. :stuck_out_tongue: … I thought you were just trying to get a craft flying but STABLE. Even Jacky’s project (which is a complete game so enormously useful to learn from), is tricky to fly… Because the thrusters are on the edge of losing control all the time… So its a delicate balance to get right. Its worth checking out that project: Here it is… As regards trying to match real world physics in game dev, its often easier to cheat and use smoke & mirrors instead (FAKE the thrusters and use ‘stability circuits’)… Trying to go for realism may mean ending up losing lots of weekends… Good luck. :slight_smile:

ClavosTech: Jacky’s project have similar solution. Thrusters are separated from effects and positioned manually to the “rocket” BP. So you cannot easilly add new thruster just like that.