VR-Mess/research/sources/nimso-transcripts/nArwDeA2Ko4.txt

# Unity - Stabilising Fixed Joint Logic - Compound Rigidbodys (nArwDeA2Ko4, 623s)

it's me nem suni welcome back to another physics video today I'm messing around with some joints so not the usual place that I mess around with physics physics stuff but today is a specific demonstration for a specific thing which is about fixed joints I'm just gonna run the game and we'll see what I'm looking at so here I've got a very simple joint based physics gun that just grabs things and moves them about and you can see here two sets of two objects the one on the left here the blue object is a very very heavy object while the one on the right is the red object is a lot lighter so it's actually 50 kg on the right and 4,000 kg on the left the blue boxes both sides so both of these this one and this one are exactly the same where they saw a fixed jointed between two objects the 4,000 kg on the left and 50 kg on the right and the same thing on this side here except you'll notice something a little bit different so obviously here I can pick the pick it up from the blue side or the red side and move it and you can see it works back quite nicely you can tell it's a fixed joint and here same thing again except when I lift it on the red side and the reason for that is obviously it's a quite a standard problem of having jointed objects in a physics engine in any game game engine or any physics engine that you you can use in a game where the light light object very very light object here because it's 50 kg as opposed to 4,000 will always have this wobble whenever you lift lift it and it's all hooked onto something very very heavy and that's what I have sort of well tried to fix here now essentially what this is working as is a compound Collider so essentially just two colliding while colliding shapes that fit together to create one single rigidbody object so the rigid body itself handles the physics here we've got one on the left hand side and one on the right whereas here we've got one rigid body altogether and obviously that means there's only one moving object so it's literally physically impossible for them to split or wobble relative to each other so here if I push down you can see absolutely nothing happens they never split because it's physically impossible for them to do so here obviously if I do that you can see a lot of wobble but that of course creates a problem and this there's a reason we don't generally do that is because obviously it then acts as a single object so if you think over in in something like what's it called Garry's Mod so if you if you were playing carries mod right now and you take a bunch of pieces and then you solve weld them all together you get something like this where the heavy object can you know lift everything but the light object let's say you had a wheel underneath your heavy object always has this sort of sagging behavior just of wobbles a little bit and it's a little bit too light on the object and that's what I wanted to try and solve solve here now obviously if you did this normally your left object here would have a center of mass here in the center and your right object here would have a center of mass here in the center and then obviously when they're connected the heavier one will generally move the center of mass all the way towards itself so what you end up with is when you balance it you get this sort of most of your weight is here on the left-hand side because obviously we've got 4000 kg here and 50 kg here on the right so most of your weight is on the left-hand side that's not gonna happen when you lift something that is all one piece your centre of mass will just be wherever the heck it wants to be in our case it will always be in the centre by default unless you move it and that's what I'm trying to do here I'm actually calculating when I create the joint between them which in actual fact is not a joint it's just a single piece when I create that object I'm actually doing the calculations to position the center of mass appropriately based on what the mass would have actually been so here we got a mass of 4,000 plus 50 so the overall object is 4050 kg except most of that is on the left-hand side so it balances here on the left the same thing here the overall object is 4050 kg there's no separate objects themselves and it's still balances in exactly the same spot if I could position it correctly let me do some flying so yeah I've gone with the standard carriage mode controls here and you'll see here that we do balance basically the same spot so here we've got basically the same you know physics they they both react and move the way that they should as a fixed jointed object same with this simulus except this one is obviously very wobbly whereas this one completely rigid and what I wanted to do here essentially is fix that problem of having those wobbly wobbly joints in everything that we play he reacts and interacts the way that separate objects would do so obviously everything including the center of mass just reacts as if you've got two pieces two rigid bodies but it's only one rigid body and we can actually tell that when we switch over to our side here so I've got a little control that allows me to just switch on and off the mouse so I can still move it while while you know holding the mouse so you can see here on the left-hand side I'm going to switch to the scene view here if I select the red box here on the left one so this is the connected ones these are the physics the actual fixed jointed ones on my right hand side here you can see the mass is 50 kg and then of course if you look at the blue one you can see the mass is 4000 kg but they are still two separate objects completely separate whereas here on the right we've got two objects but you can see they don't have rigid bodies that's because overall they have one connected rigid body that holds them both at 4050 kg but what you'll notice is I keep the mouse following the object watch what happens when I unwell when I stop the game look here on the right-hand side we don't actually have a rigid body that holds emboss that is being created at runtime so if we look at the actual separate objects now we can see that both the blue boxes have a 4000 kg weight both the red boxes have 50 kg so these are actually two separate rigid bodies being generated well actually two separate rigid bodies and then it generates one overall piece using my little clever script here which is the compound body so this is basically what this video is about creating a compound body to prevent all of the wobbliness for example here I've been watching a lot of hot films recently and they've been playing trail makers so if you have a look-in trail makers and if you play that game because I've played a little bit of it you'll see that whenever you take a bunch of objects and you put them all together and you put loads of objects together because of one of those vehicle building games you end up with a lot of wobbly wobbly physics and honestly that game has some really dodgy wheel physics as a result because there's so many pieces being fixed jointed together this would really really help and you can see once I press play and if we look on the right hand side here once I press play you get that rigidbody that is added together you've got 4050 kg added together it works as if it's an actual connected body and you can see every time I pick it up you can see the configurable joint being generated that's my joint for for actually picking it up that's that's how I'm thinking it that's why it's so wobbly as well and the same thing obviously with this one except it doesn't have the wobble now literally only all you'd have to do for for it to function correctly is just save the you know save the previous rigid body so for example the face box left here the blue one you'd have to store the values like the current drag that it had or the the mass that it had before it got created as a compound body and then when you you know disconnect them you'd be able to disconnect them and they would fall to pieces like they should like any other fixed joint hood and that's basically what I wanted to show so something like this if I had a hundred objects all put together you wouldn't have to have millions of fixed joints connecting them all together like you do whenever you watch someone playing Garry's Mod you know carries mod sandbox or if you play yourself when you try and put things together you always end up having to make a world between these object and then a world between another object on this piece and this piece and this piece and you try and put a seat on top you after weld it to this one and this one and and the front of your car and everything otherwise when you lift it it all wobbles all over the place this fixes that having a compound body instead of having fixed joints solves a lot of problems and prevents a lot of stability issues with with having things like this and you can imagine if I move it so quickly you get a load of wobble whereas in reality a welded object no matter how light one piece is sure that piece might break eventually but this is basically what it'll move like instead and that pretty much solves this this hole that that ends this video itself so let's just fly off grab a little test ball here this was the one that I was using to test me the the grabby joint and fly off into the yonder that is the end of this video goodbye [Music]
	`# Unity - Stabilising Fixed Joint Logic - Compound Rigidbodys (nArwDeA2Ko4, 623s)`

	it's me nem suni welcome back to another physics video today I'm messing around with some joints so not the usual place that I mess around with physics physics stuff but today is a specific demonstration for a specific thing which is about fixed joints I'm just gonna run the game and we'll see what I'm looking at so here I've got a very simple joint based physics gun that just grabs things and moves them about and you can see here two sets of two objects the one on the left here the blue object is a very very heavy object while the one on the right is the red object is a lot lighter so it's actually 50 kg on the right and 4,000 kg on the left the blue boxes both sides so both of these this one and this one are exactly the same where they saw a fixed jointed between two objects the 4,000 kg on the left and 50 kg on the right and the same thing on this side here except you'll notice something a little bit different so obviously here I can pick the pick it up from the blue side or the red side and move it and you can see it works back quite nicely you can tell it's a fixed joint and here same thing again except when I lift it on the red side and the reason for that is obviously it's a quite a standard problem of having jointed objects in a physics engine in any game game engine or any physics engine that you you can use in a game where the light light object very very light object here because it's 50 kg as opposed to 4,000 will always have this wobble whenever you lift lift it and it's all hooked onto something very very heavy and that's what I have sort of well tried to fix here now essentially what this is working as is a compound Collider so essentially just two colliding while colliding shapes that fit together to create one single rigidbody object so the rigid body itself handles the physics here we've got one on the left hand side and one on the right whereas here we've got one rigid body altogether and obviously that means there's only one moving object so it's literally physically impossible for them to split or wobble relative to each other so here if I push down you can see absolutely nothing happens they never split because it's physically impossible for them to do so here obviously if I do that you can see a lot of wobble but that of course creates a problem and this there's a reason we don't generally do that is because obviously it then acts as a single object so if you think over in in something like what's it called Garry's Mod so if you if you were playing carries mod right now and you take a bunch of pieces and then you solve weld them all together you get something like this where the heavy object can you know lift everything but the light object let's say you had a wheel underneath your heavy object always has this sort of sagging behavior just of wobbles a little bit and it's a little bit too light on the object and that's what I wanted to try and solve solve here now obviously if you did this normally your left object here would have a center of mass here in the center and your right object here would have a center of mass here in the center and then obviously when they're connected the heavier one will generally move the center of mass all the way towards itself so what you end up with is when you balance it you get this sort of most of your weight is here on the left-hand side because obviously we've got 4000 kg here and 50 kg here on the right so most of your weight is on the left-hand side that's not gonna happen when you lift something that is all one piece your centre of mass will just be wherever the heck it wants to be in our case it will always be in the centre by default unless you move it and that's what I'm trying to do here I'm actually calculating when I create the joint between them which in actual fact is not a joint it's just a single piece when I create that object I'm actually doing the calculations to position the center of mass appropriately based on what the mass would have actually been so here we got a mass of 4,000 plus 50 so the overall object is 4050 kg except most of that is on the left-hand side so it balances here on the left the same thing here the overall object is 4050 kg there's no separate objects themselves and it's still balances in exactly the same spot if I could position it correctly let me do some flying so yeah I've gone with the standard carriage mode controls here and you'll see here that we do balance basically the same spot so here we've got basically the same you know physics they they both react and move the way that they should as a fixed jointed object same with this simulus except this one is obviously very wobbly whereas this one completely rigid and what I wanted to do here essentially is fix that problem of having those wobbly wobbly joints in everything that we play he reacts and interacts the way that separate objects would do so obviously everything including the center of mass just reacts as if you've got two pieces two rigid bodies but it's only one rigid body and we can actually tell that when we switch over to our side here so I've got a little control that allows me to just switch on and off the mouse so I can still move it while while you know holding the mouse so you can see here on the left-hand side I'm going to switch to the scene view here if I select the red box here on the left one so this is the connected ones these are the physics the actual fixed jointed ones on my right hand side here you can see the mass is 50 kg and then of course if you look at the blue one you can see the mass is 4000 kg but they are still two separate objects completely separate whereas here on the right we've got two objects but you can see they don't have rigid bodies that's because overall they have one connected rigid body that holds them both at 4050 kg but what you'll notice is I keep the mouse following the object watch what happens when I unwell when I stop the game look here on the right-hand side we don't actually have a rigid body that holds emboss that is being created at runtime so if we look at the actual separate objects now we can see that both the blue boxes have a 4000 kg weight both the red boxes have 50 kg so these are actually two separate rigid bodies being generated well actually two separate rigid bodies and then it generates one overall piece using my little clever script here which is the compound body so this is basically what this video is about creating a compound body to prevent all of the wobbliness for example here I've been watching a lot of hot films recently and they've been playing trail makers so if you have a look-in trail makers and if you play that game because I've played a little bit of it you'll see that whenever you take a bunch of objects and you put them all together and you put loads of objects together because of one of those vehicle building games you end up with a lot of wobbly wobbly physics and honestly that game has some really dodgy wheel physics as a result because there's so many pieces being fixed jointed together this would really really help and you can see once I press play and if we look on the right hand side here once I press play you get that rigidbody that is added together you've got 4050 kg added together it works as if it's an actual connected body and you can see every time I pick it up you can see the configurable joint being generated that's my joint for for actually picking it up that's that's how I'm thinking it that's why it's so wobbly as well and the same thing obviously with this one except it doesn't have the wobble now literally only all you'd have to do for for it to function correctly is just save the you know save the previous rigid body so for example the face box left here the blue one you'd have to store the values like the current drag that it had or the the mass that it had before it got created as a compound body and then when you you know disconnect them you'd be able to disconnect them and they would fall to pieces like they should like any other fixed joint hood and that's basically what I wanted to show so something like this if I had a hundred objects all put together you wouldn't have to have millions of fixed joints connecting them all together like you do whenever you watch someone playing Garry's Mod you know carries mod sandbox or if you play yourself when you try and put things together you always end up having to make a world between these object and then a world between another object on this piece and this piece and this piece and you try and put a seat on top you after weld it to this one and this one and and the front of your car and everything otherwise when you lift it it all wobbles all over the place this fixes that having a compound body instead of having fixed joints solves a lot of problems and prevents a lot of stability issues with with having things like this and you can imagine if I move it so quickly you get a load of wobble whereas in reality a welded object no matter how light one piece is sure that piece might break eventually but this is basically what it'll move like instead and that pretty much solves this this hole that that ends this video itself so let's just fly off grab a little test ball here this was the one that I was using to test me the the grabby joint and fly off into the yonder that is the end of this video goodbye [Music]