WEBVTT 00:01.010 --> 00:03.640 Welcome to the centre of mass. 00:03.650 --> 00:07.130 So where is the centre of mass and what is it. 00:07.130 --> 00:09.680 Well it is where ever the origin is. 00:09.680 --> 00:14.220 Blender uses the origin as the centre of mass. 00:14.270 --> 00:19.330 Now that means you have control over all over this which isn't always a good thing. 00:19.490 --> 00:25.250 If you've inadvertently constructed something away from the genome bit from the origin itself that geometry 00:25.250 --> 00:27.230 is going to act very weird. 00:27.500 --> 00:32.540 When you start applying physics to it so it can lead to some strange results. 00:32.540 --> 00:37.920 Now they might be desirable depending on the type of thing that you're doing. 00:38.090 --> 00:44.390 Now blender can calculate for us the centre of the mass and you've probably seen this before when we 00:44.390 --> 00:46.670 move the origin to the centre of mass. 00:46.670 --> 00:52.310 Now in most object that's going to pretty much put it in the middle unless you've got a lopsided object 00:52.340 --> 01:00.190 in which case you'd want to adjust the centre of mass so it behaved realistically when it comes to physics. 01:00.200 --> 01:05.640 Now let's go ahead and hop on over into blender and play with the Centre of Mass. 01:06.410 --> 01:08.240 Hey so welcome over into blender. 01:08.260 --> 01:14.570 Now at this point we're going to focus on something very similar to the wall you saw that the tank was 01:14.570 --> 01:15.940 breaking through earlier. 01:16.100 --> 01:19.290 But we're going to build it up from scratch. 01:19.340 --> 01:22.090 So in order to do that we're going to use a raise. 01:22.130 --> 01:28.040 So my first mini challenge for you is to pause a video and go ahead and make a wall. 01:28.070 --> 01:32.290 This isn't going to be one of those major challenges but this is a mini mini challenge. 01:32.360 --> 01:38.270 Challenge yourself to build a wall made of standard size bricks if you will or a pretty standard ratio 01:38.270 --> 01:41.910 of bricks you don't have to worry too much about the size at the moment. 01:41.930 --> 01:45.170 So go ahead pause video now and give that a quick go. 01:48.010 --> 01:50.290 Okay now did you give that challenge a go. 01:50.280 --> 01:52.710 It's very important to practice your skills. 01:52.840 --> 01:56.910 Now I'm going to go ahead and I'm going to build up my wall super quick here. 01:56.920 --> 02:04.390 I'm literally going to scale in the y direction my break by half and scale it's in the z direction by 02:04.390 --> 02:05.140 half. 02:05.140 --> 02:10.930 I'm going to go to the control not the control panel sorry the Properties window for the 3D editor and 02:10.930 --> 02:13.070 shift it up by point five. 02:13.150 --> 02:14.470 So I've got my brick here. 02:14.470 --> 02:18.180 Finally I'm going to apply scale now because we're working with physics. 02:18.220 --> 02:21.850 It's good if things are the right size from the beginning. 02:21.850 --> 02:27.580 Now I'm going to shift this across a little over here and I'm going to add a ground plane in and whilst 02:27.580 --> 02:28.550 I'm at it. 02:28.720 --> 02:33.100 And you might not have done this because I didn't ask you to create a black a ground plane that's absolutely 02:33.100 --> 02:35.770 fine you can pop one in now is your following along. 02:35.830 --> 02:41.440 I've added a ground plane I'm going to make sure I start saving my work and can as save as wall because 02:41.440 --> 02:45.210 we're going to start applying physics and physics can crash blender occasionally. 02:45.230 --> 02:51.570 Now whilst I've actually got selected I'm going to go ahead and apply the scale that I've just bumped 02:51.640 --> 02:58.060 that floor up to four and whilst I'm here I'm also going to apply a rigid body and make it passive because 02:58.060 --> 02:59.990 the wall needs somewhere to stand. 03:00.060 --> 03:06.020 Now with the array itself I'm going to use 10 bricks and then build it up from there. 03:06.020 --> 03:12.600 So let's go ahead and add an array and if I'm happy with how it looks let's go to 10 of them. 03:12.910 --> 03:15.560 Okay let's shift over here a little so it's more in the middle. 03:15.610 --> 03:16.900 Excellent I'm happy with that. 03:16.930 --> 03:22.240 Apart from the gap in between I'm going to go for one point one nine bit big so I'm going to go for 03:22.240 --> 03:23.710 one point not five. 03:23.890 --> 03:25.010 That looks much better. 03:25.130 --> 03:32.050 Okay so that's my first array am now going to a race a race so relative offset I'm going to say that's 03:32.050 --> 03:37.090 a zero for the moment and says Z to one and I'm going to just going to zoom in here so I can see the 03:37.090 --> 03:42.290 relative gaps now because my brick is half as high as it is wide. 03:42.400 --> 03:48.500 I should imagine that the relative offset here if we said it's a point 0 5 like the other one we are 03:48.510 --> 03:54.010 going to end up with a gap that's half the size which has happened so by go one point one. 03:54.400 --> 03:59.730 We've then got a nice gap between here let's say for the mortar or anything along those lines. 03:59.860 --> 04:01.880 And it's a good idea to keep an idea. 04:02.080 --> 04:08.230 Or it's certainly an eye on these numbers that we've used because we're going to use them in a bit for 04:08.230 --> 04:10.120 the margins for physics. 04:10.210 --> 04:16.900 Okay so now I have done that I just need the offset in the x direction by wellpoint one would be one 04:16.910 --> 04:22.530 brick because there are 10 bricks so I won half a point once again open in 0 5. 04:22.690 --> 04:29.020 Okay so that's the first stage and the second stage of the wall down and now it should be a matter of 04:29.320 --> 04:32.740 just offsetting in the z direction going up. 04:32.740 --> 04:34.360 Now that is too big. 04:34.360 --> 04:38.420 So that again that's point nor a one point not 5. 04:39.690 --> 04:40.230 Excellent. 04:40.230 --> 04:47.420 In fact if we go to prospective mode we can see it from the side and that looks even which is nice. 04:47.430 --> 04:53.700 So orthographic MO go from perspective mode and we can use a couple and make it super high. 04:53.700 --> 04:56.370 We wanted so that's fine with me. 04:56.370 --> 05:00.480 In fact we could link this together and build a building but I'm going to leave it as a wall for the 05:00.480 --> 05:01.110 moment. 05:01.110 --> 05:06.930 Now looking at that the ground is far too small some deerskin to scale it up a little bit more and apply 05:06.930 --> 05:07.840 that scale. 05:08.010 --> 05:13.590 Okay so now we've got this wall on this ground. 05:13.590 --> 05:15.780 We've got a basis to work from there. 05:15.780 --> 05:21.630 If I go ahead and apply physics to this whole wall you probably guessed the ball was going to move as 05:21.630 --> 05:24.870 one object with its centre of mass. 05:24.870 --> 05:30.810 Interestingly enough all the way over here so that's not where the centre of mass of this would be at 05:30.810 --> 05:33.430 all it would be somewhere in the middle of the wall. 05:33.540 --> 05:38.160 And if we go ahead and run the physics engine it just wobbles because already sat on the ground. 05:38.340 --> 05:45.690 If we were to just let's say for argument's sake lift the wall up so it was up here and then dropped 05:45.690 --> 05:53.570 it onto the ground rules see that again you saw there it twinged or twinged around that centre there 05:53.580 --> 05:54.510 so that's wrong. 05:54.540 --> 05:55.740 That's just wrong. 05:55.740 --> 05:57.620 It's not going to work like that in real life. 05:57.660 --> 06:00.570 So we need to separate out all these bricks. 06:00.630 --> 06:07.850 Now it is important at this point to remove the physics from the break itself. 06:07.980 --> 06:14.460 Otherwise when you try and move the origin and stop that from bouncing around if you try when we go 06:14.460 --> 06:20.880 to if we scroll down here and set the origin to the centre of mass Well it's not going to work is all 06:20.880 --> 06:21.870 based around here. 06:21.870 --> 06:26.190 And of course at the moment we still got all the array modifiers UN applied. 06:26.340 --> 06:29.950 Now remember to turn this off some going to do that now. 06:29.960 --> 06:33.220 And I'm also going to save my work that is always important. 06:33.230 --> 06:40.070 If I use the right shortcut keys ever get up save my work and I'm ready to do a challenge. 06:40.110 --> 06:45.330 But before we get on to that challenge I just want to run through with you really quickly a small change 06:45.330 --> 06:47.880 that's happened since this video's been recorded. 06:47.910 --> 06:49.920 Has it jumped forward now to two point seven. 06:49.950 --> 06:52.530 This is the end state of what you'll be going for. 06:52.560 --> 06:57.570 And of course when we go ahead and set the origin we have a few different options. 06:57.690 --> 07:04.650 We've got set the origin to the centre of mass by the surface or by the volume. 07:04.660 --> 07:10.250 Now in general unless you've got a reason to do so I would recommend using the volume itself. 07:10.410 --> 07:11.100 So there we go. 07:11.100 --> 07:17.830 And in this case because they are cuboid us it's going to be the same no matter which one you pick anyway. 07:17.880 --> 07:20.410 But just to say there's two separate options there. 07:20.460 --> 07:24.550 In general I would pick volume unless you've got a reason to pick surface. 07:24.610 --> 07:27.070 Now here comes your challenge. 07:27.120 --> 07:32.070 I would like you to go ahead and create a physically stable wall so. 07:32.100 --> 07:36.640 So basically one doesn't fall over or explode on us one not yet anyway. 07:36.690 --> 07:42.140 So all bricks should be individual so they can be acted upon individually. 07:42.630 --> 07:49.410 Now move the centre of mass for each brick to the right location at the moment is all focussed around 07:49.410 --> 07:53.850 that original brick and that's going to end well that's going to cause some interesting results and 07:53.850 --> 07:57.830 we'll certainly throw the bricks around something crazy. 07:57.900 --> 08:03.050 If he had chaske leave it where it is you might want to just try where it is currently. 08:03.050 --> 08:04.660 Just to see the effects. 08:04.770 --> 08:12.090 If you want to take it so they should rest on some invisible mortar or gap that matches the existing 08:12.090 --> 08:12.720 gap. 08:12.780 --> 08:20.400 So when you add the rigid body to the actual bricks themselves remember to include a margin so that 08:20.400 --> 08:23.620 the bricks essentially float on top of one another. 08:23.700 --> 08:30.330 But that is to imitate more to being in between them so they're slightly separated. 08:30.450 --> 08:34.110 Now make all the bricks have the same physical properties. 08:34.230 --> 08:39.270 And remember you can do that in one fell swoop rather than doing it individually. 08:39.270 --> 08:44.760 If you start playing about with bricks and given them slightly different properties that's fine. 08:44.760 --> 08:50.230 That could add to the realism of a scene but it be good to have a starting point where they're all identical. 08:50.250 --> 08:54.370 There may be some instances where you'd want to change that but not in this case. 08:54.390 --> 08:57.470 So go ahead post a video now and give that a go. 08:59.830 --> 09:00.910 Okay guys welcome back. 09:00.910 --> 09:04.470 Let's go ahead and create a physically stable wall. 09:05.400 --> 09:09.300 Okay so we left off over here with our wall as individual items. 09:09.300 --> 09:11.670 Now I'm going to go ahead straightaway and hop into edit mode. 09:11.670 --> 09:13.700 And of course we've got all of these bricks. 09:13.830 --> 09:15.780 Well no actually we can't do that. 09:15.870 --> 09:17.150 I'm getting ahead of myself. 09:17.160 --> 09:19.440 You see because they aren't individual bricks. 09:19.440 --> 09:24.090 They're in a ray at the moment all silly me. 09:24.090 --> 09:28.230 I'm applying my array in the wrong order so apply from the bottom up. 09:29.240 --> 09:30.740 We go and the final array. 09:30.740 --> 09:37.430 Okay so now when we go into edit mode there we go we've got all individual bricks now let's go ahead 09:37.490 --> 09:44.520 and separate them by loose parts because they're not connected anywhere at all. 09:44.540 --> 09:47.670 We can just literally separate them apart. 09:47.720 --> 09:53.210 Now that we've done that we can well literally apply physics to them. 09:53.210 --> 09:57.590 So in order to do that there are a couple of things that I'm going to do to make my life easier so I 09:57.590 --> 10:03.080 can select them all every time is I'm going to turn off selection for the camera and I'm going to turn 10:03.080 --> 10:07.960 off selection for these these items here just in case I managed to select them. 10:07.960 --> 10:12.840 The lamp as well and the playing I don't want to be selecting the floor and changing its properties. 10:12.860 --> 10:20.270 Now whenever I select all I should be selecting in object mode I'll be selecting only these mesh objects 10:20.270 --> 10:21.640 themselves and nothing else. 10:21.650 --> 10:25.530 Literally nothing else in the sinkers and nothing else selectable ho case. 10:25.530 --> 10:30.180 Now we've done that we've got all of these bricks selected and an active selected brick. 10:30.290 --> 10:36.530 So the one that's active is the one that's going to take on the rigid body and it was actually the furthest 10:36.530 --> 10:42.260 one away from here so if we go ahead and well basically play that. 10:43.160 --> 10:49.490 We will see once the it starts it falls down and does something weird when it hits the floor. 10:49.580 --> 10:54.560 It does something weird it gets dragged along because its centre of gravity is actually passing beneath 10:54.560 --> 10:57.890 the plane itself so it's actually being pulled in line with it. 10:58.010 --> 11:00.260 I think we're going to need some more frames. 11:00.260 --> 11:03.200 Anyway I'm going to go up to one hundred fifty so you can see here. 11:03.200 --> 11:08.300 He gets pulled in so it's directly above that and then scoots around the surface so it's worthwhile 11:08.300 --> 11:13.060 knowing that that centre of gravity will be funny when we apply it to the rest of this. 11:13.060 --> 11:14.040 And let's do that. 11:14.090 --> 11:16.630 It's all going to be sucked into this one place here. 11:16.850 --> 11:20.830 So good to go to the physics tab and copy from active. 11:21.060 --> 11:25.380 And will we do that the whole thing boils down and all gets sucked into one place. 11:25.520 --> 11:26.320 Yay. 11:26.450 --> 11:27.610 That might be here a. 11:27.650 --> 11:32.630 Awesome effective a portal opened up and you wanted it to be pulled into one place. 11:32.630 --> 11:36.160 Well that isn't what I want to happen here. 11:36.170 --> 11:38.160 I want them to be individual. 11:38.300 --> 11:43.550 So in order to do that I'm actually well kind of stuck here because I've just applied physics to everything 11:43.550 --> 11:48.050 and I can't unsupplied physics to everything without undoing so I am just going to undo. 11:48.050 --> 11:53.600 In this case another case in point for saving is that you don't want to end up doing a ton of work and 11:53.600 --> 11:58.290 then having it ruined or stop the playback for the moment and reset it to zero. 11:58.310 --> 12:05.780 And now I'm going to remove the rigid body from that can select everything again and then whilst we're 12:05.780 --> 12:10.070 in object mode and it gives the tool shelf and I'm going to set the origins of the centre of mass now 12:10.070 --> 12:13.840 because there are now separate objects and it's got no physics applied. 12:13.850 --> 12:14.520 There you go. 12:14.580 --> 12:17.760 Everything's now got its own centre of mass. 12:17.980 --> 12:24.290 Let's add a rigid body to the active one and then go into the physics tab copy from the active one to 12:24.290 --> 12:25.230 everything else. 12:25.330 --> 12:29.390 And of course hit play says go ahead and hit the right keys. 12:29.390 --> 12:32.680 Now well that's actually dropping from quite a height. 12:32.690 --> 12:34.590 We did play with that earlier. 12:34.850 --> 12:37.000 So let's set that back down to zero. 12:37.010 --> 12:38.300 Does that make a difference. 12:38.300 --> 12:39.020 No. 12:39.020 --> 12:40.280 No of course it doesn't. 12:40.280 --> 12:42.950 So let's move everything back down here. 12:42.950 --> 12:44.830 Case looking at this. 12:44.960 --> 12:47.320 What have we move moved with just moved this one down. 12:47.330 --> 12:48.720 So that's Paul. 12:48.740 --> 12:52.120 I don't know where it was before some was going to have to undo to that's in the right place. 12:52.130 --> 12:58.730 Okay so everything there is at the beginning of the scene and now removing the whole block as a whole. 12:58.910 --> 13:01.310 That looks like it's now on the surface again. 13:01.340 --> 13:04.340 That's what whilst were in orthographic maybe can confirm that. 13:04.350 --> 13:07.020 Perfect and let's run the physics simulation. 13:07.270 --> 13:13.080 Now the moment the bricks drop on top of one another which is fine but we need to leave a gap for mortar. 13:13.100 --> 13:18.440 Now we remember earlier we had a margin something to enable collision collision margin and I'm going 13:18.440 --> 13:22.410 to set it to nought point five. 13:22.430 --> 13:31.160 I think that was what we had before and well Convex Hull is not working so I'm going to try mesh K mesh 13:31.220 --> 13:38.120 isn't working quite as I expected to either stop the physics simulation here and rewind and just see 13:38.120 --> 13:39.950 if that makes difference. 13:39.960 --> 13:42.680 K It is not making a difference which is surprising. 13:42.680 --> 13:48.010 I thought it would have done up the margin now to 1 hour you know whats happening. 13:48.080 --> 13:51.990 Tony forgot to apply from the active side to copy from active. 13:52.070 --> 13:53.080 So going down that point. 13:53.090 --> 13:54.340 Well let's actually be funny. 13:54.350 --> 13:59.020 Let's set it a point five and I'm going to hit copy from active. 13:59.080 --> 14:00.140 Boom. 14:00.150 --> 14:05.060 The bricks are literally so confined together that they literally explode. 14:05.060 --> 14:09.170 Now that's not the faked we're going for although it is quite interesting so let's try. 14:09.170 --> 14:10.220 Nope. 14:10.430 --> 14:12.040 The point oh five again. 14:12.990 --> 14:17.970 And then copy from active that's important and how it's not being crazy anymore. 14:17.970 --> 14:20.590 Let's go around to the front again and zoom in. 14:20.610 --> 14:22.110 That is that gap right. 14:22.340 --> 14:22.930 It is. 14:22.920 --> 14:28.170 And you could see they're kind of jostling and floating on top of one another almost as if there was 14:28.170 --> 14:29.410 a magnetic field around them. 14:29.420 --> 14:31.560 That's a bump that up to 150 again. 14:31.950 --> 14:34.500 And this brick is toppling away. 14:34.590 --> 14:35.100 Oh. 14:35.950 --> 14:38.570 Well hey the whole thing falls over eventually. 14:38.570 --> 14:40.700 So it's not inherently stable at that point. 14:40.700 --> 14:44.440 But we can tweak the physics settings in the bit to improve that. 14:44.840 --> 14:51.470 Okay so after a few minutes of confusion the wall just kept falling down and I thought well hang on 14:51.470 --> 14:55.380 a minute all my trial runs that I've done this has not happened so. 14:55.480 --> 14:58.810 But the other thing I did do is make the wall explode violently. 14:58.820 --> 15:01.430 So perhaps something ahead crashed. 15:01.520 --> 15:06.280 I remembered some of the physics of a splosion and was toppling for some reason. 15:06.290 --> 15:08.630 Now I don't understand why it would do that. 15:08.750 --> 15:15.130 But it turned out that going down to the shape itself and switching it from mesh to Convex Hull I thought 15:15.130 --> 15:15.590 at first. 15:15.600 --> 15:16.090 Okay. 15:16.100 --> 15:17.890 I just picked the wrong colation shape. 15:17.990 --> 15:22.950 But when switching it directly back to mesh again well what happened. 15:22.970 --> 15:29.240 Well it was still working okay so this is a case in point that sometimes the physics can get a little 15:29.240 --> 15:30.540 bit confused. 15:30.590 --> 15:37.060 So switching the collisions shape can almost reset the physics engine itself and do some recalculations. 15:37.070 --> 15:41.700 And literally after switching between those two it started working again. 15:42.080 --> 15:46.370 One of the things you can do when this thing is moving is if I grab a brick and move it. 15:46.490 --> 15:50.470 Well it really starts throwing things about course it resets. 15:50.480 --> 15:52.250 So after sorting that out. 15:52.250 --> 15:54.110 That seems to have fixed everything. 15:54.110 --> 15:59.180 The other thing of course that we need to sort of figure out at this point and we can have a look at 15:59.180 --> 16:03.200 this brick that's tumbling is does it look like a break when it hits the ground. 16:03.200 --> 16:05.170 Is it too bouncy. 16:05.480 --> 16:08.530 Not particularly bouncy but it does slide a little. 16:08.540 --> 16:12.940 So let's go ahead and sort that out so I'm going to go ahead and select everything again. 16:13.220 --> 16:16.640 And we need an active Brecken let's use the one that's falling. 16:16.670 --> 16:19.330 So select everything after selecting the active one. 16:19.460 --> 16:22.210 And let's go ahead and have a look at physics properties. 16:22.280 --> 16:23.570 So it's got strong friction. 16:23.600 --> 16:29.490 And if we set the bouncing to one as we've discovered before it's a combination of both. 16:29.570 --> 16:32.080 The floor itself the floors properties. 16:32.330 --> 16:35.990 And this here we discover that in the last lecture. 16:36.050 --> 16:38.940 So we don't want any bounciness because bricks don't bounce. 16:39.020 --> 16:41.380 I'm going to up this number again. 16:41.390 --> 16:47.540 The resistance to translation and a little bit of resistance to rotation see if that makes the break 16:47.540 --> 16:49.090 just a little more. 16:49.340 --> 16:50.700 Yeah that looks a bit better. 16:50.780 --> 16:53.200 And of course up here the mass of the brick. 16:53.480 --> 16:55.850 Now these bricks are quite large. 16:55.850 --> 16:57.270 They're not to scale. 16:57.290 --> 17:00.410 That's certainly the fact there are whole metre long. 17:00.410 --> 17:01.100 She's huge. 17:01.100 --> 17:03.800 That brick is not going to weigh one kilogram. 17:03.890 --> 17:08.840 It's going to weigh significantly more so let's say it weighs 10 kilos. 17:08.930 --> 17:12.920 And let's see how it tumbles from the wall at this point of course is going to do more damage as it 17:12.920 --> 17:13.650 does. 17:13.760 --> 17:18.460 But that feels like that brick now has more substance to it. 17:18.620 --> 17:23.480 So of course that's actually apply that to all the rest of the bricks as well. 17:23.660 --> 17:28.660 And they should now be inherently more stable anyway because they're a bit heavy for their size. 17:28.790 --> 17:35.080 If we set Well let's do it let's set the mast to point one so we've got a 10 Gramp now 100 gram break 17:35.390 --> 17:38.690 and then copy from Active's of the whole wall is like this. 17:38.740 --> 17:42.130 It it's not going to come to a complete stop when it lands. 17:42.140 --> 17:46.350 In fact if we make it even smaller you see it doesn't even affect bricks at this point. 17:46.370 --> 17:47.850 So that set back up to 10. 17:47.930 --> 17:51.820 Now here's a good example because those bricks don't weigh anything anymore. 17:51.830 --> 17:55.730 They were 100 grams and this weighs ten thousand grams. 17:56.030 --> 18:00.080 You can see the effect it's having on the wall it's actually shifting the entire lot sideways as it 18:00.080 --> 18:03.950 falls because it's so much heavier than the rest of the water. 18:03.980 --> 18:08.960 Now of course at this point I'm going to copy from active again to the whole wall and now you have to 18:08.960 --> 18:13.130 wait for the physics engine to reset of course go back to the beginning and there we go. 18:13.130 --> 18:18.110 There's the one brick tumbling to oblivion because it's got no support. 18:18.110 --> 18:18.820 Excellent. 18:18.950 --> 18:22.670 So how did you guys get on did you manage create a wall that was stable. 18:22.670 --> 18:26.440 Do you have any problems like I came across and have to troubleshoot. 18:26.540 --> 18:32.590 Please share your falling walls in the discussions and I will see you guys in the next lecture.