In this lesson, we'll complete a top down view sketch. After completing this lesson, you'll be able to create a sketch mirror, create a link dimension, and create a projection. So, let's go ahead and rename the sketch roller out. Let me just call this top down cut. And I want to go back and edit the sketch. So from this sketch, we've got our ten millimeter outside wall. We still need to add some offset to this line, and we need to add a bit more information in various areas, we need to add some offsets on the inside as well. So, let's go and add a bit more detail. So, I'm going to do an offset of this line, and we're going to say that this dimension is five millimeters. And you'll notice that while I'm inside of this operation, it doesn't let me click this. So I'm going to go ahead and just say five, then I'll double click on it. Sometimes, it helps if the constraints are in the way to hide the constraints. And let's go ahead and do another offset. Can say minus five, and again, we can make it equal. Now, one thing you'll notice when we offset a line is, because this line ends at a point, what we're actually doing is recreating a shorter version. Now again, trim or extend if we use this, it's going to undo that dimension. And you can see that it takes it away. That's actually okay, but it also undid some additional dimensions. So the way to get around this is, instead of using that offset, is to simply just draw a horizontal line. Now, if the line doesn't happen to be horizontal, you can make it parallel or you can do some additional constraints to make sure that works. But in our case, they are perpendicular to this vertical line or a horizontal would do just fine. I'm going to make this one construction, and any center line that I don't need I'm going to make those construction as well and that helps with the selection process down the road. Then I want to apply a dimension. So in this case, because I'm in the middle of applying a dimension, I can simply just add it there. And also, if you know the dimension, we can simply type in D19, and it'll be equal to that as well. Under modify, you can go down into change parameters, and you can make universal parameters. They're called user parameters, and you can simply name them ahead of time. So for instance, if you wanted a specific five or 10 millimeter offset, instead of having it called D19, we could name it, offset. And notice that it re-references all of these to be equal to offset. You could make that ahead of time, or you could name it on the fly, instead of being D19, and you can do it that way as well. So that way, you don't have to remember D19, right? So, for instance, this 10 right here, we can say that this is offset times two. And that is equal to 10. So that way, if we ever come back and we change this dimension right here, which is currently five, if we change it to six and then this one will equal 12, and so on. So again, it's just a way to make sure that we're keeping those numbers fairly consistent. All right. So now, we've got a bit of structure in the center. We've got the structure around the outside. We've got the structure going to the motors, and again, we don't have to worry specifically about trimming this up. If we trim it, then we will lose some of the offset information because of how the offset tool works, but we can simply leave it long because we can still select these areas. So now, we want to add a little bit more. So we need to make sure that we have some structure for the motor that comes to the sides here. And the way that we're going to do that is, we're going to carry a line from the center, that goes completely out. So again, I'm going to start a line. I'm not going to snap to the midpoint, I just want to snap to the line over here. And the way that I'm going to make this work is I'm going to make it coincident, not in a midpoint relation. And then I'm going to make it perpendicular to this line here. So this is a center line. This is where we're starting our structure. And then we're going to carry a line from this point, it's parallel out to the side. So, we'll find that intersection point and it snaps to it automatically, and notice that that's coming up perpendicular automatically, and we can take it out to the wall and we didn't have to add any additional constraints. Now, it's a little bit different when we get out here because we don't have anything to snap to but I'm actually going to take it and drag it out and it's tangent, and all I have to do is I need to make these parallel and it'll fully define it for me. So if I temporarily hide the constraints, you can see what we've done. We've added some structure here and we've added the bulk of the structure here because this is a shorter section. So, we're going to have a lot of structure at the center of the quadcopter, and this arm here is quite a bit shorter, so we want to carry that structure into the motor as quickly as possible. So, it carries it around this corner. And then this one here actually helps provide some additional support to this edge right here. We will be adding some additional structures to this line. This will be a solid panel area and this will be a small line here that has some structure to it as well. So keep that in mind that, this is the reasoning for offsetting this in this one way. Now in general, as we go through our course, we're going to have a section on engineering where we add some more strategic supports, we add some different features to help make sure this thing is fairly strong. Those types of features will also help us dictate how this thing should work. And again, since I've done this before, I just sort of know that this will work out better and still keep it fairly light. Don't be too worried if you don't understand why some of the design decisions are the way they are. Sometimes, it just comes from doing this many times. Sometimes, it just comes from experience, and so on. We're going to carry on this process on the other side as well. We could mirror this but sometimes, it's just good practice to do it. So again, if you're new to this and you're new to applying these constraints and dimensions and creating these sketches, it's a good idea to just do it. Just take the repetition as some practice, some experience. So again, find that intersection point. We're going to make these two lines parallel, and then we're going to do the same thing on the back. We're going to come over here. This is tangent, so we're going to make sure that's parallel and that fully defines it. So, that is going to give us some structure for the motor and it's going to carry that structure right to the center point. And we still need a little bit more. So we're going to have to add a little bit more structure here. We're going to go ahead and we're going to offset this line right here. We're going to not offset this line because we're going to leave some of this open in the middle, but we want to carry a line out. We want to offset it in the back, so we have a little bit more structure. So, I'm going to do this by, first, I'm going to draw a line from this to here. I'm going to hit escape. I want to select these two and I want to make them colinear. So what collinear is going to do is it's going to allow me to essentially follow the path of this line without having them connected. Again, this is going to give me some structure on the back side right here. And we could also just carry it horizontally. But in this case, I actually want to keep it going this direction to help with the shape, that X shape that we're going for. So, to add a little bit more structure to the back as well. And again, using repetition, we're going to follow the same thing up on the front. We're going to use colinear which we can pre-select if we want to. And we can make these two colinear. And then just make sure that it's deselected once you start modeling again. So at this point, as we're looking at this design, there are a few areas that are going to be open and there are a few areas that are going to be closed. So this area right here, and this area right here, and this area right there, I'll go ahead and I'll just select them all, all these areas are going to be open. Now, this is going to allow the most amount of air flow that we can get without obstructing the prop. Now, this area right here is going to be closed off but it's going to have a minimal thickness sheet right there. So, while the majority of this body is probably going to be about eight to 10 millimeters tall with some areas that are going to be reduced for weight, obviously. This area right here will probably be one to two millimeters thick and it's just for some additional structure. Because of the location of the prop, if we simply just took this brace out and just carried it all the way out here, we would probably have a lot of flex in this area. So again, we're going to leave some of this up to the engineer and do some simulations and figure out where the weak spots are. But in general, that is the design process for, or at least the thinking behind, why these areas are the way they are. Because we have the circle and we want to make sure that the prop itself can pull as much air flow through there, so we don't have any obstructions. We're not restrict in the amount of airflow. We're not artificially decreasing our flight time because we're having to use more current to try to pull more air and we're not getting the ideal thrust. And we're carrying the motor back to the center point of the chassis, and we're also carrying it as close as we can to any additional structure. So at this point, that is going to be the majority of the sketch that we're going to need to start to create some solid geometry. So, we're going to go ahead and stop the sketch. We're going to make sure that we save our file. And this is going to give us a great foundation to start creating our solid and surface geometry to start to see how this thing will take shape.