# Base Parametric Design for the Frame Centre

Ok I’ve started modeling the CAD file for the main centre of the frame, which will contain the electronics and hold the arms in place.

The first step is to create a base sketch that maintains the shape that I want. One thing I do want to ensure is that the motors are all equidistant; that they form a square. This, while not strictly necessary, means that the quad will react in the exact same way in both directions.

Because I’d rather have a longer and thinner frame than a big fat one, I’ve decided to have a rectangular space for the components in the middle and have a separate space on each end for the attachment of the arms:

In the CAD software (Autodesk Fusion 360, which is essentially the same as Inventor but cloud-based), I have opted to make extensive use of ‘parameters’, akin to variables/constants in code: I can set dimensions to ‘centre_width’ or ‘fitting_depth’ etc. and then change these values in a central menu should I need to change anything. It makes it a lot easier to follow.

So here’s my first sketch for the base of the design:

I drew one corner and then mirrored it to the other 3: that’s the easiest way. As you can see, I’ve done what I wanted concerning the spacing of the motors by drawing a construction line to where the motor will be, and using constraints to specify that this point should be equidistant from the X and Y origin axes (which I extended using more construction lines). The line representing the arm is dimensioned at 130mm (an arbitrary value for the distance from the body to the motor along the arm, but I can change it later) and I have added a perpendicular constraint between this line and the wall of the frame that will contain the fitting. What this means it that, whenever I update any dimensions within the frame, or the length of the arm, the angles of everything will adjust so that the motors are still equidistant.

I also used more construction lines to represent how far the attachment point juts out into the interior of the frame (15mm at present), and constrained the frame so that this is allowed for in ensuring there is enough space for the internal components.

My only worry at the moment is that the length of the whole thing won’t exceed 200mm (the maximum build length on my 3D printer), but if it should I will consider the problem then.

Next, I projected this to a new sketch and drew in the locations of the walls – 5mm width as it stands:

Again, all dimensions are set in the parameter menu, which is shaping up:

Anyway, I went ahead and extruded the base up 5mm, and the walls up 75mm. The height of the walls will change when I finalise the space requirements of the electronics.

Now to put in the fittings, as I modeled for the test print I did last time. I did the same process apart from converting all lengths to parameters, of course), with the difference that I only countersunk the top hole, as discussed last time: the other three screwheads will be inside the arm, so I’ll countersink them then.

I mirrored this fitting over to the other 3 attachment points, and it’s all looking rather nice:

Here’s a drawing of the main dimensions, for future reference:

Next, I need to model in the component holders, do a lid and a battery holder, holes in the sides for connections, and make it all look good with lots of fillets.

## 2 thoughts to “Base Parametric Design for the Frame Centre”

1. Colin Falck says:

Looks great.

2. Good article. I definitely love this site. Keep writing!