3D Modeling & CAD for Motorsport: Geometry Measurements and Mass
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Geometry Measurements and Mass
07.04
| 00:00 | - Most designs, whether they're fabricated manually or modelled in CAD are going to be based on some initial measurements to ensure that the part fits and functions correctly. |
| 00:09 | When a part is fabricated manually, you'd expect to have at least a ruler, verniers or tape measure on hand to check critical measurements as you go as well as after it's complete. |
| 00:19 | The same thing goes for modelling designs in CAD, taking measurements during and after the modelling process is a critical part of the design and with access to more advanced measuring that allows us to understand factors like the mass of components we can actually use these measurements to develop and optimise our designs. |
| 00:38 | While modelling, we're most likely dimensioning features on our components as we go. |
| 00:43 | Since we directly control these dimensions, measuring them isn't really necessary. |
| 00:48 | However there are often cases where we're interested in the measurements of geometry that's indirectly controlled, meaning we haven't dimensioned that measurement specifically, it's just a result of other dimensions. |
| 01:01 | Measuring is a quick way to check we've got it right and we might always want to use this information when modelling other features that interact with the part we're currently working on. |
| 01:11 | We've used the measurement tool briefly in previous modules but it's a really useful feature so it deserves a more in depth look. |
| 01:18 | Let's jump back into Fusion 360 and open up our three bolt flange again. |
| 01:22 | If we look at the sketch used to model this, we can see that the PCD or pitch circle diameter method has been used to define the spacing of the three bolt holes, meaning the holes are equally spaced on a circle of 92 mm diameter. |
| 01:38 | Now let's say we have a physical sample of the flange and we wanted to know if it matched this model. |
| 01:43 | It's quite difficult to measure the PDC when there are an odd number of holes so instead we can measure the distance from one hole to the next. |
| 01:52 | This wasn't directly controlled by our dimensions in the sketch when modelling the part as we didn't specifically dimension the distance between the holes. |
| 02:01 | But we can measure it easily in CAD. |
| 02:04 | In Fusion 360, all we need to do is select the measure tool under the inspect tab or hit the quick key i on our keyboard. |
| 02:11 | By selecting two of the three holes, we can see that we have a 79.6 mm measurement from the centre to centre distance between each hole and we're also given the minimum distance between them being 68.6 mm edge to edge. |
| 02:28 | Which would be even easier to measure with verniers. |
| 02:30 | On top of this, for each selection, we're also given some of the key measurements like the diameter and arc length, AKA the circumference in the case of these circles. |
| 02:41 | The measure tool also includes a few extra helpful options. |
| 02:45 | We can change our selection filter for example from face, edge or vertex to body or to component. |
| 02:53 | The body or component options are helpful when working with an assembly and finding the distance between components. |
| 02:59 | We can also choose secondary units, so the result will be given in both our normal units, mm in our case, and alternative units like inches, saving us time converting units if we need them. |
| 03:12 | Next we need to talk about mass. |
| 03:15 | In performance automotive and motorsport applications, mass, more specifically reducing it, is very important. |
| 03:22 | It's good to understand the mass of a part for planning or making changes to try to minimise it. |
| 03:26 | We just need to keep in mind the resulting changes to the strength of the part. |
| 03:30 | If we remove material to reduce mass, we're more than likely decreasing the strength so we need to be careful how we go about it. |
| 03:38 | In order to calculate mass, the density property of the material you're going to be using is required. |
| 03:44 | This value, along with our model geometry, needs to be correct and accurate in order to get a good estimate of the mass once the part has been manufactured. |
| 03:53 | If the density value used in CAD is different to the actual material density, this same percentage error will be carried over to our calculated mass. |
| 04:03 | It's important to understand that the actual mass of a part will always be different to what we calculate, we just want to minimise the difference as much as possible. |
| 04:12 | In Fusion 360 we can find the mass of the part by looking at the browser, finding the body of the component we're interested in, right clicking and selecting properties. |
| 04:23 | We can now see a range of measurements of the body, including the mass of about 250 grams for our three bolt flange as well as some more advanced information like moments of inertia and so on. |
| 04:36 | These units can be easily changed to imperial if our document units are also imperial. |
| 04:41 | It's important to note that this is all based on the material of the part which is set to steel by default. |
| 04:48 | We can change this by right clicking again on the body and selecting physical material. |
| 04:53 | Fusion 360 has a huge library of materials to choose from so it's just a matter of selecting what is most suitable for our component and what we intend to use to manufacture it. |
| 05:04 | For example, let's change the material to titanium. |
| 05:07 | By dragging it up to the in this design section over top of the current steel material. |
| 05:13 | Now if we take a look at the properties again, our mass has significantly reduced to 144 grams as the density of titanium is about half that of steel. |
| 05:23 | Another key consideration in motorsport, specifically around handling, is lowering the centre of mass. |
| 05:29 | While it's unlikely we'll be modelling the entire car assembly, the overall centre of mass position is a function of the centre of mass of each component. |
| 05:38 | For any components we model that are stationary and don't move relative to the chassis, we can find the centre of mass and optimise the design by working to lower this point, relative to the orientation that'll be mounted in the car. |
| 05:53 | The position of this was defined in our properties pop up window but we can also use the centre of mass tool under our inspect drop down list here to display the point in our model space. |
| 06:04 | This is now shown in our browser so we can easily come back to it and the position is shown in the bottom right corner of our screen. |
| 06:11 | We can also use the measure tool to measure to this point from existing geometry. |
| 06:17 | OK so to quickly recap this module, our measure tool is really helpful for checking that our model is correct and comparing it to physical samples that we may have. |
| 06:26 | We can also use it to easily measure factors like arc length that are really difficult to measure by hand. |
| 06:33 | If we have modded our part as an accurate representation of the final manufactured piece, and understand the material that will be used, we can get a good understanding of the final mass of the part and also where the centre of mass is. |
| 06:46 | As you no doubt are already aware, both of these are important aspects to vehicle performance so we can use this information to optimise our design. |
| 06:55 | Of course, keep in mind how any modifications will affect the part's strength and function. |
