3D Modeling & CAD for Motorsport: Motion and Contact Analysis of Assemblies
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Motion and Contact Analysis of Assemblies
05.50
| 00:00 | - As we discussed in the assembly section of this course, being able to model assemblies of components helps us to understand how they fit together and in some cases how they move relative to one another. |
| 00:12 | Vehicles are complex machines built up of 100s if not 1000s of sub assemblies. |
| 00:17 | It's unlikely we'll be wanting to modify the vast majority of them for performance advantages and some we might just want to remove from the vehicle all together. |
| 00:26 | Then there's an even smaller number of assemblies that we might want to really get a better understanding of. |
| 00:32 | Suspension systems would be a good example of this as the geometry and how it moves has a drastic effect on how a vehicle handles. |
| 00:39 | It's also one of the areas most commonly modified on a vehicle. |
| 00:43 | Simply due to the fact that most OEM setups involve a lot of compromise. |
| 00:47 | Most notably for comfort at the expense of performance. |
| 00:51 | To get a better feel for how these tools work, let's bring in an assembly I prepared earlier. |
| 00:56 | This is a very simplified representation of a macpherson strut rear suspension for a front wheel drive vehicle and the files for this can be found below this module if you want to open it up on your system and follow along. |
| 01:10 | Our assembly has the chassis pickup points here in blue which are part of the grounded component so they can't move. |
| 01:17 | A lower control arm connected to the chassis via revolute joints. |
| 01:21 | A toe link connected to the chassis with a ball joint, then connected to the lower control arm and toe link we have an upright, from which we have he main upper strut with a slider joint to model the damper motion. |
| 01:34 | This is then fixed back to the chassis with another ball joint at the top. |
| 01:39 | At first glance it seems pretty obvious that we're missing the actual physical models for the hardware at the joints but these are represented by our assembly joint as we covered in the assemblies module. |
| 01:50 | So there's really no reason to create solid models for these parts, at least for this example anyway. |
| 01:57 | There's also no spring showing, again it's just not needed for this purpose. |
| 02:01 | Having a system like this modelled as an assembly can offer us a massive advantage because we're able to understand the kinematics which is the motion of a system of bodies and make adjustments to optimise the design with quick revisions before spending the money to produce it. |
| 02:17 | In Fusion 360 we have a range of motion and contact related tools that can be really useful and they can be found looking back under our assemblies tab. |
| 02:27 | If we drag the assembly from the hub where the wheel would mount, we can see how all the components move together. |
| 02:34 | The key issue here is that there's no limit on how far we can move the assembly so the parts will eventually just move through each other. |
| 02:42 | Clearly not a very accurate representation of reality. |
| 02:45 | To fix this, we'll look back under our assemblies tab and use our contact tools. |
| 02:51 | Here we have two options, enable contact sets and enable all contact. |
| 02:56 | Enable all contact will activate a contact analysis for all components. |
| 03:01 | This means that the software will know when the components make contact and will not allow the bodies to move through each other. |
| 03:08 | Enable contact sets is the same idea, however we can choose specific bodies or components we want to recognise contact and prevent further movement. |
| 03:17 | If we select either of these, we get our contact controls in our browser and we can toggle between contact sets or all contact and no contact from here. |
| 03:27 | OK so let's have a closer look at how these work. |
| 03:30 | First, if we have it set to enable contact sets, then we can right click and choose new contact set. |
| 03:36 | Now, we select the upper section of our damper and the bottom section of the strut and click OK. |
| 03:43 | We can see that now when we drag the components, the movement will stop when the shock bottoms out and also at full extension due to some geometry that has been put in place to make contact at the top of the stroke, therefore defining the damper travel. |
| 03:58 | Let's look at what happens when we change our contact setting to enable all contact. |
| 04:03 | Notice how when we drag the suspension, we can no longer bottom out the shock. |
| 04:08 | This is because we're actually getting contact between our toe link and its mounting bracket. |
| 04:13 | Clearly this is something that would need to be modified as this system would almost certainly break the first time the vehicle was driven. |
| 04:20 | Further to this, the ball joint we use will have some limitation on the angle of motion it allows which would also need to be accounted for. |
| 04:28 | It's this ability to identify issues and make revisions in CAD that's usually beneficial. |
| 04:33 | With our current model, it's also possible to move the system through its range of travel and take measurements between the origin planes and the face of the hub. |
| 04:42 | From these we can understand how the toe and camber changes with travel and again modify the geometry to manipulate this, making revisions and testing them relatively quickly with no expense. |
| 04:54 | With a more refined and detailed approach, this can provide some very useful data, taking the guessing game out of the initial development and allowing us to get to a good starting point which can then be tuned and developed further on a vehicle. |
| 05:08 | To summarise, once we've modelled our components and set up the joints between them, the next step in creating a realistic model is to ensure the parts can't move through each other. |
| 05:18 | Our software can do most of the work for us with the contact analysis tools under the assembly tab and we have the options of activating this contact analysis for all components or just the bodies we select. |
| 05:31 | These settings will be captured in the browser so we can come back and make changes if needed. |
| 05:35 | Moving our model through its range of motion can help us find issues and better understand how it will function and we can make iterative revisions and check our model as we go to develop it further. |
