Time to read: 5 min
Welcome to the next installment of our Butterball EV conversion! In case you didn’t read our introductory article,Butterballis our pet name for the cream-colored 1966 Fiat 500 that we converted to an electric vehicle this past year as a means to foster community here at Fictiv while we were all working remotely.
You can read more about theelectrical designand原型该项目的阶段！
Modeling the Existing Car
机械设计是该项目的重要方面。它始于对汽车的内部空间进行建模。能够计划重要组件（例如电机和电池盒）的布局，并确定这些组件将如何安装在哪里以及如何安装。
建模步骤首先需要对所有空间和现有组件进行详细测量。空间必须手工测量。因为这辆车是如此古老，所以文档不可用或易于查找。幸运的是，我们团队中有一个人（向Veda大喊！），非常关注细节，以收集详细的测量。这些测量值使我们在汽车的后备箱和毛孔（前躯干）中建模OnShape，使用其钣金功能方便的在线CAD平台。
Modeling the EV Components
Next, the other components had to be modeled. Some of the modern components, like the motor and batteries, were easier to model because they had existing CAD files that we could use. Additionally, we knew the batteries would be mounted within boxes, so they were simple to model in CAD.
然而，电动机的铃铛外壳很难建模。铃铛外壳是覆盖原始汽车传动系统的飞轮和离合器的变速器的一部分。将盘子上的一组孔固定在电动机上的安装孔上，而另一组孔被固定在钟楼上。
Because we couldn’t find documentation for the car, we had to measure the specific hole pattern on the bell housing by hand. First, we tried shading the holes on a piece of paper that we laid on the bell housing with a pencil to make a tracing of the holes. Then we took pictures of the bell housing, measured the number of pixels, and equated those values to inches to find the measurements. In the end, those efforts combined with oversizing the holes for extra clearance were sufficient to create a bell housing plate model.
Designing the Component Layout
随着空间和零件的建模，下一步是找出汽车内部组件的布局。这不是一个简单的壮举；如果您看过60年代的旧菲亚特500，那么您就会知道它们是很小的汽车！
Getting back to the layout, the assembly feature in OnShape was useful in determining the orientation of the parts. However, it’s important to remember that just because you can do something in CAD doesn’t mean that it will be easy, or even possible, in real life. We were reminded of this lesson the hard way when trying to fit the engine mounting plate in the trunk — in CAD it worked, but in reality, the plate was too big to fit through the opening of the trunk!
So, we had to cut the plate in half and create mending plates to join them back together. While the large plate was made out of aluminum, the mechanical team decided that steel would be better for the mending plates to avoid creating a structural weak point along the split. And that mounting plate was a part we outsourced, using one of Fictiv’s manufacturing partners to machine it for us.
On the other hand, we built the battery boxes ourselves (you can read more on that decision in another article). We wanted to make cheap boxes that were both easy to seal (with silicone around the edges to make it waterproof) and strong. What we came up with was a two-layer box design with steel angle bar on the corners to connect the plastic faces. We made 2 boxes: 1 larger box to hold two batteries in the trunk, and one smaller box to hold one battery in the frunk.
The steel bar made these boxes extremely heavy. The mechanical team decided that this was appropriate because the boxes would be supporting a significant load and contain a high-value part of the car. However, it was still important to be aware of where we used steel, not just for the additional overall weight, but also to maintain safe and efficient weight distribution.
Another important part that we designed was the coupler that fits over the motor shaft and mates with the transaxle shaft. With all of these different parts interfacing, tolerances were critical, so we used ISO 2768 tolerances unless otherwise specified. For the coupler, we used a key from McMaster to fit into a keyway that needed a precise fit, so tighter tolerances were required.
Connecting the motor to the transaxle
Once the components were constructed it was time to tackle mounting them. The inside of Butterball has precious little space structurally capable of serving as a mounting point. Although there’s plenty of sheet metal in the engine bay, it’s not structural and certainly not strong enough to support a 120-pound battery. So, we had to use the actual chassis of the car, which required extra attention to detail. For stability, we used lock nuts where we could and aircraft cable instead of simple wire to hold the battery box in the frunk.
One of our goals in converting this car was to keep everything quiet while driving. One benefit of an electric car is that you don’t have the noisy engine roar, but that means you can also hear every little vibration and rattle everywhere else. To mitigate sounds from internal components, we added foam between the battery boxes and sheet metal of the car and dampeners on the motor.
Overall, we tried to modify the structure of the car as little as possible, so we only removed the original engine, and an exhaust pipe from the trunk area. We avoided messing with the sheet metal so that we could convert the Fiat back to internal combustion if we wanted to.
Lessons Learned
当涉及机械设计时，我们学到的第一教训是，为组装设计与建模完全不同。即使我们最终能够适合所有组件，但我们也必须通过运营顺序获得创造力才能使其正常工作。随着一开始的更多计划，组装过程可能会容易得多。我们使我们的一辆汽车实现了这一目标，但是当涉及到大规模组装物品时，仔细考虑设计用于组装更为重要。
What’s Next
在我们的其他Butterball文章中，我们讨论了电气系统进入的工作，以及我们对原型制作和建造零件的了解与购买。汽车转换是一个大项目，但是有一个积极进取的团队，我们使它起作用了！
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