For common electronics, hardware, motors, gears, you really want to find the model - not make the model. A DB 37 and RJ 45 connector are available on
www.3DContentCentral.com in any model format you want SolidWorks is the default, but you can select Inventor.
For the case of the DB37 and RJ 45 you must decide what type of mounting. There are a few options.
In assembly parametric modeling here are my rules of thumbs.
1. If there are mating holes - use the cylndrical face of the hole from two unique parts. This is the face that looks like a soup can label. When you mate holes - you can find issues, like fit and tolerance.
2. When you complex plastic geometry like some of the casing on an RJ45, then you need to use planes. Planes can really be your friend.
3. If you can find a model created by a vendor - use it. This is even better than models created on the fly in software - for example, if I was going to work with a gear from Boston Gear or pneumatic from SMC - I would go to their supplier catelog directly or from 3DContentCentral. No one is going to pay you to design something already created and in robot competitions you have no time.
4. It has been a while since I taught different CAD tools, but SolidWorks can help you understand what is the "assembly process" and "different types of mating techniques" for you robot. Go to
www.SolidWorks.com/roboticstutorials. Select on Unit 3, Assembly and watch the video.
Marie