Richard Stubley
Richard Stubley, Fusion Senior Product Manager shows you how to easily coordinate multiple hinged joints using motion links in Fusion. Learn best practices for joint placement and assembly modeling for smooth, realistic motion.
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If you’ve ever struggled to coordinate multiple hinged joints in a complex assembly—like a folding A-frame cart with several moving parts, you’re not alone. Many designers want to know: How can I add joints to hinges so they all move together when I drive just one joint? Let’s break down the solution using the powerful assembly tools in Fusion.
Where should you place joints?
First, it’s important to understand that, technically, the placement of joints in your assembly hierarchy doesn’t affect their ability to compute correctly. Joints can be at the bottom, top, or scattered throughout your assembly—they’ll all function at the top level. However, for your own sanity and ease of troubleshooting, it’s best to place joints at the lowest logical level in your assembly.
Think of it like disassembling your model: where would the joint “survive” if you broke the assembly down into its smallest parts? Place your joints there. This approach makes duplication and fault-finding much easier.
Introducing motion links in Fusion
The real magic happens with motion links. If you want multiple hinges to move together—so driving one joint moves all the others, motion links are your answer.
Here’s how it works:
- In the assemble menu, select motion link.
- Link the relevant joints together. For example, if you have two revolute joints, you can set up a one-to-one relationship so that as one joint moves, the other follows in sync.
- You can also set up gear ratios. For instance, a three-to-one relationship means that for every degree one joint moves, the other moves three degrees.
Real-world example: Planetary gearbox
Motion links in Fusion aren’t just for hinges – they’re great for simulating gearboxes too. For example, in a planetary gearbox, you can link the rotation of the carrier to the planetary gears, setting up the correct gear ratio. This makes your digital model behave just like the real thing.
Pro tips for assembly modeling
- Place joints as low as possible in your assembly structure. This makes duplication and troubleshooting easier.
- Copy and paste subassemblies with joints already in place to save time.
- If you only add joints at the top level, your subassemblies won’t move independently—so always build from the bottom up.
Conclusion
Coordinating multiple hinged joints in Fusion is straightforward when you use motion links and thoughtful joint placement. By building your joints at the lowest level and linking their motion, you’ll create assemblies that move realistically and are easy to manage.
Ready to take your assemblies to the next level? Try out motion links in Fusion to see how much smoother your design process becomes!