Is there a way to link animations? Basically, I have a biped with a walk cycle animation and a back pack with a walk cycle animation that uses a different skeleton mesh. How can I get both walk cycles to play at the same time?
OK so first a basic understanding as to how things work is best practice wise the animation needs to match the naming convention of the rig used to create the animation so being able to do something simple like sharing a common animation BP is not really possible or problematic at best There is however a work around that will allow you to consolidate two different SK rigs.
The most common way of compositing a character as a single entity is via the use of the Character BP, or any BP for that matter, to act as a container that will allow you to combine different SK elements with out consideration as to dependencies. What is normal is to add components, to the left of the view port, and then add a master pose component to the event graph so that all of the animations for the components are driven by a single animation BP instead of each component being driven by their own animation BP.
In your example you would add the biped character first as the mesh that gets inherited and then add the backpack as a sub component that can be driven by it’s own animation BP that matches the rig as an added component. That said there are a few options available as to the use of sockets and bone linking so that the backpack goes along for the ride with out the need for animations or blueprints but as to answering the question of how to get the two to work with the same walk cycle there is a brute force approach.
1st create a BP to act as container. The character BP will work well in this example as by default a movement component is add.
Next take all of the animations use in the base mesh and re-target to your backpack. You should now have a duplicate animation set.
Then create an animation BP using a mirrored version of the base. (this can be a bit tricky)
On the right side of the view port you can add the animation BP that is unique to to the rig the animations are targeted to.
As you can see not a very slick solution but since a blueprint is a blueprint and is not dependant as to the same problem of matched animation resources you can add SK objects that have unique animation requirements. A better solution that might work for you is to convert the backpack to a static mes and attach it to the biped via a Parent Socket under sockets on the right side of the view port.
Thanks for your answer FrankieV. The problem is that the rigs are totally different and retargeting won’t work. It’s a biped with normal joints and a rig with just joints for the back pack. They both have an blendspace that include run,walk,idle, left and right animation for each rig (biped and backpack). I also have a character blueprint made from the biped that includes the back pack. I have two variables for both blendspace (speed and direction). Now, I want animation to play at the same time. Maybe, the biped animation gets sends it to the back pack animation. Something like casting or linking the blueprints with an interface? Could it be just the speed and direction variables drive the animation?
Well if the question is “how would I fix it” I would export both the biped and backpack to 3ds Max, dump the rig, and skin wrap the backpack to the biped and convert to skin weights and reimport the bp back to UE4 with the new rig.
That said what to do is really based on the need, what is the project all about, as say in the same way that the boy and his kite uses a backpack so if it’s just something that your playing around with then as I mentioned you can combined the two as components of a blueprint and attach the bp via the use of a socket. Usually that’s the most typical way of doing it.
Trying to sync two totally different SK is a near impossible task depending on the complicity of the bp. Does it have shoulder straps? Does it need to deform with the biped character?
So the problem here is not so much as how to combine the two, as I’ve given two very good answers that will solve the problem, but rather one of the lack of context as to the purpose the solution needs to serve. The “A Boy & His Kite” project is a much more complex project as to needs as say compared to hot gluing a backpack to a video game player model. 
Yeah FrankieV, having the same rig for both biped and back pack would be a solution. That’s how I had it originally but my project lead wants the pack to be able to animate taking off the biped if needed (with shoulder straps, waist straps, and main back piece) . I was looking at this video for linking two blueprints https://www.youtube.com/watch?v=EM_HYqQdToE&t=2371s . Do you think it’s a possibility?
This might be helpful;
Nice one! Got a good understanding of some Basics going on. But at the end you mentioning many other stuff, do you got some Videos recommendations on that topics to dive deeper?
And dont want to crosspost, but you got a good knowledge of this stuff, maybe you could get a look about my problem with getting added Bone Hierachie for animations shared over different animationsset at initialization. https://forums.unrealengine.com/deve…ditional-bones