Ignoring the fact that it seems to mangle my model after the side profile, it says in the Joystick Controller README:
[…] You can create multiple sliders and combine different poses.
and
…Similar to 5, 7 frame. But the power of slider is that you can combine whatever the value of 3 and 5 frame is.
So I’m curious because I have no idea what that last part means.. does that mean I can combine all these sliders? And if so, how?
@veermetri05 is the author of the plugin, maybe he can help 
But whoever knows, please help him. 
There is a long forum thread here about his plugin: Joysticks in Synfig (Controller Plugin) .
Joysticks consider 5 waypoints as a default (neutral/center) position and Right, Left, Top, Down.
Running the script calculates all the min/max and moving the joystick interpolates.
For the sliders, it is a bit different, there is always the first pose/waypoint as a start.
Then, for each other waypoint, it is the end of an animation.
And for each of them, there will be a slider, using the defined waypoint as the end of the animation.
You can combine them.
For example, think about a first waypoint as a closed fist.
Then you do other waypoints where each of them is an extended finger.
Each slider will animate from the closed fist to a specific extended finger, independently.
You can do the same with closed and both opened eyes.
One waypoint/slider per eye, so you can animated them independentely, with intermediate (tweening) value, instead of using on/off switch layer.
Note: it is not compatible with what you expect to do
@veermetri05 If I may suggest an approach, you could implement ValueAtTime using the Time Loop converter. This allows the data to be stored as waypoints, with values retrieved at a specific time (t) through a controller.
You can take a look at how it works in this file:
play_mode.sif (578.0 KB)
input_mode.sif (103.6 KB)
@Slam , for the usecase, using a joystick is more suitable. And to answer your question, yes you should be able to combine multiple sliders. What it means is : You have slider1, slider2, now you can create slider3 which controls slider1, slider2.
I will attach a small demo, to showcase how I can use joystick for such head turning animation.
@zainal , I will take a look into it. Ideally sliders and joystick should control anyway waypoints whose value can be interpolated, so I will take a look at it.
sorry for the delay getting back to you but these are really interesting examples and while I still don’t fullly understand how they work - I’m very excited to understand it 
It’s been mentioned here a few times that you can combine sliders but I’m actually wondering: how do I do that? After I create the sliders, I have 5 of them but how do I actually combine them into one unit?
My approach is not directly related to the joystick plugin. I’m developing a new plugin with functionality similar to SmartBones in Moho, although some aspects are similar to joystick/sliders controls.
You can try out the plugin. It’s still in the testing phase, so you might find some bugs. Feel free to download it and give it a try.
All this week I’ve been trying to figure out how/when I should finally switch to Linux and this plugin just added another important reason to make that switch :')
Sorry, I should clarify I’m still very interested in understanding how Sliders can be combined. I saw Khemardi’s recent rig build videos and at the end he’s demonstrated how multiple sliders can work together. But he didn’t actually explain how that can be done and I can’t see anything in the documentation. I thought it might be a case of grouping all the controllers and then renaming that group slider_all or something but that didn’t work so if you could explain how this is done, I would really appreciate it thank you!
Maybe he did one at a time?
Apologies, I might be being more vague than I realise because I’m still relatively new to Synfig and my usage and understanding of the terminology (trying to learn it and use it more/better) might not be the best but for example:
In the video below, Khemardi has managed to combine several sliders into one at 17:10.
Not only that, but he’s also somehow managed to utilise the Sets panel to control each element instead of working from the Layers panel.
I’ve tried what (my understanding) is of the solution from the original post on Sliders/Joysticks:
Create several Keyframes in a Group while Animate Editing Mode is active, run the plugin, then be presented with (example) 5 sliders. I then group all of them and name them slider_id3_eyes but when I run the plugin, it hasn’t merged anything, all the sliders are still seperate.
The sliders are separated. Create the sliders and joysticks one by one.
Then, you use the Layer Set to ‘group’ them. Khemardi made a tutorial about it too.
Be careful though, the current development versions have a crash issue when you try to create a shape with a layer set selected o.O I believe now I realize a good way to solve this problem: fix: crash on creating new layer while Layer Sets Panel is open by rodolforg · Pull Request #2906 · synfig/synfig · GitHub .