so today i thought i'll see if i can learn to animate in blender 2.8 so i made a robot guy based on the irobot film (just because it's a simple design but still looks cool), keyframing in blender took a bit of trial and error but i think i got the hang of it - i'm not very good at making natural looking animations, to be fair i blame the fact that it's weird trying to animate a moving object which is stationary
couldn't get the GG importer to accept the model (maybe it doesn't like the rig? it's an automatic rig from blender but might have too many bones, i forget what the limit is in GG these days) but if anyone would like to try import it i'll include the .fbx file here (only has a basic walking animation right now, this is just a test model and no point taking it further if i can't get it into GG)
also a video of the "finished" animation in unity just to prove it does work

GJ, iam thinking also about start to animate in blender cuz fragmo has a limited poly number.

it's fairly easy to learn, i guess keyframe based animations are pretty similar whether they are 2D or 3D (i'm more used to spriter as i normally only animate 2D stuff) - just getting used to the menu and quirks is the hard part
i was going to stop but i realised i also need to know how to split animations into different files so i did that as well - this isn't well explained for 2.8 yet but basically you swap from dope sheet to actions and then there's a new menu which allows you to create a new set of animation keyframes (though it duplicates your previous animation by default which confused me at first as i didn't want to overwrite my animation).
so as a quick test i now have 3 animations (crouching and getting back up is split in 2 so i can add the option to remain crouched easily later)

the new fbx file is quite a lot larger now so i'm not sure if i did it completely correctly but i'll include it anyway just in case anyone wants to look at it

Great work ..
Something I must get into ..

I there any tutorial on how to rigg a model to existing animated bones like in fragmo?

weight painting you mean? i'm sure there is on youtube but basics would be to ensure your model and armature starts in t-pose for easiest set-up, that way you can be sure you're spreading the weights more realistically without any bends or shortened limbs already in the scene.

No weight painting, just simple basic rigging a weapon and hand model to the existing animated bones.Like here
https://www.youtube.com/watch?v=Pxcdy1uZ5XE
I have a problem with the enhanced weapon pack if i open a HUD model in fragmo theres a limit o vertices.Blender could do the trick but i found only tutorials how 2 made own bones from the beginning.

I don't really understand then, I see no reason you wouldn't just import both the mesh you want to attach and the animated object you want to attach too, delete any meshes you don't want (with them selected press x or delete), then parent the mesh you have left to any bones as needed (select the child first then the parent and with both selected press control-p) and assign the correct weights (you can try auto weight but if the new mesh needs to bend etc this will likely need tweaking).