Looks fine to me what you did there.
Probably there is something not working right when setting the axis values inside of your Pincal_Blueprint. Did you check if it works with a keyboard? Maybe the engine is not receiving your controller input. Make sure that your input is setup correctly and also that the input is interpreted to a rotation.
Sorry but i have no idea if there are better solutions for simulating a robotic arm. But you can definitely do it with unreal engine as well you just have to learn some parts of the engine.