Design new figure from scratch

Has anyone tried to create their own figure from scrstch (not repainting, reusing part etc)
Ive been trying to find how to's for different kinds of joints and hinges, slides and extensions, with little success.

Any help would be awesome

Pinterest has some boards and YouTube has some videos, in both cases you need to do some deep dives to find what you want and be ready to experiment.

Can't help you much more without knowing what type of figure you want to build. Action figures are kind of straight forward, a transformer is going to be hard if you want contemporary engineering.

I'd suggest starting simple with 5 points articulation and go from there.

I've dabbled a little with concepts in the past, mostly transforming accessories, never had the Capitol to put into a legit CAD package to do anything with it.

I think you might find a lot of this is stuff that you'll only find in an engineering design text.
Working in plastics, you need to consider geometry shape and thickness changes - when a part cools, different thicknesses will cool at different rates, this will potentially introduce a stress in the material causing it to physically deform, especially if you have a very thick and very thin part without any gradient between the significant thicknesses.

Manufacturing tolerances for moulds, draft lines, plastic shrink specific volumes are things you need to consider for mating parts, be it ball joints, mushroom pegs or even a pin joint. Assembly procedure, interfacing material properties, hardness, flexibility.

All these considerations make trial and error an inevitability. Prototyping is an essential part of the process. Over time you will develop an understanding of material behaviours and this will assist with reducing the test-design repeat cycle.

This type of information isn't generally freely distributed simply because massive amounts of research and development have gone into it and those people need to make a living from those efforts.

I wouldn't be surprised if a place like Takara have a design principles book that they continually update and share amongst their design engineers.

Key search words for Pinterest scratch build, Gundam, gunpla and of course, Gundam custom.

Because Pinterest is a media aggregator click on images will also provide links to sources.

I have a Badboy resin toy that is all original design. It's a bit fragile because of the materials used but it's quite nice as a display figure. HLJ has a lot of parts like ball joints, hinges and articulated hands.

The link here is one I found on Pinterest, the customiser is making his ball-joints from scratch with beads, some scrap sprue and a pen.

Does anyone know what software 'jjizaitoys' uses to animate their transformer models?
Saw the use of it on their website, was impressed. : )