Alrighty! First off, congratulations on getting through this challenge. I've gone through your set and have found three main points to address that should help you push forwards. Two of them are structural, and the last is more of a breakdown on how to think about design itself, and how to actually come up with the things that allow you to flesh out your designs.

Firstly, I noticed that when you were drawing the large rotational ellipses for the chests with open lids, you may not have been as specific with those ellipses as you could have been. There are two main considerations to how we draw those ellipses that allow us to place them in the correct position, orientation, etc.

• Firstly, we're rotating on an axis defined by the hinges themselves - this coincides with our ellipses' minor axis, since the minor axis is effectively the "spine" on which an ellipse or a cylinder will rotate.

• Secondly, given that this circle in 3D space must be centered on this axis and must extend out with a radius equal to the side edge of the chest's lid, we know that the resulting ellipse should touch the corner at the front of the chest, where the base and lid meet.

Here's a diagram of what I mean.

You were mindful of the second point, but I noticed that your minor axis alignment seemed to be off fairly frequently. When placing ellipses that require any specific alignment, always focus on the minor axis as your first consideration, then think of the degree as what you can dial in to hit whatever landmarks you need. Of course I can see that you were working with an ellipse guide, which could suggest that you were locked into certain configurations with no perfect option available. For things like the wheel challenge where the ellipses make up the entire structure, I'd recommend sticking with the ellipse guide. For things where the ellipse only helps to position another element but doesn't necessarily serve as the foundation of the whole structure, freehanding the ellipse may be the better choice.

Onto the second point, I noticed that in a lot of your constructions, when you started getting into more structural detail, you would often add elements either as a single plane with no thickness of its own(rather than a complete 3D structure with defined side planes), or you'd kind of try to leverage line weight to imply that thickness, giving a sort of impression that the side planes were filled with black.

Here's what I mean. If you look at the bands on the lid, they're generally drawn as a single plane with no thickness, though there is sometimes inconsistent line weight along their sides. Not sure if the intention was to convey thickness through that, though it's in many cases not a great tool for that purpose, instead serving a lot more value in establishing how different forms overlap one another as shown here. At the end of the day line weight is a tool, and it can be used towards many different ends (overlaps being the focus we use for it in this course), but it is important to ensure that these tools are used towards a consistent end - and not switching from one to another throughout a single drawing.

Considering the fact that different objects has thickness goes beyond how we convey that thickness - it also contributes to how we think about the objects we're designed, because it means that every new component you add now has to interact in 3D space - not just as a flat sticker-like decoration pasted onto an existing form's surface, but as its own structure. This leads us to the last point I wanted to address, although much of this will be on the diagram itself.

The heart of design is problem solving - design itself serves to solve problems. But without knowing what those problems are, we're left kind of grasping at things based on their aesthetic value, which tends to really mess with the believability of the design, as it doesn't end up serving any particular purpose, or solving any particular problem. The key to this, I've found, is to ask yourself questions. Questions reveal problems, which we can then solve.

As explained here, those questions can be directly related to the construction of the object - "how does this board attach to this other structure" - or it can be as abstract as "who produced/crafted/built this object". A question like that may seem completely irrelevant, until you start asking yourself further questions - what technology do they have access to?

A treasure chest's lid is often curved, and we certainly stress that in this challenge - but it's worth considering that creating a curving surface like that out of a single solid piece of wood would be very difficult. It's certainly achievable, but depending on the point in time this chest would have been made influences what techniques would be used. And of course, wood isn't the only possible material to be used - a chest could be made entirely out of steel, where achieving a single curved piece would be more feasible with the basic techniques required to work the material.

Of course if you're limited to the most basic of technologies, you'd be stuck making a lid out of wooden boards or slats, which themselves have to be secured together somehow - which opens up another question. Is it adhered together with glue? Or are there nails, or rivets? When you start asking questions, you will often find yourself with yet more questions, until they overwhelm you with options and possibilities.

I talk about this more in this video (it's a preview from a larger video course I sell through Proko, although this video is specifically the one that touches on this technique for ideation and exploring your designs, so you don't need to purchase the course).

And that about covers it! All in all you've certaily explored your designs a great deal here, and hopefully I've helped highlight the path forward to expand further into pushing design as far as you reasonably can.