Jumping right in with the structural aspect of the challenge, here you're largely doing a pretty good job. There are a few small issues, but overall you're demonstrating a great deal of patience in building out the body of your wheels using your ellipse guides, then building out the various forms involved to establish the rims/spokes as solid forms.

A couple of the minor issues I wanted to call out include:

• On number 17- er, that is, the second 17 which looks like a bicycle wheel - you made the right call in drawing the spokes themselves with two edges. Many students figure that since they're so thin, they should be drawn just as a single line, but unfortunately that would not read as an actual form, and so two edges (though they'll make things thicker than one might prefer), are better for establishing a solid structure. That said, where you have those spokes connect with the outer rim of the wheel structure, you have those lines stop suddenly, which does flatten these structures out. As shown here, the way in which you close off that silhouette - being sure to imply different planes of the structure by establishing corners, will help make it appear more solid. You can ostensibly also use an ellipse to cap off the end, since these spokes are generally fairly rounded, but I find that going in with sharp corners reinforces the solidity a little more effectively.

• The other thing I wanted to call out is honestly technically the same issue, just in a different context - this wheel here where the rear edge of the side plane on some of the spokes extends all the way to the front of the tube it's connecting to (the same as the front edge of that side plane), rather than stopping sooner. This is something you do correctly a lot of the time, so I suspect you may have gone a little bit on autopilot, or otherwise struggled with drawing in such a small size - but ultimately the solution to that is giving yourself more time to think through each action you're taking.

• Additionally, as marked in on top of wheel 22, don't forget that even smaller cut-outs still form side planes in the structures, and including them will help your construction maintain more solidity.

Continuing onto the textural aspect of the challenge, this is an area that we've laid out as something of an intentional trap. As the case is for most students, being as far removed from the textural material from Lesson 2, it's very common for students to either forget entirely that texture is something we've engaged with in this course using a very particular methodology (implicit markmaking and all that), or to remember that we use filled areas of solid black, but apply them as form shading or other uses, instead of as cast shadows. This challenge serves as something of a poignant reminder that sometimes we forget about things if we don't incorporate them into our warmups or find time to explore them further elsewhere, and that prior to completing the course, it would be a good idea to review both the textural material and reflect on any other areas that may need to receive similar treatment.

That said, you are not such a student - you actually just finished up with the texture challenge less than a month ago. I think the issue here is that you did not realize that the problem you were facing - that is, conveying the presence of small forms that rest along the surface of a larger object - constituted a texture (although that is exactly the definition of a texture that we employ, per what's explained here: https://drawabox.com/lesson/2/2/understandingtexture

Texture - that is, what people tend to think of as detail - isn't actually all that different. While we treat it a little differently, texture is also made up of three dimensional forms. The only difference is that these forms adhere to the surface of some other object - and this difference fundamentally changes how we approach drawing it.

An example I like to use is fish. If you've got a fish swimming in the ocean, then we draw it similarly to how we draw the boxes and sausage forms we've tackled thus far. We apply constructional means - drawing through our forms, defining their silhouettes with outlines, describing how their surfaces move through space with contour lines, etc.

If, however, you take a bunch of fish and use it to wallpaper your bedroom, it becomes a texture - and the way we draw it changes. The fish is now a part of the wall itself. If the wall turns, the fish will follow. If you were to strip down this fishy wallpaper and wrap it around a box instead, the fish would come along with it. They cease to be an independent object, but rather become a part of this texture that can be applied to any other surface.

Ultimately I don't really have additional advice to offer on this front that I haven't already provided in response to your texture challenge work, and ultimately I don't think the issue has to do with you not knowing how to approach texture. Rather, I think you just didn't realize that this was a problem that demanded textural techniques be applied.

Actually, to that end, I do have one bit of advice to offer, since one of the reasons you may not have immediately realized that what you were dealing with was a textural problem may have had to do with the intentionally shallow groove-based tire tread I chose for the example demonstration. When it comes to those tires with shallow grooves, or really any texture consisting of holes, cracks, etc. it's very common for us to view these named things (the grooves, the cracks, etc.) as being the textural forms in question - but of course they're not forms at all. They're empty, negative space, and it's the structures that surround these empty spaces that are the actual forms for us to consider when designing the shadows they'll cast. This is demonstrated in this diagram. This doesn't always actually result in a different result at the end of the day, but as these are all exercises, how we think about them and how we come to that result is just as important - if not moreso.

This last point, the fact that sometimes the results do come out looking essentially the same, but the process being what's important, may have caused you to assume that the way to achieve those results was to simply approach it as you would constructing any other object.

Now, I don't assign revisions on textural issues here, since it is a reminder I expect to provide to students, and one I don't take steps to help students avoid in the first place. But that said, do take care to consider the problems you're facing in these assignments (and in your general drawing) in the context of the course as a whole, going forwards. I'll go ahead and mark this challenge as complete.