Starting with the structural aspect of these wheels, you're doing well. You're mindful of how the wheel structure is built to widen through the midsection, which helps to convey a sense that were it to be dropped, the wheel would land with a bounce, rather than a heavy thud. I'm also pleased to see that you've been mindful of not only drawing the outward faces of your spokes, but also considering their side planes as well.

In terms of the textural aspect of the challenge however, here you unfortunately fell into something of a trap. Most people do, so don't worry too much about it, but we intentionally present this challenge at this point to serve as a reminder that there are many topics covered throughout this course, and there may be things that you've allowed yourself to forget about. In this case, it is as my wording may have already suggested: texture.

Specifically, the concept of conveying the presence of textural forms not through explicit markmaking (which is what you've used most of the time here), but rather through implicit markmaking, drawing the shadows our textural forms cast to imply their presence rather than drawing them directly.

If we were to take wheel 20 for example, which is extremely detailed, and used that in a larger illustration, the viewer's eye would immediately jump to the wheels whether you wanted them to or not. Reason being, with all of that detail they create a great deal of contrast, which then attracts the viewer's attention. Using implicit markmaking allows us to convey the presence of those forms, but in a manner that allows the manner in which it's drawn to change without changing the nature of the forms themselves.

As shown in this diagram, depending on how far the form is from the light source, the angle of the light rays will hit the object at shallower angles the farther away they are, resulting in the shadow itself being projected farther. This means that we can assert that the light source (which we have control over, as we have control over all the things we draw) is closer or farther away from certain sections. When the light source is close, the shadows shrink to the point of most being blasted away, whereas when the light is far away, the shadows expand so much that they engulf much of the structure. Both of these allow us to diminish the amount of contrast produced, whereas in between those extremes we can have more/less individual shadows.

Now, there are certainly cases where you did shift away from outlining everything, so it seems that you suspected you may have been approaching it incorrectly - although it doesn't seem like you necessarily went back and reviewed that material, but instead tried to wing it based on what you remembered. These attempts were certainly better (cases like 18 and 19 in particular, whereas 22 appears more to be a matter of filling in the side planes rather than drawing the shadows being cast), but as a whole it does suggest that you will want to review that material.

I strongly recommend that you do so, and that you consider anything else you may have allowed to slip through the cracks, so you can review it all before completing the remainder of the course. When it comes to texture, I recommend that you start by referring to these reminders, then going back over that section's notes/videos.

Given that this was an intentional trap, I will still be marking this challenge as complete.