This is obviously a little late to be pointing this out (since you're getting towards the end of the course), but I wanted to quickly note that when submitting your work, both PDFs and scanning your work (more specifically using something that actually tries to boost the contrast as it would a normal document) are far from ideal. We actually talk about PDFs being kind of a pain for us to work with when critiquing in this video from Lesson 0 (somewhere around the 16 minute mark). When it comes to scanning however, the reason it's better to avoid anything that performs additional processing like this on your images is that it can make it a lot harder to determine whether the linework itself was executed poorly, or if it's the software deciding to throw out a lot of extra marks that help give the ones that did show up context. The phones on most cameras will work fine, especially if the photos are taken in sunlight, which really helps to maximize the potential of that hardware.

Anyway, I'm going to be critiquing the work based on what I see - so do keep that in mind in case what you've submitted doesn't accurately represent what the pages look like in real life.

Starting with your cylinders around arbitrary minor axes, when it comes to the core cylinders themselves, you're doing pretty well. I did catch a couple cases early on like numbers 4 and 7 where your edges were too parallel on the page (going against what's stated here), but this did not appear to persist into the rest of the set where you generally did a good job of varying the rates of foreshortening and avoiding forcing vanishing points to infinity.

The area where I am more concerned however is with the linework itself. A lot of your straight lines are fine - they're confidently executed and come out looking quite straight. Your ellipses however tend to be much less consistent, and frequently come out unevenly. This is often the result of either not executing your marks confidently enough (which itself can be the result of not applying the ghosting method when executing these ellipses), or drawing more from your wrist/elbow instead of your shoulder when executing them. It's likely a bit of both, so do be sure that you are applying the three stages of planning, preparation, execution to your ellipses and that you are executing them with your whole arm without hesitation.

One side point - since we draw through our ellipses (two full times, by the way - you frequently tend to stop at 1.5, so make sure you're completing two full turns of the shape), if we're executing them incorrectly or just out of practice, they can come out a little loose. In these cases, always treat the outermost perimeter as defining the edge of the ellipse itself - don't choose to work with the inner lines when deciding where to draw your side edges to, as this will leave some of that ellipse outside of the silhouette of your form, undermining its solidity.

Moving onto the cylinders in boxes, you appear to be doing this well, although this is definitely where the scanner software causes issues as there are cases where I can only just see traces of certain line extensions (and a big part of this exercise is ensuring the student is using them correctly). This exercise is really all about helping develop students' understanding of how to construct boxes which feature two opposite faces which are proportionally square, regardless of how the form is oriented in space. We do this not by memorizing every possible configuration, but rather by continuing to develop your subconscious understanding of space through repetition, and through analysis (by way of the line extensions).

Where the box challenge's line extensions helped to develop a stronger sense of how to achieve more consistent convergences in our lines, here we add three more lines for each ellipse: the minor axis, and the two contact point lines. In checking how far off these are from converging towards the box's own vanishing points, we can see how far off we were from having the ellipse represent a circle in 3D space, and in turn how far off we were from having the plane that encloses it from representing a square.

For the most part this does appear to be done correctly, although the issue I noted before with the execution of your ellipses will definitely have an impact here. The looser/less evenly shaped the ellipse, the more loosely the line extensions we derive from it actually describe the plane of the box itself.

The last thing I wanted to note is that it is very important to always ensure you're not just falling into the habit of marking the minor axis where you think it ought to be. Since most of our boxes here are going to end up being drawn with squared planes in mind, the minor axis isn't usually a big problem. Where it does become an issue is where we end up drawing boxes that deviate from those proportions more dramatically. That isn't a problem in and of itself - but it becomes a problem when our line extensions aren't drawn correctly, failing to identify the issue. If we look at 218, you'll see that the actual minor axes as marked here are pretty far off from how you marked them. That means that there was a mistake here (again, which is fine), but you were a little careless in appyling the steps so that this issue was not revealed to you. It's important to avoid this when practicing these on your own in the future, to ensure that you're always progressing in the right direction with this exercise.

Anyway, I'll go ahead and mark this challenge as complete, but do be sure to incorporate both exercises into your warmups, and to give yourself some time to do more focused practice on the execution of your ellipses (the exercises from Lesson 1 are best for that).