I cannot draw this guy bro…

Hey thank you! I can actually answer that one!

TLDR: study artbooks / mecha artists! Most of them, like me or dear friend @anoxthon are usually just bullshitting the actual mechanics behind the robots we draw, but, if you want something more in-depth, I'll have an archive org links list behind the post break with some artbooks that I like to keep around for reference.

Delving deeper - it's all about shapes, actually :)

I'll provide some examples with the designs I've made based on some thoughts on how to work with shape language -

^ Here is a somewhat standardized mecha design with a more humanoid approach - something you'd see most often in common media. A lot of choices in such cases are actually a rudimentary from foundational artists which you will be able to see in the artbook selection I've provided below.

Longer legs and overall "knightly" look is often made to infer a heroic imagery due to holding resemblance to human anatomy (you can take a look at the armor designs as well for this reason). Good news though - you can shift around the actual proportions and are able to just as easily subvert this into, say, making a commentary on propaganda of human imagery (Gundam) or designing a mech which reads as more beastly/lycanthropic (Evangelion).

You can do whatever you set your heart onto! Armored Core, for example, really has its own mech style due to how their designers work with proportions (sometimes dipping into the more Gundam-esque approach for thematic purposes).

Managing proportions is also highly important for them to look realistic enough to exist while not toppling over (a weight similar to composition in general). A more restricted approach is often used by artists when designing a gritty, war-oriented machines - in which Ultrakill's Guttermen/Guttertanks might be an example you'd be familiar with! You can see this clearly on dear friend @jerichorus concept sketches:

^ Here, functionality overbears human recognition towards heavy weaponry - and take a look at those silhouettes! It's all shapes again :)

The focus on the functional parts is a trait which is actually shared with more industrial-oriented mechs as well. Back to my own examples:

^ Here, I wanted to experiment with "grounding" myself - both literally and figuratively, since my art tends to be floaty. While I added some certainly nonsensical parts in order to keep the proportions rhythm (that weight I've talked about earlier) - the more bulkier shapes are reminiscent of a toad so you can imagine it in motion just as easily :)

Speaking of a toad - you can take inspiration for the shapes practically anywhere you'd like; for example, just take the time to look at the animals if you want to completely bypass all recognizable humanoid logic:

^ Here, I'm directly referencing the artwork and melding the birds together into a more horror-ish look. Doesn't have to be like this, though! The solutions are endless. For example, try designing a mosquito-like drone and see where that gets you based on shape alone.

For everything else (details, joints, actual functional compartments) you can just look at the actual machinery! Personally I enjoy looking up stuff like mining facilities, control surfaces, electric pylons, warships, space probes - whatever you set your mind onto. The details and inner workings also have their own shape language - just smaller, inside other shapes (and they don't even have to make actual sense...)

A similar functionality to the reference material might set you off in the right direction on how to wield shape language specific to that function, but you can just as easily combine different aspects of it :)

I feel like I've only scratched the surface but I trust in your ability to derive some of your own lessons from the links I'm going to provide: