Reading this topic gave me an idea for another one and I think it is different enough to have a thread of its own. In my case I do not like doing bodywork but no doubt the hardest part to do on my MOCs is whatever movement of a arm or bucket. I always look for the maximun realistic movement and I can easly spend weeks improving a small linkage because those mechanisms change a lot with less than a milimeter in any direction. I am waiting for my family to get up and I have to spend my time  .

You never know.

On my last moc longest time per parts used took rear attachment, that plow, which turned out pretty simple at the end.

I always get stuck with driven and steered axles, especially at smaller scale. Lego lacks certain parts that would make this easier, but I digress. Another hard part is wire and/or cable management. If you are building a large MOC with lots of electrical or pneumatic components, you know the struggle is real.

This may be particular to me, but sometimes I run into the problem of I have a good solution, but I don't have enough of a specific part, and I don't want to buy parts. There is an easy fix, of course.

I also sometimes have issues where I have to figure out what everything does after leaving a WIP, and coming back weeks or months later. Again, this may be a just me thing.

Lastly, space management. Sometimes it's hard to fit in/around parts of your MOC you already built, like you thought you gave enough space for another component, but didn't.

12 minutes ago, Jurss said:

You never know.

On my last moc longest time per parts used took rear attachment, that plow, which turned out pretty simple at the end.

This is the way, a lot of tryings to find the best solution and while you are building different approachs you learn and have fun, if we conquer what we exact need at first it would not be funny  .

The hardest part is to call it FINISHED and NOT touch it during the 3d model creation /for instructions/.
Sometimes I disassemble the MOC after the PDF is done. Frees the mind from any future fixes to it.

For smaller MOCs the FINISHED part takes another day, for the bigger ones it takes two weeks.
And the questions from relatives/gf/wife - isn't it ready yet? - YES IT IS, but it is not READY READY...

Second hardest part is to give up and use a 3x simpler solution that works better than your "dreams" of how it should work.
A.k.a. the 3 hours before saying f*ck it, THAT'LL DO about a feature that you insisted on being there.

Third hardest part of MOC-ing is to just SIT and MOC. Not toy around on how to begin mocing - just to sit down, grab them parts and start it.

Crude mechanisms are still mechanisms :)

Hardest thing is to maintain correct width because LEGO tires are often to wide in comparison with real one...example is my Fastrac - maximum tire width is mostly 600mm which in my scale gives 40mm, but after consulting with local JCB distributor I found out that there is factory option 710/60R30 and max permitted tractor width 2700mm so I had solution for my initial problem; otherwise it would have turning circle like original tractor 

Another thing is how to incorporate mostly characteristic features / functions since machinery that I make have very narrow and very stiff chassis and lots of motors...and technic battery box is not small 

There are lots of hardest parts and because every MOC is actually a compromise, you need best possible compromise...

Hope that my post is not to long ...

For me the hardest part is accepting that I'm not as good as most guys posting here, and not holding my MOCs to that standard. When I do, it usually ends up with no progress for weeks since I just keep redoing the same parts. I don't currently have access to my LEGO but when I eventually start building again I will try to focus on getting something done, and keep improvements going, instead trying to build the perfect front axle and never actually ending up with a truck.

I've currently got a MOC in progress and have been paining myself on how to get a motorised compressor in decently. I've currently got something which actually works, but doesn't leave enough room for the HOG steering, so I'm going to have to rip it back out and think of something else.

For me it's the body work/finishing a model beyond the functional inner workings, because I'm not really excited by that as much. So if I really want to finish a MOC I'll start with building the outer shell first.

As I consider myself as a technic focused guy, the hardest part of building my MOC is to prepare decent looking body. I can fight all day with the mechanisms inside, enjoy it and at the end have the functionality what I wanted. But good looking body is my nemesis. Unfortunately the body is very often the first and the last thing many people from general audience look at :(

For me is getting idea of mocs. I want build lot of various thing but I can't make outside design so model is very limited.

18 minutes ago, keymaker said:

As I consider myself as a technic focused guy, the hardest part of building my MOC is to prepare decent looking body. I can fight all day with the mechanisms inside, enjoy it and at the end have the functionality what I wanted. But good looking body is my nemesis. Unfortunately the body is very often the first and the last thing many people from general audience look at :(

100% agree.

Don't say that; I spent more than half a year to make decent bonnet... perhaps I should make tractor without bonnet...

19 minutes ago, I_Igor said:

Don't say that; I spent more than half a year to make decent bonnet... perhaps I should make tractor without bonnet...

We all take care of aesthetic on our MOCs, but the search of the minimum aesthetic, structural if possible takes a lot of time, I could say that I spend the same time with aesthetics than someone that only do aesthetics MOCs, well almost... and that is why I do not like aesthetics I loose a lot of time... I could loose even more time doing perfect aesthetic MOCs but I would have to sacrifice efficiency, functionality and they would be fragile, I want them for children to play with not for only see.

It’s 100% bodywork. The challenge of  creating aesthetically pleasing bodywork is just tedious - and the end result is simply not as rewarding as that of designing a nifty mechanism.

I'll have to double the comment from sm1995 in regards of bodywork - aleit in my case I've had several chassis made and either had no idea what bodywork to build on top or started a certain part of the rear or front and never finished. 

And in general I find hard to simply finish a MOC, as it takes a very long time and my attention&interest span is shorter than the memory range of a gold fish. Hence I rarely finish a WIP 

Edited December 25, 20204 yr by syclone

For me it is hands down, dimensions. 

My creations always end up being wider, taller or longer than what I am shooting for. So that in the end they always look a bit off or just plain stupid looking.

Even with careful planning.

Part of the fun though, so I don't stress out on it too much.

13 minutes ago, Johnny1360 said:

For me it is hands down, dimensions. 

My creations always end up being wider, taller or longer than what I am shooting for. So that in the end they always look a bit off or just plain stupid looking.

Even with careful planning.

Part of the fun though, so I don't stress out on it too much.

For thazt reason I learned to import a scaled down 3D file of the original model into LDD, so I can follow all the shapes. Also for me the hardest part is also bodywork, but I'm getting better at it!

Edited December 25, 20204 yr by Zerobricks

I hate doing rear view mirror supports on trucks and other machines where they have to stand out to the sides from the roof. They always end up either to straight or precisely shaped but easy to disfigure.

For me, the hardest part is the shaping because when you think you're almost done, you'll notice some flaws...

Interesting topic.

For me, it very much depends on what I am making. For cars, yes, styling/bodywork, but another big one is rigidity. Getting to fit everything inside a nicely designed elegant strong chassis is something that somehow always goes wrong. I always end up with a strange chassis that has to go around a mechanism, and rigidity suffers. Also, for cars, I somehow still haven't found a nicely designed, satisfying steered, driven, independent-suspended axle design that's compact, strong, doesn't have too much slack in the steering and has with not too large travel.

For cranes, it's extension mechanisms. I find in general that sliding things are harder than rotating things. I often get problems with friction. Especially if the end of the sliding thing needs a function. In fact I have an almost-finished MOC where almost the only thing remaining is some mechanism to control the sliding function (probably a string will be the best solution).

Another hard one is pneumatics. Especially routing the tubes. I love pneumatics, in a way, but I also often find it frustrating to work with because I so often end up with huge ugly loops of excess tubing because the actuator is somewhere at the end of a moving part.

Another biggie is keeping the friction maintained. Especially for one-motor-many-function models. This goes hand-in-hand with rigidity: in a weak frame, friction builds up fast. This is where I often miss studded building; it was much easier back then to build stuff that's just strong and doesn't bend in all kinds of ways...

That said I also support the post by @GTS that deciding when something is done can also be hard. In fact I recognize this from a game development hobbyist forum, where many people had this problem :)

For me it’s trying to make less convoluted mechanisms. I often struggle with the fact, particularly on my current moc, that the ideal position for the functional result, eg: engine input is at odds with the gearbox output. I’ve started going back to stage 0 when this happens now and trying to rebuild any variable bits I can. 

It would be great to have some kind of master list to help us with a more efficient order in the development of our MOCs, or think about something similar between all of us in another thread or steal the Lego one I suppose it has one  . First to choice a reference, second to scale it, third whatever I know it there would be thosand ways to do it... a powerful topic for sure...

delete

Edited December 25, 20204 yr by keymaker
wrong topic

By far the hardest part is: finishing the thing.

I tend to get ideas and start to work on them but when I'm finished with the core thing I wanted to achieve often I find myself without much motivation to continue. This is especially true when the finishing only consist of aesthetic parts like bodywork.