Hi Janz,

Well, I am going to toss in my thoughts just to keep you thinking. 

You know, I have NOT yet tuned any of my quads; everything is running
on the stock default settings as it has from the factory. I have literally run 
pretty much the same settings on builds from 4 inch to 7 inch with NO 
adverse affects. What I am saying here is that you probably won't have to 
change any settings or the tune to run 3 inch props on that rig. In fact, 
if you get an exact replacement GEPRC frame, try a set of 3 inch props 
and see if you can really tell much difference {except for the fact that 
the 3 inch props will have a less thrust due to the smaller prop area}.

If I was looking for an alternate frame for a 3.5 inch quad, I would 
definitely be looking at a 4 inch frame which will handle the 3.5 inch 
props AND 4 inch props PLUS 3 inch props with or without prop guards 
{not that you want to, but it actually works quite well}. I think that
a 4 inch frame would be the better choice.

For me, any frame over 50 grams is too much for a sub-250 gram build. 
It just causes you to compromise somewhere else. There are quite a few
4 inch frames that are way less than 50 grams. Personally, I like RoninUAV
frames which have a dual mounting setup and plenty of space in the frame
and only weigh about 42 grams. Although you can find lighter ones, most
4 inch frames are in the 35 - 45 gram range. I think the GEPRC exact 
replacement frame weighs about 47-48 grams ???

I maintain a spreadsheet which contains a lot a lot of information with tabs
organized by item or subject matter. There is a tab for each frame size, one
for motors, one for batteries, and other stuff. I have added a new "Build Guide" 
tab in an effort to make it easy to plug in some of the weights and see what the
AUW of the quad will be. You might find this spreadsheet interesting especially
for comparing components. It is a challenge to keep it updated with the most
recent information, but I do try. Anyway, Click to download --> Parts Guide.

Just chiming in here cos I was saying the same thing on Lemon's thread. I used the same 1404s and same tune / filtering on a 3" and 3.5" variant and it flew great. The half inch makes a material difference in throttle authority but didn't seem to require any additional rejigerring of tune.

Thanks for all the suggestions guys, greatly appreciated and will keep my brain moving. This winter I think we will look into either building a replacement quad for the current Smart35 or we will swap frames and use all the components from the 35 for the build. Our summers are short enough, I didn't want any lengthy down times as we sort out a new frame and getting everything swapped over. Its more important right now to get as much seat time as possible, have fun and keep progressing.

The one piece bottom plate from a beginners standpoint leaves a lot to be desired. Although, it only took me 20-30min to swap everything over and re-calibrate the accelerometer. The big issue I have is that we are so close to the 250g limit that we have no room for any sort of accessory. Id love to put some printed arm skid plates on or a small bumper to protect the camera.

We would have to give up some battery size to make room for anything at this point. Its just nice having the power and flight time that these 4s 850mAH batteries provide.

Yes.  It is challenging to do the most we can and keep the All Up Weigh below 250 grams.

The battery is the heaviest single component. It just is. To get anywhere decent, you need
to allow at least 75 grams, but 100 grams is better as it will allow for a little bigger LiPo or
even a 2S Li-Ion pack. So that limits the entire rest of the quad to 149 grams MAX including
all action cams, mounting hardware, payloads, literally anything and everything. 

If you count the prop and prop bolts with the motor, then the drive train is often the in
competition with the frame as the next heaviest subsystem. Here where it gets interesting.
Stronger frames are heavier. Bigger Motors are heavier. As you add power and strength,
you also add weight...quickly. 

I did build a 5 inch with 20 gram (each) motors, but having a dry weight of 198 grams,
it was only sub-250 grams with a very small battery. Any decent battery pushed the AUW
right on over the 250 gram mark. So, there is the harsh reality: Motors that weigh 20 grams
each are really too heavy. Now, selecting a motor to fit your desired flight characteristics
can sometimes be challenging. Personally, I try to keep the motor weight to about 15 grams
each. This is why the sub-250 gram performance quads tend to be the smaller ones...
3.5 inch and smaller. 

The stronger frames are heavier while the lighter frames tend to be weaker.  Ah, but this
is the place where you adjust a bit if you need to loose some weight.  

The electronics package tends to be about the same for each type of video; analog vs digital.
There really isn't a lot of room to negotiate much weight here. Each type has things with
pretty much consistent weights...so we are just stuck with that. 

Building a sub-250g definitely seems like sitting on a teeter totter. Everything is a compromise to get you to the magic number.

What is the advantage of building a 5" sub 250g versus a smaller 3.5, 3 or even a 2.5" quad? Looking at the numbers it would seem like going to a 5" you would need to give up a significant amount of performance over a well built 3/3.5"? More stability at speeds?

(14-Jul-2022, 02:09 PM)Janz99 Wrote: Building a sub-250g definitely seems like sitting on a teeter totter.  Everything is a compromise to get you to the magic number.

What is the advantage of building a 5" sub 250g versus a smaller 3.5, 3 or even a 2.5" quad?  Looking at the numbers it would seem like going to a 5" you would need to give up a significant amount of performance over a well built 3/3.5"?  More stability at speeds?

Hi Janz,

The advantage of bigger props is that they push a lot more thrust, period. It is not about acceleration
or performance, but rather being able to push enough thrust to fly at lower throttle {less RPM} for
endurance AKA long range. That is precisely why the true long range guys start with 7 inch and go
up from there...9 inch, 10 inch, and up. 

I have actually built two 5 inch sub-250 gram quads. The first had 20 gram (each) motors which 
meant small battery, but that thing was butter smooth and didn't take much throttle to fly. She
was a real dream. Yep, lost that one. 

My other 5 inch was running smaller motors and yet, butter smooth and didn't take a lot of
throttle to fly. Yep, that was the Unsanctioned-1 which is now in a tree. I am going to try
to get this one back since it was built on a one-of-a-kind prototype frame.

Any sub-250 gram build that is 4 inch and larger is NOT going to be a Hi-performance quad;
it just isn't. The motors required to push a quad this size to a performance point that the
ACRO pilot likes are just too large and too heavy. That is why these will end up just being
cruisers and perhaps long range.

My next build, GT_LT6-X1, will be built on a 6 inch frame and assembled to be a sub-250
gram quad. The frame is a special cut by gt40 and only weighs 32 grams. I think that I can
get a nice 6 inch sub-250 gram cruiser. You know, 250 grams is pretty light when compared
to the thrust of 6 inch props; probably only need about 10-15 percent throttle to fly it. 

I predict that it will be the 3 inch and, maybe, the 3.5 inch that will end up being the sub-250
gram Hi-Performance quads. For the smaller prop size, the smaller motors will spin up fast
enough to get that acceleration that is so desired by the ACRO pilot. New motors seem to be
coming out every day for the sub-250 gram builds. I have seen one of the fastest ACRO pilots
run only on 3S batteries. Interesting... With the right motors and props, a 3S battery will 
provide plenty of acceleration power. It all depends on the components and how the quad is 
built. Personally, I like a 2.5 inch to play around with and try ACRO stunts. This size is my
favorite quad to just have fun especially in smaller locations.

I will be the first to admit that even on its best day my best build on my best frame with the best tune will not hold a candle to an equally well built, well tuned 5" Apex.

And 100% iFly, 3.5 in my opinion is *currently* the sub250 sweet spot. And to me, I define sweet spot as excellent speed and throttle authority, bando-worthy durability, 3-4 min of hard acro flight time, capacity for a 4K cam. Emphasis on "currently" since power trains and HD cams are getting smaller and better over time. So it may be at some point sub250 5" will be the norm as tech progresses.

Yeah, until the regulators get wise to the fact that everyone is managing to bypass most of the regs with sub-250g quads, so they will just raise the bar even higher and change the limit to 200g instead

Just build what you want without worrying about the weight or having to make compromises, then fly it like you stole it well enough away from civilisation where there is no-one to bother and no-one to care whether it's over or under 250g

If it's small (whoop, 2-3"), it's possible to get away with it in the city, but if it's noisy and runs on 4-6S, do as Snow mentioned and fly it in the countryside as far from people as possible. People are the bane of our hobby, avoid them at all costs.

I used to worry about flying my whoop in the city, but literally no one cares. People just ignore me (or maybe I look crazy and they are too scared to approach me). Either way I can live with people not going near me. I found a few places to fly, a mixture of parks and bandos. You find other people in parks, but bandos only FPV pilots, Urbexers, Grafitti Artists (and very rarely) Junkies. You will probably be able to find similar places to fly near you.

Even if only 2mm clearance,
I would definetly prefer larger 3.5" over 3".
Do it.
Find a way