So, I'm a beginner and up until now I've owned only a tiny whoop. I recently decided it was time to step up a bit and get a "real" quad. 5" look scary, loud and expensive, and 3" just don't look very powerful, so I thought 4" would be a nice middle ground.

I really need some guidance as I'm trying to keep this as cheap as possible, but still durable enough since I don't want to keep changing broken parts. The general lack of information around 4" quads + my lack of experience made it incredibly hard for me to find parts, and even though right now I have a build that seems fine, it's way more expensive than I anticipated and I'd like to see if anyone knows if and how I can make this cheaper (and if there's anything wrong with it, of course). Here's what I came up with:

• FRAME: STEELE 4 (most likely a clone)
  Should be pretty durable, the arms look a bit wider than most 4" frames I've seen.
  

• FC/ESC: SpeedyBee F405 mini 35A stack
  This was recommended pretty much everywhere as the best cheap FC/ESC combo, it seemed like the most reliable choice.
  However, I just noticed that there's gonna be a discount soon on the F405 V3 50A, so... maybe I should get that instead?
  

• MOTORS: XNOVA Lightning 1804 3500kv
  I lost way too much time looking for motors. I broke 3 motor shafts on my tiny whoop, so I didn't want to have the same problem on this quad. That's why I avoided T-mount motors, and these XNOVA seem like one of the few cheap, light, powerful enough and available products around me. I've seen Joshua Bardwell recommend the FPVCycle 23mm short motors and I've also found these T-Motor F2203.5, which seem like a better choice but I can't get them for cheap as I live in Europe.
  

• PROPS: HQ Durable Prop 4x3x3V1S
  

• RX: BetaFPV ELRS Nano 2.4GHz
  

• VTX: Eachine TX805
  I've seen Oscar Liang's review, and even though it doesn't perform as well as it should on higher mW it still looks like a decent VTX for the price. It also has an integrated mic.
  

• ANTENNA: Rush Cherry
  Recommended by Oscar Liang.
  

• CAMERA: Caddx Ratel 2
  Also recommended by Oscar Liang (if you see this THANK YOU, your website is incredible)
  

• PDB: I've read about it for the first time on this thread, do I actually need one?
  

With this setup, the quad should weigh around 215g cost about 250€, without lipos. If anyone has any suggestion, I'm all ears!

Looks like a pretty good setup! The frame appears spacious and tough, and all of the parts have good specs to roll with. Don't worry about a PDB as that's effectively part of your 4-in-1 ESC. They used to give an easy way to route power to all of your high draw components, and went where we put the ESCs in our stack now.

.. looks like you have done your research..that ratel is one of my favorite cameras… I have a 4” rig I love, AlfaRC 175 fighter.. with a 20x20 stack.. and 1408 motors.. and it flies awesome.. sub 250.
Best part, it RIPS! And when I do crash, the impact isn’t as “hard” of a impact..
I’m in the middle of a recon 4” with HDzero.with those xnova motors .. real curious how it will fly..

Do NOT get the Speedybee F405 V3 FC. It's plagued with design flaws which is probably the reason why it's going to be on discounted, to clear any remaining stock. Speedybee have just released a V4 of the same FC, hopefully all the issues that are present on the V3 FC have been resolved on the V4. I guess we'll find out in due course once a few more people other than reviewers have it in their hands.

i would suggest bigger motors for a freestyler, bigger will be more precise, better and more linearity in motor response and better efficiency: 1408/1507/2004/2203.5/2104/1806

joshua named 4inch a usless size over years, he doesnt understand the whole size. while his suggestions for the motor does match in my eyes, dont use jbs suggestions for 4inch - cause he would never build and fly one for personal reasons xD

my personal choice for 4inch are more lightweight frames, it allows much more motorchoices and configurations, it is benefical about durability with a very low ampunt of protection throw the low amount of mass, its much more efficiency and performance.

just as a sidenote, 3inch can be build differently. we used 1408 motors regulary on our 3ibch quads in the past, huge motors which learned 5inch quads how to feel slow against a micro ;-)
common build trend opened by new market options for 3inch is ultralight build culture, but the heavy power 3inch micros does still have options on the market :-)

I really like in V3 that Dshot does not work when connecting a compass

(28-Sep-2023, 06:05 PM)lyoha Wrote: I really like in V3 that Dshot does not work when connecting a compass

Not just that. Onboard analog OSD doesn't work if you have Blackbox enabled, or vice versa, because they used the same SPI bus for both devices which means there is a conflict between the two if you have them both enabled, so you have to choose to use either one or the other. And if you are using a digital VTX with the MSP connected to UART1 as shown in their official wiring diagram, you also have to switch on MSP for UART4 even though it has nothing to do with the MSP connection data on UART1 otherwise the MSP data connection via UART1 doesn't work. There are probably other design faults too that I'm unaware of, but no matter how cheap the Speedybee F405 V3 FC is, it's definitely one FC to avoid unless you like tearing your hair out in frustration.

I'm using Ardupilot on this and can't understand how someone bravely made firmware for this. In my anti-rating this is the next place after Betafpv. Beta is in first place due to a near-successful attempt to burn down my house.

Ok, first of all THANKS for all the great info! You spared me a lot of trouble with that F405 V3, didn't know about all those problems. I tried to google around and see if there were any problems with the F405 mini, but I didn't really find anything so I guess that's ok.

About the weight, I didn't really think about how lighter quads don't crash as hard... However I still think I'll stay on this frame choice, cause I don't want it to feel too snappy (like my tiny whoop was), plus hopefully that will make it less prone to get carried around by wind (if that's even a problem with this size).

Finally, I found another motor: X-NOVA Lightning V2 2203.5
The problem is I don't know what's the right KV to get. I tried to compare it to the 1804 (here's the 1804 specs and here's the 2203.5 specs), but there's different props used AND different voltages, so I'm just very confused about it. I don't even know if it's worth it, cause the 2203.5 is marketed as "for cinewhoops"... so does that mean it's less responsive than the 1804?

2203.5 is more responsive compared to 1804 by size on that frame.
for kv it depends on the rotorsize, for 4inch on 4s 850mah batteries; 3200kv works with high pitched rotors (but there arent many) 4000kv works with low pitched blades.
i would suggest around 3500kv 4inch.

the gemfan 4032x3 might work well on 3500kv 2203.5

I would suggest start where you are.. buy ALL the different 4” props you can find..fly them all.. then proceed in the direction you want… response, agility, weight, efficiency..,
You can have the best motors, fc, frame, battery, .. if there is not a prop to allow you to access any of it.. what good are they?

If your quad feels too "snappy" as you put it, adjust your rates. Nearly any quad can flip and roll about as fast or slow as you could ever want. Weight is more about how it'll maintain momentum when we're talking about flight feel. I've got two 3" inch quads, and it's incredible how differently they behave when I kill the throttle. One will fling about an eighth mile if I blip the throttle, and the other practically falls straight back down.

My bad, "snappy" wasn't the right word. What you said about momentum was my problem, the whoop was just too light to throw it in the air, so that's why I want some weight this time.

Ok so, I did some more research, and I think I'm finally done.

After seeing Chris Rosser's video about motors, I looked around for taller options and finally found these 2005. I feel confident about these BUT, once again, I don't know what KV I should get. Here's the specs and here's my reasoning... I'm sorry, I know I'm overthinking this, but please tell me if I'm getting anything wrong cause I'm going crazy trying to understand how this KV thing works.

From what I understood, the battery size will be the greatest limiting factor in KV choice. Since I'm gonna fly with 4S, if I use an 850mAh 95C I'm gonna have about 80A available, so no more than 20A for each motor. I'm planning to use bigger 4S batteries as well, but this is the "worst case scenario". Now, the thrust tests are all over the place since they use different props/batteries for each KV (btw, why do they do this???), so I can't do a direct comparison. I thought I could get away by comparing the input power (W) at same levels of thrust (g)... but for some reason it looks like the 2800KV draws more power than the 3450KV, both with 3" props. This makes me feel like the 2800KV model has some sort of efficiency problem maybe?

Long story short, since 3450KV draws too much current (23A with 3" props, which I guess will be even more for 4") and 2800KV's may have something wrong, I was thinking to go for the 2450KV. This seems low for a 4" though, I don't even know if it's enough, but I also don't want to go overboard with KV and drain batteries too quickly. I'm just SO confused right now.

And yes, I will buy different props, thanks for the suggestion. I really underestimated how important they are.

fwiw these 1504.5s weigh almost half as much as those 2005s:
https://www.brotherhobbystore.com/produc...5-motor-cw

on a lite 3.5" or 4" frame it'll skoot!

Just to clarify- battery cell count is the limiting factor on kv, not battery capacity/size.

Higher cell count batteries have a higher voltage output. Motor kv is how fast the motor spins when fed 1v, unloaded.
So with a 6s battery for example, you would want a lower kv motor than you would want with a 4s battery, because that 6s battery would spin that motor significantly faster since it’s got more volts to give.

I’d go with the 3450kv version for 4s.
The 2450kv and 2800kv versions would feel gutless on throttle punches on 4s, and since you’re talking about being able to throw it, I’m assuming this is an acro build- you want a bit of power for that, or at least I do in my acro builds.

Amp rating comes into play when choosing your motors and esc- for example, if you’re using 40A esc, you want to make sure that your motor and prop combination will not draw more than the 40A the esc is rated for,

Also, esc ratings are per esc- so for example, with a 40A 4in1 esc, that is 40A that can safely be pulled by each motor, not 40A split between motors.

Edit- just to be clear, having for example an 850mah vs 650mah battery has nothing to do with your motor choice, other than that if your motors are pulling a higher amperage, your flight will be shorter. Running an 850mah 4s battery vs an 850mah 6s battery will absolutely have an impact on your motor choice, because of the increased voltage.

There’s more to it than that, like weight considerations and whatnot, but, yeah. An 850mah 4s battery doesn’t mean that you’re limited to a motor that pulls 20A max.