mpbiv's Ultimate SCX-140 build log!

mpbiv

New member
So I haven't posted one of these in a while!

Some of you may be aware I designed the SCX-200, and thanks to everyone's interest in it, it caught the attention of Armattan, and we took it mainstream with the Armattan Lite SCX-200.

But since then I have been continuously working on other designs in my free time, continuously building and testing. One of my favorite designs to date has been my SCX-140, which is a scaled down 3" version of SCX-200. It shares a lot of the same design cues but at the same time it is entirely different. I've been flying SCX-140 since the May/June time frame, and I really have come to love 3" multirotors. Up to this point I have built three of these little buggers for myself; partly because I enjoy building, but also because the market for 3" motors/props/batteries has really grown over the past few months, so I keep finding new combos to try.

Now I have decided to do what I consider a final SCX-140 build, using what I think are a great set of components to build a really nice 3" multirotor.

So let's start with the specs:

Frame: Space Cowboy Drone Designs SCX-140 (made via Armattan Productions)
Flight Control: Brain RE1 + MPB PDB (on Betaflight)
ESC: Aikon 20A BLHeli-S (on Multishot)
Motors: XNova 1407 3500kv
Props: RaceKraft 3030x4 clear
FPV Cam: HS1177 w/2.5mm lens
FPV vtx: UBAD 200mW w/raceband
FPV Antenna: cheap MRM color dipped right angle SMA LHCP
RC rx: KS-Servo FM800 FASST compatible
RC tx: Futaba 14SG
Battery: 4S, testing Lumenier 500mAh LiHV 80C, Tattu 650mAh LiPo 75C, and Lumenier 850mAh LiPo 75C

Now for everyone's favorite part, pictures!

Brain RE1 and Aikon ESCs:
IMG_2238.JPG

XNova 1407 3500kv:
IMG_2240.JPG

Space Cowboy Drone Design SCX-140 via Armattan Productions:
IMG_2250.JPG

Now for the build process:


Other than being a really tight build, these 3" quads are pretty straight forward. Since SCX-140 used a unibody lower plate, the build goes real quick once you have the motors, esc, and pdb wired up. Here is everything wired up to the Brain MPB PDB:
IMG_2253.JPG

Brain RE1 in place, all fpv wiring ready to go, just need to add the receiver:
IMG_2255.JPG

At this point I got too excited to finish and quickly wired in the RC receiver and buttoned up the build!
IMG_2257.JPG

First flights:


So now, after taking time to flash Betaflight to the RE1 and configure everything, including using the new BLHeli Chrome app to correctly program motor direction to the ESCs, I was ready for my first flights. For the maiden flights I wanted to see if I could get away with a small 500mAh LiHV Lumenier 80c battery. This battery actually worked pretty well in the past with my less powerful 1306 powered SCX-140 builds. Check out the video below to see some dvr from the first couple flights.


From this outing I learned two things! One, 500mAh, even though LiHV and 80C was not going to cut it. Copter flew great in the video, but the batteries were coming down puffy. Although I had some 650 75C LiPo's with me, I opted not to fly them. Pretty sure the power hungry 1407's will require 850mAh right off the bat.

Second thing I learned is that the antennas on the KS-Servo FM800 are not sufficient even in short range. Not enough antenna exposed from the carbon seems to be causing fail safe issues. This has happened to me on past builds, but I thought it was ESC desync at first. With the Brain RE1 OSD I was able to see the disarm failsafe on the screen when it happened. This led me to the idea of lengthening the antennas on the FM800:


Here is a macro picture of the new antenna connection to the board:
IMG_2285.JPG

And lastly, as of last night I quickly designed and printed an antenna holder to keep the antennas out of harm and to position them clear of the carbon. I designed this part and printed it in TPU using my Prusa i3 MK2 printer, and it works with standard 3mm OD RC antenna tubing:
IMG_2296.JPG

Next Steps:
Get out and fly some more! Test out the new antenna mod, and also try out some new Lumenier 850mAh 75C 4S batteries I just recently bought! This should be fun. I might even try to race this quad with the big boys this weekend just for kicks and giggles.

-Patrick
 

Habakkukk

Fly Eagles, Fly!
Man that's awesome. That thing really gets after it lol. I've yet to build anything below a 4" but you at have just inspired my next build
 

mpbiv

New member
Beautiful build again mpbiv.

I love my Brains and RE1. Autotune!!! :)

Autotune only works on dRonin right? I'm actually flying Betaflight, and I haven't spent a whole lot of time tuning it. It flies pretty good, but I get a little propwash on hard direction changes when punching the throttle hard. Need to mess with that. Also I was a bit confused on the gyro refresh and PID loop speed to run on Betaflight. Some of what I have read said the Bosch IMU can only handle 2.6 (or maybe 2.7k) refresh rates so that is what I have Betaflight set to, but then I also read somewhere else to just set the drop down menu to 8k/8k and it would run at max refresh rate.

Just raced this rig against some 5" quads at this months race, and did surprisingly well! Had a lot of people asking me questions about my motor/prop/battery setup after they saw how quick it was :)

Video below:

 

mpbiv

New member
Also learned that while it will fly with the smaller 500mAh 4S 80C LiHV batteries, that the higher you go on the battery capacity, you get better returns on performance despite the weight gain. You can see it in the flight stats too. Basically the bigger batteries don't struggle to supply the current and my overall perception was that it felt incrementally faster going from 500mAh 80C LiHV->650mAh 75C LiPo->850mAh 75C LiPo.

Typically max current also went from ~28A (on 500mAh), to mid 30A (on 650mAh), to low 40A range (on 850mAh). And surprisingly the 850mAh pack felt the best despite the significant weight increase. Might have to try a 1000mAh high C pack to see if that is where the diminishing returns begin. Although I have to say I think it flies nearly perfect on 850mAh 75C 4S right now.
 

grnd flyr

Member
Can not wait... :)

Think I'm sold on the concept, and that your work is dangerous to my wallet... ;)

3 brothers:

big bro gets the Ooomphs & BrainFPV RE1, Armattan 30A ESCs
one little bro gets BH 1407-3600kv motors, Kombini FC, Armattan 20A ESCs
other little bro gets prolly RX 1306-4100kv motors, Armattan 20A ESCs, and if RF1 ever gets finished: Revolt Fc

gotta keep busy when it's too wet to fly...

2mg4hfa.jpg

Thanks for the build log & making them available!
 

mpbiv

New member
Think I'm sold on the concept, and that your work is dangerous to my wallet... ;)

3 brothers:

big bro gets the Ooomphs & BrainFPV RE1, Armattan 30A ESCs
one little bro gets BH 1407-3600kv motors, Kombini FC, Armattan 20A ESCs
other little bro gets prolly RX 1306-4100kv motors, Armattan 20A ESCs, and if RF1 ever gets finished: Revolt Fc

gotta keep busy when it's too wet to fly...

View attachment 78210

Thanks for the build log & making them available!

Thanks dude!

I have to Oomphs on my SCX-HD prototype (Stretch X with Connex ProSight), and they are smooth as butter! Loving them so far.

But those little Brother Hobby 1407-3600kv....... they look like they are going to be beasts. I just got in a set the other day which I am going to throw on a new 3" prototype I am working. Those motors cog like nothing I have held in hand before. The arc magnets are very strong, and the air gap between the stator is like the bare minimum. I am excited to try them out to say the least, and I have some high expectations that they may even out perform my XNova 1407-3500kv setup.
 

LitterBug

Troll Spammer
I've found the 1050mah batteries to be the sweet spot for my 3" builds... Tried some 650 and 850s that didn't have much as far as C and they were pretty much instaPuff. There are a lot more options for smaller capacities now that have higher C ratings. May have to try some of the new 850mah high C batteries. Getting ready to throw together a Falcon 130 F20 4100kv to go along with my Owl 118mm 1306-4000kv/ 1407-3300kv 3" frames. Still flip flopping on throwing RE1 or DTFc on the Falcon...

Cheers!
LitterBug
 
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mpbiv

New member
I've found the 1050mah batteries to be the sweet spot for my 3" builds... Tried some 650 and 850s that didn't have much as far as C and they were pretty much instaPuff. There are a lot more options for smaller capacities now that have higher C ratings. May have to try some of the new 850mah high C batteries. Getting ready to throw together a Falcon 130 F20 4100kv to go along with my Owl 118mm 1306-4000kv/ 1407-3300kv 3" frames. Still flip flopping on throwing RE1 or DTFc on the Falcon...

Cheers!
LitterBug
I have a DTFc which I have avoided using due to gyro noise issues. RE1 is doing good for me so far, although it uses a Bosch IMU which is different from the Invensense gyro's that come on just about every other board.

I did end up trying the 650 75C Tattu on this setup and they were ok: no puffing or issues, but the 850 75C Lumeniers really had a ton more punch to them especially throughout the whole pack. The little 500mAh LiHV felt ok only at the beginning of the flight, but would puff from the current draw, however they appeared to rebound and returned to normal resting voltage of 3.6V a cell after sitting for ~10-15mins so I may still use them but on my less power hungry setups.
 

mpbiv

New member
Forgot to mention I got some new antennas last night!

Lumenier AX II. These little guys seem to be just the right size for this frame, and supposedly offer higher gain than even the TBS Triumphs, so I am really looking forward to trying them out.

IMG_2312.JPG

Also another thing I forgot to mention was I think lengthening the receiver antennas may have solved my failsafe issues. I didn't have a single fail safe event over the weekend while racing.
 

LitterBug

Troll Spammer
I like the design of your frame better than the Falcon130. The FC is part of the top plate structure on the Falcon. :( I've run the DTFc on my hellbender with no vibration issues. Was going to soft mount with rubber bobbins regardless of which FC because of the vibes these motors have coupled with the small stiff frame.

Cheers!
LitterBug