88gr: 1108 rcINpower + 8.5gr Minimalist 128 frame

By Kruizen on Jun 01, 2018

4  417  19

Based on a 8.5gram 2mm baseplate, this 88 gram quad (137gr AUW w/ GNB 3S 450) uses rcINpower 1108 6800KV motors, GF 3025 props, a HGLRC F3 XR25A EVO V1 4in1 ESC stack, Frsky XM+ RX, XT30 connectors, two 470uf capacitors, and an AIO camera.

It's running multishot which is the reason for so much capacitance (it seems to run smoother but one is probably enough). This HGLRC stack (6.5gr) with the XR25A ESCs is only rated 35A (total) for 10 second bursts while the 1108 motors can hit 50A peaks with 3S. Due to this, I only run 550mAh 3S or smaller batteries, which even at 65C are still within ESC limits. I get about 3 minutes on a tight track w/ the 550mAh 3S. These motors trap debris inside with their design - I've found tapping on the prop hub while rotating the prop with the motor upside down will clear it. They really don't get that hot unless you're full throttle the majority of the time - something that's hard to do as I can fly out of my 25mw VTX range in under 10 seconds.

It's running Betaflight 3.17 (the latest release for the PIKOBLX F3 FC). I had to halve all the PIDs in order to run 3S (2S ran great on stock PIDs) as it would shudder terribly after about 1/4 throttle. This thing flies really well with hardly any prop-wash (unlike my only other 3" quad - a RotorX Atom - which is terrible). Typically the only ultra smooth flights are after prop changes as I typically fly straightened props ;)

The entire air-frame comes in at 16.7 grams (8.5gr baseplate, 4.4gr hardware, 3.8gr camera mount). Weight matters A LOT with these small motors/batteries. A note on the 8.5gr baseplate - it's only 2mm thick PLUS the carbon is NOT cut with the carbon weave going down the arms, so a hard crash could crack it - I'd stay away from pavement. That said, I went with the 2mm version thinking the flexibility (vs 3mm) helps it flex instead of crack (it hasn't so far), and it's only $12.50 to replace. I certainly wouldn't put any heavier motors on this then these rcINpower 1108s (8.9gr). This frame is advertised as having 30.5mm stack holes, which it does. It doesn't state however that the etched grooves in it just happen to perfectly fit mounts for a 20x20 stack. The pod uses 25mm AL standoffs (total hardware weight of 4.4gr w/ 4 AL + 4 Ti screws) with a $2 camera mount (3.8gr) from banggood.

This tiny quad is awesome for my small local park and playing under and around trees. It's plenty fast and is great at shooting gaps.

Here's some DVR in my local park:

Here's some info on these motors:

Thrust:

Feel + flight footage:

Photos

Discussion

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Quadlite   Jun 28, 2018  

Sorry to spam your page lol. i just had this crazy idea though. Since these motors are nearly on par with 1407's, what would happen if you put the 1108 4000kv 4s version on 4 inch biblades? I bet itd actually fly well, it just wouldnt be efficient at all lol. people have already proved that 1306's fly great on 4045x2 props, so why not the 1108's? They are even stronger and lighter than a 1306. imagine a 110gram 4 inch lol. itd be hilarious to see even if it wasnt all that fast.

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Quadlite   Jul 01, 2018 

I've heard the superman motors are really good too. They are 1404 3850kv and can go up to 5s on certain props. It came darn close to 500grams on 4-5s depending on the prop. Over 400grams for suure, and with very impressive flight times. I believe it weighs 8.5g, about he same as the 1108.

Kruizen   Jul 04, 2018 

I think I'm going to try out RotorX RX1404B 6500kv now - it puts out 420grams of thrust on 3S w/ 3025 props and weighs less then the 1108s. By the way, GF3025 props are my favorite 3" props due to their durability and weight. As most of my batteries are 3S 450-800mAh, I need a high KV. I've found when you start going to 4S and 5S w/ 400-650mAh batteries, the internal resistance is higher then larger packs 800mAh+, so the weight gain is noticable. I've broke 4 of my 5 quads now - it's rebuild time (currently waiting for Armattan to ship some frames), but I've been enjoying 3" LOS flying lately (since it's all I've got left).

Quadlite   Jul 04, 2018 

i'll definately have to check that motor out. Sounds very promising. I picked up most of the 3 inch t style props but havent been able to try them out sadly. I'm in the same boat as you, I'm still waiting on frames from armattan productions. it seems to be taking longer than normal. I ordered it in the 17th and it hasnt even been machined yet. I'm getting too anxious to try out these builds lol. I want to build my brothers one too, but these machining times are killing me lol.

Mello-cello   Jun 02, 2018  

What is your flight times? ive got the same notors but having issues.

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Kruizen   Jun 19, 2018 

I'd try cutting down the P and D terms to lower your motor temps. I'm running about half of the stock Betaflight PID rates for my 3025 bi-blades for a tune that worked for me. Your 2.5 minutes isn't that far off since when the motors are hot, the efficiency goes down. I'd suspect it's specifically the D term that's causing your hot motors. Let me know if tuning it helps.

Mello-cello   Jun 19, 2018 

I'm not so familiar with tuning....is there any specfifc guide or video you suggest to help out?

Kruizen   Jun 26, 2018 

This is the technique I use:

There are other techniques as well - if you have blackbox data on your flight controller and use plasma tree software:

One thing you could do before investing much time, is just lower the D values by a third and see if it's better. You might have to halve the D term (which allows you to turn on a dime at the expense of heat) to see a notable difference. Also try 2S and see if all the issues go away (that would point to PIDs). If motors are still hot, you really need to focus on softmounts for each motor and the flight controller. Stock PIDs worked great for me on 2S but it seriously shuddered on 3S. I reduced all stock PID rates by half and it flies great now...

Good luck - tuning is a continuing learning process for me.

Quadlite   Jun 09, 2018  

Thats an awesome setup! I'm looking to do a nearly identical build, but using the tribus 117mm frame. he has multiple versions, but the 117mm version with m2 standoffs and 2mm plate is the one I will be using. You should look into that frame. It's only 13grams with aluminum hardware, and it's a sturdier frame thats cut well. Unfortunately its tight on space so I'll be using a camera with built in 200mw vtx. Otherwise it won't all fit.

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Kruizen   Jun 13, 2018 

Wow - I never imagined Cobra motors could be that inexpensive! Checking them out though, it looks like they weigh 17gr w/ 3" leads & prop nut – lighter then my rcINpower 1506 @ 18.2gr w/ 5” wire & prop nut but heavier then my RCX h1407 @ 15gr w/ 6” wire & prop nut. Did you have to splice on some wire for the Cobra's to use it w/ a 4-in-1 ESC (that'd be a bummer)? I'm actually pursuing 4" builds on multiple fronts. Not including camera mount/plate, my current posted 1506 build Schnapp Dragon V2 w/ 5” arms has a carbon weight of 35.9 grams (4” arms only save 2 grams total), the Quattuor V2 4mm @ 25.5gr, and lastly a under 20 gram Adam Wilkinson 4” 4mm arms (16gr total) w/ Lemon Tree Quad Lite 1mm plates (~3gr total). I can attest to the durability of the Adam Wilkinson 5” arms w/ the RCX h1407 motors on a 250gr AUW w/ Runcam V1 Split build on gf 5035 bi-blades (I'll post it once I get it updated w/ the new plates). I have broke two arms but they were serious crashes – I imagine the 4” arms will be even more durable w/ less length. The arms are so thin I have ZERO prop wash – equivalent to flying a vertical carbon frame I imagine. I haven't braved putting 1506 motors on the tiny arms as +3.5gr would break the arms even easier. I wish the arms had motor protection, though I haven't killed an h1407 yet. I was thinking about a Rotorgeeks 1407 with equal weight to the h1407, but w/ a third higher thrust but don't know about their durability. Stay tuned for some exciting sub 250gram builds!

Quadlite   Jun 13, 2018 

True, they weigh slightly more, but im using "deez nuts" prop nuts, I save about half a gram per motor with these, plus the motor has a little less weight to spin! so extra gains there. as for soldering them to a 4 in 1 esc I has zero issues and used the full wire thickness. i even have 12 gauge wire and xt60 on this quad although i might switch to xt30 to save even more weight. btw, you should add me on facebook and we can share builds. look  for Alex Crowder. My  picture is of my Nile monitor. Its a 6ft lizard in a cowboy hat. You literally cant miss it lol. send me a request and ill send you some pics of my setups.

Quadlite   Jun 19, 2018 
1

Ps: wherever you filmed that video is gorgeous! looks like a really fun flier! also I posted my 4 inch setup finally heres the link. https://rotorbuilds.com/build/12841
I'm going to start on my 3 inch setup soon too! all the parts are ordered. I'm going to try the rotorx 3044tx 3 blade props with these motors. ive got 3035x3 and 3025x2 also just to test everything out.  

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