Crux 2.5

By fw42 on Mar 03, 2021

15  833  8

Inspired by the Quad66 video Gemfan 2512 impressions with 1103 8000kv 2S.

This was a bit of a "leftover build" from spare parts that I had lying around, so I didn't expect much of it. And I keep hearing people say that 2.5" is useless and everything is better about 3", so i wanted to see for myself. I have to say I was very positively surprised. This might actually turn into my daily flyer and favourite default quad.

It's basically a Happymodel Crux3 but with lighter higher KV motors (still 2S) and the new Gemfan 2512 props (and a buzzer).

Motors: After ordering them, I heard KababFPV say in one of his videos that they are terrible, so my expectations were very low. Not sure if he was only talking about 3" but I really like them in combination with the 2512 props. They are pretty light (3.8g), feel very controllable, have enough punch to go reasonably fast (not rocket ship fast, but fast enough for the kind of space in which you would fly a 2S 2.5" toothpick, i.e. large backyard, small park, etc.).

Props: First time trying those and I absolutely love them! Compared to the only other two 2.5" props I know, they are noticeably less amp hungry than the EMAX Avan 2.5" tri-blades but have noticeably more grip than the HQ T65mm bi-blades. The pitch is very low which makes it easy for the motors to spool up very quickly which then makes the entire platform feel super zippie and nimble.

Flight controller: I don't know if I got lucky and got a good one, apparently HappyModel electronics are often a bit of a gamble, but this thing has taken a beating already in other builds that I've used it in and it's still holding up great after lots of crashes and lots of throttle. The built-in 200mW VTX is surprisingly great (even on 25mW). I don't know if all the antennas on my other micro VTXs suck or what, but this one (with a tiny shitty little bare wire as antenna!) easily outperforms my NamelessRC D400, my NamelessRC Nano, and my PandaRC Nano.

Frame: It feels surprisingly sturdy. I believe it's 2.5mm and something like 5.8g. It's actually a 3" frame but works great on this 2.5" build too. A little bit heavy though but it's what I had lying around.

Total dry weight is about 42g (about 3g lighter than my Crux3 was out of the box), but you can (without any compromises, really) easily shave off another ~3-4g or so by using a smaller frame (like the PicklePick 65), a lighter camera (like the Caddx Ant Lite instead of the Caddx Ant) and a lighter canopy (like the UZ85, which even almost looks the same). I use a 2x1S adapter and Betafpv 1S 450mAh batteries which bring the AUW up to about 66g and which gives me flight times of about 5-6 minutes of fast flying with very little voltage sag. I have a feeling 300mAh might also be awesome (much more nimble even and probably still around 4 minutes). Will try that soon.

For me, this build feels like the perfect middle ground between my Babytooth and my TP3 but for some reason I like it better than the 2S 3" toothpicks I've tried (maybe because it feels less floaty). Babytooth is nice because it feels so safe and is so controllable but also gets really annoying if the space is even slightly too large, it always feels a bit fragile to me, and I always feel like I'm murdering my batteries because of all the voltage sag that you get all the time. TP3 is nice because it has a lot more power and much less voltage sag, but it also feels like a tank in comparison and like you could seriously injure someone, plus I find it a bit too intimidating, too loud, and too hard to control in smaller spaces. This build sits right in the middle.

Only thing I don't like (compared to a 2S 3") is the noise: The 2.5" props are noticeably louder than 3" props. Not terribly loud. Still quiet enough not to alarm people. But definitely a bit louder.



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GRIzmak   Mar 27, 2021  

Hi. How the canopy is holding?
I'm using it in my 1S 3" build and I have smashed 3 of them in 6 weeks.

fw42   Mar 27, 2021 

Interesting. I've used this exact one for months, crashed it lots of times, still good as new.

GRIzmak   Mar 27, 2021 

I wonder if this is not related with the temperatures. Can you tell me what temperature you are flying in? I was flying in the snow and in temperatures around 0-7 °C. Now it's getting wormer. Maybe this will stop cracking.

bvonbla   Mar 10, 2021  

What kv, 8000kv or 10000kv?
I just built one with a crux3 frame and 3" props on 6000kv. Like it a lot!
Also no battery sag!

fw42   Mar 10, 2021 

I'm using the 8000KV ones!

daich   Mar 10, 2021  

nice, clean and good looking build! up some dvr please!

OptimaZe   Mar 03, 2021  

Very cool! I love my "Crux3" build, but have been thinking about making similar changes myself. It performs very well on GNB 300mah 2S, but I know I can get more out of it with a couple quick and easy changes.. Thanks for sharing!

BaTTaN   Mar 03, 2021  

Bet that’s fun! I had a 65mm Pickle frame built up very similar to this that I really enjoyed. Got it stuck up about 30 feet in a tree on day and never was able to recover it. I had another one milled in true and stretch x I need to get around to building out one of these days.

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