Tiny Quad Motor Selection- Advise Needed!

[Montiey]

I've been working on a 3D printed mini acro quadcopter for the past couple of days now. Originally, I was going to use the DYS 1306 BX series set in either the 2300kv or 3100kv variants.

http://www.hobbyking.com/hobbyking/store/

After reading the reviews on both, I decided I shouldn't cheap out. I don't want to find an exact replacement for these motors, as I didn't really do any research when I chose them.. Rather, I'd appreciate any help finding a new, proper set.

My frame is a 135mm X Quadcopter of my own design. It should easily fit 4" props. I don't plan on installing any FPV gear or a camera at all, so it should be pretty light for it's size. The frame alone weighs 36g right now, but the front 2 arms are still printing as I type.. I'd expect it to weight around 60 - 65g once completed without electronics.



What motors do you people recommend for a small acrobatic flyer like this on 4" 3S? Its too small for the racing motors and too big for those used on most micro indoor planes.

Thanks !

 

[cranialrectosis]

I haven't built or flown one that small, but Altitude Hobbies (I don't know where in the world you are) has eMAX 1306s in 3300 and 4000 kv models.

The eMAX 2205s are pretty popular today.

The DYS 1806 3000kv motors are not bad motors. I am loving them on my 4" Alien. You might be surprised by DYS.

 

[Craftydan]

60g frame . . . bit heavy for a 135, but it's printed not cut. I think you might be overestimating what is "light" in this scale.

I do recommend the RCX 1407's. A lot lighter than the 1806's with a better punch than the typical 1306's. The 3800kv version is better sized for 2-3S, where the 3200kv version is better sized for 3-4S. the 3800kv version can also drop you to 3" . . . just because you can swing 4" over the body doesn't mean you want to loose that part of the thrust column. GetFPV carries them domestically, MyRCMart carries them via slowboat.

Despite the sizing, I fly the 3200kV version on 2S all the time and it's still got enough pep to stay interesting.

Also . . . might want to check your numbers. Cross motor distance of 135mm will give you no more than 96mm (3.7") between the nearest motors. You'll need at least 145mm frame to support a 4" prop, and even then it needs to be perfectly square and the props will be tight . . . not to mention the body eating a quadrant out of each thrust coulmn.

 

[Montiey]

Oh, never mind. Its a 135mm square.. That gave me an absolute maximum of 5.3" so I was a bit confused.



The frame only weighs 56g with all the parts, but this could be heavy as a rock for its size as Dan noted..

Trusting GetFPV doesn't stock crap in their store, I'm leaning back towards the DYS motor sets assuming that they are the right fit. They have nice pairs of CW and CCW threads, but other than that I don't see any real advantage over a different brand, so as always I would greatly appreciate a suggestion of any kind.

I want to run 4" instead of 5" since I know I will have a printed canopy of sorts to protect the FC; that will take up some room. Also, the DYS motors do, and others are bound to have multiple KV options.. Which is best? Or rather, how do you choose? Would I get the higher one because it's more efficient, or the lower one because it's more powerful, or whatever Dan says because he's a legend...

 

[Craftydan]

. . . Legend in my own mind, maybe. So if you believe that, does that mean it's a shared delusion?

So a 190 quad. Ok, frame weight and sizing sounds a bit better, and the 1806 doesn't seem bad at all.

As for "best", that's a relative term. You've mentioned it's not going to have FPV gear -- no law against that -- So what do you envision doing with this quad? At under 200mm, this airframe will probably zip out of LoS range amazingly fast, even running sedate motors on 3S with pretty red arms (they do look nice). Lights can increase the LoS range, but even then you're looking at flying something that can be quite fast in a relatively small bubble of airspace.

The "what do I want to do with it" will help determine how sedate or aggressive your power system needs to be.

 

[Montiey]

I envisioned that this would replace my Nano QX, and add acrobatic ability to the mix. I understand that it is nowhere near the same class as the Nano, but I just want something to fly around the trees in the backyard.
I don't think I'll need that huge of a motor configuration to get it to flip, and I definitely don't want to have too much power since, yes, it will be hard to spot at 200ft. Bigger motors won't help me when it's just cruising, they'll just weigh it down. And when I choose to do acro it doesn't seem like a setup that is somewhere from "enough" to "just enough" for cruising wouldn't be able to do some stunts.

I hope that makes sense. Anyway, I suspect I'm getting too picky. Maybe I should just look at what motors are available to me and narrow it down to the best?

 

[Craftydan]

Makes perfect sense.

Going light on the power system should give you the power you need to fly and keep her tame. The lower thrust:weight will make her a bit more sluggish than a NanoQX, but should still have some aerobatic ability without getting too far away too fast.

Spitballing, but I'd expect with that frame and 1306/1407 motors and a 3S 1000mAh should get you in the neighborhood of 300g AUW. That means you'll want to target 150g/motor WOT minimum. 175-200g/motor would be a bit better. Look at the motor/prop spec's and find something at 3S with 4" prop putting out that kind of thrust. Just looking at the prop data, the 4" length, the kV in the high 2000's/ low 3000's for 3S will be up around 250-350g. Dropping those motors to 2S would help. Otherwise, kv in the low 2000's for 4" prop are near what you want for 3S.

So . . . more headroom but you've got to watch out for the aggressive punch, then 4", 3S, 3000-ish KV -- prop down or drop to 2S for a gentler ride. Less headroom but 3S is friendly-but-capable, 4", 3S, 2000ish kv.

Clear as mud?

 

[Montiey]

Verbatim, Dan, verbatim.

The DYS 2300kv motors would fall right in with your suggestion. I'm curious about what would happen on 2s now that you mention it.

Alrighty; Here are my options so far as I see them:
DYS BX 1306 (2300, 3100kv)
http://www.hobbyking.com/hobbyking/store/__66402__DYS_1306_2300KV_BX_Series_Set_of_Two_CW_CCW_Motors.html
http://www.hobbyking.com/hobbyking/store/__66403__DYS_1306_3100KV_BX_Series_Set_of_Two_CW_CCW_Motors.html
I think these are good, but I still want to look around for other options.

EMax RS1306 (3300, 4000kv)
http://www.altitudehobbies.com/brushless-motors/emax-racespec-multi-rotor-motors/emax-rs1306-3300kv-racespec-motor-cooling-series-cw-rotation
http://www.altitudehobbies.com/brushless-motors/emax-racespec-multi-rotor-motors/emax-rs1306-4000kv-racespec-motor-cooling-series-cw-rotation
The EMax motors seem like a good match, especially since they list prop test data. I worry that they don't list it to be 2s capable; if 3s doesn't work well I would like the option to try a 2s pack.

RCX H1407 3200KV
www.getfpv.com/rcx-h1407-3200kv-micro-outrunner-brushless-motor.html
As cranialrectosis suggested, the RCX H1407 3200kv is another option. It seems very similar to the EMax motor, but it is slightly larger; I don't think I will use this one unless I have to.

LDPOWER MT1306 3100kv
http://www.hobbyking.com/hobbyking/...R8fCzMy629CqPqrWNq8qBUAc9wYH5qqLo4aAq708P8HAQ
On the flip side, LDPowers MT1306 again, seems like a good motor but it is only 2s capable. If it lacks power, the 3s option would be really nice to have.

~

The KVs are also interesting on these motors. Dan suggests the low 2000s, but these motors are much higher than that. Is that just because they are actually good and not just "small"?

 

[Craftydan]

"Small" lends to higher kV. It's just the physics of the thing. It's not really as much an effect of "quality" as much as size and how it's wound.

The same motor can be rewound in a few different ways (more/less turns, Y vs Delta) to impact the kV, but the smaller the motor, the higher the middle kV will be. 22xx motors are going to be very high 1000's with hot windings typically in the low-mid 2000's. 18xx motors are going to be low-mid 2000's with hot windings in the high 2000's. 13xx/14xx's are going to be low-mid 3000's, with hot windings in the high 3000's (4000 is just about as hot as it will get). Hotter windings are a bit less efficient but allow you to dump tremendous power for the size . . . not quite what you're looking for. DYS's 1306 wound to 2300kv is actually a fairly cold winding -- you won't get much power through it, but it'll have a much wider efficient range. For 3S it looks fine . . . but 2s? probably not so much.

Keep in mind, the kV specs I've made are not for "getting the most", but "getting just enough" out of a 4" prop on 3S. You can bump up closer to "getting the most" out of this size motor and reduce your throttle, voltage, or prop to calm her back down. In the latter case, picking up the 3000-ish kv motors will give you more headroom.

 

[Montiey]

That makes sense; running a lower voltage would mean that you need to get more from less; thus a higher kv.

I think I want 3s now. Seems like my quad is just too large for 2s, and the LDPower motor doesn't give much thrust with 4" on 2s according to it's test data. Emax it is, then.

The 4000kv motor will give 1.3x the thrust than the 3300kv, and draws 1.3x the amperage- reasonably logical. Is there any real reason that I would want the 3300kv version? the 4000kv test data uses a 4 blade prop while the 3300 uses a tri, but this doesn't matter to me much.

Thanks for everyone's help!