** Blu-Baby Primary Trainer ** Plans, Pics and Fun! - Page 1258 - RC Groups
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Oct 10, 2012, 08:17 AM
springer's Avatar
My 42 flys fine with an Emax cf2822 (1200kv, 39gm) and a 8x6 prop on 3s. For 2s probably a 9" prop, or maybe a gws 1060dd (been a while, but I think I flew that combo) the beauty of the emax is it's only 6 bucks from hobbyking. I just bought two of it's cousin the cf2812 (1534kv or so). Nose bearings aren't the best on 'em, so doinks can be a problem, but bearings available at HK. But for the money ....

Your other problem is the big heavy 2s battery. The biggest pack I have is 1550 but I fly the BB with 1k or 1300mah 3s packs. You will get sedate flying and long flights with the 2s.
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Oct 10, 2012, 08:37 AM
jackerbes's Avatar
Originally Posted by Chattercoma
Hey guys, I am planning to build a 42" BluBaby and thought I should seek some expert advice. I am on a severe budget, however, and already have some gear to use.
This 20A ESC
This 1800mah 2S lipo
So the only real things I need are a motor, prop, and servos. I am planning to buy these 9g servos and a Blue Wonder 1500Kv. Can you recommend a prop and motor? Thanks.
Better deals on the servos are easy to find, here are two examples:



I don't have any of the Power-Up brand but at $2 each when you buy two or more they are worth a try. I learned long ago that it makes sense to choose one brand of 9g servo and never buy any other. That gives you spare parts and full interchangeability on servo arms and retaining screws. My lifetime choice was the TP SG90 or HXT900 (same servo with different names).

If you can shop on eBay, do a search there for "SG90" and there are some good deals.

A 24g BW is not a good choice for a BB 42. You can get about 5A on 2S and that will put you trying to get in the air with 40W of power. Underpowered flight is an invitation to disaster and frustration.

You want a motor that weighs at least twice that amount and if you want to long term power for adding weight to the plane or flying in more trying conditions a 75 gram or so motor is not too much motor for a BB 42.

And for a BB 42 you don't want smaller higher RPM props, you really want larger and lower RPM props. For a newbie, even big slow fly props are a better choice.

But you already have 2S packs so now you have to buy a higher Kv motor to get the prop speed up a little. And that is narrowing your choice of props.

Here is a motor (46g 1350 kV) that will work and you can see from the prop tests there how the prop choices change as you go from 3S to 2S:


Here is a 71 gram 1100 kV motor that will work:


The sequence for making your power system choices should be in the following order to get the pieces matched up right:

1 - Plane
2 - Prop (sized to plane and of the right type for it)
3 - Battery (get cell count/voltage that is best)
4 - Motor (choose power level and kV to make prop work best)
5 - ESC (sized to handle the load)

We all went though the same learning curve probably. But if money is scarce and you have to get it right on the first try, you can do that.

Oct 10, 2012, 12:27 PM
haha lol id never buy that. you gotta get the clone. works just fine. its called: hacker clone 20-22l

yeah that should work too.
Oct 10, 2012, 01:16 PM
sir_clive's Avatar
also sold as kda or keda.
Latest blog entry: Wing Helper 1.3.0 Released!
Oct 10, 2012, 02:35 PM
Cheese eating monkey.
If the nose of my blu baby tends to drop quite a lot in turns, presumably my COG is too much forward.

Am I right?
Oct 10, 2012, 03:09 PM
sir_clive's Avatar
I'd say you are too slow in turns, or your turns are too steep. Some nose drop in turns is normal (that's why one always gives some elevator to compensate).
Too large fin can also be a problem, but if your build is true to the plans, I would not consider that option.

Where is your CG at?
Latest blog entry: Wing Helper 1.3.0 Released!
Oct 10, 2012, 05:16 PM
Registered User
Sorry for changing my mind, but after reading your posts and doing some more research I decided that instead of buying a new ESC and an expensive motor, I would be better off buying a smaller 3s lipo and building a BB33. Sorry again for changing my mind, but I could still really use some gear recommendations. Thanks, guys.
Oct 11, 2012, 02:57 AM
Must not buy more planes!
mclarkson's Avatar
My niece finished decorating her plane today. (Yes, it has a tongue.)
Oct 11, 2012, 08:08 AM
Ken's CAD Models
dz1sfb's Avatar
That is just too cute! Whiskers and all.

Latest blog entry: Mini H Quad Project
Oct 11, 2012, 09:27 AM
Registered User
JohnsPop's Avatar
That's awesome MC! You'll have to get us some close-up video of that one flying for sure so we can see that tongue flapping!
Oct 11, 2012, 03:16 PM
mine isnt going so well:
BB42" flight fail (0 min 16 sec)

what do you think? i followed the bb42 plans pretty much exactly. motor is tilted a few deg down + right. the CG is pointing up slightly when held at 50% of the wing. sorry for the vid. someone else made it. does the same thing each time.
Last edited by sirbow2; Oct 15, 2012 at 05:05 PM.
Oct 11, 2012, 05:02 PM
Originally Posted by sirbow2
mine isnt going so well:

what do you think? i followed the bb42 plans pretty much exactly. motor is tilted a few deg down + left. the CG is pointing up slightly when held at 50% of the wing. sorry for the vid. someone else made it. does the same thing each time.
went to my LHS and they say its the CoG. will move the batt up
Oct 11, 2012, 05:22 PM
jackerbes's Avatar
With the plane supported on you finger tips at a distance of 1/3rd of the chord back from the leading edge, the plane should be level. If you hold it at eye level and arms length the bottom of the wing should be flat as will the horizontal stabilizer.

Being tail heavy is the worst possible situation for a maiden flight.

Hand launch and don't use full throttle. Run the motor up until you just feel the slightest pull in your hand. Then face into the breezes, and do a level, full arm forward push, from shoulder level with the motor at that speed. That should put it in level flight.

Use small control inputs and add throttle one or two clicks at a time and only if needed.

Good luck with it!

Oct 11, 2012, 05:31 PM
yeah thanks! i think that was the issue with my other one. ill just hollow out the foam a bit more and slide the battery up.

wow lol. mine is a good 30deg tilted back when at 3in (30% of 10in wing).

would the polyhedral change anything?
Last edited by sirbow2; Oct 11, 2012 at 05:50 PM.
Oct 11, 2012, 05:38 PM
sir_clive's Avatar
jack, you are much more experienced then I am, but wouldn't 33% also be pretty far back? I think mine is somewhere at 28-30% and I felt very comfortable with that (kfm3 wing)
Latest blog entry: Wing Helper 1.3.0 Released!

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