766 Center of Gravity - Balance

[TokenLefty]

I've looked through as many pictures as I can find to determine how far the battery sticks out the front of the frames. In order to get mine to balance correctly, the Lipo's are extremely far out. Actually to the point where I can't put the canopy on. I'm running a relatively typical setup with a scorpion 4525 ult and castle 160. On the trey is a spartan vortex and a WR BEC pro G2. So nothing excessively heavy in the back. With the battery in this position, I'm getting perfect balance but I will have to lengthen the Lipo leads to reach the connector.

I'm running home made stick packs from Gens ACE 5300mah which barely fit in the frame. But these packs are much heavier than Pulse. I really don't understand why my 766 is so tail heavy? The tail is stock boom running synergy 116 blades.

I'm sort of at a loss. Any ideas?? Any suggestions?

[Chris Sexton]

The only real difference in my setup is the bEC is under the esc on mine and the motor I run is slightly heavier. But I know many people, Matt included, running the ultimate motor.

Can you take some pictures for us?


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[TokenLefty]

Thanks for the Reply Chris. I can snap some pictures. What angle are you looking for? The way I have always checked the C.G. on my Heli's is by holding it up at 90 degrees by the main grips and moving the body around in a circle. It should stop wherever I put it. It is a little more challenging with such a large model but possible. If I just check it by raising it off the table with fingertips under the grip bolts , it isn't completely obvious. With what I would consider a normal battery position (the pack an inch or so in front on the side frames), that method hangs just ever slightly tail down. But using the 90 degree method, I kept moving the battery forward until I could make it stop in any position and it's about 3/4 of a single 6s pack sticking past the front of the frame sides.   -Mark 

[TokenLefty]

The attached photo is what I am referencing. The Heli balances perfectly like this. If I leave it like this, I will have to move the batteries on the trey. In the photo is one of the packs that I made up. It uses 6S Lipo's that weigh 786 grams each. Add all the extension and junk and they are easily 1600gram hefty packs. The canopy installs fine with plenty of room in front, but I would have to turn my ESC around or extend the wires on the packs so they aren't under tension. The entire back end is stock 766.

[TokenLefty]

Electronics on the rear trey

[Chris Sexton]

Looking at mine, your pack is noticeably farther forward than mine.  You would be surprised how much the weight on the back (bec) can play a part.  also the lighter motor will make a huge difference. The BEC is closer to the main shaft where you have it than when it's up front with the ESC like mine. Also I think my ESC is mounted lower on the ESC tray than yours.

I have never like the holding the heli by the head method as you outlined for checking balance. Seems like motor coging and drive train resistance could throw that off.  I also just use the fingers on the blade bolt method and if the tail doesn't drop more than a degree or two, you're good to go.

I don't think your pack is dangerously far forward. it is still supported by the CF tray, assuming it will reach the lock holes.

Here is the best picture of my 12s machine I could find here at work. I would love to go take a good one for you, but its in pieces right now. It had an unexpected ground impact

[TokenLefty]

Thanks Chris! Sorry to hear about the ground incident. It gets in my way also! Hopefully not too much damage. I set the battery and moved the trey back were it actually locks in and I'm a little further forward than you are but not much really. I was sort of expecting the Lipo's to be contained within the frame. But as long as they are secured well, it really doesn't matter. Plus I can easily add a strap around the nose of it. I added some yellow tape to the pack as a marker so I can just drop them in to the edge of the trey and line up the tape without tinkering on the future on pack swaps. I may drop the ESC down a little and add fan.

I could move the bec G2 up front but I initially chose that style because of the individual Servo power feeds, so I would lose that benefit if I were to move it and don't want to run all those extensions to the font and then back. I hope to maiden the 766 this weekend. Keeping my fingers crossed! Thanks again for the help. -Mark

[Chris Sexton]

Yeah man you're good there.

Looking forward to hearing how the maiden went!

Yeah my 12s is banged up lol but we'll get her tinkered back to life for IRCHa!


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[Danny Dugger]

Token are you checking COG with the canopy on? That makes a difference, too. I also check mine by holding the heli sideways. I check it twice to prevent the issue of fighting the motor - once with the tail left (tells you if it's nose heavy) and once tail right (tells you if it's tail heavy). In my experience it's been a very reliable and repeatable method. Nothing wrong with fingertips under the grips either - just my personal preference

[TokenLefty]

Hi Danny, Thanks for the ideas, but yes I check it with the canopy on and tail blades installed. I generally pull the main blades off. As you point out, it certainly makes a difference. When I do the sideways CG check, I do it both ways so that it falls away from the motor cogging and is only dropping against the one way bearing when its not engaged. Flip to both sides and then pick it up the other direction (from right up to left up) to test the other. It's very smooth. With the battery position in that last photo, the CG is perfect. No dropping nose or tail with the sideways method and using the finger method it lifts directly off the table with no tilt. - Mark

[Mahfu]

I'm having a CG issue too.  I have my 766 nearly complete in the 806mm configuration.  I seem to be fairly tail heavy.  I have my 5300mah packs all the way forward on the tray.  If I try to go any farther towards the nose with the batteries I’ll have to cut out a new notch on the battery tray for the Velcro strap.  When I lock in the tray I use the forward most hole.  If I had to make a guess I would guess I need to add around 4 oz of weight to the nose of the frame to get the CG right.

I built it with Xnova 4035 and a Jive Pro 120.  I actually still need to put on the flybarless and receiver before I’m finished.  I want to put on an Optiguard too.  I was planning on trying to put it in the back with the flybarless but I might have to try to find somewhere for it in the nose.  I actually tried an experiment and taped the Optiguard to the end of the battery but the CG still felt way off.

Originally I got an Xnova XTS 4535 to go onto this heli.  I didn’t put it on because I thought that I would be wasting weight on power that I might never use.  I’m thinking that maybe need that weight now. 

I’ve included a couple of photos to give you a feel for what I got going on. If all else fails I have 6 oz of lead weights I could use to get the CG right.  I would prefer not to.  I would also prefer not to use the 4535 just because it weighs more.

[Chris Sexton]

Yeah the 4035/jive120 combo is a bit light. That's the weight issue. My 4530 and scorpion 160 has no cg issues on my 806 with 5000packs.


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[Mahfu]

I ended up putting 6.25 oz of lead onto the noise of the frame. Very nearly perfectly balanced it but ran out of weights. I'll run it with the 4035 motor for now and see how i like it. I think the 4535 is only about 2 oz heavier than the 4035.  I would likely still need some weight in the nose even with the 4535.

[Chris Sexton]

Well that esc is easily 3-4 oz lighter than the 160 amp escs most are running on 806s. But if that power plant fits your style run it! Would love to see video.


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[TokenLefty]

I was hoping to install the boom wrap. Does anyone know how much it weighs? -Mark