SAB, Alz 380/420 COG fixes, plus 380 stretch to 420 - RC Groups
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Oct 22, 2017, 12:49 PM
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SAB, Alz 380/420 COG fixes, plus 380 stretch to 420


There are a few of these 380/420 topics on the rc heli sites and some sites specifying sab product in their forums of interest, rcg has no manufacturer specific forms so I'll post my cog fixes here.

One, I drilled two m4 holes 12mm forward of the original magnet mounts used to fasten the frame where the boom is. I then chamfered the original holes and put a counter sunk screw in them. I used a nut behind the magnet mount in between the frames and the upper main plate where there is enough space to do so. This allows the lipo to be moved more forward. Now you may see the front of the canopy droop a bit if the lipo isn't there to help keep it up, one don't worry a whole lot if you can put some tubing on the frames and the canopy to make it fit good.

If you can do step one then move the lipo an inch forward of the frame sides and stand the lipo up on the side.

Additionally I cut the top fin portion off and cut 15mm of boom off the back. Not much weight to be saved there but it might be a gram or two, every bit counts.

Attach your under tray esc as far forward without extending out the front of the frames.

For those who are more daring it is possible to re-drill holes for the tail servo about 15mm forward of where they are on the stock frames (or by the same amount as you will get when you flip the servo and position the horn center as it was stock). You have to flip the tail servo so the servo horn is in the same place. Because the frame has an angular cut at the front servo tray hole you will have to follow the angle and keep some cf between the screw and the edge, this is not a problem. The tray will begin to become more horizontal at the front but there is enough cf at the back hole to keep it on the same horizon line as the original. A slight deviation from the original position is negligible.

CF tail blades, always lighter than plastic, another few grams worth but every gram counts on a lever.

On my 420 I was able to reduce more weight with some personally fabricated parts, those will have to wait for a time and place to announce, because it could be a game changer with potentially many fans wanting them. I've designed some skis where they hold the canopy up so it isn't moving around, show you those one day soon perhaps.

The first four mods are very simple, the others a little more crafty. It isn't a big heli so the smallest details can affect performance, a large diameter boom full of resin and fiber is no different than that from a scale canopy, a small one diameter tube will be so much lighter but the 380/420 is not a pod and boom affair.

Good luck, there you have it, pics to come.............
Last edited by icanflyheli; Oct 28, 2017 at 09:34 AM.
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Oct 22, 2017, 04:40 PM
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my 380 before my new skids,

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where the lipo should be furthest forward in the heli, of course the tray will be sticking only one third of where it is in the pic as it was originally engineered,

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could have gone further forward with the magnet mount but 1cm was the first time it was done, ever, problem is when you go too far forward the canopy will hit the frames and begin to flare out at the trailing edge, it would be ok to move the mounts on the canopy back if the choice to do so was an option with un-drilled hole locations (no doubt a lot of doods would mess up the paint and put the holes in the wrong place making the whole ordeal less entertaining,,

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and two portions removed for neatness and coolness, AND, I discovered a way to tension the tail by putting a thumb on the boom end and pulling the tail mechanics back with the other fingers holding the fin and then the shaft side alternately then while keeping it tight screwing the side screws tightly. After that I stepped it from one side to the other to get it even tighter and/or to align the tail 90 to the chassis,

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On my 420 I made a 4mm thick cf side plate for the slider side that was a few grams lighter than the alu one. Next step in practical sense is to consult a cad programmer to look at an assortment of optional parts made for the 380/420's to improve upon it's shortcomings. Why, that's the hobby for me anyhow, mess with improvements and hot rodding, nature of the beast.
Last edited by icanflyheli; Oct 22, 2017 at 04:50 PM.
Oct 23, 2017, 08:51 AM
Registered User
It has to be corrected, the tail servo tray should only be moved 1cm forward as that is the difference when the servo is flipped and the horn is rearward mounted away from the main gear. This will affect cog minutely but still every g counts. If you make up a new tail control rod with some additional length the 15mm re-position forward will be possible. At 15mm the tray should not be pressing against the boom underside but be just in front of it.

Another mod I forgot about and only rediscovered as of checking the tail servo tray re-positioning on my 420 was the tail control rod ends. If you go to a bike store and pick up 4mm cable ends that are plastic and substitute those for the metal ones that came with the kit you can save another gram or so, the plastic ones weight nothing.

About the lipo in thepic it's a 5s 2700mah, doesn't matter what lipo you use the observed forward position should be adhered to to get better cog.

btw, I was on rr and talked of providing aftermarket parts for a 420 kit and some other things and the first reaction I got was PAY UP AD FEES BUDDY by a few responders . "Free Stuff" was the topic moved around to ots and subsequently closed before I had the chance to post a pic of the free stuff I am riding my self of. Same reason I got the boot from hf, TALKING of business even though it was only a consideration and I was no where near putting any kind of product out, thanks people, your the greatest.
Last edited by icanflyheli; Oct 23, 2017 at 09:11 AM.
Oct 23, 2017, 01:26 PM
Lord of the Strings
Bro, appreciate the tips, thanks for sharing. I like that green canopy!
Oct 23, 2017, 09:11 PM
Registered User
Quote:
I like that green canopy!
yeah thanks, the black "eye" looking thing is mine as is the total blocking out of the alz d380 emblems, distracting to me, and I did whittle off 1cm of the trailing edge.

well, I did it, moved the servo forward 1cm and did get an ever so slight change in boom angle, 1 or 2 degrees is so little, I then later did something that would instill fear into the hearts of the weak, hacked off some frame at the back and moved the servo up 22mm, of course restyling the frame at the same time and making some room for the canopy to hug closer to center. there's a small gap between the boom and the servo tray now and all that's needed to fill it would be some thin mylar and two side tape or glue. Have to make a longer control rod now. Contacted a cnc cf guy last yesterday (cog fix refit v1 frames now being taken more seriously)
Last edited by icanflyheli; Oct 23, 2017 at 09:17 PM.
Oct 23, 2017, 11:33 PM
as much as I can
beenflying's Avatar
I'm starting to think the Devil 420 has a heavier tail than the Goblin 420. I've double checked my Goblin 420's CG and it's perfect with a nano-tech 2650mah 25-50C 6S battery center of the battery tray (not even over the tapered front part of the battery tray).

I notice SAB making comments like "Boom obtained with different technology... lighter"...
Oct 24, 2017, 11:13 AM
Registered User
this'll fix ya, errrrr, it,

first time setting the servo tray forward, messed the hole at the back a little,

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the space between boom and tray now,

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and while I messed the back hole why don't I move the servo tray even more forward and get a newly styled frame profile, screwing up the first tray move led to going all out and this,

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new holes for the servo tray 22mm ahead were drilled after this stage of cutting and sanding the cf to clean up the cut line,

now aside from the gap between boom and tray and need of a longer control rod it looks very racy indeed, ohh, mine doesn't have original flippers and also has some frontal skis I fashioned making it look very very, racy, AWESOME. lost 6.2gr.
Oct 24, 2017, 11:20 AM
Registered User
,,,duplicate post, ooops

re sabs tech, vacuum bag would do it.

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edit;

speaking of vacuums, I spooled up and slightly flew my 380 in the back yard moments ago and wondered what the sound coming from it simulated when I went into st1 with 98% throttle, a frikin vacuum cleaner isn't that odd. I opted for 75% throttle in idle up and even though it is very windy the heli held firmly, but then there's some shadowing going on back there in the yard. Pleasantly pleased with the heli all rsu orientations performed flawlessly in hover and the heli stayed put mid air like a larger heli. Nice stuff the 380 with the 420 on the way to completion next, the 380 drops like a rock when trying to auto.
Last edited by icanflyheli; Oct 24, 2017 at 02:48 PM.
Oct 24, 2017, 03:15 PM
as much as I can
beenflying's Avatar
Thanks for sharing this. I don't think I would like the bottom of the boom to not sit on the plastic of the tail servo tray. I believe this does provide some support to the boom.

Also FYI, your tail belt tensioner is on the wrong side.
Oct 24, 2017, 06:49 PM
Registered User
tail belt tensioner goes on the trailing side because if you were to constantly pull it tight with the motor the trailing side would loose tension and defeat the purpose. Why wold you think otherwise?
Oct 24, 2017, 07:16 PM
as much as I can
beenflying's Avatar
Sorry, brain fart. You are quite correct. It should always be on the return side of the belt to take up the slack. Apologize.
Oct 25, 2017, 12:05 AM
GREY.riddles::{used}? hmm
Flying Pitcher's Avatar
Icanfly,
your support to the community is greatly appreciated. Although I don't have either helis, I admire your engineering. impressive, sir!

Thank you for posting.
Oct 25, 2017, 09:18 AM
Registered User
no problem, it's fun stuff and the 380/420 a much more stable heli than a 450 type or smaller.

On the matter of the servo tray and space between it and the boom I took some white card paper and white vynil and covered the gap, looks great. About the structural support the tray might supply to the boom as long as it isn't hard fastened with screws somewhere it's going to be free to move around therefore of no support to the boom. I was thinking of adding some frame to boom attachment braces and the holes where the servo wire is held with a zip tie would be used for that, or holes in the servo tray.

I don't know if you realize that were the servo tray parallel with the chassis and 90 to the boom it could be used as a gyro mount location and put a rx where the gyro tray is too. Also putting the gyro under the servo tray would allow a person to use 6in rx wires and get the most distance between them. Running servo wires under the servo tray could be interesting. Then you can see the gyro bright lights when the heli is in the air.

Look, were I to come up with a v1-380/420 re-designed side frame, landing gear, all cf refit kit (as I stare back and forth between my comp and the 420 with mod'd frames) and a few other part kit like all cf tail and something else I don't know if anyone will like the price, like sab's frames are $23usd each. Unless someone can provide something so supa cool you'd just have to play some more $50 including shipping for a pair to replace something you already have and use well may not be a consideration ($5 to ship north america wide envelope snail mail) After shipping it comes to $22.50 each, who might be up to that and does it put some money in my hands? I'm asking myself this atm.
Oct 25, 2017, 09:52 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Moving the tail servo way forward to sit just behind the battery was the thought I had but that would require a completely re-designed servo mount.
Oct 26, 2017, 09:11 AM
Registered User
the biggest problem in pushing the lipo more forward is that the wires will hit the canopy. My lipo wires are at the back so all I worry about is making sure the velcro strap doesn't hit the motor pulley. with the 2700mah lipo I could only use some velcro at the very back of the tray so as not to touch the pulley with the strap, because my lipos are on their sides even though it fits in flat with label up. I choose to keep the lipo vertical because it won't hit the canopy immediately ahead of the frames that way. I also have red and black on right and left side split connectors, attach the red and only have to connect the black on the left side from the esc to energize.

and if your wondering, the tail servo shown in the earlier position change pic is there only for fitment/location of the servo horn . A proper hv ds will be fitted in the flying model. I believe I'm going to extend the 380 to a 420 due to the non auto-ability of the shorter model, what happens when you put narrow chord blades from a smaller model on a larger heavier one like 325's on a 500 and sun up like a micro at blistering rpm.
Last edited by icanflyheli; Oct 26, 2017 at 09:23 AM.


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