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250 Class Electric Helicopters 250 Class Electric Helicopters manufactured by Align, Tarot, SYMA, Airhog, Chaos, HK and similar.


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Old 09-25-2018, 10:51 PM   #1 (permalink)
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Default Custom Parts.

I wanna bring the 250 back. I love this heli, but it's got some issues. Issues I'd like to address.


First order of business, I'm addressing the main issue with the heli: the tail. Slop, slop slop. Impossible to get rid of. My solution is to design custom tail parts, and use what I can from the Oxy2. At the moment I'm planning to use the Oxy2 tail grips, slider, and pitch arm.


Currently this is what I have. It's a 3-piece tail box. 1 main piece and 2 side pieces for easy tail shaft replacement. Theoretically I could even alter it to fit the Oxy2 tail shaft as well, though I likely won't because that would make the tail ratio too low for comfort.
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Old 09-26-2018, 12:09 AM   #2 (permalink)
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Prototyped.
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Old 09-26-2018, 07:01 PM   #3 (permalink)
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I will be following this thread as I am attempting to use Oxy parts on my 250.
The issue I am having is the Oxy grips are not a direct swap on the Align tail rotor hub. The Oxy tail shaft is 2.5MM, where the 250 shaft is 2MM.


I have machined a sleeve to fit the hub on the 250, but the diameter of the Oxy hub is larger, screwing up the geometry of the pitch links.


I have been messing with this thing all summer trying to get it to work.


By the way,I am doing this on a shaft drive tail as I want to put this in an Airwolf fuselage. This thing will weigh a crap ton.
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Old 09-26-2018, 07:26 PM   #4 (permalink)
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I was actually thinking of using the Oxy2 tail shaft. Only issue I'm having is that the Oxy2 tail shaft is 15T. Not sure how many teeth the 250 has.
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Old 09-27-2018, 07:06 PM   #5 (permalink)
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The plastic gear 250 shaft that I removed from my SE has 16 teeth.


The Oxy does have a 16 tooth gear.


https://www.lynxheli.com/product_inf...99fc94ade1228f




And 15 tooth gear.


https://www.lynxheli.com/product_inf...99fc94ade1228f
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Old 09-27-2018, 07:11 PM   #6 (permalink)
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That's great news!
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Old 10-02-2018, 03:10 PM   #7 (permalink)
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The Lynx 180cfx bet drive tail conversion is the cure. Just have to transfer stock 250 tail shaft pulley to lynx shaft and extend tail boom slightly.
Done and done. Click image for larger version

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Old 10-02-2018, 03:15 PM   #8 (permalink)
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Quote:
Originally Posted by Tech 4 9 View Post
The Lynx 180cfx bet drive tail conversion is the cure. Just have to transfer stock 250 tail shaft pulley to lynx shaft and extend tail boom slightly.
Done and done. Attachment 757141
The oxy2 blade grips are a drop in replacement for stock 180 grips on the Lynx 180 tail.
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Old 10-02-2018, 04:59 PM   #9 (permalink)
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Wow... so the entire 180 tail can be transferred to the 250? Never thought about doing that. All you needed to do was use the 180 CFX tail shaft and what did you do with the tail boom exactly?
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Old 10-02-2018, 06:11 PM   #10 (permalink)
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What I think he did was use the Lynx tailcase for the 180 belt conversion.......




https://www.lynxheli.com/product_inf...99fc94ade1228f




It fits their tailboom which measures 8.5MM according to their website.

The Trex 250 boom I measured is .336 in. , close to being the same dimension.


Would have never looked at this option for a belted tail.
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Old 10-02-2018, 06:32 PM   #11 (permalink)
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Looking at this further, the 180 conversion tail uses 2.5MM bearings for the tailshaft, so could the Oxy 2 tailshaft be a direct swap for the 180 shaft?


The 180 tail gear is only 12 tooth.


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Old 10-02-2018, 07:35 PM   #12 (permalink)
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I think I knew there was a 16t lynx shaft but wondered about the diameter differences..it being bigger than the 250 therefore bigger than the tail drive pulley. At that point in project I didn't know if ANY of it was going to work let alone getting into pulley ratios/tail speed changes. This was before I knew I could use O2 tail grips and was wondering how the 180 blades were going to work. Too fast? Too small? Using stock 250 pulley kept it 1:1..which in itself was a unknown. Also, is the O2 shaft the same length as the Lynx 180 shaft? Probably. Trying it would def be worth a shot. It isn't hard, especially if done a coupla times, but being faced with having to fabricate another custom replacement tail shaft after even a minor crash kinda steps on motivation to fly it. It's a awesome mod, works great, but it's also kinda like having a 'glass tail'.
Tail boom needed to be lengthened about a 1/4". When enough tension is put on belt the very front end of stock tube BARELY fits in forward most part of tail boom mount. This fabrication is initially worse than tail as I had to find tube stock that would fit into stock 250 boom. I ended up with oversized tube chocked in a drill with sandpaper under kitchen sink for at least a hour to turn down to proper diameter to just slip into 250 boom. Then add a small piece of scrap stock tail boom to match O.D. Only saving grace here is that if you get a good length of tube the right dia it will last for a few tubes as you only need a inch or so for lengthening of custom 250 tube. The other plus of this is that having the tube inside the tail boom where it mounts adds rigidity. I use the metal tail boom mount and in combination with the stiffer boom tube end I don't have to wrap end of boom with tape to keep it from wandering in mount, loosening up belt anymore. So far anyway. I have VERY little flight time on this mod as early test flights revealed weird pitch issues. Like pitch is dead at center stick. I have slop in head and have new swash I'll be trying soon.

But my T-lynx 250 tail is rock solid. 😎
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Old 10-10-2018, 06:54 PM   #13 (permalink)
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Found out the Oxy 2 16 tooth pulley is much larger pitch diameter compared to the 250 pulley.


It will not fit in the Lynx belt conversion tail case for the 180CFX.


Bummer !!!
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