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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 05-31-2015, 11:19 AM   #1 (permalink)
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Default Trex 250 DFC plus, tail cannot lock firmly

Hi guys, I've just get my 250DFC plus BTF and I'm using my JR DSX9 to bind this bird.
Everything seems OK after binding and it flies. However, the tail cannot lock securely. Whenever I give a slightly harder throttle up, the tail will go right and vice versa. Same situation when I turned to idle mode. Have tried the Gain switch on the 3GX MRS but it does not help the situation.

Cannot anyone help me how to solve this issue?

Thanks very much.
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Old 06-01-2015, 05:19 AM   #2 (permalink)
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It almost sounds like the tail / throttle pre compensation is too much, as I would expect the tail to kick left if the pre compensation was too low from due to not being able to counteract the torque from the main rotor.

I don’t know if you are able to turn down your pre comp on the 3GX MRS ?
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Old 06-01-2015, 09:37 AM   #3 (permalink)
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Other way round Toocool4, torque from the main rotor pushes the tail right, so you would actually need more pre-comp if that was the cause.

I'm not sure if the 3GX MRS will have any tail precomp settings though, I haven't used that one myself, but I believe tuning options are fairly limited.

The tail on the 250 can be tricky to get right, but before we get onto 250 specific items, there are a few possible physical causes of this. Firstly, what headspeed are you running? If the headspeed is too low the tail rotor may not have enough torque to counteract the changes

Once you're happy the headspeed is good, check the tail gain settings. Ensure you're in heading hold mode, and then increase your gain until you get a bit of a wag after hard stops, then drop it down a few points.

With that out of the way, to get the tail working well on the 250 generally requires a fast tail servo. The DS95i is the top dog, it has the speed and torque to make any tail work well. I personally like the DS76t, it doesn't have as much torque but it's a lot lighter, so with chinese weights on the tail it works great.

The 250 tail can have a lot of slop which contributes to the issues, the 681X double bearing mod works great (basically add an extra bearing to each tail grip to remove some slop).

But for me personally, I could never get the tail to really hold well using a 3GX, it wasn't until I upgraded to a Spartan VX1e that my 250 really started flying well.
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Old 06-01-2015, 10:20 AM   #4 (permalink)
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Thanks for the advises. So do you mean that actually the MRS doesn't work well with the tail? Actually I can change it to another better 3 axis gyro but I don't want to waste this if it can work. (It comes as a BTF version) But it really seems that it cannot even hold the tail properly if I am trying to give a little harder throttle.

And do you guys think the pitch degree also contributes to this issue??

Tks in advance if anyone can give me some advices.
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Old 06-01-2015, 11:19 AM   #5 (permalink)
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Quote:
Originally Posted by myxiplx View Post
Other way round Toocool4, torque from the main rotor pushes the tail right, so you would actually need more pre-comp if that was the cause.
Are you sure about that? The main rotor on the T-Rex250 is spinning clockwise (right) yes looking top down? Which means if the heli had no tail the whole thing (nose) would want to rotate right (clockwise) and that means the tail is rotating left (counter clockwise). Yes / No ? or do i have it wrong?
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Old 06-01-2015, 12:51 PM   #6 (permalink)
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Nope, with no tail, the body rotates opposite to the head.

Its physics, for every action there's an opposite reaction. So for the head to spin clockwise it has to push against something. That's the body of the heli, and without something to hold it still it gets pushed the opposite way :-)
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Old 06-01-2015, 01:38 PM   #7 (permalink)
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Hey myxiplx I am familiar with Newton’s 3rd law.

I stand corrected I did have it the wrong way round
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Old 06-07-2015, 06:56 PM   #8 (permalink)
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Quote:
Originally Posted by sherman View Post
Thanks for the advises. So do you mean that actually the MRS doesn't work well with the tail? Actually I can change it to another better 3 axis gyro but I don't want to waste this if it can work. (It comes as a BTF version) But it really seems that it cannot even hold the tail properly if I am trying to give a little harder throttle.

And do you guys think the pitch degree also contributes to this issue??

Tks in advance if anyone can give me some advices.
even with a good gyro (BeastX, Spartan, Ikon, etc...) the tail needs a lot of work to get it solid. Namely the double bearing mod single-handedly did the most for mine. After that, making sure the links are sized correctly and tail is as loose and slop-free as possible (a challenge into its own). After that, making sure the head is set up well can make or break the tail. A sloppy swash or main shaft movement will cause all kinds of problems, especially at higher rpm/frequencies.

Once you've got all that sorted out, look at the FBL unit itself. Your precomps need to be turned all the way off before you start tuning and make sure all you're geometries and pitches are where you want them to be. I turned all my settings down to zero and started from the ground up. It took quite a few flights to get it closer but now it's just minor adjustments. Once you get it locked in and happy with it but maybe need just a little more out of it then the precomps and such will come in handy.
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