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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 06-21-2016, 12:41 PM   #1 (permalink)
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Default New T-Rex 250 FBL with 3GX and Futaba

My 250 just came yesterday. I have 40 hours on a T-rex 150 and wanted a little bigger plane.

Build and Setup are fine so far, except I wish I had seen some video or something showing that the AIL servo needs to be reversed on my Futaba 6K transmitter.

Also, not much info on if it is better to have the 3GX with wires pointed toward the motor or the rudder servo. I'm having the wires pointed toward the rudder servo, and will set up the compensation with it in that orientation.

Also, how does one tighten the motor mount screws to set the mesh? I undid the two front screws connecting the top and bottom of the frame (boom not on yet) and hinged the top and bottom part of the frame to get to the screws, guessed at a mesh, and hinged the top and bottom down to check it. then repeated until the mesh was right.

This looks like a fun heli and I can't wait to fly it.

Looks very delicate with so many tiny screws. I think I'll make some trainer legs for the maiden flights.
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Old 06-21-2016, 01:39 PM   #2 (permalink)
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Quote:
Originally Posted by ic-racer View Post
My 250 just came yesterday. I have 40 hours on a T-rex 150 and wanted a little bigger plane.

Build and Setup are fine so far, except I wish I had seen some video or something showing that the AIL servo needs to be reversed on my Futaba 6K transmitter.

Also, not much info on if it is better to have the 3GX with wires pointed toward the motor or the rudder servo. I'm having the wires pointed toward the rudder servo, and will set up the compensation with it in that orientation.

Also, how does one tighten the motor mount screws to set the mesh? I undid the two front screws connecting the top and bottom of the frame (boom not on yet) and hinged the top and bottom part of the frame to get to the screws, guessed at a mesh, and hinged the top and bottom down to check it. then repeated until the mesh was right.

This looks like a fun heli and I can't wait to fly it.

Looks very delicate with so many tiny screws. I think I'll make some trainer legs for the maiden flights.
Setting the mesh can be a pain on this helicopter because the upper frame obstructs the motor mount screws. I generally get the screws tight enough to restrict movement of the motor, but loose enough to allow me to shift the motor slightly. I then loosely install the upper and lower frames, shift the motor a bit to get a desired gear mesh, remove the upper frame, and then tighten the motor mount screws. Of course, I will check the gear mesh again to make sure it's correct, but I have found it usually stays where I intended.
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Old 06-21-2016, 04:18 PM   #3 (permalink)
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You will enjoy the 250 itís a lovely heli a word of warning though, it crashes like a big heli.

I have my FBL unit with the wires coming out the front towards the motor, I no longer use the 3GX but a Spartan VX1n see pic below. Iíve put the S-Bus receiver above the FBL unit behind the tail servo.



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Old 06-22-2016, 02:24 PM   #4 (permalink)
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Got the kit built. This is an 'expert' kit. I spent a whole day just setting up the servos and swash. Another whole day figuring out how to program the 3GX and a whole day programming it.

I got it hovering, so, at least a day or weeks getting settings appropriate for my flying style (just hovering at this time.)
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Old 06-22-2016, 03:16 PM   #5 (permalink)
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This is an 'expert' kit.
Do you mean it's a Pro DFC kit? if so that is what i have too.
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Old 06-22-2016, 05:22 PM   #6 (permalink)
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Do you mean it's a Pro DFC kit? if so that is what i have too.
Meaning, as you already know, not for a first-time RC hobbyist. But, yes it is the DCF Pro kit.

My battery has not arrived, so I'm using a 2200 2C pack taped between the skids. It is 113g compared to the original at 70g.
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Old 06-23-2016, 05:33 AM   #7 (permalink)
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Quote:
Originally Posted by ic-racer View Post
Meaning, as you already know, not for a first-time RC hobbyist. But, yes it is the DCF Pro kit.

My battery has not arrived, so I'm using a 2200 2C pack taped between the skids. It is 113g compared to the original at 70g.
Okay i see now.

I am wondering if you are getting longer flights due to the bigger battery, but on the other hand are you losing the bigger battery advantage due to the extra weight?
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Old 06-23-2016, 07:47 PM   #8 (permalink)
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Got two Align 850ma packs today. The heli is perfect today. No wind, and the higher prop speed and lower weight made it fly very stable.
I guess if anyone tries a large 2S battery, just consider it a mechanical test, not a test of 3GX settings or flight response.

The little zippy 2200 2S packs did not last very long in the heli. I thought I might get 20 min but not so. Not sure why, in a Tamiya F1 car or Tamiya Mini Cooper M05 in my driveway the packs run 15-20 minutes.

The only mistake I see that I made was in the DIR settings to make both Aileron and Elevator both have 8 degrees of pitch. That gave me different swash percentages. Maybe the 3GX needs aileron and elevator swash percentages on the transmitter to be the same (it does say so). I do notice my elevator is weak compared to the aileron. I'll redo the DIR settings tonight.

My Fubaba 6K has a knob on the front. Seems logical to have the Gyro gain controlled by the knob to get the correct gain in flight, yes? But I have never see any setup use it that way, or never see that recommended.
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Old 06-24-2016, 07:16 AM   #9 (permalink)
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You can run your gain via a wheel or slider on your TX. You would have to setup a mix in your TX mixing gyro to to the slider. I'm not sure if your TX is capable of doing it though.

Generally once you get a helicopter tuned though gyro gain is never adjusted there after. You also want your rates for aileron and elevator to be the same.

Unfortunately with helis learning to fly is only 1/2 the battle. There is probably an equal amount of work to be done in building, setting up and maintaining them. There is a fine ballance between power, weight, and head speed, get any one thing too far out of whack and performance goes down and not up.
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Old 06-24-2016, 11:53 AM   #10 (permalink)
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To set motor mesh I remove the two front servos from the frame. That way it is possible, albeit a bit tricky, to tighten motor mount screws
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Old 06-26-2016, 11:07 AM   #11 (permalink)
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I finally got the 3GX 5.0 software and ran through the settings. I saw the 'hidden' settings. I read some threads about setting the rudder delay to Zero. I figured out how to do that. I also fine tuned my rudder mechanical midpoint which was way off.

During all this I had a sudden loss of power. The ESC was a little hot, but maybe not 80C (the cutoff). Not sure why it cut out, but when I checked the ESC settings (RCE-BL15X) they were totally different than the the manual. For example battery cutoff was low and gyro was enabled and timing was high. That explains a nearly-drained battery pack and perhaps the overheating.

Note to self: always check everything, even things that are supposed to come pre-set.

Last edited by ic-racer; 06-27-2016 at 04:05 PM..
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Old 06-26-2016, 03:26 PM   #12 (permalink)
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It is running fine through 5 packs now that the ESC is properly programmed.

Now that it is all setup it takes off straight into the air and flies smooth and stable, yet responsive to battle wind.

I'll post all my parameters for other beginners. This T-Rex 250 3GX would be difficult as a 'first heli.' You need to get it in the air to make it flyable, so you need some flying skills, otherwise a beginner would need an experienced heli pilot to set it up and maiden it.

It is also difficult because some of the 3GX parameters indicate "adjust to suit flying style." Randomly adjusting settings can easily make a heli that barely gets off the ground, a total write-off on the next take-off.
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Old 06-27-2016, 04:02 PM   #13 (permalink)
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Now that it is setup and I have had about 10 or 20 packs through it, I am amazed at how docile it is. This thing is a puppydog; It hangs in the air almost unreal, like its on a string. Yet it is very responsive to control inputs.

The V5.0 is getting close to technology so a beginner can fly a 'hard to fly' heli.
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Old 08-07-2016, 07:06 PM   #14 (permalink)
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I took the 250 on vacation with me but one of the servos went bad. Savox replacement comes in the mail tomorrow.
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Old 08-08-2016, 11:05 PM   #15 (permalink)
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New servo installed in ELE position. Ready to test fly tomorrow.
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Old 08-09-2016, 08:48 PM   #16 (permalink)
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Flies great again. Looks like the Savox servo is an upgrade from the Align servos, so, rather than looking for a new Align servo, I may just order two more of the Savox servos.
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Old 08-11-2016, 11:38 AM   #17 (permalink)
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The Align servo horns do fit on the Savox servo. The number of splines is the same but the diameter is slightly different. The servo horns are a tight fit but they do fit. This is good, because the Savox servo horns don't have holes in spots that exactly match the Align servo horns. The servo horn screw thread seems to be identical and the servo size and mounting holes are identical.
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Old 08-11-2016, 11:41 AM   #18 (permalink)
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Also, the initial servo event, which was a sudden full swing of the AIL servo as soon as the battery was connected, no longer happens now that I swapped servos. So that was not a 3GX mediated event. There must have been something wrong with that servo from the start.
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Old 08-24-2016, 06:59 AM   #19 (permalink)
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I started doing flips with my T-rex 150 then moved to the 250. The first one felt like I killed the heli. While upside down with full negative collective it sounded as if the engine totally bogged down and lost power. I was able to save it because the heli was pretty high in the air.

Turns out that when I installed the new servo, I totally re-did the setup, including throttle curve. To do that I set idle up throttle curve on the transmitter from 0-100 linear. So, I forgot to set it back; no wonder it behaved that way.

I fixed the throttle curve, now it flips fine.
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Old 09-02-2016, 05:21 AM   #20 (permalink)
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Maybe more ESC problems with the RCE-BL15X. It has gone back to cutting out before the battery is finished.

I was looking for a battery indicator to mount on the heli as I thought I kept on putting spent packs in as it would fly a short period and lose power.

I checked one of those packs and it was 3.9v per cell. So not done yet. Motor not hot and esc normal warmth.

I got some new Turnigy 850mA packs yesterday and noticed they have half the resistance. From 7 to 9 vs around 20 for the Align packs.

The thought being the Align packs are sagging voltage down below the cutoff due to pack resistance limiting the current it can deliver near the end of the pack in idle up.

A few hovers in idle-up before night with the new Turingy packs and no problems all the way down to 3.7v end voltage.

My thought as of now is to set the RCE-BL15X cutoff voltage lower (it is currently set to 'high') and keep using the Align packs in addition to the new Turingy packs.
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