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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 02-04-2010, 05:37 PM   #1 (permalink)
pos
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Default Some picture of my flybarless T-rex 250 project

Hi all

I just finished my flybarless T-rex 250. If other people have the same thoughts I therefor happily share my pictures.

I choosed to widen the frame instead of destroying it as I have seen that other people have done. Also... the new Mikado head upgrade is on.



The rest of the pictures are here...
http://www.incedo.eu/~sjoholmp/misc_...less-trex-250/

I have used two extra special screws (12 mm in lenght) as the the longest std screws were 10 mm. Also I put in a Microheli bottom plate to make it more stable as the frame to bottom plate fit wont be the same. The rest you can see in the pictures.


enjoy

Do I have to tell you it flies

/Per-Olov
Sweden
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Old 02-04-2010, 05:55 PM   #2 (permalink)
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Thanks for posting that - some really nice photography too!
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Old 02-04-2010, 07:11 PM   #3 (permalink)
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nice job!!! i should post some pics of my mini-v T-250........ i did the hack job on my frame but since i use the micro heli head and it comes with cnc braces, it doesn't look so bad. what did you do about the CoG??? i used a DS520 for a tail servo and had to add several OZ. of lead weight to the canopy to get a good Center of Gravity.....now im using the JR290 and i get a better CoG with-out adding any weight, but the DS520 was a much better tail servo....

Lando...
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Old 02-05-2010, 12:19 AM   #4 (permalink)
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I took a t-rex 500 main shaft and rolled the 250 on that. It seems the center of gravity is on the exactly correct spot under the main rotor shaft. I rolled the 250 back and forth and tried to be critical in my measurement... But even so, the CG i _perfect_. Probably I was lucky as there isn't so many ways to do the electronic placement on the heli. I thought the JR3500G should cause a CG that have moved backwards compared to the use of a DS420 , but it did not. The JR3500 is a small midsize servo. Note that the Fut 9257 and MKS 8910 which are also midsize is bigger than my 3500. I have a MKS 8910 on my T-rex 500. That midsize servo is bigger and heavier.

The batteries I use together with the tail servo and the electronic placement seems to be a very good combination. Mostly I use Outrage 3S860mAh 25C, but I use Flightmax as well. However, the CG was measured with the Outrage and I haven't checked it with the HobbyCity flightmax batteries.

/Per-Olov
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Old 02-05-2010, 12:44 PM   #5 (permalink)
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i just checked the weight of the different servo's and batteries that we used and the difference is very very small, so maybe its just the extra mods you did to your heli that help with your CoG...... the thing that i didn't like about using the heavier tail servo was that the piro's looked strange, as if the lateral weight was not evenly distributed (not sure how to explain)....

anyway all that matters is that it fly's good and your happy
as for me. well.....not happy just yet, maybe i will give the 3500G a try

Lando....
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Old 02-05-2010, 01:10 PM   #6 (permalink)
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Check what Bert Kammerer prefer as a tail servo on his 250...


http://www.bertrc.com/my-equipment
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Old 02-05-2010, 02:21 PM   #7 (permalink)
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Quote:
Originally Posted by THMA View Post
Check what Bert Kammerer prefer as a tail servo on his 250...


http://www.bertrc.com/my-equipment
he uses both the 3500G and DS520........lol......guess i will give the DS520 another chance
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E-flight Blade MCX & mSR
Ultra micro Sukhoi Su-26 and P-51 Mustang
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Old 02-05-2010, 02:54 PM   #8 (permalink)
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As an aside, as I was setting up my 250, I tried running the motor without the rotorhead or tailblades. It's quite impressive how much force it takes to move the tail pushrod by hand... I could understand for the first time why a big servo was required. Problem is, they look terrible.
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Old 02-05-2010, 03:37 PM   #9 (permalink)
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Search for Robin Renzetti (alias "heimjoint") on youtube and look at his videos measuring the force needed for full pitch on the tail on T-rex 250, 450 and 500. He is the person behind the Chinese weights that I have on my T-rex 500. Some servos used by many people are simply to weak compared to the heli size it's used on. VERY interesting videos.

However... I think there are smaller servos that can handle the 250 tail. But the 3500 is simply a killer servo compared to its "small" sized midsize servo (there are two sizes of midsize servos). I got a DS420 in my initial super combo. The heli flew ok with it. But I had _very_ little tail wag all the time that was impossible to get rid of. And people often say I am quite handy for being an electro engineer. Even so, this small wag was hard to get rid of. When I put a MKS 8910 on my T-rex 500 the JR3500G was moved to the T-rex 250. GOD LORD! what an improvement for the 250. I did nothing except exchanging the DS420 for the JR3500G. It was like the tail was nailed to a wall with the 3500 servo. It was so rock solid. Even a intermediate pilot will note this immediately.


/Per-Olov
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Old 02-05-2010, 06:27 PM   #10 (permalink)
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Quote:
Originally Posted by pos View Post
Search for Robin Renzetti (alias "heimjoint") on youtube and look at his videos measuring the force needed for full pitch on the tail on T-rex 250, 450 and 500. He is the person behind the Chinese weights that I have on my T-rex 500. Some servos used by many people are simply to weak compared to the heli size it's used on. VERY interesting videos.

However... I think there are smaller servos that can handle the 250 tail. But the 3500 is simply a killer servo compared to its "small" sized midsize servo (there are two sizes of midsize servos). I got a DS420 in my initial super combo. The heli flew ok with it. But I had _very_ little tail wag all the time that was impossible to get rid of. And people often say I am quite handy for being an electro engineer. Even so, this small wag was hard to get rid of. When I put a MKS 8910 on my T-rex 500 the JR3500G was moved to the T-rex 250. GOD LORD! what an improvement for the 250. I did nothing except exchanging the DS420 for the JR3500G. It was like the tail was nailed to a wall with the 3500 servo. It was so rock solid. Even a intermediate pilot will note this immediately.


/Per-Olov
There's a subforum in the 250 forum that pretty much only contains info on the HJ weights. I use them and the crushable spacers he sells, and I am able to use a DS290g servo with no issues. His video also shows how to find and eliminate binding in the tail by sanding certain links, bushings, etc. Even that made a great improvement!
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