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


View Poll Results: What is the weight of your 250?
less than 320g 56 17.72%
320g to 340g 103 32.59%
340g to 360g 92 29.11%
More than 360g 67 21.20%
Multiple Choice Poll. Voters: 316. You may not vote on this poll

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Old 06-23-2016, 04:52 PM   #221 (permalink)
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You can actually shut off the over-current detection through the CastleLink software. In that case it will put out current until the switches burn out. You wouldn't know it until the ESC quits working permanently. Still I believe in having some head room. I'd rather take the weight penalty and provide some margin to be assured things will stay cool. It's also better for efficiency. I get pretty good flight times with the motor and ESC I'm using even though it adds 15 or 20g.

For example the motor I'm using has about 30mΩ resistance compared to 75mΩ for the stock motor. At 20A that's 30W wasted in copper loss for the Align motor versus 12W wasted for the 4000Kv motor I'm using. There's also the difference in heating which further adds to the disparity in resistance. All in all it's enough of a difference to have a pretty noticable impact on flight time. The same is true for the ESC, the Talon 25 has lower resistance than the Talon 15, but not to the same degree as the motors.

Another limitation comes with the Kv of the motor. The best you can do is about 90% nominal voltage times Kv. On 3S the stock 3600Kv motor even with a 16T pinion is not going be able to put out more than about 4800 rpm head speed and that will fall off as the battery discharges and voltage gets lower. The only way to increase speed after that is to increase Kv with a motor rewind or use a higher voltage battery. Anyone who is saying you can get 5500 rpm head speed with the stock motor on 3S is either full or it or has found a way to defy the laws of physics.

There's also the issue of gearing. Surely you could go even higher than 16T to get a speed theoretically higher, but that just won't work. You get to a point where torque delivered to the rotor is not adequate to overcome drag created by increasing head speed. There's also the electrical issue of increasing currents as torque demands increase. There's a point of no return where current keeps going up without any increase in torque. As it is the stock gearing takes it to the limit at 8:1. With the bigger, higher torque motor I could probably run 7.5:1, but I won't go that tall. The torque for it really isn't there even with a bigger motor. Running that tall ratio takes a bite out of efficiency since you get to where current goes up with less increase in torque.

Last edited by CraigHB; 06-23-2016 at 06:20 PM..
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Old 06-23-2016, 07:28 PM   #222 (permalink)
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I have a 14T pinion. You know of a higher Kv motor with a 2.5 shaft?
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Old 06-24-2016, 12:02 PM   #223 (permalink)
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I don't have anything to recommend other than motor I'm using. Motors and pinions for the 250 are hard to find. The shaft sizes are not common and the 0.4 mod pinions are not common. The motor I'm using actually has a 2.3mm shaft and I was able to find a 0.4 mod 15T pinion for it. I have pinions smaller and larger for that motor, but as I said I would not run any taller than the stock ratio. Though for really high head speeds you have to go taller to keep motor rpm in the correct range.

It's important for efficiency to run motor rpms 70 to 90% of nominal voltage times Kv. You also want the motor to spin 30k to 40k rpm, lower for bigger motors higher for smaller motors. If motor rpm is too low efficiency may suffer, if motor rpm is too high bearings can wear quickly and vibration may be excessive.

It's not always easy to find a motor with ideal Kv you need for the speed you want to run. About the only way to get things perfect is to find a motor that's right in terms of mechanical fit and rewind it yourself for the Kv you want. I actually rewound the motor I'm running. It was originally 3400 Kv and I rewound it to 4000 Kv.

I just remembered, I did see a 2.5mm shaft motor with higher Kv that might work, though it might be too wide, this one; http://www.scorpionsystem.com/catalo...HK-2206-3900KV
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Old 06-24-2016, 12:29 PM   #224 (permalink)
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The 2206 was designed for the 250, it would be perfect. But, it's really expensive, so I haven't bought one.
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Old 06-24-2016, 05:17 PM   #225 (permalink)
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The scorpion is rated:
Max Continuous Current14 Amps
Max Continuous Power150 Watts

The align is rated:
Max Continuous Current: 16/24A (5 sec.)
Max Output Power: 170/250W (5 sec.)

The align motor is more powerful. But, I do use the pinion pack.
http://www.scorpionsystem.com/catalo...ar_1/04pinion/

which has a 14t, 15t and 16t mod .4
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Old 06-25-2016, 02:27 AM   #226 (permalink)
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You can't always compare manufacturer ratings since they don't always use the same standards. I'd say the Align motor may or may not be more powerful, you'd have to bench test them next to each other to get a reliable comparison. The Scorpion motor does have higher Kv which will provide an increase in head speed 400 to 450 rpm depending on gearing. Also motor power is a function of Kv. Higher Kv increases current demand and thereby power.

Stator size is usually a good gauge for torque output of a motor. In this case it's 22mm x 6mm for the Scorpion motor versus 19mm x 8mm for the Align motor. In terms of volume they're almost identical.

I just checked on my 250 since it's sitting next to me on my desk right now.The width of the frame is barely over 28mm so it would be a tight fit. There's a chance it may not clear. Possibly a little filing on the frame cutouts might be required.
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Old 06-25-2016, 11:42 AM   #227 (permalink)
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This is Scorpion motor.

All I'm saying is, there's no way you could do this with the Align 250 motor.
Super Insane T-Rex 250 with 5500 RPM Headspeed (3 min 3 sec)
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Old 06-25-2016, 08:04 PM   #228 (permalink)
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Finally got a nice calm day and flew the 250 through all its packs. First real test with the Lynx servos. No issues, the heli actually feels better. Had to turn gains up a tad, but after I got it adjusted it feels really nice, tighter more precise.

That was 36g of unneeded weight I got rid of going with the Lynx servos. Plus I lost 10g by ditching the case for the BeastX and another 8g with the plastic canopy. So it's a ~lot~ faster after losing that dead weight. I actually like the plastic canopy better, it's easier to get on and off. That fiberglass canopy was kind of a bear.
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Old 06-25-2016, 08:42 PM   #229 (permalink)
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Awesome, I'm glad you got to test I was thinking of doing the same thing with the lynx servos, but decided not to.

I've ditched the canopy all together for the time being but I have a plastic full fuse being made up for it special. I still don't quite have mine dialed in but it's getting close. I like the lightweight build it crashes like a feather. I've even had a couple emergency auto's that came out unscathed with it and one that broke a landing gear strut.
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Old 06-26-2016, 01:46 AM   #230 (permalink)
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I had a hard landing out flying today, thought I might have cracked the landing gear but it didn't. Probably would have at its previous weight.

Oh BTW I wanted to see if flight time improved so I ran one pack all the way to ESC low voltage cutoff at 3.4V per cell. It ran for 8 minutes 40 seconds flying mild sport. That's up almost a minute from what it was before. I normally run the timer down from 6 minutes and that now leaves the battery about 75% discharged. I don't actually like to fly much more than six minutes at a time anyway or I get tired and make mistakes. I think that's pretty good run time for an 850 mAh battery. I think I can call that an efficient setup.
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Old 09-14-2016, 04:24 PM   #231 (permalink)
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Quote:
Originally Posted by Number View Post
This is Scorpion motor.

All I'm saying is, there's no way you could do this with the Align 250 motor.
Super Insane T-Rex 250 with 5500 RPM Headspeed - YouTube
that video look like i has beeen sped up.
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Old 09-14-2016, 08:35 PM   #232 (permalink)
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Quote:
Originally Posted by bazsound View Post
that video look like i has beeen sped up.
Doesn't it? Thing is my 250 with the same motor and setup pretty much flies like that too. I just don't get how he does tick tocks. Mines just flops and drops. Probably a setup issue.
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Old 09-14-2016, 10:12 PM   #233 (permalink)
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Definitely not sped up. The sounds are totally normal. I was able to do fast tic tocs with my 250 all day, just look for the thread "my 250 build" and the videos in it. I loved that heli, even with the Align motor.
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Old 09-15-2016, 08:44 AM   #234 (permalink)
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Nah, not sped up, if he flew slower than that he wouldn't crash so much :-D

A lightened 250 has plenty of power to do tic-tocks, but you've got to be super precise with your timing. Mine have never been anywhere near as accurate as Keith's.
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Old 12-13-2016, 12:40 AM   #235 (permalink)
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Bearing in mind this is using a super cheap not so great mechanical scale really only meant for weighting flour suger in small amouints that also doesnt like to centre very well.

After measuring multiple times, mines tlooke to be around 340g.

Im using turnigy tgy-213c servos for cyclic and turnigy tgy-306hv on the tail, Nice looking servos perform well but are heavy, cyclics are 16g each and the tail is 23g. If i moved to the 7.6g servos id save 40g right away.

Im also using the FG copterx canopy so theres some more weight i can save.

Im using a mini bar with no reciever, instead a lemon rx sat which is 3g so i saved some weight there (had an ornange rx before which was 12g)
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Old 03-30-2017, 07:45 PM   #236 (permalink)
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what do you guys think is too heavy for the 250 ?
seems like a lot of them are about 300-350gr
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Old 03-31-2017, 12:25 AM   #237 (permalink)
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It depends, some people are happy with how it flies at 340g. In the main for 3D flying, under 310g seems to work well. I got mine down to 280g and for me it always flew best in that 280g-290g range.
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Old 03-31-2017, 07:06 AM   #238 (permalink)
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Flies the best around 290g. At 270g it flies better but that usually means you're using plastic geared servos which isn't the best. I dont fly canopies on 250s.
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Old 03-31-2017, 09:17 AM   #239 (permalink)
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I guess thats why i struggle to anything that resembles a tic toc. It just dooesnt stop suddenly like i see the videos unless you really jamn the collective, but then it shakes and usually falls out the sky.

mines is i guess 350g now iwht the painted canopy....

i might try putting a 16 tooth pinion on it to increase the headspeed.
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Old 04-04-2017, 03:15 AM   #240 (permalink)
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Quote:
Originally Posted by CraigHB View Post
Finally got a nice calm day and flew the 250 through all its packs. First real test with the Lynx servos. No issues, the heli actually feels better. Had to turn gains up a tad, but after I got it adjusted it feels really nice, tighter more precise.

That was 36g of unneeded weight I got rid of going with the Lynx servos. Plus I lost 10g by ditching the case for the BeastX and another 8g with the plastic canopy. So it's a ~lot~ faster after losing that dead weight. I actually like the plastic canopy better, it's easier to get on and off. That fiberglass canopy was kind of a bear.
what lynx servos???? i think 1 of my 213c servos has taken a bit of damage, its got a bit more slop than the others and feels a little sitffer to turn than the others.
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