Tail Wag Cures

[Harbormaster]

Originally Posted by Gregorio0428

I hear about this all the time with the 250 mine flys awesome no ways at all even with a 3gx I also put 3 Tt bearings in the boom

That's great! I hope it lasts--250 tail stability can be fickle, and one crash can change things.

I don't think TT bearings have much to do with tail wag (certainly not for those of us with belt drives ).

[skunkworx]

I hate to disagree on any of your findings because I think they have a lot of merit and if it works well for you then there's nothing wrong with these methods. However;

Originally Posted by mba83

1) Make sure there is no binding AT ALL in the tail. Including links on the pushrod (size them by pinching them with pliers slightly), the control arm, pitch slider, grip links, etc. And try to eliminate any slop you can find.

4) Install a DS76t servo. For many 250s, the DS76t is sufficient, but the torque on it isn't great. To decrease the torque needed to move the tail grips, install the chinese weights. Alternatively, get a DS95i servo, but keep in mind that's it will add undesired weight to your heli.

Sizing your links should never be done by squeezing the links. The reason for this is it distorts the shape of the link giving you uneven contact around the eye of the link which can actually give you more binding under load. The best method for sizing links on the 250 IMO has been using a spare ball, scoring it lightly with an Xacto knife, add some grease/oil, and then spin the ball in the link until they are close to falling under their own weight on a non-scored ball. I actually used an electric drill to speed this up, but you have to exercise some caution when using that method. I repeated the process on all the links for the whole bird and it went form nearly uncontrollable on the maiden flight to ripping it up just like my 450!

As a caveat though, there are two different balls used on a 250 and they are ever so slightly different in size (balls with the center screw and the solid types). I personally found the solid ones to break off very easily and promptly threw the whole bag in the trash. I lost two swash plates on account of the crappy metal in them, but that may have been the batch I got. If they're not falling out, don't go out of your way to remove them, and if it's possible, I recommend swapping out to the center tapped balls.

Lastly, I can definitely agree that a better tail servo (DS95i, OMG H1) would be a very worthwhile 'upgrade' and I don't feel that the weight consequence is enough to make or break any model. Mine is closer to 400g all up weight and it's a freakin' rocket! 10-14g of extra weight isn't a massive amount and the side benefit is that you don't have to be as critical on the tail setup because the servo will have the torque to push the tail around with ease (plus, the reliability is a lot better).

[ryem3]

That 95i servo overcomes a lot of ills. My tail was perfect, but it still would get massive wags. The servo solved the problem. Dozens of flights with no wag. If you want a 250 to fly, you simply need to buy one.

[skunkworx]

The OMG H1 is a really good alternative to the 95i, IMO. Maybe not as quick (.005 seconds slower according to specs) but it has more torque. I put one on my 450 and 250 and so far they are doing really, really well. Actually, on my 450 the OMG is doing better than the 95i did, so I'm pretty well convinced that they're the same if not better.

[Harbormaster]

Originally Posted by skunkworx

The OMG H1 is a really good alternative to the 95i, IMO.

Duh, "H1"?

[skunkworx]

It's their short name for their micro MR-CF30S cyclic and MR-CF20Q tail servo series

[Harbormaster]

Originally Posted by skunkworx

It's their short name for their micro MR-CF30S cyclic and MR-CF20Q tail servo series

Googling...

http://www.rcomg.net/index.php?act=pShow&id=62 The "Only Manufacture Golden" Chinese-lish slogan doesn't inspire confidence, but the photos of the metal gears and the MKS-clone color scheme look good, as do the specs, especially at 8.4 volts! And the skunkworx endorsement, of course.

[skunkworx]

I admit, it was a little wierd seeing the name in either form, but they're very nice quality and solid as the MKS where the KST are open on the sides (aka- dirt is going to get in there).

I ended up having to put a piece of heat shrink over the input wires and sand the case lid a bit because they don't have a rubber grommet. I know some people complain about having to mess with them from the get-go since it's a 'premium' product, but it's easy to fix and is probably better than a rubber grommet over the long-haul anyway. That's really the only downside I can see with them (it's maybe a couple pennies worth of heat shrink and about 3-5 minutes of your time). I'm not sure if they're going to fix this in future models, but it's not going to stop me from buying more of them (I already own 10 )

I'll see if I can get at least as short cllip of them in flight. I haven't been able to fly the 250 much because the head block was all bent up, but I have the DFC setup fixed and almost ready to fly. Now just waiting on the weather.

[ktm250]

I finally got rid of my tail wag. I was having a hard time justifying 85 for a 95i servo. So I installed a Kst ds215mg and the wag is gone. what a joy it is to fly now.

[Harbormaster]

Originally Posted by ktm250

I finally got rid of my tail wag. I was having a hard time justifying 85 for a 95i servo. So I installed a Kst ds215mg and the wag is gone. what a joy it is to fly now.

Congratulations! Just out of curiosity, how much did that servo cost?

[daveapplemotors]

Blade DS76t from a Blade 180CX is a good tail servo ($22 at my LHS). No wags on my 250s.

[ktm250]

Originally Posted by Harbormaster

Congratulations! Just out of curiosity, how much did that servo cost?

You can get them from 25 to 30 bucks.

[skunkworx]

Aloft hobbies carries the KST for about $25-$29 I think? I felt that it's a bit too slow fo the 250 tail, but it might be enough if you're not really pushing it hard or if you don't need the gain up high. The main reason is I think the BEC runs at only 5.5V which means you'd be getting as low as .08-.10sec+ transit speeds with a 215, so not quite enough for good tail control. The 95i is rated at under .047sec on 4.8V, so that's a really good target speed. The H1 is a teensy bit slower at .050sec on 6V, but makes a little more torque so they seem to balance out. I flew both a lot in my 250 before the winter hit and I'd say they are nearly identical in flight.


I plan on giving the 215s another go when I get all my 250s up and running again. I've always wanted to see if it was just a setup problem or if the servos really made the difference, but so far it's leaning toward the former of the two.

[ktm250]

The 215 even at 4.8v has a speed of .07 and a torque 2.5 kg if you can run them at 6v it's .06 and 3.1 kg. I believe the torque is a bigger factor in fixing the wag then the speed.

[daveapplemotors]

I have had absolutely no tail wag on my HK250. There is a short video showing how atrociously loose my tail components are. But it is rock solid in the air and flies fine. . https://www.dropbox.com/sh/pki8xndip...w=CAM01474.mp4

If you can see another video there it will show the solid tail behaviour.

Right now using an Open Pilot Copter Control board and ELFDS76t servo..

[Harbormaster]

Originally Posted by daveapplemotors

Blade DS76t from a Blade 180CX is a good tail servo ($22 at my LHS). No wags on my 250s.

Glad it's working for you, but a DS76 is not even in the same galaxy as a DS95i. Little, low-torque plastic thingy. It sure is way way lighter though! If one would work for me, I'd use it!

[myxiplx]

The DS76t can work, it's doing a great job on my main 250. I get the impression it sometimes needs some tinkering or the right combination of parts to do it, whereas the DS95i just has the brute force and speed to work no matter what.

[Harbormaster]

Originally Posted by myxiplx

The DS76t can work, it's doing a great job on my main 250. I get the impression it sometimes needs some tinkering or the right combination of parts to do it, whereas the DS95i just has the brute force and speed to work no matter what.

Exactly. The DS76 is light and cheap and a great choice if it will do the job, but if you have demons in your tail that you can't otherwise exorcise, the expensive, heavy, brute force DS95i solution can save tons of time and tinkering, and your sanity.

[daveapplemotors]

If weight and $ didn't matter then I would concur. I used a $22 7 gram servo. I resisted DS95 $95 and what 20 grams?

For 13 grams difference I could tinker if it came around. But other than installing dbl brgs and Chinese weights about 4 years ago I haven't done any. Except to bolt on a 7 gram servo. The tail worked fine with the 9 gram $20 HK servo that I removed and 2 grams was worth the tinkering.

[skunkworx]

I don't know how most people fly their 250s but I can't imagine you'd be able to feel 13 grams difference in weight. Especially not at the tradeoff that a bigger and servo provides. Granted, I don't think I'm an insane 3D pilot on mine, but I can hammer it around nearly as well as any of my other machines. Having a good tail servo makes a huge amount of difference to me, and even more important - no tinkering! They do their job so you can do yours.