This copy of a message I sent to another Micro Spirit owner explains the tail wag problem I had this morning. The HK 250 has an original red Spirit gyro.


"Finished my Trex 250 Pro DFC build this morning. Set failsafe and did final checks. It's a little windy but decided to do first flight anyway. Got it into hover and I could tell the tail was not solid. I already have a Hobby King HK 250 and I've always had a problem with a little tail wag in a crosswind with that one. It's got the old type tail slider with just one attach point on the slider. Thus I bought the Trex 250 Pro as it is shaft drive tail and has the newer style tail slider all the bigger Trex helis have.

So I'm hovering in the wind for a couple minutes and the tail is waging a bit so I decide to land and change the tail gain when the tail wag becomes uncontrollable and I end up crash landing on the concrete driveway. Yeah; it was bad.

This was a beautiful build. Did the best I've ever done. Hours of time; hours. I was using the same tail gain settings; actually lower gain settings that I've used with the HK 250 for hours of flying. I've flown the HK 250 in winds of 15 gusting to 23 successfully without too much difficulty. This is a huge disappointment. The most expensive loss I've ever had.

When I was building I noticed the tail torque tube had some warp in it. Thought about getting a new one. Tried it anyway and when I did the vibration analysis with Spirit it showed some vibration but not an excessive amount. Shouldn't have been a problem. At this point I don't know if it was the Micro Spirit acting differently than a normal Spirit or what.

I do know that I shouldn't have been so confident in the equipment and should have waited for calmer winds and taken the time to drive over to the grass field."

Hello,

it is very sad you have had bad experience, but I am little bit confused what is the link between another pilot and your helicopter?

First you can send me what servos you are using and also attach your settings.
The flight charcteristics will be not same as with normal Spirit, but more similar to Spirit Pro. So it will require some modifications to fit your model.

Unfortunately without any details I can't help you more. Please send more details, I am sure we can fix the problem perfectly.
Also your HK250 could fly with no wag.

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Spirit System developer

Thanks for the response Tomas, I'm much better now that I'm over the shock of a failure. The other Micro Spirit owner is having trouble too and we've been having a conversation so instead of typing the whole thing over I just copied and pasted.

Anyway, I now remember reading that you said the tail gain in the Spirit Pro was a little more aggressive than the original Spirit. I was warned. I have ordered repair parts as it wasn't as much damage as I first thought (still bad though). I thought it was going to be a new kit.

The cyclic servos are the Align DS450 and thankfully they are still good; no damage. The tail servo is the Align DS426M. All included with the 250 Pro DFC kit. The tail gain in the Micro Spirit I was using was 38. No change to the Rudder Common Gain at 1.00.

Along with repair parts I've ordered an MkS DS95-i tail servo as it has an online reputation of curing tail wag problems. I've had tail wag problems in the past with Align tail servos. Brand new ones.

If you could give me a good starting tail gain to start at that would be helpful. I don't want to start so low that I loose control of the tail but not so high that I get a wag again.

In the past with a Trex 450 and 3GX gyro I've had the tail gain low enough the helicopter did un-commanded pirouettes. I'd like to avoid that if possible.

Very important thing for T-Rex 250 is to get servo arm as small as possible so that ball linkage is very close.
This is the main reason for so low tail gain.

So by changing this it is very likely that the tail will perform much better.

Well, MKS DS95i is probably the best servo you can get for your 250 - 450 so it must be better whatever will happen. But unfortunately tail wag issues are mainly caused by something wrong in the mechanics. If mechanics is super smooth, the tail simply must hold and will be very solid even with a slower servo. So by taking much better servo you may overcome the mechanical issues, but it is usually possible to do so in a cheaper way.
But for sure you will not regret money as the servo is really perfect.

Just remember to change neutral impulse to 760us and 333 - 560Hz. Rudder Delay at 2 will be fine.
Pirouette Consistency for this helicopter can be fine at 140 - 150.

But again, very short servo arm is necessary to make it work well.

After changing servo and/or servo arm don't forget to update Rudder end-points too.

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Spirit System developer

Hi Tomas,

Ball on servo arm is as close to center pivot as it can be; that is factory setting. Mechanics are super smooth; that is why I bought this kit; it has the newer improved and more expensive slider assembly like the bigger Trex models. End points were almost correct before I adjusted them. Only had to move them out a small amount. Thanks for the reminder on servo timing; I will need to change that before connecting the new servo; good reminder, can't forget. 760 / 560. As I mentioned in first post; torque tube had some warp in it. For sure that didn't help. I've read where vibration in the tail will mess up the gyro. Spirit analyzer said OK though. Ordered new torque tube anyway (little late now).

My current Pirouette Consistency is default; 160 I think. Did that cause wag?

Rudder delay is currently 7 I think. That should reduce wag as opposed to a smaller number correct? Or did it make it worse? DS426M servo is supposed to be pretty fast.

What rudder gain setting should I start at and will I end up at probably (approximate)? I was using 38 and 1.00 common.

Hi Tomas,

What should the tail gain be with a 250 and the Micro Spirit?
20?
10?
5?
How low is low enough to start without being too low?

Can you help me with this one please Tomas?

Well, it should be around at least 40% for any heli. If it is lower, than the mechanical gain is very high.
Isn't it possible to get a shorter servo arm?

If no, then I recommend to decrease Pirouette Consistency to 140. Then it should be possible to increase the Gyro Gain with no oscillation.

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Spirit System developer

What exactly does pirouette consistency do? If it is too high can it cause tail wag?

Yes, it can cause tail wag - in a bigger angle but slower frequency.
So it is better to increase Gyro Gain as high as possible first (but with the lowest Pirouette Consistency value).
Then if the rudder is not holding well in a demanding maneuvers, but you can see that tail is stable (e.g. in hovering) you should increase the Pirouette Consistency value until it will hold also in such maneuvers.

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Spirit System developer