DS420 Faliure

[Sndflea]

I had just taken off and was hovering fine when I lost the tail. Landed fine. Seems like the Align DS420 is dead. I probably don't have 50 flights on it. All of my electronics are stock. Is it fairly typical that a servo would fail this soon? I am replacing with a MKS DS95-i.

[JoeW]

Sometimes... I find if it's going to fail out of the box, it will usually do it within the first 20 flights or so. If it survives past that you'll be fine.

I've had about 1 in 4 420s fail within the first dozen flights... the others were fine for hundreds of flights.

Even a light crash though can bump the servo case just right so the servo starts binding a bit and it will fry itself within a few flights.

You won't be disapointed with the DS95i though.

The DS420 is fine for light flying, but you'll want something better if you're doing more than loops, rolls and maybe stall turns.

I heard Bert Kammerer recommend the Futaba 9257 or JR 3500g... they're bigger and heavier but he seems to think it's a fair trade.

I haven't used that Futaba or JR but prefer the DS95i, it's not that much more money than the Futaba or JR and it's the same footprint as the DS420 and it's the undisputed champion of 250 tail servos

[litehawkdown]

Originally Posted by Sndflea

I had just taken off and was hovering fine when I lost the tail. Landed fine. Seems like the Align DS420 is dead. I probably don't have 50 flights on it. All of my electronics are stock. Is it fairly typical that a servo would fail this soon? I am replacing with a MKS DS95-i.

Not sure. Were your gyro settings right to begin with? I noticed a warning that you can fry a servo if you set it up wrong.

[Sndflea]

I've been flying with my Gyro settings for quite a few flights so I don't believe that was the culprit - but who knows. I was just surprised that it failed so soon.

[litehawkdown]

Originally Posted by Sndflea

I've been flying with my Gyro settings for quite a few flights so I don't believe that was the culprit - but who knows. I was just surprised that it failed so soon.

Might want to check it over to make sure.

[upankatz]

i've blown my last 3 tail servos all within about 5 mins of flight time each, after a couple of minutes flying I noticed the tail servo getting real hot...These were all different name brands, one was the 420, the rest were cheapies....I noticed my gyro plate was sitting in the frame a little loose so it was vibrating quite abit....I fixed the vibrating, and now tail servo seems okay....Is it possible for the gyro vibrating to cause the tail servo to overwork itself into self destruction?

[Sndflea]

I don't believe this to be the case but I'll check when I install the new servo. I had a minor crash / boom strike on the flight before the failure so it does bear looking at.

[ahahn]

Originally Posted by upankatz

i've blown my last 3 tail servos all within about 5 mins of flight time each, after a couple of minutes flying I noticed the tail servo getting real hot...These were all different name brands, one was the 420, the rest were cheapies....I noticed my gyro plate was sitting in the frame a little loose so it was vibrating quite abit....I fixed the vibrating, and now tail servo seems okay....Is it possible for the gyro vibrating to cause the tail servo to overwork itself into self destruction?

You need to check if the tail control system is binding under load. I assume you have setup the gyro servo update rate correctly.

3 blown tail servos aren't normal.

[litehawkdown]

If the servo limits are not correctly set I could see that killing a servo too.

[JoeW]

Possibly... One direction will cause it to bind... The other bends the crap out of the flimsy pushrod

I'd be more inclined to blame the crash. Don't let the metal case fool you. They're easy to pinch enough that it causes binding internally. They go belly up within a few flights after that.

[Sndflea]

OK - got the 95i today (great service from A Main Hobbies). Lead on the Align was black / red / white. The 95i is brown / red / orange. Which way does it get plugged in? i.e. does the 95i brown wire equate to the Align black wire or white wire?

[JoeW]

Brown=black=negative
Orange=white=signal

Make sure you change your gyro to 760uS mode before you plug it in.

[Sndflea]

Will do - thanks

[GeorgiaBoy]

The Align 420 case is put together with two screws instead of the standard four making it easier to rack so even a slight offset on the boom mount could cause bind. And running your gyro on digital will constantly feed power to the servo and cause it to get hot. If it cooks another servo of any brand maybe consider setting gyro to analog and see if you can live with it. Servo replacement can get expensive after a short run.

[ahahn]

Originally Posted by GeorgiaBoy

The Align 420 case is put together with two screws instead of the standard four making it easier to rack so even a slight offset on the boom mount could cause bind. And running your gyro on digital will constantly feed power to the servo and cause it to get hot. If it cooks another servo of any brand maybe consider setting gyro to analog and see if you can live with it. Servo replacement can get expensive after a short run.

Most of us fly the 420 in digital mode with no issue.

Update rates are just that. If the gyro detects motion, then it can tell the servo to move to correct it. A faster rate is just that. A properly setup heli isn't going to cause any issue.

On the other hand, if you have a severe vibration in the heli, it is possible that the gyro interprets that as a motion in constant need of correction. In that case it is indeed possible that the gyro overworks the servo which can cause it to overheat. Going to analog rates in that case may actually help the servo, but it is masking the problem.

Also binding in the tail can really overheat a servo. Testing for binding when the tail isn't spinning may not catch the issues with bearings going south, or other dynamic problems (see the whole Chinese weight threads). In this case, going analog won't help.

By the way, the gyro isn't sending power to the servo. Power is supplied by the middle servo lead (and the return ground lead). It is always there "DC". It is the signal line that is being updated at the higher digital rate. If the update pulse width is the same as the previous pulse width, the servo does nothing, if it is already at the commanded position.