Advice please. 450X spins when I shut down

[Hummingbird]

Silly question coming up - what is OWB?

[tomatwalden]

Advice please. 450X spins when I shut down

One way bearing.

Do the blades spin freely when the motor isn't running?

[Hummingbird]

Yes they do. It might be something to do with the tail blade pitch at center. I will check it. The OWB is working correctly as far as I can tell

[Hummingbird]

I have moved the tail servo back very slightly on the boom. This seemed to help but then the tail was drifting slightly so I increased the gyro gain. Does this make sense or give any clues? It is much better but still turns to the right when I spool down although no where near as much. But I can't seem to find the "sweet spot". A couple of times on take off it swung round to the left but I landed safe. So then I moved the servo forward again. Seems something to do with center??

[tomatwalden]

Are you sure it's in heading hold mode? Even with the servo not centred, I would expect the gyro to keep the heli pointing straight - just have limited leverage in one direction. The tail drifting on take off and landing sounds like you've got it in rate mode ...

[Hummingbird]

Another thing to check! It's in HH mode as far as the DX8 is concerned, but I admit I haven't checked anything on the 7200BX unit. I assume the default is HH, but I'll have a look. Tomorrow I am flying it proper at our club so will be able to check it over properly. So far these tests have been just hovering in the garden.
BTW, the tail was working fine on the last attempt, turning fast and positive in both directions, and stopping accurately.

[Guest]

For the tail to spin round on spool up or shut down normally means your tail blades are not set at zero pitch in their 'centre' position......

Make sure you are in Rate Mode with a purple LED in the AR7200, then fold your tail blades in so that the end are towards each other, at zero pitch they should line up. If they need adjusting, adjust the length of the pitch rod, easier than moving the servo. Sometimes it helps to have a small amount of pitch on the tail blades, try winding the tail control ball links in by one complete turn to give an initial bit of counter-pitch to the tail, just gives some instant hold to the tail on spool-up whilst the AR7200 (or any gyro) gets a grip on the position! Make sure when you fly that you are in HH mode, or the LED on the AR7200 is blue.....

Failing that, check all of the bearings in the main shaft and tail assembly, the stock bearings are cheap Chinese ones and often develop 'tight spots' which sometimes only cause binding at certain speeds, which would explain why it sometimes only occurs at spool-down, as the loadings on the bearings change when the motor stops driving the geartrain......

[Guest]

PS - I have a 450X and a DX8, my gyro gain is +55 for HH, -55 for Rate

[Hummingbird]

Thanks for that, I'm ashamed to say that I haven't yet ventured into the depths of the 7200BX controller. Everything is at the defaults. I will have a look at the tail pitch in Rate mode and see where it's at. I suspect it is something to do with the pitch at center. But after tweaking the position of the tail servo (moved slightly back to the tail) it has improved the problem, although it's still there. Anyway, I will give it a better test tomorrow and report back. Incidentally my gain in my DX8 is +65.

A final thought, would it have something to do with Parameter Menu F (torque precomp)? The default is "off". Might play with that too.

Thanks for now.

[Hummingbird]

I just put the heli in Rate mode and noticed that the tail was way off center. I've now got the tail pitch dead center and will fly tomorrow and report back.

[tomatwalden]

.... Incidentally my gain in my DX8 is +65.

Thanks for now.

Seems quite high - but just checked mine in my DX8 and it's at +54 which surprised me. Can't recall what the default is ...

[Hummingbird]

You're right it is high. Last night I checked my tail pitch which was way off center. This is now corrected, as is the tail servo throw and my gyro is now 54.
I tested it again this morning and I think the tail spin problem has gone.
Going to fly it now for the first time proper so will report back tonight. Cheers

[Hummingbird]

450X update: well guys, the final word on the 450x. I solved the tail spin by correcting the position of the tail servo and making zero pitch on the tail. Went to take it for a spin today and it seems fine with my limited experience. I notice how much more stable FBL helis are. This thing sits there solid waiting for you to tell it to do something. In comparison, my flybarred T Rex 550 drifts if you leave it, although it is perfectly stable. So there you are, my 450X tail spin on shut down was apparently due to the tail pitch not being set up properly. Thanks for your help everyone. I have another question but will start a new thread!