Odd Gyro Behaviour

[Steve]

Please can someone explain this.

I decked my Sceadu a few weeks ago and have only got it back in the air today, and all is fine except the gyro gain (CSM 560). It's the same servo and the same gyro as I have been using in this heli for a long time.

The gyro gain setting in all flight modes used to be 87% and it worked a treat.

As of today I've had to reduse the gain to 40%, 37% and 33% in the 3 flight modes (normal, idle up and v-curve) that I use.

Why the sudden huge difference in the gain values?

During the repairs, I made a few changes to the heli to make it more responsive as follows;

1. changed the 3 blade control servos to new digitals over the old standard ball raced versions.
2. removed the brass weights out of the paddles.
3. changed the position of the push rod balls on the see-saw assembly from the 'steady' to 'aerobatic' positions.

By the time I'd finished with it today, it was flying fine, but I'm struggling to understand why any of the above alterations have or have not affected the gyro gain so dramatically. Something odd has happened?

All other repairs are as per the standard kit.

Any ideas?

[jimbob]

I can only imagine that a reduction in possible gain is the result of less coupling or greater interference between the tail and the gyro.

This would normally be due to slop or vibration or similar.

Could be the after effects of the crash - are the gyro and servo both ok?
What parts remain not replaced after the crash?

I think that any extra vibration or similar will affect gyro gain as it will be harder for the gyro to accurately control the tail.

[Ade_Law]

normally gain reduction on CSM gyros means there is some vibration in the model.

If you didnt replace the mainshaft/spindle/tail shaft then check those.

Also check your mainshaft bearings, tail shaft bearings and that the flybar is centred.

Ade

[Steve]

Thanks

All shafts were replaced except the tail, and all the shaft bearings were replaced about 6 weeks ago.

The gyro and servo seem ok after the crash, but how can you be absolutely sure?

The new main shaft is a Quick UK one, and is (to be absolutely honest) a pile of c**p! It came out of the packet with a really rough finish, and was very tight when trying to get the swash plate and other bits onto it - a touch over-size on diameter I think.

Will try a new tail shaft and a proper Hirobo main shaft - they are much more highly polished than the Quick UK one.

[Ade_Law]

QUK stuff is normally very good.

i used them in my sceadu when I had it and raptors etc maybe you just got a dodgy one? Give quickuk a ring and see what they have to say.

did you check the mainshaft bearings after the crash?

Ade

[Steve]

I agree, Quick UK stuff is usually pretty good, so I'm a bit disapointed this time.

I use Inwood models for a lot of my modelling stuff as I drive right past them on my to and from the office, and I popped in today to get a new Hirobo main shaft and tail shaft. They had a load of Quick UK Sceadu main shafts on the rack, which I pointed out to them were in fact Shuttle shafts - only 8mm diameter (or there abouts - I used to have a Scuttle and the shaft is definately not 10mm)

The packs are wrongly labelled from Quick UK, and hanging right next to the Shuttle shafts. Funily enough, the shafts in both the Shuttle and Sceadu packs are the same!

I didn't check the bearings but I do have a few spare ones. I'll check them over when I replace the main shaft.

Something else occurred to me today - the gyro is now stuck down with non-CSM gyro tape which I forgot about. I've got a roll of 4mm gyro tape from Quick UK (funily enough) which I've used in the repair, having run out of the proper CSM stuff. This is the first time I've not used the CSM pads. I'll get some of the proper stuff at Sandown on Saturday.

Could this be significant in the vibration transmition stakes?

Cheers

[Ade_Law]

CSMs are well known for being sensitive to vibration so its a pretty safe bet!

Ade

[Steve]

Sorted it - the CSM gyro mounting tape did the trick.

Cheap fix - makes a change!!!

:P