GY401 setup on Trext450SE and DX7

[jiberjaber]

So I have rebuilt the Trex since it decided to take a liking to the pear tree in the garden. I took the time to strip it down a bit and re-build it back up, it's been a while since I last took an interest in setting the thing up from scratch (the pear tree trashed a servo and a link and a few other bits so it was a all - servos out head apart and a few other bits job!).

I also took the opertunity to stick a Futaba 3154 on the tail while I was at it.

Anyway, took delivery of a new DX7 the other week, I have the pitch and throttle all fine.

From a visit to the CAMFC, Nutz pointed out how to get the gain of the gyro correct by punching the heli up and observing the amount the tail kicks out. So armed with this knowledge (or my recollection of it) I have been punching the heli up and increasing the gain to see if I can erradicate the tail kick.

I have been upping the gain each time to remove the anti-clockwise tail kick I keep getting, but to no avail and now have the gain at 100%!

Delay is set to 0 and the gyro is in DS mode.

Any ideas on what is going wrong? The only things I can think of is that the rudder may not be fully central (mechanicaly) so less pitch available to counteract the sudden surge of the main motor. Or... the servo arm is bending with the initial demand from the gyro working the servo very hard all of a suddon... but surly this isnt a good thing

Never had this problem with the old align servo thats been in it since I got the heli!

[Twister3D]

Sure your gain settings are working ?
If I had 100% gain the tail would wag uncontrollably with my 3154

Just a small point to make, I was told if there is any binding at all
it will burn out the 3154 so be careful.

[jiberjaber]

Just checked the radio, its set for GEAR=Gyro, I am pretty sure that is where it is plugged in (it is not here with me in the loft at the moment so will check tomorrow).

I think the gain is working as when I switched between rate and HH it worked.

A bit more info I forgot to mention...

I am running 2400rpm h/s with woodies and a Jazz ESC if that makes any difference. It has been a while since I flew with woodies - I'm not good enough to do carbons any justice, but the extra h/s helps I made sure the h/s was 2400 (previously it was a lot higher) but I would have thought that would have made less of a tail kick?

[chugga-bug]

Make sure you've got REVO MIX turned off (may be called something else on DX7).
This mixes a bit of rudder to counter-act the extra torque from the main rotor when you punch collective. For use only on NON HH gyros.

[Rick Rotorhead]

Quote ""I am running 2400rpm h/s with woodies and a Jazz ESC if that makes any difference. It has been a while since I flew with woodies - I'm not good enough to do carbons any justice, but the extra h/s helps I made sure the h/s was 2400 (previously it was a lot higher) but I would have thought that would have made less of a tail kick?"""

Oooooo, glad I saw this. Ok mate, your most very likely problem here is simply headspeed, its waaaay too low for the tail to be spinning fast enough to get you the tail authority you need. Nothing to do with gyro gain at all. The slow tail just can't blow hard enough to counter the torque when you punch the pitch up. Been there and got the T shirt!!!!!!

Here's why - The Trex used to have a higher gear ratio for the tail drive, but as folks started upping the headspeed towards 3000rpm, the old tails began disintegrating in flight, soooooo, Align reduced the gears on the later rexys thus lowering the tail speed. To get the tail spinning fast enough you need about 2800 on the head, or higher. I'm running 2700 and get a slight kick out at full pitch (+11)! When previously I used 2400rpm and loads of pitch (like +13) I ended up with a one and a half turn climbing piro! Scary for a newb eh!).

So I'm afraid that lower HS doesn't make less kick, it actually makes it much worse................ Hope this helps
Regards
Rick

[jiberjaber]

Chugga - I checked the Revo and it is inhibited by default.

Thanks Rick, any idea on how fast I can safely wind the wooden blades up to then? I recall 2400 on the packet from a long time ago... (they are the Align ones)

[robgt]

Yes, don't use woodies over 2400 - 2500.
Best bet would be to put some cheap-ish carbon blades on and get the headspeed up higher.
Cheers,
Rob

[jiberjaber]

Ta Rob, I think I'll investigate the tail again, perhaps it needs that last mm of travel to get enough pitch ? I amtrying to use up my woodies, I have another two packets as they were nice and cheap at the time, I think my level of flying at the moment doesnt justify the crash expense of Carbons (25 quid vrs 10 quid!)

Cheers

[moyesboy]

The lower the head speed the more the torque on the rotor becuase the main blades are at a higher pitch to hover. The tail is running slower so needs more pitch for the same effect.

If you wound the gain up really high, be sure the tail doesn't wag in FFF and rapid stops from pirouette. Wagging tail will soon life the tail servo and mechanics.

If you have a lot of woodies to fly with you could fit the old gear ratio to speed the tail up by buying some old syle spare gears.

Another way would be fit some more efficient tail blades. I have the align ones with the curvy ends. Maybe some carbon tail blades would work better.

With larger helis there is a choice of wider chord or longer tail blades but maybe not with the trex.

Next thing is to look for more tail pitch travel. It may be possible to move the tail hub closer to the end of the tail shaft and allow more travel. you can also assemble the linkage the other way round (balls leading instead of lagging) so the seervo has to be reversed. If there is more travel avaiable one way than th orther this might help get more pitch in the direction you want.

In the end, maybe you have to put up with the tail swing until you get back on to carbon blades. I had GLX ones from rc-mods for 16 quid. I smashed a few of them. I then splashed out on radix and the same pair have survived quite a few crashes and have thus worked out cheaper!

[jiberjaber]

Cheers MB.. I will check out the amount of movement available, I think I limited it to about a hairs width from the end, but worth re-checking when I get home. Not given it any fff yet as I was just setting it up in the garden. Seeing as it is chucking it down for the rest of the week, looks like I will be stuck in teh shed experimenting

[Rick Rotorhead]

Unless you change your tail drive gears to the ealier design 'non-reduction' gear set, you will need to run your head at a min of around 2800rpm to prevent loss of tail authority on full pitch climbouts.

Align's latest woodies packaging features a revised warning label that states the blades are ok for use upto 2800rpm. In practice, many folks run them routinely at 3000rpm no problem. Some folks have reported in other forums that they use or have used woodies upto 3200rpm, but at this speed they are more likely to pull out with the slightest, probably invisible, damage or weakening. Its your call, but certainly 2800rpm.
Also as Moyesboy says move that tail hub out another mm on the tail shaft, you can get upto 45 degrees pitch on the tail blades by doing this (Not sure what he means by changing the balls to leading, cos the standard setup is already with the balls leading the blades on the tail).
My tail has enough blow at 2700HS to limit the stepping out to a couple of inches at +10 degrees main rotor pitch. At 2900 my tail was solid (but I didn't like losing the extra flight time, so I'm staying at 2700 for now).
As for gyro gain, you only need it sufficiently high that the tail just stops any tendency to wag, my gain with a Futaba 9C Tx is 45%.