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Old Jul 18, 2005, 10:14 PM
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More Corona tail wag woes

Been doing some experimenting with this one....swapped out the CF boom for an aluminum one and moved the Dean's around...still wags. Put the CF boom back on with an extra mount on the crutch, then swapped out the HS81 for a Futaba S3101 servo.......still wags. Made sure the spider, pushrod, linkage, control horn were as slop-free as possible, adjusted the gain all over the place, tried expo, no HH, reversing, etc.....still wags. Noticed throughout it all that the TR servo arm (regardless of servo make) has a nice, rocking back and forth motion during flight....question is: Is the gyro causing the servo to fluctuate thereby resulting in wag, or is something badly wrong with the TR setup causing the gyro/servo to constantly try and correct the heading? -thumbs
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Old Jul 18, 2005, 10:34 PM
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The forum probably needs a bit more info on your set-up to help out.

What gyro are you running and where/how is it mounted?
Belt or shaft drive tail?
Servo horn and bell-crank holes used?
Wood, Aluminum, or CF crutch?
Any other mods from stock?
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Old Jul 19, 2005, 01:44 AM
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hi thumbs...askman once did a great dissertation on wagging/hunting...so that he doesn't have to revisit or duplicate the thread, here it is...fwiw...

http://www.rcgroups.com/forums/showt...nting+wagging+
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Old Jul 19, 2005, 06:30 AM
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Setup is stock 120 blades @ 4 deg., Matt's CF boom & belt drive tail w/stock TR blades, Matt's CF feather, wooden crutch, GY240 mounted w/double-sided tape to a ply base I fitted to the crutch high & just behind the rotor (very, very solidly mounted gyro!), Dean's ant. various locations, VE gear, Mega 16/15/3 w/heatsink & 9 tooth pinion, 8XGP3300, CC35, Electron 6, 2XHS81MG, 1XHS81 (tried1XFutabaS3101 also), tried both the wire & CF pushrod to TR, clevises & Z-bends both at one time or another...no slop, inside holes @ servo to outside holes @ horn (then swapped 'em...no good). -thumbs
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Old Jul 19, 2005, 07:17 AM
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OK, the wag is caused by one specific thing, however, it is agrivated by a number of others.

The TR setup is very poor on Coronas. The tail belt drive increases teh ratio of the tail. This gives more tail authority. However, it is also pushing the TR faster than the terrible linkage likes. A good digital servo is a wonderful cure. However, alot of people have gotten it to go away in other ways. I think the LMH TR pitch linkage must be changing (more sloppy?) over time because this has become a far bigger issue than it ever was. It used to be that I heard from one person every month or so. Now it is one person every week to two weeks. Go through the thread that Askman did. That will help. Also, bear in mind, I am working on a new TR and I am also looking into a lower TR ratio that will help the wag and still give good tail authority.

Matt.........
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Old Jul 19, 2005, 08:08 AM
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Well and good all, but getting back to my original Q: Why is the servo arm refusing to remain centered during flight? The ratio diff.? There's zero slop in the spider & linkage, BTW. -thumbs
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Old Jul 19, 2005, 08:46 AM
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Thumbs,

I don't have any additional advice re: your tail wag problem, but wanted to say I like what you've done with the stock canopy. Open cockpit, purple pinstripe.....classy!

Norb
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Old Jul 19, 2005, 11:17 AM
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Matt -- if too much TR authority is the problem, could the answer be as simple as cutting down the TR blades until a happy medium is found?
Norb -- thanks, motor & ESC run cool and the canopy is held on w/4 rare earth mags, BTW. Pops off nice & easy for maint. & errrm....emergency landings. -thumbs
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Old Jul 19, 2005, 06:21 PM
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Fumblethumbs

Many people do use the 110 tail rotor blades - personally I found these to be an improvement - however others have tried and had differing results.


Another thing you may have noticed that when people use the large Futaba digital servo they mount it on the boom right behind the crutch because the servo doesn't fit the crutch.

Well on my woodie I mounted my HS81 servo on the boom again right behind the crutch using the side rail mount plastic thingy that now comes with the HS81 servos and two of the LMH 2 bolt clamps - real easy. This isolates the rear crutch flex from the servo to the tail rotor bell crank - again made a big difference to my woodie Corona.

Cheers
Dave
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Old Jul 19, 2005, 10:12 PM
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thumbs,

This is the process I went through that may be helpful to you.

Weight the heli landing gear down and watch the tail servo as you apply power to the main rotor (wear eye protection and watch your head). See if the tail servo starts oscillating as you slowly bring the throttle up (No need to throttle up very far, the oscillation will be more pronounced at lower speeds).

1) If no oscillation, then check for crutch flex between the servo mount and where the boom exits the boom clamp. It is important that the gyro moves or flexes with the boom. As others have mentioned, try a lower tail drive ratio or smaller tail blades. I personally did not like the 110 blades as they are very flimsy, but others have good luck with them. If you have some older 120 tail blades, you could try cutting them down a little at a time to see if there is any improvement.

2) If it does oscillate, remove the servo from the craft and mount it on a stationary (read heavy and solid) stand very close to but not touching the heli. Then with the gyro still wired to the heli (make sure the wires cannot transmit any vibration to the gyro stand) run it up again and look at the servo to see if it is oscillating.
a) If it does not oscillate, then there is vibration on the heli, check your gyro mount location and drive train balance.
b) If it does oscillate, then check for interference in your electrics.

-Bill-
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Old Jul 19, 2005, 11:06 PM
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Good stuff, Bill....will do... and much appreciated! Had pretty much already decided to sacrifice my old set of TR blades for the sake of experimentation, I'll report my findings (good or bad) here. Odd thing happened today, BTW....got two flights in w/almost zero wag...this after a very (very!) minor adjustment of the "at center" pitch on the TR blades. Then it came back..same 'ol- same 'ol happy-dog impersonation. Go figure. Thanks all for the help, stay tuned. -thumbs
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Old Jul 20, 2005, 08:04 AM
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The tail authority is not the problem. The issue is one of precision of the TR assembly in the pitch system. A good digital servo cures this, but only because it is so wildly fast that it can compensate for the TR slop and imprecision.

From my eperience with this whole issue, part of the wag is due to the heavily cambered TR blades and partly from the TR slop. I have experimented with different tail blades and the problem goes away. I have experimented with various ratios to the tail as well. When the TR belt drive was designed, the whole point was to increase the ratio due to the terrible tail authority. The fact that I used a belt drive to achieve the taller ratio was merely because of the ease of obtaining pulleys and the difficulty obtaining gears. So I went with a belt drive. The added benefits of a belt drive were only realized after I designed the kit and got the ratio worked out. Now, at the beginning, I only had a couple people mention the wag. Then I had a rush of people mention it. Since then, I have gone for quite a while with very few mentions of it. However, now I am getting alot of mentions again. I have a feeling the new aluminum crutch is a big problem. I know some people are evenhaving wag with a stiff crutch. However, it sure seems like it is alot more common with the flexible aluminum crutch.

I have 2 separate TR systems figured out. One is very simple and will be looked into once I get the bearing blocks and V2 Rotor head ready for market.

Matt.........
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Old Jul 20, 2005, 08:41 AM
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Matt, when you think about it it's a wonder the system works as well as it does...18" away from the servo is a fairly complicated linkage system with many moving parts, all subject to abuse from the pilot and the elements, wearing away tolerances even in the best of worlds. Will your new TR system be belt driven as well? Do you ever sleep? -thumbs
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Old Jul 20, 2005, 09:18 AM
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In my case I've found that vibration makes a big difference to the accuracy of my GY401. I posted my experience here.
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Old Jul 21, 2005, 01:19 AM
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Matt,

Just ordered the CrazyTail and 7mm. The Crazy Tail comes with modified tail blades (look a little smaller). Therefore, have you found less people with the wag problem using the Crazy Tail? Phil
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