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HelicopterCentury Radikal G20-30 N640 Hawk Predator › raven 30 tail servo swap
09-05-2003 12:27 AM  14 years agoPost 1
Windy488

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St Austell,Cornwall, UK

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Hi, I just changed my tail servo from a standard futaba 3001 to a Hitec 605bb. This is to give it more torque, plus it is to try and fix a problem with the tail trim drifting during flight. I kept the same servo arm and settings, and when I fired it up this evening, it was far too sensitive. I put some expo in to tame it a bit, and I played with the gyro settings til the light went, but I still couldn't get the tail to lock straight and smooth. Is there that much of a difference just from changing to a higher power servo??? How do I tame the tail and get it back under control? Do I need to try a different length servo arm, and if so, do I need a longer or shorter one. Will I have to make any other adjustments to the tail servo parameters??

Thanks

Brendan

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09-05-2003 12:31 AM  14 years agoPost 2
Al Magaloff

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12,199 Posts- Enough Time Wasted. See Ya!

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Brendan, what gyro?

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09-05-2003 12:36 AM  14 years agoPost 3
Windy488

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St Austell,Cornwall, UK

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Century PG2000

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09-05-2003 02:12 AM  14 years agoPost 4
SteveH

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Texas

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Brenden,

I seriously doubt that your servo is drifting. I've been doing this R/C heli thing for a long time and I've never seen a servo drift. I've seen glitchy pots in servos causing them to be jittery, and I've seen a lot of them just fail completely, but not drift.

I believe you are having a gyro problem causing the drift. You can check the mounting and make shure it is not subjected to engine heat, and if that doesn't stop the drift, you really can only swap the gyro to either prove or disprove that it's the problem.

The servo you have switched to is much faster than the one you were using, and different brands of servos MAY have a different amount of angular output for a given input. That is probably why your tail is more responsive. I would suggest you turn down the rudder ATV in your transmitter until the tail "feels" like it did with the Futaba servo.

Hope this helps,

The government cannot give you anything without first taking it from someone else.

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09-05-2003 12:44 PM  14 years agoPost 5
Windy488

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St Austell,Cornwall, UK

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Steve,
Thanks for the info, I did not suspect the servo was the cause of the drifting, I just wanted to put a better servo on the tail. I am suspecting the gyro, and thought it might be heat that is affecting it but although it's mounted just in front of the engine, it doesn't seem to even get warm. I will try to adjust the ATVs next time I can get out and see if it calms down any.

Brendan

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09-06-2003 02:23 PM  14 years agoPost 6
Windy488

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St Austell,Cornwall, UK

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Had some time last night and tried to sort this tail problem. the ATV for the tail was reduced to 50% both sides and still the tail is sensitive. It was hunting at a low gain setting. Reducing the gain,I could stop the tail hunting, but rudder control input caused the tail to turn in a series of jerks rather than a smooth movement. Reducing the gain even more to remove this jerkiness took me back to a position where the gyro was ineffective.
Am I missing something obvious somewhere? Maybe the Tx setup is wrong, I confess to not really understanding the gyro setup on th Tx.
Can anybody put me on the right track?

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09-06-2003 11:07 PM  14 years agoPost 7
MarkF

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Palo Alto, CA

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Hi, Brendan!

I'm a newbie, so please take what I say with a huge grain of salt, but I just managed to get my Raven tail fixed today, thanks to tremendous assistance from the instructors here at the Bayside R/C club (THANKS, guys)!

Since your setup was working previously, the main thing I'd recommend checking would be the linkage to the tail rotor. Is everything smooth, with little force required? The first problem my machine had was that there was a binding in the carbon pushrod that prevented the tail from locking in properly, and also caused some tail drift. I mention this one since I've noticed that my Hitec servos appear to have a higher output shaft location than Futabas do, and wonder if that might cause some binding in a pushrod that was set for the Futaba height.

The second thing that was wrong with my bird was that the mechanical centering was off. A great tip from the folks at Bayside is that if you flip both of the tail blades to the same side of the tail output shaft symmetrically, the tips of the two blades should be about 1" apart in terms of their left/right position (i.e. when the tips are adjacent to one another, there should be about one finger width of space between them when the tail rotor servo is centered). If the mechanical centering is too far off, gyros can definitely drift.

Finally, I'd guess that it would be necessary to change the delay setting on your gyro. With the significant improvement in servo speed, a faster (i.e. smaller) delay setting may well be necessary.

I have no idea if any of this will help, but good luck to you! It sure was a great feeling watch my squirrely bird suddenly become rock solid!!!

Cheers!
MarkF

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09-07-2003 02:53 PM  14 years agoPost 8
Lift

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Houston, TX

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Windy488,
When you mounted the new servo have you retrimmed the tail? More than likely you have a change in your trim as a result of swapping the servo and that is what is causing the drift. You need to set the servo arm 90 degrees to the pushrod with your rudder trim and subtrim neutralized. Then, hover the helicopter and alther lenght of the pushrod till the tail stays put. Just be SURE that you don't have the ATVs to high or the tail rotor pitch slider will contact the bellcrank mounting lug and cause an in-flight failure.

As for the sensitivity I would just add expo till the tail feels soft again.

Set the gain till the tail wags and then back it down till it's smooth. Make sure your motor is tuned right or all this to difficult to work out.

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09-07-2003 10:01 PM  14 years agoPost 9
Windy488

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St Austell,Cornwall, UK

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Thanks for the responses,
The carbon pushrod action is silky smooth, and the servo is properly centred, mechanically and digitally! The blades are set right, and the ATVs are such that the slider does not have too much movement.
Setting the gain was proving almost impossible. I was getting hunting down to about 35% - but backing it off a fraction to remove the hunting meant that it would not then hold the tail at all, giving me large and rapid swings in either direction. I spent 2 tankfuls making adjustments to the gain, and still could not get it to hold straight. The engine (OS32) is fine, and although head speed is fairly high(to my untrained ear!) it sounds sweet as a nut. Must buy or borrow a tacho - would like to know what the headspeed is. Does headspeed have any bearing on gyro operation??
I decided last night to go back to the previous servo (futaba 3001). I know its only a basic item, but at least I could lock the tail in when it was previously fitted.
I too am a relative newbie - and if I can't fix this tail snag, I am destined to remain one. I do not trust the heli at the moment, - the tail never feels like I am in control of it, rather the other way round. I am beginning to think that the only way forward is to replace the gyro with another make.

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09-09-2003 11:34 AM  14 years agoPost 10
MarkF

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Palo Alto, CA

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Hi, Windy488!

Another suggestion I don't see listed here is trying to improve the gyro's vibration isolation. What you're looking for is a soft, spongy mount that provides a fair amount of freedom of movement for the gyro. In other words, if the gyro is clamped down tightly by double-sided foam tape that's too thin, it can pick up too much airframe vibration, and drive the gyro bonkers. At our local field, the folks recommend using soft ~1/4"-3/8" thick servo mounting tape in two ~1/4" wide x 1" long strips. If you can't easily move the gyro around with your finger as a preflight check, you might want to consider trying out a softer mount.

Another perhaps less likely possibility are the servo wires. On our Ravens, the area right in front of the motor is pretty busy, where all the servo wires are run. You want to be careful to run these wires so that they don't touch the gyro. In my case, the gyro is mounted ~under and slightly ahead of the radio's power switch (to the left as you look at the nose of the bird), and the wires are routed behind the gyro, then pass to its right to connect to the receiver. If the wire bundle is touching the gyro, it can easily induce its own vibration interference.

I encourage you not to give up, and to keep trying. The problem I had on my Raven left me in exactly the same shape as you - I couldn't "trust" the bird, because of the tail drift, and the tail seemed to wander completely in and out of control. After working everything through, the ship was suddenly transformed to the point where the tail just locks in absolutely solid (so much so that one of the instructors at the field mentioned "now I could count 360 individual degrees in a circle with that tail"). Once you get there, it's all the difference in the world, and you can finally start learning!

Good Luck!
MarkF

P.S. My apologies about the "delay" suggestion - while that's appropriate for the gyro I use (a GY401, which is a GREAT gyro), it's irrelevant for the PG2000, which I've since learned doesn't have a delay control! Oops!

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09-09-2003 12:01 PM  14 years agoPost 11
MarkF

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Palo Alto, CA

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Hi, again!

On another tack completely, there are a couple of additional checks that you might make that could be part of the problem. If you hold the main gear in place with one hand, then twist the tail rotor manually with the other hand (twist one way, then the other, with a fair amount of pressure), do you feel any slop or slipping? With the Raven's carbon drive shaft, you should just feel an elastic pressure as the carbon drive shaft winds up. If you feel any skips or play, one of the set screws on the drive shafts could be loose. Alternately, if the degree of pressure buildup is significantly different in one direction than the other, the drive shaft might be cracked.

Another possibility is that the bellcrank or the ball that mates with the bellcrank is loose. If you hold the tail pushrod firmly in place, and twist the tail blades in pitch, do you feel any slop, or is it solid?

One quick question. Do you have the M3x5x.5mm washers installed in the tail blade grips? These weren't included in the kit or directions I received, yet are very important. Without them, the tail blade grips can "stick", preventing smooth operation. For more info on this one, check out Raven 50 Tail Blade Grip Washer.

Finally, since no one else has chimed in on the topic, under normal operation, increased headspeed should just increase tail authority, making the gyro more effective. However, it also changes the resonance modes in the machine, and changing headspeed may well make a vibration interference problem come and go. Having said that, there's always the possibility of a design glitch - I just don't know if others use faster servos with the PG2000.

Once again, please keep at it - the result is worth it!!!

Cheers!
MarkF

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09-09-2003 02:38 PM  14 years agoPost 12
Lift

rrElite Veteran

Houston, TX

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Windy488,
You could have a defective gyro.

Also, if you are more than about 14mm out on the servo arm then your electronic gain will be set very low. That is because you have in effect created a "mechanical" when you moved so far out on the servo arm.

This is 14mm is a ruff guess from memory. But, please measure how far out on the horn you are set at.

Also, please describe you rudder trimming method.

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09-11-2003 03:11 PM  14 years agoPost 13
Windy488

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St Austell,Cornwall, UK

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LIFT
The servo arm is 11mm, haven't tried any other arms. As for rudder trimming, I set the Tx trim &sub trim to 0, set the rudder pushrod as described in the century manual, measured at throttle mid stick. I then powered up and used the tx trim to hold the tail steady, landed, and adjusted the pushrod to put the Tx trim back to 0. When I first did this, the gyro was set about right and only needed a slight turn on the gain to tune it in. Then I changed the servo for the Hitec unit, and it all went to pieces! I have replaced the original Futaba 3001, but have not yet had the chance to test it again. I do recall that the tail has never been smooth in all the time I've had it. It moves in a series of jerks when i try and rotate to the left. No amount of adjusting the gyro gain gets rid of this.

MARKF
Thanks for the posts. The Raven 30 as standard, has a wire tail drive. The tail pitch control rod is carbon. The tail assembly is smooth with no slop, and the bellcrank is slop free. As for the washer you mention, are these for the Raven 30 as well as the 50? There were none in the kit, and were not mentioned in the instructions. The gyro is mounted on thin double sided foam tape as supplied amd recommended. I will try something thicker. As for the wiring, it is close to the gyro, but is well secured, and I don't think it can touch or interfere with th gyro. Will double check this also.

Once again, thanks for all the help and advice, I'll report back when I've had a chance to test it out again.

Brendan

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09-11-2003 06:08 PM  14 years agoPost 14
oldfart

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Vancouver, Canada

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Gyro/drift/etc.

Windy488
1 -The HiTech 605 servo is NOTa very good choice with any gyro. In fact there was a time when even Hi-Tech recommended that they NOT be used in helicopters (...something to do with their operation in the higher vibration environment of a helicopter.)

2 - The PG2000 is a YAW RATE gyro, not a Heading hold unit, so you must use revo mixing (a rudder to throttle/pitch mix that is built into the TX). Many (most..except for the top end PCM 10's and 9ZH) radios have this set up internally so that it mixes starting from MID STICK. Consequently, if you do not have your throttle/pitch curve set to hover at exactly 1/2 stick you will get drift. As soon as you move the stick past 1/2 or lower then 1/2, the revo mixing software starts to feed in a rudder command.

Setting for a 3D hover at 3/4 stick becomes even more difficult to accomplish. Why? Because the software in these radios are not designed for a 3/4 stick hover, but rather a hover at 1/2 stick. To compound the problem, some have a default setting of 50% which is WAY TOO MUCH, so be sure to go into your revo mix screen and change that down to about 18% ( a good place to start.

3 - Because it is a yaw rate device you can set it to "overthrow" on the ground and it will NOT do so in the air. Why? Because, in the air, the gain takes away rudder movement. So try using a longer servo arm (15 to 18mm) and you can even up your rudder ATV (servo throw in this case as it is a yaw rat device) for faster piro rates and better resolution.

4 - These inexpensive yaw rate piezo gyros operate at a relatively low frame rate so if you are using a short arm on a slow analoque servo (they take a lot of time to accelerate to speed) and are using low resolution (lower ATV settings), then you can get "jerky" response through a pirouette.

For a better understanding of what is happening check out the articles on Gyros and Servos on our web site under hints and tips.
http://www.leisuretech.ca

Phil Noel

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09-11-2003 06:12 PM  14 years agoPost 15
Wisdom-Seeker

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Danville, CA

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One thing that contributed to my similar problem was that the links that connect the tail fan blades to the slider had stiff hinges causing some minor but apparently significant binding. I was able to fix this by driving out the hinge pins and carefully trimming the interior edges of the hinges. In my case, you had to force the outer hinge tabs over the inner hinge cylinder. I fixed things so that the outer hinge tabs slipped easily over the inner hinge cylinder without any slop.

--

Wisdom-Seeker
Protest letter to insurance co.: What do you mean "Act of God"?

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09-13-2003 12:26 AM  14 years agoPost 16
Windy488

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St Austell,Cornwall, UK

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Thanks for responses.

Wisdom Seeker,
I have already fixed the pitch slider pivots, and the whole tail assembly is now nice and smooth. It's a point worth noting though, for those who have not already done it.

Old Fart,
Loads of helpful information, thanks for taking the time to pass it on. The Hitec servo has been replaced, and I will fix a longer output arm to the 3001. The EPAs (ATVs) are set at 100% both sides, but I have inhibited the Revo Mix, having been told by more than one source that the gyro will take care of any torque induced yaw. I will re activate it. My Raven was set up for mid stick hover, but I will have to check if it is hovering at exactly mid stick. I have copied the information contained in your link - it is one of the best explanations I have found regarding gyros and their application, and I shall keep reading it until I get my head around it fully!

Finally, at the moment the gyro is switched in or out using a 2 position switch on my 9C. Should I be using the built in gyro rate adjust feature, even though I am not yet using the heli in FF? If so can someone explain in simple terms how I set it up??

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09-13-2003 03:37 PM  14 years agoPost 17
MarkF

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Palo Alto, CA

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Hi, Brendan!

You'll definitely want the tail blade grip washers in your Raven 30 - that could definitely be a contributing factor to the jerkiness of the tail movement. Fortunately, they're easy to add.

Please let us know how things go!

Good Luck!
MarkF

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HelicopterCentury Radikal G20-30 N640 Hawk Predator › raven 30 tail servo swap
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