Help! my heli just spins in circles

[boozie2]

Just bought a Raptor G2 when i try to fly it just spins in circles even if i push the stick the opp way its the same if not worse. took it to hobby shop they think it might be the gyro but not 100% sure . ive tried the reverse switch on the gyro but nothing please can anyone help ive had nothing but problems with this heli

[spork]

Alrighty - you may have to walk us through this.

First of all, when you spin your main gear such that the main rotors turn in the normal direction (clockwise when looking down on them) your tail rotor should spin - even if you try to hold it still lightly.

Next, with the tail rotor blades oriented fore and aft, the forward blade should be going up toward the main rotor when the main spins in the normal direction.

When you move your rudder stick to the right the leading edge of the forward tail blade should go left.

If you leave the stick at neutral and turn the heli a bit to the right, the gyro should cause the leading edge of the forward tail blade to go right (thus fighting the right turn).

With the stick in neutral and the gyro in non-heading-hold mode, the slider on the tail rotor shaft should be somewhere near center - and the leading edge of the forward tail blade should be a bit to the left.

When you lift off your headspeed should be steady and appropriate (e.g. somewhere between 2200 and 3000 for a T-Rex 450; I'm guessing the Raptor would be in the 2300 rpm range?).

Tell us whether all these things are in order. Shouldn't be too hard to trouble shoot from there.

P.S. Welcome to HeliFreak. Whatever problems you have, you can be reasonably sure someone here has already had them and gotten it figured out. Sounds like you got a new toy for Christmas?

[Pinecone]

Want to bet the gyro needs to be reversed? :)

But Spork is right, you have to start systematic trouble shooting.

But when this happens to mine, I first try changing the reverse switch ON THE GYRO. Especially if using the stick seems to make it worse.

[boozie2]

Hey thanks for the advice spork
ok here goes. i tried spinning the main blades slowly while holding them and the rear rotors would not turn. They are both turning the correct way.when i move the rudder stick they move correctly as you say.
When the stick is in neutral and i move the heli left or right it does seem to move to compensate but not very much.
Lastly i noticed that when in the tx is in centre position the slider on the tail shaft was almost all the way to the left so i adjusted the arm so as when in neutral it was in the middle. the other thing i noticed is that unlike all the other controls when i release the rudder on the tx the rotors dont return to centre i dont know if this is normal.
Anyway i was so chuffed that i thought id finally fixed it so i took it out for a test and straight away it started spinning again aahhhhh!!
anyway if you can help furhter ill be in your debt forever
Boozie2

[brgsstm]

It is normal for your tail slider not to recenter if you are in heading hold mode. you need to switch to rate mode to center your tail slider. If you do it in heading hold mode it wont work as theres not realy a centre reference for the gyro to go off.

Tom

[boozie2]

thanks but i dont know what head holding mode or rate mode are could you explain
thanks

[brgsstm]

sure no problem,

In rate mode the tail slider has a set position either flight neutral (so the heli needs no input on rudder while in the hover usually), or slider neutral (where the centre position of the slider is used to get equal throws in each direction). In rate mode a stick input translates to a RATE of yaw, ie the further you push the stick the faster the heli piros. This is the same in Heading Hold mode other than the fact that the centre is not predefined. This means the gyro will always compensate for drift and wind effects so basically keeping the tail "locked in" unless you give stick input. in rate mode when there is no input on the rudder stick the tail may drift if not trimmed out.

where do you have the gain lead plugged into your rx?

Tom

[brgsstm]

by the way, what gyro and transmitter are you using?

Tom

[spork]

i tried spinning the main blades slowly while holding them and the rear rotors would not turn.

I'm not sure I follow this. What you need to do is to turn the main gear by hand in the normal direction. That should cause both the main rotors and tail rotors to turn in the proper direction even if you apply manual resistance. Is this what you did?

Also, brgsstm is right of course about rate mode and HH mode. To keep things simple, I'd probably be inclined to do everything in rate mode until the current problem is resolved. Do let us know what gyro and TX you're using.

It sounds like your gyro gain may be low if you didn't see fairly significant correction when you moved the tail.

Finally, what is your pitch range on your main blades. Too much pitch with low head-speed can cause this problem as well.

[WJackson]

Why not start by watching this, different bird, heck might be different gyro, but the principles will be the same.

http://video.helifreak.com/tmp/6beb785f870fada54671ccc9e23e8385/gyro_setup.wmv?downloadmedia

[boozie2]

[quote=spork;492511]I'm not sure I follow this. What you need to do is to turn the main gear by hand in the normal direction. That should cause both the main rotors and tail rotors to turn in the proper direction even if you apply manual resistance. Is this what you did?


Hey spork
ok if im understanding this properley : so i turn the toothed wheel by handto make the main & tail rototrs spin, if i haol the main blades then i cant turn the toothed wheel anymore but if i hold (with very little force) the rotor blades i can still turn the motor .should holding the rotor blades prevent me from turn the main gear? The belt seems fairlly tight but if its toothed (smooth side on the outside) should i be able to turn the rotors?
am i right in thinking that this could be why the heli spins countrtclockwise not enough torque getting to the rear rotors?
thanks once again
boozie2

[boozie2]

ok so i just took the side of the rear rotor off so i can check the belt.
the small cog that the belt goes around spins independantly to the shaft that its attatched to. Whats the point of having a toothed belt should this toothed wheel be fixed to the rotor shaft?

[Pinecone]

Sorry, after reading the description of rate mode, I am confused. :)

Rate mode is where the gryo only works to keep the tail steady by responding to and zeroing out any yaw rate. So if the tail starts swinging the gyro will stop the yaw, but it will not return the tail to where it was.

Heading Hold mode is where the gyro responds to any change in tail position such that if the tail swings, the gyro will stop the swing, and then actually correct the tail back to where it was before.

In rate mode, it is typcial to see some drift as the tail moves a slight amount, the gryo stops the motion, but the tail is now a degree or so off of where it started, and then it moves, the gyro stops it and a few more degrees have gone by, and so forth, so over time the tail slowly (or more rapidly if things aren't set up properly) drifts.

Things can drift with heading hold, a bit also, but much less. The gyro doesn't actually have a heading indicator, so it only knows that the tail was displaced by x degrees, and it tries to get it back to that point, but errors do creep in.

If yuo want to fly in rate mode, setup is very important as you have to have the tail setup to counteract most of the yaw tendancies without the gyro working, otherwise you get lots of drift. And you do this by test flying and adjusting the servo position or the tail pushrod to eliminate the drift. Of course, if things are way off, the first couple of tests could be exciting. Some people have used turntable affairs to allow only yaw to get the setup close.

In heading hold mode, setup is less critical because the gyro self corrects for the errors. Many people just set things up so the tail pitch slider is centered and let the gyro do its thing.

In rate mode, the tail pitch follows the stick. If you push the stick left, the pitch changes. When you center the stick, the tail pitch slider goes back to is neutral position. More or less stick motion means more or less tail pitch change. And the amount of pitch change is proportional to stick movement. So the pilot is commanding tail pitch changes directly.

In heading hold mode, you are commanding the gyro to give you a given rotation rate based on stick position. So on the bench you may push the stick halfway and see the tail pitch slider move to the limit, because the gyro is trying to make the tail move at a given rate, but since it doesn't move, it keeps adding pitch to make it move. It also won't center when you center the stick. With the gyro in headnig hold mode, the tail is a true fly by wire setup, where the pilot commands not a movement of the tail pitch, but what they want to happen, which is move at a given rate.

One of the common things that can cause a heli to spin out of control, is to have the gyro sense reversed. There are two reverse controls for the tail. First is the Tx reverse which reverses what the stick tells teh tail to do. So it you push the stick left and the nose moves right (it is more common to set the stick motion to nose motion), you reverse the channel at the Tx.

Second is the gryo sense. And this tells the gryo which way to correct for detected yaws. This is required because different tails (and servos) move in different directions to give a desired motion. Also the gyro can be mounted upright, or as is common on Trex 450s, upside down. So normally if the nose moves left, the gyro detects this and moves the tail servo to make the nose stop and move back right. If the gyro sense is backwards, the gyro input to the servo is backwards, so when it tries to make the nose move right, it actually command the nose more left, and of course the more left motion makes the gyro send more nose right command, which is actually nose left, making the heli rotate faster, and so forth. To correct this flip the reverse switch or control ON THE GYRO.

[spork]

am i right in thinking that this could be why the heli spins countrtclockwise not enough torque getting to the rear rotors?

That's your problem right there :YeaBaby: When you turn the main gear (the big toothy wheel) it's gotta turn the tail rotor like it really means it. Otherwise the tail rotor won't do it's job.


ok so i just took the side of the rear rotor off so i can check the belt.
the small cog that the belt goes around spins independantly to the shaft that its attatched to. Whats the point of having a toothed belt should this toothed wheel be fixed to the rotor shaft?

I don't know why it's turning free of the shaft, but it definitely shouldn't. Perhaps it just got stripped.

Now, bear in mind, when you turn the main gear (in the normal direction) it must turn both the main blades and the tail rotor (with some real grip). BUT... if you turn the main blades in the normal direction it should NOT turn the main gear. This is because there's an autorotation clutch that allows the main blades to freewheel if the motor stops so you can glide (autorotate) down to a safe landing.

[brgsstm]

Sorry, after reading the description of rate mode, I am confused. :)




I dont realy see what there is to be confused about?? My explanation was basically the same as yours. And as for the "fly by wire" thing, arent all helis fly by wire? After all any input given is processed first by the receiver and then the servo is commanded to move as the stick input commanded.

as far as i was aware fly by wire indicated that the pilot is not connected directly to the control surfaces or linkages. my trex 450 has no room for a pilot in it!

boozie2

so are you saying that the tail drive pulley rotates on the tail shaft?

Tom

[spork]

And as for the "fly by wire" thing, arent all helis fly by wire? After all any input given is processed first by the receiver and then the servo is commanded to move as the stick input commanded.

as far as i was aware fly by wire indicated that the pilot is not connected directly to the control surfaces or linkages. my trex 450 has no room for a pilot in it!

"Fly by wire" can be used either way. True all (R/C) helis are fly by wire in the sense that the pilot is not mechanically pushing any control surface. But I think Pinecone is referring to the other common way "fly by wire" is used. When an aircraft is designed to be inherrently unstable (intentionally or not) they put closed loop control systems in place so the pilot commands the desired result (e.g. a given pitch or yaw rate). In that case the closed loop control system sees to it that the commanded rate is achieved.

While it's true that our signals are decoded by the RX and sent electronically to the servo, the command is strictly feed-forward. The servo is simply going to where we tell it to be. There's no component (such as the gyro) governing the servos actions at higher bandwidth to insure we get the desired control.

[brgsstm]

"Fly by wire" can be used either way. True all (R/C) helis are fly by wire in the sense that the pilot is not mechanically pushing any control surface. But I think Pinecone is referring to the other common way "fly by wire" is used. When an aircraft is designed to be inherrently unstable (intentionally or not) they put closed loop control systems in place so the pilot commands the desired result (e.g. a given pitch or yaw rate). In that case the closed loop control system sees to it that the commanded rate is achieved.

While it's true that our signals are decoded by the RX and sent electronically to the servo, the command is strictly feed-forward. The servo is simply going to where we tell it to be. There's no component (such as the gyro) governing the servos actions at higher bandwidth to insure we get the desired control.


Thanks Spork,

So what you are saying is that because the gyro has some authority over the tail without the need for input that that is true fly by wire?

Thanks

Tom

[spork]

So what you are saying is that because the gyro has some authority over the tail without the need for input that that is true fly by wire?

Yes, but... technically you're right that "true" fly by wire only requires that the pilot is insulated from the controls. But the more common usage of "fly by wire" is that there is some brains between the pilot and controls.

In our case the brain is simply an electonic gyro. This does one of the three things fly-by-wire is typically used for. It controls the tail pitch at a much higher frequency than the pilot is comfortable doing.

The other two common uses of the "fly-by-wire" brain are:
- Keep the controls from doing bad things like stalling the aircraft or overstressing it.
- Make the controls have similar effects in various flight conditions (e.g. flying fast or slow).

[brgsstm]

Yes, but... technically you're right that "true" fly by wire only requires that the pilot is insulated from the controls. But the more common usage of "fly by wire" is that there is some brains between the pilot and controls.

In our case the brain is simply an electonic gyro. This does one of the three things fly-by-wire is typically used for. It controls the tail pitch at a much higher frequency than the pilot is comfortable doing.

The other two common uses of the "fly-by-wire" brain are:
- Keep the controls from doing bad things like stalling the aircraft or overstressing it.
- Make the controls have similar effects in various flight conditions (e.g. flying fast or slow).


Aaah i see, thanks for that Spork, now i know!

Thanks

Tom

[spork]

Aaah i see, thanks for that Spork, now i know!

Sure thing. For me the geek side is one of the fun parts of the hobby. I just hope we've got boozie2 on the right track now.

[brgsstm]

Sure thing. For me the geek side is one of the fun parts of the hobby. I just hope we've got boozie2 on the right track now.


He just PM'd me actualy sayin that he tried to glue it, told him it would not be a good idea because if it came loose at 50ft he would have a swift piro down to the ground:shock:

Tom

[Pinecone]

Actually you said that in rate mode you command a given piro rate and the gyro delviers it.

That is NOT the case. In rate mode you command a tail pitch slider motion directly. That's why you can set center and travel limits in rate mode. If you set full stick travel to be full pitch slider motion, half stick travel gives you half slider motion( except for some error due to the rotary motion translation).

In Heading Hold mode you command a piro rate and the gyro does what it needs to do with the tail pitch to deliver that piro rate. That's why you can give it a small amount of stick motion, but have the slider move almost or all of full travel as the gyro tries to make the tail move. And why the servo doesn't return to center when you return the stick to center.

And Spork is right, we are FBW in that we are not directly connected to the surfaces, but in control systems, FBW normally means that the pilot does not command the surface (or other flight control) to do anything. The pilot commands a desired change in the attitude or flight path of the aircraft and the control system provides that action.

In an F-16, the pilot doesn't control the elevator (actually all flying horizontal stabilizer). The pilot, using the stick commands a certain G loading, the computer drives the horizontal stab to provide that G loading. Just like in heading hold mode we tell teh gyro what we want, then it does its thing to do that, if possible.

[brgsstm]

Rate mode does give you a rate of yaw. If you give half stick the rate of piro is less than if you gave full stick.

Also I never said Spork was wrong??

Tom

[spork]

In rate mode you command a tail pitch slider motion directly.I think I may be reading too much into what you're saying here. But in rate mode you are still effectively commanding a yaw rate. The gyro provides a negative feedback to get you to the commanded rate - it just has no integrating term. So even in rate mode, if you use full stick to get full slider throw, you'll find you have less than full slider throw in flight (when the negative feedback comes into play). That's why the 401 lets you set limits on the gyro. This lets us effectively overdrive the tail slider without hitting mechanical limits. Then in flight we're generally using full stick to get full deflection.

Also I never said Spork was wrong??

Who would dare? :YeaBaby:

[brgsstm]

Here is a scan of the manual from a CSM SL420e manual, i cannot find my 401 manual but i'm pretty sure it will read the same.

Tom