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Old Feb 07, 2013, 10:46 PM
SF Bay Area
Joined Jan 2013
233 Posts
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450 weak tail

Sorry if this has been answered before, but I couldn't find a similar problem.

Basically my tail authority is weak, and seems to be getting weaker. I've reduced the pitch to the minimum to reduce torque and increase tail speed, and still it blows out at the slightest chance.

Based on that, I thought it was a slow servo or a loose tail belt. A new MG servo made zero difference, and the belt is tight.

But, it also will barely hold position with full right stick when I add power. So I can't even command (and wait for) the tail to give enough thrust to counter the main rotor torque.

I've checked the endpoints and they are fine. I can't seem to get more pitch on the blades, and it's still slow to turn right.

I've tried all gains on the gyro to no avail. Although, the HH mode does seem a bit intermittent, but the controls in general seem intermittent, which would lead me to think it's mechanical downstream.

The only other things I can try would be swapping out the gyro, but that shouldn't help with full right stick.

Could I just have too much drag somewhere in the rotor head, causing increased torque? If there's no way to increase tail thrust, must that not mean I've got abnormally high rotor torque? The head seems to spin fine, but is a bit noisy with vibration.

Thanks!
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Old Feb 08, 2013, 04:27 PM
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what is the throttle when hovering/midstick?
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Old Feb 08, 2013, 07:53 PM
SF Bay Area
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Originally Posted by resago View Post
what is the throttle when hovering/midstick?
Right around half. A little above if I reduce the pitch knob to zero.

I used to be able to run around 30 degrees more pitch gain (not sure what that did to the copter). I'm not sure if something shifted in the linkages/servos, or if the replacement wooden blades have a different effect on torque.

I haven't checked the actual pitch values lately...but I guess dialing out some would get my head speed up.

Thanks,
Greg
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Old Feb 08, 2013, 08:39 PM
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United States, CA, Vacaville
Joined Dec 2008
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What kind of helicopter are you flying?

How is the condition of the belt? No teeth missing anywhere?

If your helicopter is running this type of gear, which is very likely, make sure the white pinion and or the black belt pulley are not slipping on the shaft...
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Old Feb 08, 2013, 10:40 PM
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Joined Aug 2012
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I also have a similar problem. I can get my heli off the ground. But at around 40 percent..it seems like the tail gives out and my plane begins to spin.
I havent flown in about we week because i havent had time to really look into the issue
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Old Feb 09, 2013, 12:49 AM
An Ordinary User
United States, VA, Fluvanna
Joined Jan 2011
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sounds like your gyro limits prevent the tail pitch slider from moving all the way in. When you check the endpoints in RATE mode, does the slider completely touch the tail box assembly? It should.

To get into rate mode you usually set the gain to a low number but it depends on the Tx. Spektrum/JR set rate mode when gain is 0-49.5. HH is 50-100.
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Old Feb 09, 2013, 10:47 AM
SF Bay Area
Joined Jan 2013
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Quote:
Originally Posted by ASTREA1 View Post
What kind of helicopter are you flying?

How is the condition of the belt? No teeth missing anywhere?

If your helicopter is running this type of gear, which is very likely, make sure the white pinion and or the black belt pulley are not slipping on the shaft...
It's a cheap clone, Hausler 450V2 (or knockoff thereof) from Leader Hobby.

Belt and teeth seem fine. Metal spur gear on the tail. Belt is tight...can't get it to slip at all. I can drive the motor by turning the tail rotor.

Thanks.
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Old Feb 09, 2013, 11:21 AM
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Originally Posted by GooberSB View Post
sounds like your gyro limits prevent the tail pitch slider from moving all the way in. When you check the endpoints in RATE mode, does the slider completely touch the tail box assembly? It should.

To get into rate mode you usually set the gain to a low number but it depends on the Tx. Spektrum/JR set rate mode when gain is 0-49.5. HH is 50-100.
Yep, tried that. It touches both end. That was probably the first thing I checked because it seems to be the most likely culprit based on the phenomenon.

It does seem like perhaps the one end isn't generating enough pitch, since the "neutral point" of course isn't centered. But a) there's no way to increase the pitch as the linkage seems fixed and b) that would probably just make the blades stall out.

But that got me thinking...I locked out the gyro by putting it at 50%. It spun all over the place with very little stability., but at least I could get it to go both ways (and fast).

So that makes me think I just have a bum gyro. It doesn't hold well in either rate or HH mode and kills the steering. I'll try another and see what happens.

On that note, this setup tutorial seems to be valuable. Any thoughts?

Quote:
INITIAL SETUP
Power up the transmitter (Tx).
If gain can be controlled by a gear/gyro switch, program the Tx to give 20% Heading Hold in one position, and 20% Rate Mode in the other. On a Spektrum Tx, this means 60% and 40% Gyro Gain.
If there's only a single setting available, use 20% Rate Mode for now.
Change the "Analog" or "Digital" switch on the gyro to match the type of tail servo you have. The Analog setting is safe for digital servos, but may impact performance. The Digital setting will most likely cause permanent damage to an Analog servo in a matter of minutes.

MECHANICAL SETUP
Power up the model, but make sure the motor won't start up accidently by either disconnecting the motor plugs, or hitting throttle hold (the former is HIGHLY recommended).
Zero the rudder trim & make sure the servo horn is at 90-degrees to the pushrod. Adjust with subtrim.
If supported by your radio gear, rebind the Rx to lock in fail-safe value for the now-centered rudder.
Adjust the tail linkage so the tail-control slider ball is roughly in the middle. In a hover, there needs to be about 6-8 degrees of pitch pushing the nose to the left in order to counter torque from the main motor.
Switch Tx to Rate Mode
Adjust "Limits" on the gyro to give the maximum tail slider movement without binding. Check both sides! This setting must be done on the gyro, not on the transmitter. Some gyros don't have the ability to set limits, or can only set overall limit rather than separate limites for each side, in which case you can try offsetting the servo horn away from 90-degrees to mechanically give more throw one side than the other.
Turn "Delay" up to maximum. Don't try to fly this way - the helicopter tail response will be very mushy if you do.
Power off, plug in the motor, then power back up (outside!)
Switch to Rate Mode
Bring the helicopter light on the skids and watch for rotation.
Mechanically adjust the tail linkage to remove helicopter rotation, until the tail is stable in a hover.
If the model spins uncontrollably in one direction, double check your gyro's servo reverse switch. When you rotate the heli by hand, the gyro should provide a counter command to the tail servo.
If a rudder input spins the heli the wrong way, correct the rudder channel reverse setting on your transmitter: left rudder stick should move the nose left.
If you made any adjustments, recheck the limits for binding and locking.

GAIN ADJUSTMENT
Increase Rate Mode gain on the Tx until the tail starts to wag in a hover, then lower it a couple of points. On a Spektrum Tx, this means LOWERING the Gain Setting to increase Rate Mode gain. Go figure.
If you are capable, do a few 360-piros clockwise and CCW with a hard stop, to make sure there is no wag. Adjust gain if necessary. The stops will be mushy, because you still have max delay.
I like to lower Rate Mode gain an extra point or two here (increase the Gain Setting on a Spektrum Tx), just in case I start getting a Wag of Death in HH mode... in which case I can try switching to Rate Mode and Idle-Off to avoid a crash.
Land and switch to HH mode.
Repeat the above, but this time INCREASING Tx gain until the tail starts to wag, then DECREASE a point or two. Again, do a few left and right piros with hard stops to make sure the wag is gone.
Switch to Idle Up and make sure there is no wag.

DIALING IN DELAY
Now let's find your servo's ideal delay setting.
Use divide-and-conquer to find the best setting that gives a hard stop after a full piro, but no kickback, in both directions.
Lower delay to 50% and check for kickback.
If there is kickback, try 75% delay. Or, if no kickback, then try 25%.
Keep going zeroing like this to get the best response.

DIALING IN THE PIRO RATE
Finally, adjust your Tx rudder end-points to give a consistent piro rate in both directions, at a speed that you are comfortable with: lower end-points will give a slower piro rate, higher a faster rate up to the mechanical limit of your tail.
Make sure to check and adjust both left and right setting.
To tame the tail down at mid-stick, but still have a fast piro rate, add some Expo to the rudder channel (see your Tx manual to determine if the Expo should be + or -). I tend to use between 15% to 25% on most of my models.
Take her up and have some Fun!
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Old Feb 09, 2013, 11:30 AM
Team Mulikow 3D
Oxfordshire, UK
Joined Jan 2007
4,118 Posts
What is your throttle curve ? My guess is that you have too little headspeed, which will give you little tail rotor speed and poor tail authority
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Old Feb 09, 2013, 02:38 PM
An Ordinary User
United States, VA, Fluvanna
Joined Jan 2011
1,244 Posts
Quote:
Originally Posted by gsking View Post
But that got me thinking...I locked out the gyro by putting it at 50%. It spun all over the place with very little stability., but at least I could get it to go both ways (and fast).

So that makes me think I just have a bum gyro. It doesn't hold well in either rate or HH mode and kills the steering. I'll try another and see what happens.
I bet it would well in rate mode - just not the way you expect.

At 50% the behavior of spinning is consistant with rate mode. In rate mode the tail will not hold at all with the general purpose tail setup (tail centered with 0 pitch). You must do something to help it out. With small fixed pitch helis with simple gyros you do this by adjusting the trim until the heli stops spinning. You can do this with a CP heli too but most people don't recommend it because there is no universal gyro standard that says how a gyro should handle rudder trim when it starts up. Some gyros will initialize and take trim adjustment into account and others won't. So, the best general advice is to not use rudder trim. However, advice for a specific gyro may differ.

In general, best practice is to have the helicopter in rate mode - try 30% to start - and spin it up until it is light on the skids with no rudder trim. If it rotates, loosen the tail servo on the boom just enough to move it around. Move it towards the heli frame maybe 2mm and tighten it up again. Repeat the spool up. If it still rotates, move the servo another 2mm. Do this until it starts to over compensate and rotate the other direction. Then move the servo back 1mm. This will get it close but the best test is in the air.

Next hover your heli 1-2 ft off the ground to see what happens. If it rotates, land and adjust the servo just a little and try again.

After you have the heli hovering in a steady state, see if you still have trouble turning in either direction. Providing your limits are ok it should turn with authority in both directions.

If it works in rate mode then it will work in HH mode.

Make sure the only thing you are changing is the gyro gain. On some Txs this is a dial. On my Dx6i it's a switch labeled "gyro". If you are using some other switch to do this then you may be doing something else like changing endpoints or rates which would change the whole diagnosis of your problem.

Note: In rate mode you will need to start adding trim as the battery voltage drops because the head speed lowers and as a direct result, the tail speed lowers and the heli will start to rotate. Make sure the battery is full when you are adjusting the servo in rate mode or you will find it way off when you switch batteries...
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Old Feb 09, 2013, 02:59 PM
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Denver, CO
Joined Dec 2005
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Quote:
Originally Posted by gsking View Post
----------On that note, this setup tutorial seems to be valuable. Any thoughts?
Generic setup guides for gyro's are usually worthless. Guides specific to the Gyro model is what you need. Gyro's use different technology, and different firmware. What needs to be done on one gyro, might throw another gyro totally out.
Example from that guide is using subtrims to center the servo to 90 degree's, for many gyro's that is not a good way to go, or even possible.
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Old Feb 09, 2013, 11:07 PM
SF Bay Area
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Originally Posted by MikeHRC View Post
What is your throttle curve ? My guess is that you have too little headspeed, which will give you little tail rotor speed and poor tail authority
Right. It's got 100-50-100...which USED to work. Now, it's inconsistent.

I had it working today (turned down the delay to 0%, maybe it helped)...but then I smashed it up coming down vertically with too low a headspeed

Not sure I'll learn anything in the rebuild...the old gyro may be fully trashed now.
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Old Feb 09, 2013, 11:10 PM
SF Bay Area
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Originally Posted by GooberSB View Post
I bet it would well in rate mode - just not the way you expect.

At 50% the behavior of spinning is consistant with rate mode. In rate mode the tail will not hold at all with the general purpose tail setup (tail centered with 0 pitch). You must do something to help it out. With small fixed pitch helis with simple gyros you do this by adjusting the trim until the heli stops spinning. You can do this with a CP heli too but most people don't recommend it because there is no universal gyro standard that says how a gyro should handle rudder trim when it starts up. Some gyros will initialize and take trim adjustment into account and others won't. So, the best general advice is to not use rudder trim. However, advice for a specific gyro may differ.

In general, best practice is to have the helicopter in rate mode - try 30% to start - and spin it up until it is light on the skids with no rudder trim. If it rotates, loosen the tail servo on the boom just enough to move it around. Move it towards the heli frame maybe 2mm and tighten it up again. Repeat the spool up. If it still rotates, move the servo another 2mm. Do this until it starts to over compensate and rotate the other direction. Then move the servo back 1mm. This will get it close but the best test is in the air.

Next hover your heli 1-2 ft off the ground to see what happens. If it rotates, land and adjust the servo just a little and try again.

After you have the heli hovering in a steady state, see if you still have trouble turning in either direction. Providing your limits are ok it should turn with authority in both directions.
Good input...thank. I get this part. But if my gyro only has bilateral endpoint adjustment, I guess I'm limiting my throw in the opposite direction if I bias my midpoint toward the boom. I guess it won't matter, because I'd never want full opposite throw anyways, because the piro speed would be much higher to that side than the other.

I'll dial this bias into my rebuild.
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Old Feb 10, 2013, 02:49 AM
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You might be able to offset the servo horn to regain full travel (rather than starting with it at 90 degree's)
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Old Feb 10, 2013, 07:08 AM
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United States, VA, Fluvanna
Joined Jan 2011
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Quote:
Originally Posted by gsking View Post
Good input...thank. I get this part. But if my gyro only has bilateral endpoint adjustment, I guess I'm limiting my throw in the opposite direction if I bias my midpoint toward the boom. I guess it won't matter, because I'd never want full opposite throw anyways, because the piro speed would be much higher to that side than the other.
Correct.

Some gyros let you set both left and right limits which fixes that particular problem.
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