Flymentor yaw control on ground

[rwellerj]

Hi folks

Tearing out what little hair I have left.

HK450 with Trex450 parts. DX7. Heli has been flying fine for several months. Installed FM, using FM gyro.

When I power up on the ground, heli rotates counter-clockwise at a rate of maybe 10 rpm before lift-off. Tail rotor slider is full over, and still doesn't stop the swing. It acts like there isn't enough RPM on the tail rotor - but it worked just fine before FM installed. Hard to see when it's moving, of course, but looks to me like the slider is completely to the right (boom side), as if it is trying to stop the rotation.

Pitch curve is 0 at idle, 0 at half throttle, 6 degrees at about 3/4 throttle, and 11 degrees at full throttle.

I'm in Anchorage - so first time thought it might be temp stabilization issue. But let it set for long enough to cold soak, and same result.

I think I remember seeing some discussion of this some time ago, but have searched diligently, and can't come up with it.

Suggestions appreciated.

Russ

[pril250]

Hi

Firstly to say the FM gyro is not the sharpest tool in the box and does have some drift which some times needs to be trimmed out like on the e-flite 110 gyro. Setup right it does work though.

Are you sure the travel direction of the rudder is not reversed and that the gyro corrects the right way.

If you look at the heli tail in, left rudder will cause the slider to go right towards the outside.

Now if you yaw the heli right in HH (tail to the left) the gyro should push the slider to the right, towards the outside.

BTW can you explain why you set your pitch curve to those values. Normally you would set -2 or -3 at idle so if the wind blows you up you have some negative pitch to bring her back down.

If the above are all correct then you need to first setup the tail in rate mode so it holds at the point the heli gets light on the skids at least. Once that is done return the gain in Helibal back to HH and if there is a slight drift trim it out.

I ended up going back to using my own gyro, now the tail is solid. Hope this helps.

BTW Can you explain why you set the pitch curve in that way. Normally one would set pitch to -3 at idle so if the wind blows you up you would have some negative pitch to bring her back down and to pin her down when you land.

[Trooper]

Have to agree with Pril, sounds like you need to reverse the servo gyro direction. You may need to do this both in the s/w and in your Tx.

Ian

[rwellerj]

Hi Guys

I think the servo direction is correct. Viewed from behind (tail in), moving the xmitter stick to the right moves the tail slider to the boom.

Viewed from above, rotating the heli counter-clockwise, the gyro moves the tail slider to the boom.

pril250 - You asked why my pitch curve is set the way it is, rather than a couple of degrees negative at idle. I've used it both ways. But I've never had a problem putting or keeping the heli on the deck - gravity seems adequate. In my (admittedly very limited) experience, I haven't found any need for negative pitch.

Will try setting up in rate mode and see if I can control yaw.

Russ

[Ivor Hill]

Hi, If you set it up in rate mode you will find that the slider is offset towards the boom and about 4mm of shaft will be visible, if you hover the heli the tail will be controlable with a little drift. Switching to HH and the slider will move closer to the boom, about 2mm of shaft will be visable, in a hover the slider will move back out to the 4mm position and with a little trimming the tail should hold reasonably well. Bear in mind that the higher the head speed the better the tail will hold.
If as you say the slider is fully in towards the boom and it the heli still has a fast ccw drift then something is very wrong that is nothing to do with FM.
Hope this helps. Ivor

[rwellerj]

OK, guys.

Problem identified. Last night I completely disconnected FM (though I left all of the equipment in place), reinstalled my Futaba gyro, and set everything up as original. And same result, so clearly not an FM problem.

Which still left me with a problem. After thinking about it in the middle of the night, I came back to my original statement that it was acting as if I wasn't getting enough RPM on the tail rotor. Which is gear driven off of the main shaft. So had to be some disconnect in that area.

Close inspection revealed that the pinion gear that drives the belt had sheared. Only the friction of the pinion barrel on it's shaft is turning the gear. Result is that tail rotor spins, and appears normal, until you get above about 1/3 throttle, and then it starts to slip, and can no longer overcome torque.

To all appearances, everything appears normal. No obvious damage. No missing teeth. But the gear portion of the pinion is sheared from it's top, and the top is what holds it to the shaft.

So, will replace the pinion assembly, probably tomorrow, re-set up FM, and try again.

Thanks to all for suggestions and advice!!

Russ

[pril250]

Did the heli sound normal?

[rwellerj]

Yeah, it did. Main rotor was turning at normal speed, and it makes quite a bit of noise. Maybe someone with better hearing than I would have noticed the difference, but I sure didn't.