Pitch pump tail kick

[crashjack]

I've finally gotten confident enough and overcome enough fear to start trying to do some setup based on flight. I wanted to check my gain and did some strong pitch pumps (upright). I got some right tail kick (nose left), probably 30 deg - 35 deg to the right. I increased my gain, and it got better, but I got some periodic tail wag. I increased again, and though the tail kick continued to get better... maybe down to 15 deg - 20 deg, to the right, the tail wag got worse also and was more than just periodic. I also noticed in bank turns, there was a noise that sounded sort of like the blades bogging, but maybe a little louder and a little more "clicky" sounding. I backed-off the gain my next flight, back to the middle position. The clicky sounding bank turns went away and the tail wag went back to periodic, but I still had the tail kick during pitch pumps, maybe 25 deg - 30 deg. Simply, I thought I would be able to increase gain until the tail kick went away, and then if I kept increasing, I would end up with tail wag. My gain is apparently too low as I'm getting some tail kick with pitch pumps, but increasing gain creates tail wag before the tail holds during pitch pumps.

I'm flying a T-rex 450 Pro DFC, with IU1 (where I fly) governed at 3050 rpm. My gain settings are all HH, 32% ("E" on AR7200), 40% ("F" on AR7200), and 48% ("G" on AR7200). All of my dials on the AR7200 are set to the center position or extremely close to center. I'm not finding any binding in my tail/tail slider, and my tail rod is centered visually. I even tried to measure with a ruler, and it might be off-center half-a-mm at most. I just replaced my rear TT gears and upgraded my tail links from the plastic stock links to metal/bearing KDE links. However, I think I've always had this problem as I've always gotten some occasional tail wag. I just never tested how well the tail holds with pitch pumps until now.

Any help would be greatly appreciated.

[crashjack]

Ok... I went back and re-read the manual in regards to the dials and Parameter Menu adjustments. I paid little attention to these initially, other than just making sure everything was at factory default. It appears I need to reduce Parameter D to 'low' or 'very low' and then start increasing my gain. I would probably just decrease to 'low' first, hopefully reducing the likelihood of other tail problems. If I get that worked out, I need to test piros for responsiveness to tail stick inputs and for making hard stops... for me, it probably makes more sense to adjust based on the stops as I'm not really sure how responsive the tail should be in the first place. I'm also using 85%/25% Dual Rates for rudder right now, and the tail being too unresponsive to stick movements is probably the least of my worries.

Would this be the correct approach?

[gmiller0]

I'm in the same boat... I just my 550x and it is solid and flys well.... BUT, when I do pitch pumps, my tail has a slight kick out which I would like to get rid of... So I will be following this thread until I get it fixed

[NC Hillbilly]

I too have had this problem with my 500 pro. I went thru everything but ended up having to change my tail servo to solve my problem. I'm not saying you will have to change the servo but that was my fix. When setting up your tail you need to be in rate mode and adjust you tail to zero drift via the rudder push rod. Make sure you have the revo mix set to off before adjusting the push rod. Also while adjusting your tail you need to be at your desired head speed. I set mine at 3100 rpm. If you have time here is my findings https://www.helifreak.com/showthread.php?t=638244.

[dgunawan]

If this helps, view this video:

Microbeast V1 setup part 4 (13 min 13 sec)

[sutty]

Could be the servo, but it may be as simple as moving the ball out a little on the servo horn to speed it up a bit. If you try this don't forget to reset the travel at set-up menu point E. How many degrees does your servo arm rotate to give you full slider travel. You should be looking for 80-90 degrees, or 45 degrees each way. Also, what tail servo are you using?

Setting the parameter D to low, and then fine tuning the gain method, and then resetting parameter D to a value that performs correctly in travelling piros is all well and good for fine tuning, but you have a major issue here. It should be perfectly possible to get almost no tail kick at all with the MB, since it is at least a reasonable tail gyro, if not a very good one. Those other tail setting methods are what you do to get it just perfect, when you start being more demanding with the tail. A pitch pump is not that demanding on the tail, unless you have too low head speed, thus tail speed, and a large collective pitch range. What is your full collective range set to?

It should be no problem to prevent the tail from kicking out, even with the known issues with the 450 pro tail geometry, if the servo is good. Maybe you have some collective tail pre-comp in the MB, or even a mix in your Tx, set the wrong way, by mistake. There shouldn't really be any need to set either of these two and indeed Tx based mix should definitely be off. For now at least, be sure to turn it off in the MB, whilst fault finding.

More information, as requested above, will help us to make more appropriate suggestions, as it can't be just down to MB gain. Tuning that up or down should be able to get you to the point of no tail wag and holding well in punches in about 5 minutes of flight tuning.

In the meantime, good luck with it.

Cheers

Sutty

[gmiller0]

Thanks Sutty.... I have a 550x with IU3 headspeed of 2263 governed, +12/-12 pitch and gain of 72/100 on my DX9 radio... When I pitch pump, the tail kicks to the right a bit and snaps back "past" center a bit and then to center lock... This is only my 4th flight as I just built it... Aside from the cyclics feeling a bit "groggy" which I think I can adjust in Parameter 'G' , it feels pretty solid... Head speed is dead on, temperatures are perfect and so forth...

[crashjack]

Originally Posted by NC Hillbilly

When setting up your tail you need to be in rate mode and adjust you tail to zero drift via the rudder push rod. Make sure you have the revo mix set to off before adjusting the push rod. Also while adjusting your tail you need to be at your desired head speed. I set mine at 3100 rpm. If you have time here is my findings https://www.helifreak.com/showthread.php?t=638244.

I've never set up in Rate Mode. I know a lot of people recommend, but I don't really understand why it matters (I'm not saying it doesn't matter, I just don't understand why). Also, I haven't compensated for torque, but I don't really know how to define where exactly that would be. To compensate for torque, I would need to have the tail such that it is pushing right (pushing the tail right and the nose left) to compensate for the main blades pushing the nose right/tail left. Correct? The question is, how much do I make it off-center? Too little and I'm not completely counteracting, too much and I'm over counteracting.

I'm not sure how you would adjust your tail while running 3100 rpm, but I'm pretty sure I don't want to try. Do you mean having your governed rpm set in your ESC with throttle endpoints calibrated?

I've watched this video before, and it was good to watch again. One thing I noticed is that the guy in the video gets some tail kick. If you look at around 5:48, he says the tail is holding well, but you can see it kick to the right, and his pitch pumps don't look very hard. My tail kick might be a little bigger (maybe not when I get to the point of a lot of tail wag), but I'm hitting the pitch pump hard.

[sutty]

Bear in mind he was being incredibly fast and loose with those settings, and in the video, at the point you refer to, he wasn't particularly trying to set the main Tx based tail gain, he was trying to demonstrate how stiff the tail was at 45 degrees in fast backwards flight when the flight parameter D, heading hold, was set to very high.

Also bear in mind he said that the tail held 'quite nice', not that it was perfect. He meant it was good enough, just to go on and do his next demonstration. In my opinion he was more or less just doing a quick check to make sure it was safe to fly his next manoeuvre.

Cheers

Sutty

[crashjack]

Originally Posted by sutty

How many degrees does your servo arm rotate to give you full slider travel. You should be looking for 80-90 degrees, or 45 degrees each way. Also, what tail servo are you using?

It is definitely short of 90 degrees... probably 75 deg - 80 deg. I do get the solid purple light in Step E (setting tail endpoints). The spec calls for the ball to be 10 mm from center, which is what I have. I performed the dremel mod during these last set of repairs, which elongated the notch in the tail shaft, allowing for more movement of the bell crank, allowing for more pitch. It even "looks" better as the slider arm now appears to be centered (or pretty dang close), where stock it was a little off-center. I'm using KST DS215MG servos for all 4 servos. These are micro HV servos, though I'm just running them on 6 volts through my Phoenix Edge Lite 50 ESC's built-in BEC.

Originally Posted by sutty

A pitch pump is not that demanding on the tail, unless you have too low head speed, thus tail speed, and a large collective pitch range. What is your full collective range set to?

I'm flying at 3050 rpm (governed by ESC). My collective pitch range is +12.0/-12.0.

Originally Posted by sutty

Maybe you have some collective tail pre-comp in the MB, or even a mix in your Tx, set the wrong way, by mistake. There shouldn't really be any need to set either of these two and indeed Tx based mix should definitely be off. For now at least, be sure to turn it off in the MB, whilst fault finding.

RevoMix is off (solid purple light) and no mixes programmed in transmitter.

A couple of other observations. I disconnected the tail rod, just to see how the tail slider was moving and how the servo arm was moving. The tail slider feels pretty smooth. I know it is difficult to tell much from moving a servo arm, unless maybe you have some stripped gears. When I move the arm by hand slowly, there does seem to be a point where it hangs a little, though it pushes through without any "clicks" and without any loss of firmness (e.g. doesn't feel like it is slipping like with a stripped gear). However when I power the AR7200 with my 6 volt battery (no lipo connected to ESC and ESC connector removed) and move the servo ultra slow, the arm doesn't twitch, jump, or snag in this location at all. Now, I did notice that when I make fast rudder movements starting and stopping, the tail seems to jerk around a good bit. Increasing/decreasing gain increases/decreases this effect and adjusting Parameter D increases/decreases as well, but a lot less than transmitter gain changes. Of course, this might be perfectly normal. I also felt the tail and various parts of the heli while I was doing this, and it looked a lot more jerky than it felt. In other words, the "jerkiness" didn't send a vibration through the rest of the heli. My hypothesis is, if the jerkiness was due to binding, the heli would have been jerking around as well... it wasn't.

[NC Hillbilly]

I had I/2 set at 3100 with the gov and would switch to that after take off (check for drift) land and adjust pushrod till no drift in I/2 and in rate mode.


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[crashjack]

That makes a lot more sense than what I was thinking.

[Tasteles]

I had a tail kick using the castle governor, so I was using parameter F precomp to try to compensate for it. Never did quite get it all out, what I ended up doing was to turn off the pre-comp, and up parameter D headlock gain to flashing blue then adjusted the gyro gain on the tx, that pretty much fixed it for me.

Actually I think I have parameter D set on solid blue now, can't see much difference between flashing and solid blue. I have no kickouts on punchouts what so ever, but I am running a DS95i servo on it with the ball at about 10mm on the servo horn. The KST servos are comparable to mine, maybe not quite as strong but fairly close. I run the castle governor on, set at 3200 to 3400 headspeed IU1 and IU2, and no pre-comp.

[NC Hillbilly]

Originally Posted by Tasteles

I had a tail kick using the castle governor, so I was using parameter F precomp to try to compensate for it. Never did quite get it all out, what I ended up doing was to turn off the pre-comp, and up parameter D headlock gain to flashing blue then adjusted the gyro gain on the tx, that pretty much fixed it for me.

Actually I think I have parameter D set on solid blue now, can't see much difference between flashing and solid blue. I have no kickouts on punchouts what so ever, but I am running a DS95i servo on it with the ball at about 10mm on the servo horn. The KST servos are comparable to mine, maybe not quite as strong but fairly close. I run the castle governor on, set at 3200 to 3400 headspeed IU1 and IU2, and no pre-comp.

[crashjack]

Originally Posted by Tasteles

I had a tail kick using the castle governor, so I was using parameter F precomp to try to compensate for it. Never did quite get it all out, what I ended up doing was to turn off the pre-comp, and up parameter D headlock gain to flashing blue then adjusted the gyro gain on the tx, that pretty much fixed it for me.

Actually I think I have parameter D set on solid blue now, can't see much difference between flashing and solid blue. I have no kickouts on punchouts what so ever, but I am running a DS95i servo on it with the ball at about 10mm on the servo horn. The KST servos are comparable to mine, maybe not quite as strong but fairly close. I run the castle governor on, set at 3200 to 3400 headspeed IU1 and IU2, and no pre-comp.

The other side of my equation is tail wag with increasing the gain. If I understand correctly, increasing parameter D will likely make that worse. My thought was to reduce parameter D so I could up the gain without tail wag.

I've seen some other places talk about governor gain in the ESC being too high. I'm not sure what governor gain really is... I guess how hard the governor works at keeping a consistent, precise rpm. Would this potentially cause an issue with the tail? I have my governor gain set to whatever the heli default is, but I think it can go lower.

[Tasteles]

Originally Posted by crashjack

The other side of my equation is tail wag with increasing the gain. If I understand correctly, increasing parameter D will likely make that worse. My thought was to reduce parameter D so I could up the gain without tail wag.

I've seen some other places talk about governor gain in the ESC being too high. I'm not sure what governor gain really is... I guess how hard the governor works at keeping a consistent, precise rpm. Would this potentially cause an issue with the tail? I have my governor gain set to whatever the heli default is, but I think it can go lower.

Increasing parameter D might actually help a slow wag. If you have a slow wag, I'd check the grip bearings. I don't know if you have the older grips or the new ones with a thrust bearings but the old style was notorious for the grips bearings causing a slow wag on the 450's.

Check the grips bearings by pulling outward on both grips at the same time, keeping constant pressure while twisting. If you feel any notchiness at all, change the grip bearings.

High gain in the Tx will cause a fast wag and the "clicky" noises you were talking about in the earlier post when making hard turns. It will also make the tail wag more noticable when doing a punch out with governor enabled. I noticed mine was waging a little on a high pitch climb out as the governor was trying to keep the rpm's up, and reducing the Tx gain a couple points cured that. I could actually hear it when it was wagging.

[crashjack]

The wag looks pretty quick to me. Also like you said, I hear the clicking sound (I guess that is the tail bogging) at a 48% transmitter gain, which doesn't seem that high. I have a metal tail rotor (Align version), and it has thrust bearings. I don't feel anything doing the test you recommended. I wonder if I just need to kick-up rpm's ? I have IU2 set to 3100 rpm, but have never flown on it. Maybe something like IU0 - 3000, IU1 - 3125, IU2 - 3200? If I did that, I should probably keep parameter D where it is to see if the increased rpm helps. Maybe next step is to increase the servo voltage to 7.4, which would increase speed and torque. The only thing I don't like is that the Nimh battery I have rigged to run the AR7200 is only 6 volt. Therefore, if I had to re-do setup, I would have to do with a live lipo through the ESC. Not a huge deal as I would remove blades, but I would rather power with the 6 volt with the ESC unplugged from the AR7200 and with no lipo plugged into it.

[Tasteles]

I also run mine on 48% gain. Might try moving the linkage ball in a hole on the servo arm to see what that does. I run my normal mode rpms at 2875 with no wags at that speed.

[crashjack]

The ball is spec, and the arm already moves noticeably less than 90 degrees so I guess I'm left with:

1. Increasing RPM; or
2. Increasing servo voltage; or
3. Maybe decreasing governor gain, but I need to learn a little more about that.

Short of that, I think I'm stuck trying a new servo which isn't too big of a deal as my current tail servo matches my cyclic servos, so I would have a spare cyclic servo. Thoughts?

Also, one other question. If I increase my servo voltage, does that effect my set-up. In other words, do I need to re-level swash, re-set pitch, etc.?