E7SE - vbar tail

[bmclaurin]

Guys, using the setup below, I'm at 140/140 on the vBar tail sliders and I'm still not quite at full travel on the tail shaft. It's close, but not quite there. vBar software says anything above 120 means you're servo horns are probably too short. If I manually type in 148/148, the servo starts to buzz, but I didn't want to go quite that far, so I left it at 140/140. It flies OK in FFF, but I get a massive tail kick out (to the right) on hard collective. I've tried several different pre comps (from 0 to 32), but doesn't seem to make a difference. I've double-checked my pre comp direction, and it is correct (leading edge moves toward the boom as collective moves away from center stick).

Normally, I'd just use a longer servo horn, but I don't see way to do this in this case, as it would cause the control rod to rub against the notched out section of the rear main boom clamp. It's already only a fraction of a millimeter away from rubbing as is (with 19.6mm 18mm horn). Mechanically, everything else seems spot on to me (e.g., 90 degrees on servo horn and bellcrank, and about 3 degrees of tail pitch against torque at center). Actually, to my eye, if I set the tail bellcrank at *exactly* 90 degrees (by eye), I get zero pitch against torque in the blades (NOTE: in a subsequent post, I report that I was wrong about this point, as 90 degrees on the bellcrank does indeed produce a few degrees of pitch against main rotor torque), so I cheated a bit by a couple turns on the control rod ball links to achieve about 3 degrees against pitch. The result, to my eye, is a bell crank that is a couple degrees off 90 at center (again, I report in a subsequent post that I was wrong on this point). Doesn't seem like a big deal to me.

I've thought about drilling a new hole on the tail bellcrank that is a couple millimeters closer to the mount point in order to get a bit more mechanical throw. But since I haven't heard of anyone else having to do anything similar to that, I haven't actually tried it.

vBar Silverline 5.3 Pro
Futaba BLS276SV
19.6mm 18mm servo horn
Rail 106
Rail 716
Kontronik Kosmik 200 (mode 4)
Pyro Comp 750-50
13T pinion
11T spur gear (4.9:1 tail drive ratio)
TC's set for 1850-1950-2050 rpm

EDIT (Sep 12):  The original post indicated that I was using a 19.6mm servo horn. This was incorrect. After measuring with digital calipers, it's actually 18mm. It's a Futaba car T-shape horn (link below) that I had previously used on my old E7 (obviously, the two unused arms were dremeled off). After discovering this, I tried to fit a standard 19.6mm Futaba horn, but alas, it does cause the control rod to scrub against the bottom of the rear main boom clamp and is therefore not suitable for this application. So, I decided to stay with the 18mm car horn, as it seems to provide the most optimal throws, given the confines of available space.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXSMF4

[bmclaurin]

One thing that I have admittedly not tried, is item #1 on Matt's tail kick troubleshooting list (from an earlier thread -  http://synergyrchelicopters.com/forum/index.php?topic=1883.0). And I know I'm already failing items #2 and #4. So that's 3 out of 5. 

Tail Kick on an electric helicopter is almost always one of the following things in this order.....

1. ESC Governor - this requires some tweaking based on motor/pinion
2. Tail pitch slider is not traveling 100% in both directions
3. FBL Unit is not programmed correctly
4. Tail Servo horn not the correct length
5. Ball links not sized correctly will make the servo "stick" and cause a delay in reaction time.

There are a few more but the above 5 are the usual culprits. As mentioned earlier, turning off the governor is always a good test.

Matt

So, next time at the field, I will temporarily disable the governor on the Kosmick and see what happens. But even if that does help, I'm curious about whether something else is awry in my setup since I cannot quite achieve full travel at 140/140.

[bmclaurin]

OK, so I made it out to the field for a few quick test flights. With the Kosmik governor disabled, the kick outs are gone!!! Awesome. I tell ya...that Matt is a pretty smart guy. He didn't put the governor as #1 in his list for nothing. So now I just need to figure out how to smooth out the Kosmik governor. I'll read up on that tonight over on the Kontronik boards on HF. But with healthy 12S packs and a Pyro Comp 750 at its disposal, the Kosmik 200 can dish out some seriously extreme torque.

My other issue continues to be the tail setup in general. I got around to running a vbar optimizer flight. The main rotor head numbers came back almost perfect (56/57), but the tail numbers (17/100) suggest that I have a setup issue, as I suspected. I might try the old fashioned rate mode setup (i.e., achieving hands off zero piro rate in rate mode hover), just to see how much pitch against torque is needed at hover. I'm also wondering if I need 116's on the tail, but I think I read somewhere that there might not be enough clearance with 716 mains.

Any thoughts would be appreciated and welcomed...

[curmudgeon]

I ended up with similar VBar numbers on the tail.  I could not leave bell crank at exactly 90° because I would end up with unequal left and right travels.  I adjusted the tail rod so that I would end up with equal left and right travels.  I ended up with about 5° tail pitch against torque at neutral, which is a little higher than the 2° to 3° recommended by the VBar.  Although I could bottom out the tail travels at the mid 140's with the 16mm tail servo horn hole, I left the VBar tail travels at only 110/110.  That gives me -26.0° of left rudder and +36.3° right rudder (against torque).  I figure any further travel would just cause the tail blades to stall.  The tail seems to be working very well for me.  716/106 blades at a governed 2,000rpm head speed with the stock 4.9:1 tail ratio.

[bmclaurin]

Thanks for that. I think I've read Matt, Chris, and others post that you should feel confident about using all of the available tail pitch range on the Synergy TT models. On the non-TT models, the tail box is narrower, thus exposing a bit more of the tail output shaft and providing a bit too much travel against torque (hence Matt's recommendation of leaving about a 4mm gap between the slider and bearing on non-TT models). But I think you're supposed to try to use all of it on the TT models.

I gather from your reply that you're using a 16mm servo horn. If it's flying OK, then obviously don't mess with it. But you could go to a 19.6mm longer horn and improve those numbers a bit, I think, provided that the control rod does not scrub against the rear main boom clamp.

In my case, the 19.6mm 18mm horn was definitely better than 16mm, but still not quite enough to use all the available travel at 140/140 on vbar. And, as stated in one of my previous posts, I think 19.6mm 18mm is the longest you can go without scrubbing the tail control rod on the bottom of the rear main boom clamp.

I'm very curious what other vbar users are seeing. Again, it's almost like the ball on the tail bell crank that connects to the control rod needs to be drilled and installed a few millimeters closer to the mount point. What am I missing?

[bmclaurin]

OK, I messed around with the mechanical setup a bit more last night. Turns out my "eyeball" method of setting the bellcrank at 90 degrees was off quite a bit. I was bored, so I took a much closer look last night, aided by some digital calipers and digital pitch gauge. Here is what I found:

• There is a total of ~17.2mm of travel available.
• At the midpoint (~8.6mm), I'm seeing zero pitch in the tail blades, almost spot on, but the bellcrank is not 90 degrees in this position.
• At the extremes of travel limit, I'm seeing about +/- 40 degrees of pitch in either direction.
• With control rod adjusted to achieve exactly 90 degrees at the bellcrank, the pitch slider moves ~1.3mm off center (closer to the boom), resulting in ~5-6 degrees of pitch against torque. Perfect.
• From this "rate-mode neutral" position (i.e., with the bellcrank at 90 and about 5-6 degrees of pitch against torque), there is, naturally, less available incremental travel against torque (about 7.3mm against versus about 9.9mm with)

Previously, I had been preoccupied with trying to use every last bit of travel in both directions, and as I previously posted, that is almost impossible with my vBar setup using 19.6mm 18mm Futaba horns (the longest you can use without scrubbing the bottom of the rear main boom clamp) without setting the vbar pitch slider past 140.

But now I'm thinking that, as long as I can use all of the available travel on the "short side" (i.e., against torque) while staying in a optimum (80-120) range on the vbar pitch slider on that side, that frankly it doesn't matter if you need to go into the 140's or whatever to use all the available travel on the long side. If your servo horn and bellcrank are both 90 at servo neutral, the measurements I listed above show that it is impossible to have equal vbar slider numbers in both directions while using *all* of the available travel. Can't be done. In fact, I'm not even sure it is worthwhile (or even advisable) to use *all* of the travel on the long side (i.e., pro-torque).

Anyway, not sure if anyone is following along (or even cares), but it's been fun and educational delving this deeply into this. Gives me a deeper appreciation for Matt and others that actually do all this math and geometry for us when they design these machines.

Barry

[curmudgeon]

Thank you for posting and sharing your VBar numbers.  It is always helpful.

[Mike Spano]

absolutely its helpful. and yes, there is a lot more thought that goes into the design of a heli than most think.....

[bmclaurin]

I finally had a chance to run another tail optimizer flight. This time, after resetting the servo horn to be intentionally a few degrees forward from 90, and resetting the control rod length to achieve precisely 90 degrees on the bellcrank at servo neutral, the optimizer numbers came back at 10/41, which is a significant improvement. I could probably get them even closer by rotating the servo horn forward a couple more degrees, but I think it's close enough at this point.

Unfortunately, I can't quite eliminate the tail kick with the governor enabled. Even after reducing the gains literally as far as they will go, the tail (with 106's) just can't quite overcome the massive torque that the Kosmik 200/Pyro Comp 750-50 can dish out while spinning 716 mains. And this is with a 13T pinion (9.31:1 ratio); I can't imagine how torque-y it would be with a 12T pinion (10.08:1 ratio). Also, this is with headspeed governed to ~1850, 1950, and 2050 (and stock 4.9:1 tail ratio). I'm pretty confident that it's not a tail pitch slider travel issue, as this setup can easily achieve my requested piro rate (which is set to a quite zippy 100, which equates to ~1 piro per second) both with and against torque, and the relatively low optimizer numbers in both directions tell me it's not struggling to get there. I could set it to piro faster with no problem. Increasing the headspeed helps a little but doesn't eliminate the kick out, and frankly I don't want to limit myself to higher headspeeds. I really like how the E7SE flies with 716's when it's in the 1950-ish range.

So, my next course of action is to swap out my tail blades to Rail 116's to give it just a bit more authority. From what I've read, I won't be the only one running a 716/116 combo, but this is almost certainly the outer limit on the stock boom. To be on the safe side, I'm going to slide the tail box back a few millimeters and re-pin.

The saga continues, but hopefully this next tweak will lead to heli nirvana...

[Chris Sexton]

The 716s have a ton of byte. Have some 695 to try? It may be that your tail just can't hold the 716s. On the original e7 I would always run 116 tails with 716 mains. Not really an option with the lower e7se head.

The faster tail ratio on the e7se shoukd handle it but might be harder to tune

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[Chris Sexton]

I missed the part where you were going to pull boom back. That could work!

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[bmclaurin]

Yeah...I do have some Rail 696's, and I suppose I will try those first since it's such an easy swap. But, dang, I just like the 716's so much. They match my flying style almost perfectly.

I read about a number of others that were using the 716/116 combo, but I didn't think to differentiate whether those were with the original E7 or the SE.

Not sure I want to be a trailblazer here...


EDIT:  I also have some Radix V2 710's that would provide a bit more clearance, but a Synergy without Rails is blasphemous...

[bmclaurin]

How much latitude do you think there is in sliding the tail box back? Seems to me if I went 10mm, then I'd have the exact same clearance as I have now with 106's. Just not sure how far back I can go. 

If I was able to go that far, I'd probably have to work up a new (longer) control rod as well.

[Chris Sexton]

Matt has stated 5mm is safe but  you have to remember there is already 10mm of float in the tt..you run the risk of stripping the tt mushroom gears on the inside if you back the boom out too much.

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[bmclaurin]

Thanks. I went 8mm. Wish me luck.