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04-24-2012, 02:29 PM | #21 (permalink) |
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Fed up with bench testing I decided it was time to take to the air! I've just tried a few pitch pumps in the road outside (there's not much room to be more adventurous) with the following settings.
The headlines are Plane-Slow ESC response, and Quick CGY750 response with a gain of 10% using THR.Mode of Tx.Curve. ESC HeliMid/PlaneSlow 12kHz PWM 18deg timing CGY750 Gear.Rt 8.10t ServoType DG:1520 Yaw.Comp CW/TOP Wrk.Mode Governor Response Quick Gv.Gain 10% THR.mode Tx.Curve Rv.UpDly 12 Frm Rv.DnDly 16 Frm StartDly 2 Frm On.Revo 60% LLmt.Hov 25% LLmtIdup 25% Low.Revo 1000rpm Tx 87-83-75-83-87 joe1l warned me that using DS1520 rather than Analog for the throttle servo setting might mess up my slow start, and it is rather abrupt, but still usable. It's interesting that the following shows no instability as seen on the bench. The previous issue with overshoot is still there, but reduced without the post pitch-pump under speed of the head. It drops to 2590 (at about 11.5deg pitch) and rises to 2760 from the set speed of 2720. There's a general variation of +/- 20rpm around the set speed otherwise, so the peak is only 20rpm above that which isn't too bad. It looks like the system could accommodate more gain. Steve
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04-26-2012, 02:17 PM | #22 (permalink) |
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The weather here in the UK is against me. At least the rain stopped this evening although it was too windy to fly really.
I threw caution to said wind, and just to move this along made three short flights, trying a couple of pitch pumps for each at gains of 10/15/20%. Extracts below from the full (ish) pitch pumps for each. The 20% pitch pump was perhaps half a degree short of the others. At 10% gain (CGY750 Quick mode as before, with Plane-Slow response and DS1520 servo mode). 15% showing little difference. 20% clearly too much. There's little to choose between the 10% and 15% runs except that there was a little more overshoot at 15%, RPM peaking at 2756 rather than 2742 which is a noticeable difference. At 10% the HS dropped to 2579 and at 15% to 2582, virtually identical. Looking at the overall flights, short as they were, the 15% log looks better regulated, there being a nasty overshoot at 10% to 2801rpm with a less than full pitch pump which rather puts the full pitch pump in the shade. 10% 15% So, from this brief test I'll be inclined to use 15%. I'll try Moderate CGY750 response next to see if I can run the gain any higher, or indeed use PlaneMid. Steve
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04-29-2012, 04:01 PM | #23 (permalink) |
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It's been suggested to me that Moderate rather than Quick governor response on the CGY750 might help as by slowing down the CGY750 governor it should allow more gain.
I therefore tried Plane Slow again, but using Moderate response and a gain of 15%. Much less stable than Quick, so back to that! Steve
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04-29-2012, 04:18 PM | #24 (permalink) |
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Back using a CGY750 response of Quick, with a gain of 15%, I then tried both PlaneMid and PlaneFast response.
The PlaneMid response shows overshoot more than PlaneFast, although both show evidence of too much gain. My initial tests with different response speeds had used a gain of 20% and I now realise that to have been too high. Next I tried PlaneFast/Quick with gains of 10/11/12/13/14/15% and in the following chart I've stuck these together for each of comparison showing a pitch pump and the following response. Quite a large variation for just 1% change is evident, the best response being 12% with less undershoot after the pitch pump, and no (well, very little) instability. In closeup this looks like. Next I'll re-explore feed forward using PlaneFast/Quick, gain 12%. Steve
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04-29-2012, 09:08 PM | #25 (permalink) | |
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Quote:
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05-02-2012, 04:13 PM | #26 (permalink) |
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Back on the bench...
I tried changing the startup delay, but that seemed to have little effect which was to be expected, but worthy of investigation. Running the gain down at the previously established 12% with no V on the throttle looks pretty poor. After some playing around a throttle curve of 81-78-75-80-85 with 6deg pitch pumps at 81 and 9 deg at 85 looked as shown below. I also started using pitch pumps of longer duration at this point as it made comparisons easier. A throttle curve of 83-79-75-81-87 was better. I then decided to see if a lower up delay of 8 would make any difference. The overshoot on the throttle signal when switching from 2500 to 2700 RPM is clearly visible as a difference, but also the lock during the pitch pumps wasn't as good. Up delay 10. And an up delay of 16. Here the switch from 2500 to 2700 RPM is evidently slower, with better lock, but longer overshoot. I'm not sure this should have made much of a difference, but delays of 8 and 10 resulted in more drop in the head speed and 16 resulted in longer duration overshoots in head speed which was audible. Of these 12 seemed to be best, both on the step change in speed and also in maintaining a constant head speed. I didn't really expect such an effect once lock had been attained, so I may have to look into this further. Ready for another flight I think. Steve
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05-03-2012, 02:24 PM | #27 (permalink) |
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Darn, this is frustrating.
I'd hoped that the above settings would hold some promise. Pitch pumps with a Quick gain of 12 proved unstable. A quick test of Analog rather than DS1520 servo type was a bit of a disaster. And having dropped the gain to 10% there wasn't much improvement and then it all went belly up on a right flip. Back to HeliFast as shown at post 16 where the only issue was undershoot following a pitch pump. This had allowed good gain, cyclic response was great, and I figure I can fix the under-shoot by limiting min throttle... well, I hope I can! Steve
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05-03-2012, 03:08 PM | #28 (permalink) |
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Some promise there with IdupLmt set to the max of 80%.
Compared to 25% Proves the point, but requires refinement, and perhaps a slight drop of gain from 20%. Steve
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05-03-2012, 05:14 PM | #29 (permalink) |
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Reviewing this I realise that dropping back to HeliFast was a little premature... PlaneSlow actually showed more promise before with a gain of 15%.
Time to try some flights with that. Steve
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05-05-2012, 12:30 PM | #30 (permalink) |
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I must confess to a degree of frustration in there being no clear path forward.
I decided to try Moderate/Middle/Quick with both Analog/DS1520 servo types all with a gain of 15% and using PlaneSlow ESC response. The results are shown below; Moderate Analog, Moderate Digital, Middle Analog, Middle Digital, Quick Analog and Quick Digital stitched together. This shows Analog to be consistently better than Digital servo type which is somewhat at odds with my previous observation that Quick analog was unstable. The results are also somewhat impacted by me having set LLmtIdup to 79% to prevent undershoot. I shall retest with this lowered. Thoughts on the above gratefully received. Steve
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05-05-2012, 07:09 PM | #31 (permalink) |
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And with LLmtIdup set to 25% we get:
Moderate Analog, far left, looks OK, but with overshoot, as does Quick Digital, far right, but the gain is clearly too high, which as 15% seems rather less than optimal. I think I shall repeat this again using HeliFast, or perhaps just go straight for trying the Rev Limiter mode rather than Governor. Steve
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05-06-2012, 06:24 AM | #32 (permalink) |
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Rev Limiter mode isn't really worthy of further investigation, at least with Plane Slow ESC response. 15% in all of Mod/Mid/Quick responses looked much the same, all using a 100% flat throttle curve, quick shown below.
Steve
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05-06-2012, 07:14 AM | #33 (permalink) |
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I decided to try Heli Mid ESC response. I knew that this was slower than might normally be recommended, however I thought it might be informative and indeed it was.
Using CGY750 Quick mode with a gain of 30%: The double dip previously seen to be most prevalent in Moderate mode and/or Heli Fast mode is very clearly visible. The ESC PWM signal dropped to a minimum of 1585us, which is 58% throttle. I then tried 40%: Here the throttle dropped to 1516us, which is 50% throttle. In both cases the effect was distinctly audible and the tail struggled a bit at the top of the climb. I then tried 50%, knowing it would be worse, but keen to seen what would happen. Note that the head speed variation seen in response to rudder input is the expected effect of Yaw Compensation being turned on. I've been testing will it turned off of late because it results in a legitimate variation in head speed which makes comparison of HS regulation less easy, but in this case I thought that the required change of +/-~80rpm would be interesting. More worthy of note is the effect of the higher gain, audible as hunting which looks rather like the instability seen elsewhere (approx 16.5Hz), but of a lower frequency (approx 1.5Hz). I'm now unsure if I should be sticking with Heli Mid response as this exhibits the gain response I would expect, but suffers from poorer HS regulation. The double dip in head speed is, I now realise, what Futaba acknowledge in their Team Tip #11 in which Ben Minor recommends setting LLmtIdup to 75% which echoes my findings above. Unfortunately the HS regulation is poorer than with Heli Fast. Above I see the HS drop to 2482rpm (and then to 2457 on the second drop which I know I can improve), whereas with Heli Fast the HS dropped to 2580rpm, a full 100rpm better. Reviewing my logs I see that the Plane response modes also see HS dips to ~2575rpm, so there would appear to be little benefit in using anything faster than Heli Fast on those grounds. To put it another way, Heli Fast ESC response seems to match the response of the rotor drivetrain. Steve
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05-07-2012, 02:28 PM | #34 (permalink) |
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Just for the record, here's a plot of each of Mod Analog, Mod DS1520, Mid Analog, Mid DS1520, Quick Analog and Quick DS1520 at 15% gain using HeliFast.
Again analog is better, but instability is evident, despite the low gain. Steve
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05-07-2012, 02:38 PM | #35 (permalink) |
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I then tried raising LLmtIdup to 75% as recommended in Futaba's tech tip, the following showing the logs with Analog servo mode. The throttle curve was 87-81-75-81-87.
Moderate Middle Quick All of the above show that the regulation really isn't that brilliant. Time to try the YGE ESC's built in governor I think. This is really not looking very promising. Stev
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05-07-2012, 04:34 PM | #36 (permalink) |
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Hey Steve,
I might have missed it, but have you tried simply using the YGE built in governor for comparison? You could possibly still use the RPM signal to the 750 for piro comp. |
05-07-2012, 05:01 PM | #37 (permalink) |
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I have. See HERE. Initial results are very promising. Following a heavy load there's quite a bit of head over speed, but the heli flies really well as much as I've been able to judge so far.
I've set the RPM in the gov menu to 2700, the set speed. The RPM display on the CGY750 shows the current RPM, but I'm not sure if that's used for piro comp. The manual says to use the gov basic menu to set the expected RPM. I shall try some piros at the earliest opportunity! Unfortunately yaw compensation is a feature I've lost. The manual isn't clear about the use of a phase sensor output from an external gov. I'm not sure if the "live" value is used. Steve
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05-08-2012, 04:18 PM | #38 (permalink) |
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Using the YGE's built in governor the heli flies so much better. Until excessive load in put on the head, the head speed is very will regulated (+/- 20 RPM), and even then the HS undershoot is no more than with the CGY750 gov, although there's a little more overshoot.
I may try a 14T pinion to see if the extra torque and lower gearing (potentially reducing the mechanical gain) make the CGY750 work any better, but for now I'm going to enjoy the heli and go fly. See HERE for one of today's flights. Steve
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