This should be interesting

ArduCopter Traditional Helicopter
461

Chris,
You are likely right its a phenomenon brought on by the chosen headspeed.
I know this a bit from FBL experience with helis, some units will handle low headspeed and others wont. BeastX does not have the tune ability to get rid of alot of the bad tendencies that arise at much lower headspeed, Bavarian Demon and Spirit handle it well. That being said it looks as though Pixhawk has plenty of tune ability to get it flying well also. I fly my other V3 style Trex 800 with an FL head, not DFC, at 1000 rpm all day long without any issues, save for my sloppy collective management at times. Thats a hard habit to break when your used to 12,000 watt motors with 160-200amp escā€™s that cant be bogged even at 14Ā° of pitch. It brings alot of bad habits to flights when you start flying more scale like, low headspeed aerobatics or UAS work im finding out.
The Blade 700X i have has quite a few headspeeds it just does not like, some of them in the 1600ish range, on the low side it doesent like 1200ish. . In those ranges the heli will ossicilate in a hover and just plain not fly good.
With this Trex 800 stretch im using ive had it in the range it at currently without issue so it makes me question my setup in Pixhawk more than anything?

6 or 1/2 dozen, seeing that you have far more experience with Pixhawk than I and more experience with lower headspeed and scale type flight, i will defer to your advice and bump the headspeed up 50 rpm and check condition.

I dont mean to keep comparing Pixhawk to an FBL as clearly its in a different class of its own, but unfortunalty my only heli experience at this point has been all FBL. I dont think the Kyosho Concept from years ago counts anymore? Plus that dident end well anyways, not enough patience on my part at that time in my lifeā€¦ :confused:
I genuinely appreciate the help and ideas, as yourself and Bill have helped me immensely with this Pixhawk installation!
Tim

462

Bill,
These parameters ā€œATC_ANG_RLL_P, ATC_ANG_PIT_Pā€. Ive seen them before, what is their function? Ive actually been wondering about them?
Tonight i will get a video of the behavior, probably the easiest way to convey whats going on. Although, i am taking chrisā€™s advice and bumping the headspeed up a bit so it may not be as bad?.
Tim

463

If you are using the same settings in both pitch and roll, and roll is normally the more sensitive axis, but you get pitch instabilities first, then there is a problem with the setup. So thatā€™s why I suggested it.

Tim said heā€™s excited about the possibility of doing surveys with his helicopter. In that type of work itā€™s going encounter everything from wind shear over treelines to having to fight wind accelerating off the last waypoint in the turn to hit target speed lining up on the next run so the images have the correct overlap with timed exposures. And it will be flying at higher speeds than youā€™re going to have in 3D or scale flight. While you may be able to tune out that pitch instability with settings in static hover under controlled conditions, it will show up again in higher speed flight out in unprotected areas fighting wind. Guarantee you it will.

Pitch bobbing is just one of the unfortunate results of low headpseed with a two-blade rotor. If you tune it so itā€™s stable at the extremes, it will be stable under all flight conditions. You canā€™t tune for just what you see in hover. But thatā€™s just me.

464

Tim, those are your Stabilize P gain settings. They convert the angle difference, or error, to a rate to correct it. Turning them down makes the helicopter sluggish. Although you could likely tune down the ATC_ANG_PIT_P to mitigate that pitch bob, as it would make the correction more gentle. Then you would be able tell if you still have enough pitch response to your liking.

1 Like
465

That is correct. Like my 700 likes more than 1,700 or less than 1,200. It flies fine at 900. Bobs around like a head banger at 1,500.

The problem with a lot of ESC governors is that they wonā€™t let you get down into that extreme range of low headspeed. But thatā€™s more of a novelty thing anyway. A 700 running headspeed that low canā€™t lift anything, and it canā€™t fly anywhere very fast.

466

Chris,
What I may end up doing is just increasing the headspeed substantially for mapping and run 4 Packs so 12s 10,000mah. The camera will most likely be a smaller, more compact hard mounted unit so I wont have the increased weight of the gimbal and its SSD recorder and the big DSLRā€™s.
Iā€™m guessing I will still get acceptable flight times going that route and have the benefits of higher headspeed and the in-built stability as such.
Tim

467

Chris,
Okay, that makes sense. I think after I get the PIDS dialed in a bit more I will experiment with de-tuning those parameters and see how that affects things.
Tim

468

That is an absolute.

When it comes to headspeed, full size manned helicopters run ~700 ft/sec blade tip speed almost exclusively. Except for the old Hueyā€™s used to be over 800 and they had really noisy rotors that bark pretty sharp. That would be around 2,300 rpm for your 800 stretch.

Have you figured out what the disc loading is of your 800 stretch, Tim? Full sized heliā€™s run disc loading of anywhere from about 2.5 up to 15 lbs/sq ft and is one of the reasons they are so much more stable than RC heliā€™s. To get the disc loading up to what say a Robinson R22 has, your 800 stretch would have to have a takeoff weight of 65lbs. And the R22 is just a light utility helicopter.

That should give you idea of the problems youā€™re dealing with a RC heli.

This is why the RC heliā€™s can run so much lower blade tip speed, though, but itā€™s not necessarily a good thing for stability of the machine. Iā€™m not a firm believer in running low headspeeds where you have to use more than about 5.5 degrees of collective pitch to hover it. I have just never seen good results from it. And thatā€™s pretty much the ā€œrule of thumbā€ I have used is to set the collective to 5.5 degrees, and if it donā€™t hover, speed it up until it does. If you have to use excessive collective to hover it, then you lose cyclic response and it becomes unstable.

Adjusting the headspeed is the absolute best way to compensate for carrying a payload with your RC helicopter. I can lift 22lbs with mine, but it wonā€™t do it at 1,700 rpm. I run it at 2,150 and it can still maneuver with the load. At 1,700 it canā€™t. So when you put your payload on it, speed it up and add more fuel weight. The increased disc loading, and additional headspeed will keep it stable. Itā€™s just an absolute.

When it comes to power consumption, the power increase required to turn the main rotor is exponential as rotor speed increases, not linear. So bumping it up to get more stable characteristic, within reason, really doesnā€™t affect power consumption that much in forward flight - only in hover. I ran several timed flight tests with my 600 electric running 1,800 (where it tail bobs a little bit), vs 1,900 where itā€™s stable. That helicopter has a takeoff weight of 10.05 lbs and amp draw averaging about 17-18 on 6S @ 25 mph. Four timed auto flights and could not measure the difference in flight time. In hover the difference is 22-23 amps vs 23-24. So it hovers on about 500W @ 1,800 vs 540W @ 1,900.

I sometimes think that using a H_RSC_MODE 3 V-throttle curve will yield a more efficient and stable under all conditions electric heli than using MODE 2 with a governor. I use MODE 3 with my little 500 because it has no governor in the ESC. I have not experiment with that with the bigger ones yet. But the V-curve is based on collective pitch so if it hovers at 5.5 degrees with no payload, and requires 6 degrees with a decent load, it should speed the head up some automatically. Itā€™s one of the experiments I got on my list of things to do.

469

What I usually do when I want to fly low headspeed with a 700 3d heli is leave everything the way it is and put a single 6s or 7s pack in. The reduced weight helps the float factor and the gov just runs up to 100% and sits there so it works out pretty good.
What Iā€™ve migrated to using these days on my 3d helis is the FBL governor. It was as night and day difference in holding power and accuracy of the headspeed compared to say the Castle internal gov or the Hobbywing gov. It makes sense it has much tighter control as the gov is predictive vs reactive. It knows when I move the sticks sharply and compensates in real time vs sensing a load/voltage drop and reacting after the fact. Also, on the helis Iā€™ve swapped to that on I can set a very low headspeed and still get it to govern at 12s vs having to lose a pack etc. I just pay attention to the ESC temp when doing if its a Castle as there is no Active Freewheeling and they heat up fast at partial load. With Hobbywing, YGE and Kontronik I donā€™t worry as they stay nice and cool even at 35% power out because of the Active Freewheeling.
Tim

470

Chris,
You know, I havenā€™t figured out the disk loading yet for the AUW of the heli/w gimbal with 2 packs ands with 4, but I probably should. I have the weight figures somewhere, maybe this weekend iā€™ll play around with it and do the math. Now that you mention it I am quite interested in knowing.
As for the Castle GOV, it was actually holding pretty good considering Iā€™m at such low power out. I guess it can only get better if I increase the headspeed. Iā€™ll just have to charge more than one set opf packs though as with such a low headspeed I was getting used to the long flight times for tuning. Itā€™s all give and take I guess?
I really appreciate the information Chris! I am always up for learning something new or even just getting a differing opinion. I find it a lot easier to work through an issue if you are open to new things vs being set in your ways, and throughout the helicopter hobby Iā€™ve found plenty of people that think they know everything and their word is gospelā€¦ Which I can say with certainty got me into plenty of trouble when I was getting back into helicopters a few years ago. I ran across far too much mis-information on forums like RCgroups and Helifreaks or even at my local AMA field. I will say both you and Bill have been a welcome wealth of knowledge and as I said I appreciate the guidance!
Tim

1 Like
471

The wisdom applied to those forums is mostly based on 3D type stuff. So it it may not apply to what youā€™re trying to do with this helicopter. The ones that really got it down as far as tuning for stability and low headspeed is the scale guys. Thereā€™s a fellow in our club that has a Trex 700-based Augusta A109 with a Wren 44i turbine it spinning a five blade rotor. And he also has a Bell 220 on a Trex 700 frame with a 44i in it. I just stand and stare with awe when he flies those things because they are so realistic right down the amount of rotor slap he has it tuned for, and the engine sound from startup to landing and shutdown. They are absolutely the closest it gets to the real thing.

But he has spent countless hours tuning and balancing and tweaking his radio because he flies them with no gyros at all. It is very impressive to watch him spool up that A109, taxi it out onto the runway, then lift off and pull the gear up, complete with the heat waves rolling off the tailpipes and the whine from the 44i turboshaft as he transitions into forward flight.

This is the guy that was my RC helicopter instructor when I got my 700 nitro. Heā€™s been flying RC helicopters for 36 years, he watches the 3D guys doing their stuff and he says what I think should be a famous quote in RC - ā€œIā€™ve spent 30 years trying to get my helicopters to NOT do thatā€.

So thereā€™s your two extremes in methodology and thinking.

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472

Yeah, i am always impressed with the scale builds, the time and money investment in some of them is just astonishing. I really love the sound of a turbine and see one someday in my future when i have the time to devote to such a project.
I do love the sound of a set of 690ā€™s cutting the air at 2150rpm and the thrill of doing manuvers low to the ground, but lately ive been digging the slow smooth LHS flights alot. And the basement engineer in me loves to tinker and build new things. Going to a fun fly a few years ago and seeing someone smack a heli hard low to the deck is what sucked me back into the hobby and my photography and videography hobby/work is what got me into that side of it. So ive merged a few different things and diversified what i do when it comes to my hobby and sidework.
Im a Construction Superintendent by day, and already do alot of our and other companies aerial work, but have been wanting to get into the mapping side of things as we have hired out for that and it just makes sense for me to start doing it. Also, it interests me anyways.
So the moral of the story is that although i do enjoy 3d flight, i get other parts of the hobby and appreciate scale and precision just as much.
Tim

473

It will be fun to see the final results of your project. Iā€™m especially interested in what sort of flight time you get at reasonable flight speed. The only really capable electric Iā€™ve fiddled with - my Trex 600EP - I can do 20 minutes in flight with enough reserve to land it. 18 minutes is probably safe. It seems to be the most efficient at 25 mph flight speed as long as itā€™s not fighting strong headwind, running 1,900 rpm headspeed. It has a disc loading of .66 lbs/ft^2 carrying its normal payload.

Iā€™ve been just experimenting with the electrics and not using them for flying fields (yet). I havenā€™t gotten one to fly long enough, or fast enough, to match piston power (yet). But they are fun to fly because theyā€™re a lot less hassle and the fuel donā€™t cost $30/gallon.

So it will be pretty fun to see what yours does once you get it so it can be flown a bit on auto flights.

474

Chris,
In my experience the flight time varies wildly. Lipoā€™s are a lottery and some packs live up to their specs and then some, others not even close. Ive had 4300mah 6s pack that yeilded longer flights than 5200mah 6s packs.
Ive gone to using Pulse 45c 5000mah lipos and seem to get the best bang for my buck and longest flight times for a claimed capacity.
Id have to dig up the numbers as its been awhile, but i do somewhat recall that running the gimbal with 2 6s packs vs 4 6s packs i got about 35- 38ish % more flight time, which after doubling the capacity doesent sound too appealing. I only run 4 if i desperatly need a longer flight. You can definalty feel the extra weight of the packs. But that is with a heavy fully loaded gimbal. I have no idea how it will all play out with lightweight mapping setup as i guess that will be alot more forward flight vs hovering or slow cable shots and then the reduced weight etc etc. Im actually excited to see what i can get out of 12s 10,000mah. :slight_smile: im definatly getting into uncharted territory for myself. I have that ā€œnew hobby excitementā€ all over again with the Pixhawk and gearing up for repurposing the UAS.
Tim

475

Oh and yeah, nitro has not gotten any cheaper ive noticed. I looked at some cool power the other day and almost fell over. :confused: as ive said before though, i do love that smell, and after hearing your successes with flybars am more than tempted to pick up that trex 700 nitro. Ive looked into some of the gasser conversions lately as well. Rob has successfully flow a gasser with Pixhawk hasent he?
Tim

476

Just run it distance based rather than time based. Thatā€™s what I do on my fixed wing planes.

477

So this is where knowing airspeed would be a big help. As you probably know, the two important airspeeds are endurance which the speed to fly to stay in the air the longest and the best range airspeed which is the airspeed that gives you the best distance per pound of fuel. If you are really looking to maximize time aloft then you should be flying airspeed and not ground speed. I mounted a pitot probe on my X3. I donā€™t see why you wouldnā€™t mount one on your heli. Determine the pitch attitude for the approximate speed you plan to fly and mount the probe at that angle to minimize airspeed error.

478

Bill, I will probably do that if I get serious about using an electric. For the piston heli it donā€™t make any difference. It can fly for an hour @ 20 m/s and uses right around an ounce of fuel per minute. Itā€™s virtually unlimited power for a 700 (105HZ O.S. in it).

The other thing is I am using timed exposures instead of distance based because I havenā€™t figure out how to make my camera do distance based shots. It snaps a photo every 5 seconds and getting up to the proper target speed (which is ground speed) on a run is important to get the 100 meter coverage. The camera actually does 140 meters per shot, but you need the overlap when the imagery is processed.

I donā€™t know what it would take to get an electric to fly that fast for that long. I can fly two sections (1,300 acres)/hr with turning time making 1 mile passes with the piston heli. I just have not come across an electric yet that can do it. A couple years ago I was using one of those little plastic DJI Phantom quads and that thing was (is) a joke compared to the helicopter. 20mph wind, that little cute white drone was all but done - it could barely move. The helicopter will hold right on 45 mph with a 20 mph headwind, no problem, and the engine just plays with it.

479

Thatā€™s awesome. You have a half gallon of fuel on board? Wow. Yes no doubt fuel has the best energy density, like you said.

I havenā€™t played with timed exposures. At work we have the 3DR mapping systems and they use the distance based camera trigger. I think you need a camera that can receive the signal from the pixhawk to trigger the shutter. We have cannon cameras that do this. They run a special script that is on the SD card.
As far as determining performance, Iā€™m interested in doing this for my X3 to determine if that configuration with the forward facing props can offer a more efficient high speed flight.

480

Yep. I got a aluminum belly tank in it that holds 2 qts. The helicopter is at the airport. Iā€™ll grab a picture of it tomorrow.

I use a MAPIR Survey2 camera, which is basically a modified GoPro for NVDI imagery.

I would really like to get a gasser flying. Iā€™m going to experiment with it with my Raptor 90 using an Echo SRM-280 engine. But I do plan on using the electric for a few shorter flights this year to see how it does. My season starts in June, pretty soon here.