archiebald

I know this topic has been discussed before but I have some specific questions related to some recent testing.

From what I have read on this and other forums, most people are stating that the throttle geometry should be linear. i.e. the servo and carb barrel arm should be parallel to avoid any mechanical mixing being induced.

In principle I agree with this point of view, but recent experience with my YS50 indicates otherwise.

Initial Setup
Raptor 50 - 600mm rotors
Engine YS50ST, Hatori 3D2 (#522) (tuning is pretty much spot on now)
Fuel 23% nitro
Pitch +/- 10 deg with 0 at center stick
Initial throttle curve in Normal set linear 0,25,50,75,100 (see below for flight testing results)
Throttle ATV - Low 95% - High 96% giving full carb barrel rotation when idle trim set to zero.
Throttle / Carb arms - equal length and parallel
Governor - CSM Revlock 20 (currently disabled in Normal flight mode)

I didn't have access to an optical tach on the test day but I know pretty well what 1800rpm sounds like (idle 1 is set with governor enabled to 1800rpm so I can flick in and out and use the old ears)

Now, at this initial throttle curve setting it immediately became obvious that the head was drastically overspeeding so I kept decreasing the throttle curve in the mid range until I ended up with something which was giving me a pretty stable hover around the 2/3 to 3/4 stick mark and at around 1800rpm. When I landed and looked at my throttle curve figures I saw 0, 17, 21, 29, 80. Not so much a curve as a flatline with a lurch at the end.

I know the curve shape is not as important as the result but this looks entirely unreasonable to me, and could cause the governor to cut-in and out during hovering (25% = ON)


Engine Manual
Referring to the YS50ST manual ([link=http://www.yspower.co.jp/pdf/50st_e.pdf]here[/link]) it indicates a mark on the carb barrel that should roughly correspond to hovering power (yes I know its only a guide, but it seems to be pretty close....read on). Actually, the YS manual states half stick for hover, but that's another matter. The YS manual also talks about "linkage ratio" which sounds to me as if it is recommending non-linear linkage.

With the original linear 0,25,50,75,100 curve the carb barrel was way past the mark at hover stick (which resulted in overspeeding), but with the modified curve (reasonable headspeed in hover), it is fairly close to the mark. This helps me to believe the mark on the YS carb is pretty much correct.

Governor Manual
Page 2 of the governor manual ([link=http://www.rcmodels.org/csm/Rev20man.pdf]here[/link]) states that due to the non-linear carb response of most engines, the throttle geometry should NOT be set parallel, but as per their illustrated example which will result in the carb barrel moving less at lower rpm and more at higher rpm.

Hmm, seems interesting because a setting like this correlates to what the YS manual is saying......

Hatori Manual
This claims that this muffler will give increased power in the 13,000 to 17,000rpm range (and normal power outside of that). My hover speed (8.5:1 rear ratio) puts me right in the middle of that extra power at 15,300rpm which I guess may be contributing to this situation)....just a thought.


So last night, I modified my geometry to that shown in the Revlock manual to a degree that 2/3 to 3/4 stick puts the carb at the YS hover mark (which I know from my earlier test seems to be close) and I still have full throttle travel with ATV's set around 93 to 95%. All this is with the throttle curve on the Tx set to a basic straight line 0, 25, 50, 75, 100. I know it is not imperative that the Normal throttle curve is anywhere linear but it seems to me that it ought to be somewhere nearby otherwise it makes setup of the idle 1 and 2 curves very difficult.

This is all on the bench and I won't be flying it until Saturday, but in theory.....

1) I now have my carb opening to where the maker suggests it should be when at hover stick setting.
2) I know from previous experience that this carb opening position DOES roughly equate to hover power at 1,800 headspeed.
3) I have my linkage set to a condition where the governor maker suggests it is going to give best results.
4) The throttle curve is now linear on the Tx (but will probably end up somewhat non-linear after flight testing - even so, I expect the final result will be far more reasonable than the 0, 17, 21, 29, 80 curve seen previously)

BUT.....

5) My linkage geometry is not at the condition required by conventional wisdom.

So my questions are....Am I wrong?, are the makers wrong?, or is conventional wisdom wrong / out of date?



Based on my testing in this case, it suggests to me that the conventional wisdom should change to something like;

"The most important point of throttle geometry is to have the Tx throttle output linear to the power output from the engine, and not necessarily the carb position"

But I am open any comments / suggestions.

evan-RCU

In todays world of the internet and the need for immediate gratification people have lost the ability to think for themselves. Nowadays if the helo doesn't have the right head speed a person installs a governor to fix it instead of adjusting pitch and throttle curves to get the correct head speed. What you did is what everyone needs to do to set up a helo properly. Most people do it on the first few flight of the helo by the sound of the head and motor. If you have tachs it does make it easier.

RussWisc

i agree with the point of adding a Gov to fix what can be done with adjustments ,,,, even with a Gov your heli sould fly good with out one before you turn the Gov on

evan-RCU

You agree with a governor being added to fix what should be done with adjustments?

Do you mean you agree the helo should be set up properly with or without the governor?

evan-RCU

My point is that people use technology as a crutch to not understand how to set up their helo properly. This goes for gyros too. At most people ask the forums how to set something up or watch a video and if there is something different or they make a mistake it's someone elses fault.

I gotta stop getting on these soap boxes....

BarracudaHockey

My Feedback: (11)

Archie, thats nothing unusual. Colin (Colin S Mills from CSM) has been suggesting that for a while.

I discussed this at length with a well known 3d pilot at a fun fly and what I came away with, is Americans that fly 3d spend so little time at a normal head speed hover that we don't get much benefit. Certainly he was talking about the 3d guys and not the intermediate flyers but I could see his point.

Bottom line is, do whavever works best for you.

Y'all are right, setting up proper throttle curves is becoming a lost art but alas, so is driving a standard transmission.

With the CSM governors I rough in a throttle curve and raise all the intermediate points by 5 to 10 percent or so. The CSM's use a combo of the throttle curve and the sensor input to compute the difference and thats what gets sent to the servo, the smaller the difference, the less work the gov has to do and the better it works.

RussWisc

like BarracudaHockey said 1st you do a set up ... then add the Gov ,,,, dont make your electronics do all the work set it up right 1st

I am old school setting helis up before Gov exsisted too

same thing with ,,, I want a Heli ,,,,, GET A SIM 1st ,,,, get both i feel

archiebald

Thanks for the replies guys, but I think I didn't state my point clearly enough and the conversation has turned a little off topic.

I wasn't really asking about the governor, it just happens that some of the information that backs up my testing came from a governor manual.

My main point was that the consensus seems to be saying "always use parallel geometry on the servo and carb arms".

Whereas my testing seems to suggest that using parallel geometry may be totally the wrong thing to do in certain cases.

Granted, you can run a governor to overcome a bad set of throttle curves but I always try to have my throttle curves set up correct for that time when the governor goes AWOL (as everyone should do).

I would suggest that the "use parallel geometry" school of thought is a hangover from the times when engine power was much less than we have today. Indeed my previous engine/muffler DID run nearly parallel geometry AND the resulting throttle curve was almost linear. But I think this was more of a happy coincidence than design.

Obviously, all this changes when the engine, fuel, muffler combination is changed (even main rotors to an extent).

But the point I am trying to get over is when a newb asks a question on how to set up his carb linkage and all he can find on the internet is "you must run parallel geometry", then it seems that they are being totally misled. (depending on their equipment)

The other thing I was thinking is that by running a nearly linear throttle curve, then you will get better use of the servo resolution over the range of throttle openings.

The point about 3D flying is fair comment, if the engine is being flown with an ON/OFF switch then curves are totally unnecessary. Personally, I fly a little basic 3D but I get the most enjoyment out of F3C style flying. Pushing my heli through huge loops and cuban 8's or slow stationary pirouettes is far more rewarding to me.

Anyhow, from your comments it seems that I am fundamentally correct in my assumptions (or at least not totally incorrect )and having seen this so clearly on this particular engine, I will be paying much more attention to mechanical setup of the throttle linkage on my future heli builds.

Thanks once again.

syclic

Archiebald,

I understand what you are saying and also agree that it is becoming a lost art.

My understanding of the "parallel throttle geometry" is similar to that of "90 degree pitch geometry". And just as in Collective pitch settings, one has the mechanical set-up and the software set up to be linear.... moving the same amount up from midstick to down from mid stick.

For example, with the radio set at default (0/25/50/75/100) and the throttle/collective stick set at center position, the control rod to the carb should then be set so that it will be 90 degrees to the servo arm, and 90 degrees to the throttle carb arm, when the carb arm is secured to the carb barrel, such that the carb barrel is also open by 50% (half). (This is why many carbs now have these markings on the body to co-inside with a mark on the barrel). So now one will have a linear mechanical throttle relationship, just as he should have a linear collective relationship. If the stick is down - the carb is closed, at 1/4 stick it is 1/4 open, at half stick it is 50% open, at 3/4 stick it is 3/4 open and at full stick it is 100% open.

When we first started setting up for 3D, using this linear mechanical setting, and the lower power of our engines of the day, it all seemed to work with a linear collective of -9/0/+9 (0/25/50/75/100) and a V throttle curve of 100/75/50/75/100, as at top stick (9 degrees) and 100% power we may have got the 1700 or so rpm we were looking for then. In the hover at 3/4 stick, it would hover at the resultant 4 1/2 degrees (1700 rpm) and the power delivered by a 3/4 throttle barrel opening. And at the 0 degree mid stick setting it also took a throttle barrel that was 1/2 open to maintain that head speed.

But when the more powerful engines came on scene, the simple "MAS TECHNIQUE" we (he) had lucked into, no longer worked. Radios with at least 5 point settings now were needed. Because these new engines could pull a lot more then 9 degrees of top end pitch when the throttle barrel was wide open. Of course, they also produced a lot more power at the 3/4 and 1/2 throttle barrel openings. So if we would set the top end pitch to give 1900 at full throttle we would maybe get 11 degrees instead of 9. So now, if we used the OLD straight line, we would end up with 5 1/2 degrees at 3/4 stick....way to much to hover at 3/4 (or 1/4 inverted) at a 1900 head speed. And the throttle would also be 3/4 open here, producing way more power then we want. So the head speed would be a lot higher then we desired.

As for mid stick and 0 degrees, as these engines produced almost as much power with the barrel 1/2 open as the older motors at 65% open, now a throttle barrel that was 1/2 open would make the head speed at mid stick go way up.

So with all this fluctuating head speed, the gyros where working overtime and it was now hard to get any constancy through maneuvers. Obviously we had to deviate, as the overly simple "MAS TECHNIQUE" was now "passeh".

We all know that the point of a good set up is to maintain a constant rotor speed, here is what evolved.

It is common sense that a heli cannot fly at any rotor speed if the collective is at 0 degrees. So we can initially set our normal mode for a collective of whatever we knew we could pull at the top and maintain our desired head speed (let us assume 11 degrees & 1900 head speed), then the 3/4 stick point would be set on the bench for a reasonable hover pitch at that speed (e.g. a TX % setting at point #4 that would give 4.5 degrees), mid stick would still be 50% and we would also set the two lower points at 0 (50%).

We still want to use the same linear mechanical throttle relationship, here we will just want to set the TX software to give the head speeds we want at each point. A good place to start would be; "whatever % required to start/idle"/30/40/60/100. Then we start the heli, bring the throttle to half stick (which now would be 0 degrees and 40% throttle). If the rotor speed is too low, then add more %, if it is to high, then take off some %.... until you get it turning at 1900.

Now pop into the hover (hopefully 3/4 stick) where you will now have 4 1/2 degrees of pitch and 60% throttle barrel opening. If the rpms drops, add to the point #4/60% setting, if it increases, decrease this setting, until you are hovering at 3/4 stick.

Now land and transfer these numbers to your idle up. Here is an example. Let us say for pitch you had from mid stick, 50, 65 (note: this is 15 up from 50), 100. Then for the settings (1/4 and bottom) you want the inverse. So 1/4 would be 35 (15 down from 50) and bottom would be 0. If your collective pitch is also set up as it should be, to be linear mechanically, you should now have a pitch curve in idle up that is -11/-4.5/0/+4.5/11.

Also transfer the throttle curve numbers. So let's say from mid stick we ended up with 40/62/100. The lower points would correspond with 100 at bottom stick, 62 at 1/4 stick, 40 at mid stick, 62 at 3/4 stick and 100 at full stick. Note: now this is more of a U shape then a V.

Now back to your normal mode and reset the low points to maybe a -2 at 1/4 stick and a -4 at bottom stick. And reset the 1/4 stick point for throttle so that in a descent the rpm will not change.

Now you can hover in normal, hit idle up and there will be no jump or change in head speed.

NOTE: For training you may want a lower head speed so now you can adjust your normal mode by increasing each pitch point and decreasing each throttle point settings in the TX (do not touch the mechanical) accordingly.

I have found that a linear mechanical throttle set-up also helps any governor to work more efficiently.

veralee

Well at the risk of being tedious I think the above needs to include the condition that at the centered servo position (Tx sending a 50% signal) the carb barrel should be centered (half open) and the angle between the rod and the servo and carb arms should be 90 deg. I believe that would be the "conventional wisdon" regarding mechanical throttle setup.

I think you might be misunderstanding what the desired "linearity" is about. It isn't the throttle curve. The throttle curve setup in the Tx should be whatever it needs to be to hold the head speed constant throughout the pitch range.

I suggest going over the setup. If the heli will hover at 40% as indicated by the engine manual then point #3 on the curve should be 40% instead of 29%, assuming you want 3/4 stick hover. The following are the steps I use to set up the engine.

Make the length of the throttle rod, hole to hole centers, the same as the distance from the center of the servo shaft to the center of the carb barrel. Connect one end of the rod to the throttle ball and leave the servo end unconnected. Hold the servo end of the rod near the servo shaft and push/pull the rod so that the throttle barrel is half open. The throttle arm should meet the rod at 90 deg at that point. If it doesn't, loosten the bolt slightly and move the arm a little. Next, set the Tx to send 50%. If you put the stick half up then adjust point #3 for 50%. Or put the stick all the way up and temporarily set point #5 to 50%. This centers the servo. Now install the servo arm so that it fits on the splines with the arm being 90 deg to the rod, but don't connect that end of the rod yet. Now move the stick to full throttle and set point #5 to 100%, push/pull the rod to get the throttle barrel fully open and see if the link will fit over the servo ball. If not adjust the endpoint till it will. So now 100% throttle won't bind the servo. Likewise, move the stick to the low end and set point #1 to 0% and push/pull the rod to fully close the throttle and see if the link will fit on the servo ball. Adjust that end point if not. So now you can go from full throttle to closed throttle without binding the servo, and at 50% the throttle is half open and the angle between the rod and servo arm and throttle arm is 90 deg at that 50% position. If you then set point #4 (3/4 stick) to 40% and move the stick to that 3/4 position the throttle barrel should nearly line up with the hover mark on the engine.

We're stuck with translating a circular motion to a linear motion... the circular motion of the servo moving the throttle control link back and forth, a straight line or linear action (more or less). This translation is most nearly linear in the neighborhood of a 90 deg intersection between the rod and servo arm. Look at the shape of a sine wave in the region of the zero crossing and notice how it comes close to being a straight line. As the servo arm moves to, let's say 30 deg away from that point, the change in movement of the rod in relation to change in servo arm angle drops off to around 86% of the "centered" amount. That isn't a tragedy. It almost doesn't matter because of the adjustability of the throttle curve. With this setup the value entered into a stick position point (1...5) will come pretty close to setting the throttle to that percent of max when the stick is in that position.

You have the pitch curve set so that half-stick gives zero pitch on the blades (50% at point #3), as I understand it. So set the stick there and adjust the throttle curve point #3 to get the rpm you want. Set point #2 to about half that value. At 3/4 stick (point #4) you have the pitch at 75%, which should give around 5 deg pitch, about right for hover. As you advance the stick to 3/4 the rpm should hold stady and you should hover. If the rpm changes adjust point #4 on the throttle curve to hold the rpm. If it won't hover there, at 3/4 stick, but the rpm sounds right, then you need more pitch, so adjust point #4 on the pitch curve to get the hover at 3/4 stick with the rpm you want. If you have to increase pitch you'll probably also have to increase throttle to hold the rpm with the added load on the blades due to greater pitch.

Once you have the hover adjusted, punch the throttle up towards point #5 and see what happens to rpm. If the rpm happens to pick up then you should lower the throttle value at point #5. You could increase the pitch value instead, but if you're already maxed out on pitch there's nothing left to do but lower the throttle value. If the rpm drops off at full stick, and the throttle curve point #5 is already 100%, then there's nothing left to do but reduce the pitch value at point #5.

archiebald

syclic,
Thanks for your detailed input, I was not aware of some of what you stated. BTW, I am not training - now on my 4th nitro heli and 5th engine.

I have no problem at all on thinking of the 90deg rule for all linkages and theoretically at least I would like to achieve that on throttle too.

However, the problem I have is that with a "correct" 90 deg and parallel throttle linkage, the 2/3 ~3/4 hover point on the stick translates to too much barrel opening of the carb (according to YS's recommendations, not my opinion) that then results in overspeed. I fully realize that I can rectify that by changing my throttle curve on the Tx and if I had come up with figures something like 0, 30, 50, 50, 80 in normal, then I wouldn't have given it a second thought. But the fact that my throttle curve needs to be so extremely flat (0, 17, 21, 29, 80) set the alarm bells wringing.

One point you made;
I am not going to claim to know better but that statement (which I would have agreed with before this week) contradicts what is stated in the CSM Revlock manual. And this is part of the problem I am having. They state;

"Some engines have very non-linear throttling characteristics with small throttle movements at light loads causing large changes in power while large movements are required to produces significant power changes near full throttle. You should adjust the throttle trim until the correct idle is obtained with the stick in the fully closed position with the idle-up switch in the normal position. A linear throttle curve taking the throttle from idle at bottom stick to full throttle at top stick is ideal."

I have attached the image from their manual for clarification.

It seems sensible to me that since our task is to match power versus pitch in order to maintain a constant headspeed, then the engine power output is important and the carb barrel position is irrelevant. As I mentioned, I have never seen such a radical throttle curve requirement on my previous setups and it may be that the engine muffler combination I am now using is actually giving too much mid-range power for the class of the heli. That, after all was one of the claims made by Thunder Tiger when they launched the 620mm rotor Titan.

Anyhow, the proof of the pudding is in the eating as they say and I'll give my revised setup a try at the weekend and report back if I find anything (good or bad)

-------------------------------------

veralee,
Actually, the YS manual states that the carb should be about 40% open (according to the mark on the carb body) at hover throttle.

Here is their text (they seem to assume hovering at half stick as opposed to 3/4 stick)

"Set the throttle stick on the transmitter at the center, and adjust the linkage to put the mark on the carb body and the mark on the throttle barrel in line. Hovering should take place with the throttle stick near the center position if the linkage ratio is properly set."

I have also attached the illustration from the YS manual for clarification

I would have agreed except for the radically flat curve required in this instance.

But if I set point 3 (or point 4 for 3/4 stick hovering) to 40% then the head will overspeed because the carb barrel is too far open (based on parallel servo / carb arm geometry)

Yep, 100% agree because that's how I had it set up in the first place.

This is where theory goes out the window. I agree, it should happen but believe me...it doesn't.

I know what you are saying about pitch curve, but doesn't conventional wisdom also state that pitch curves are best left linear?

syclic

Archiebald

I love these type of discussions, as they always prove informative to any readers. That is why my note, at the end of my previous post, relating to those training, was not for you, but for any trainees reading. If a newbie sets up with a 3D throttle/pitch curve, he can get into trouble very quickly. Setting for a slower rotor speed (more in the area of 1600), using a softer collective (specially at the bottom with maybe a -1 or-2), will make for a more gentle descent if he should chop the throttle stick. Doing so seems to be the natural thing for most newbies when they panic.....and the lower head speed will give him a much better fuel economy - read more flight time.

As most throttle barrels have too much throw at the bottom (note: older carbs had an set screw that could limit the bottom end throw of the barrel), my mechanical set up should have been clarified more, relative to throttle barrel opening at idle, at 1/2 and at full.

As most carbs are designed (YS is a bit different as they use a built in pressure system and a different carb design) such that there is an overlap area between the idle screw and the main needle at around the mid barrel opening point. This makes the adjustment of the idle needle/screw so important in setting for a good hover, not just a good idle.

Why it is important in the YS to be at about the 40% point in the hover (they even mark that on their crabs), is because it is just above that opening point where the top end needle settings take effect, and they know that, at a 40% opening, their motor will have more then enough power to hover any heli it was designed for. So setting as they describe, IMHO is very intuitive. They are my favorite engines (and have been for 15 years) strictly because of their integrated pump/carb design. IMHO, by far the easiest to get right on the needles for a burbling idle, through a comfortable hover and full power at the top end.

Please note, that CSM clearly state "some engines". I am sure they are referring to those (and I have experienced them) that have a poorly designed transition area. You may have seen threads in various forums about modifying the "eye" in the needle assembly of such engines to better handle the transition. This is the main area of difference between a carburetor designed for airplane use and one for heli use (another interesting area worth studying, as most think the main difference is just larger cooling head fin area - not so)

The two most frequent problems I run into, time after time, when helping someone tune their heli to optimize its performance, (at the local field or at an event), is their poor mechanical throttle set up and their ignorance of how to tuned the two needles (main and idle screw) for smooth and dependable transitions. Showing them how to do this always have them going home with a big smile after flying their heli again with these two set properly. If they are set too badly, they can wreak havoc with most any governor (some are more sensitive to this then others).

My referral to hovering at point #4 in the software (3/4 on the stick) when right side up and point #2 (1/4 stick) when inverted, is that, if one always set all his helis to hover at his desired head speed, at these two point on his stick, with 0 degrees at half stick, he will find it easy to "burn" these stick points into his brain. He will then find it very easy to transition from one to another and to identify these points through any maneuver he may wish to learn or fly. This will make it much easier for him to fly any of them with more precision and consistency.

I have to say, that I am very disappointed in the print media that cater to the R/C heli community. They seem to spend more energy reviewing and pimping different helis rather then writing detailed articles on how to do this type of stuff. Consequently many for years, just keep buying different items, that they do not need, in their quest to solve issues they may have with their heli, gyro or governors. When all they may need is a better understanding of how it all works.

evan-RCU

"Consequently many for years, just keep buying different items, that they do not need, in their quest to solve issues they may have with their heli, gyro or governors. When all they may need is a better understanding of how it all works."

Syclic that says alot. it's what I was trying to say earlier that many people don't take the time to figure things out themselves. I think it's a bad thing and is teaching the present generations not to think. I remember when you had to second guess every part in a helo, how it was installed, and how to set it up to work correctly. Back then there were no expert pilots and no internet to go to. But also back then when you bought a new helo the instructions were in english you could understand and every helo I know of had set up and basic flying instructions in the manuals. Most also had starting and tuning tips and SAFETY notes.

syclic

Evan

Very good point about the manuals (and not just re: the helicopter kit itself).

Most are not aware that one of the biggest expenses presented to the manufacturer may NOT necessarily be manufacturing the product, but having a good and comprehensive manual written by a competent individual....and the subsequent cost of having them printed. Sometimes these two costs will be more then the manufacturing cost and or a big % of the final kit cost.

As everybody is now so into "a lower cost" of purchasing they often do not consider the "value" added in what they purchase.

Also of note, is that sometimes the "value" added to the cost of the kit may not even be on a useful aid (like a good manual), but may be a far less important item... marketing ... like the cost of having & keeping a large group of hot pilots, publicly flying their product. Many who themselves, may not understand properly how to optimize the set-up of their helis, as their father or someone from the company does all of that for them....including installing "non standard" items that do not come in the kits, but are required to insure the heli can take the forces of the extreme flight regimes they will be subjecting the heli to.

Personally I would rather that in the cost of my kit, is that of a good manual rather then for any part of that cost be for giving me bragging rights to say that so-and-so flies the same brand I do. In fact, I would rather have all of my cost of the item be used to insure I have a better item, then to have any part of it be used for supporting a large "marketing" cast.

P.S. Anyone is entitled to feel otherwise.

rcjon

Guys,

I am one of those heli pilots in the "training mode" and this is one of the most informative threads I have tried yet to digest. I've printed several pages of notes from this thread that are being used to go over my entire set up on my Raptor 50 Titan.

Tomorrow I'm going to make my heli hover at the headspeed I want it to, at the stick position I want it to. Tonight I tweaked my throttle linkage and my collective linkage. I had made too many adjustments in the radio to make the thing fly. Now everything centers around mid-points of travel and I don't have whacky ATVs like 110 and 60 and subtrims deviated from 0.

Keep it up!

evan-RCU

rcjon, sounds like you've see the light!!! Good luck tomorrow...

archiebald

syclic,
Once again thanks for your detailed and patient input. It's nice to be able to discuss this type of testing without being shot down.

rcjon,
I don't know if it is any of my comments you are referring to but I take your post as a complement. thanks for commenting so positively.

---------------

Just to give feedback, I went to the field today and ran up the concerned heli. I started with a linear 0, 20, 40, 60, 80 then tweaked the Tx throttle curve as follows

After doing the same Normal / Idle 1 / Normal switching to find 1800rpm headspeed in hover, I have settled on 0, 20, 30, 40, 78 in Normal. ATV"s are at 92 low and 95 high. This is using the differential linkage as described above.

I am happy with this because;
1) 40% at point 4 is my hover point and that is now coinciding correctly with the carb indicator which is suggested to be 40% throttle opening. i.e. what I am seeing on my throttle curve is more representative of what is happening on the heli.
2) Having a wider spread than before (0 to 40% instead of 0 to 29%) means that a 1% change on the Tx curve has greater resolution (finer adjustment is now possible)
3) My governor seems to be much happier now.

The performance in Normal was less twitchy, and in Idle 1 (1800) and idle 2 (2000) which both have governor enabled, she was flawless whereas before the engine always seemed to be somehow unsettled. I had my first truly confident day today with this engine / muffler combination.

Whether this is coincidental, actual or just psychological I can't honestly say but rightly or wrongly, I am going to stay with the "incorrect" differential linkage for the time being on this engine / muffler. But, my scale Lama and 2nd Raptor will remain using conventional wisdom .

BarracudaHockey

My Feedback: (11)

Syclic you're 100 percent right about the manuals. I've yet to be impressed by any of the current crop of helicopter manuals I've seen with the exception of Audacity. That goes for many of the high end radios as well. If it wern't for Raptor Technique I may never have gotten my first Raptor in the air w/o serious heart ache.

veralee

archiebald

If you want to hover at 1/2 stick then set point #3 to 40%.

I hope I don't come across as tiresome but I don't think we're quite on the same page and I'd like to go over this again in case my previous babel didn't compute.

Maybe we have different objectives but to clarify mine: I want to get the throttle thing set up so that whatever % I dial up in the Tx for the value of one 5 curve points will actually be the % of throttle on the engine. I want 0% to close the throttle, 100% to fully open it, and to make this translation as linear as possible over the whole range it needs to be centered in that range and so that means 50% at the Tx should give an actual 50% throttle opening. Then, if I want point #4 at the Tx curve to give 40% throttle opening I'm going to be real close when I set it that way. I might find out that I have to set point #4 to 45% in order to hover at 3/4 stick, but if so then I'll read 45% at point #4 and when the stick is there I'll be pretty close to 45% on the throttle opening.

Just to be real clear about this, what the setup here does is is to give a pretty linear rate of motion to the throttle... it tracks smoothly with the throttle stick on the Tx. If you change the throttle stick by 10% anywhere in its range then the engine throttle will change by almost that same amount. That may not always be what you need or want but it's a starting place.

The stick on the Tx turns a shaft on a potentiometer control. Let's imagine that shaft going directly to the servo shaft. So now the Tx stick directly turns the servo through part of a circle. If the servo was connected to the carb barrel by means of gears then all we need to do is pick a gear ratio that will result in full stick deflections causing full throttle excursions, then synchronize this so that full stick is full throttle. That, and the gear ratio, would cause 0 stick to give 0 throttle and half stick to be half throttle and so on... 40% stick is 40% throttle. But we're using a rod instead of gears and the rod is destined to move in a sinusoidal way. As the servo turns and the rod moves the effective gear ratio between servo and throttle changes. You can see that if the servo shaft, ball, and rod are all in a straight line then a 10 deg rotation of the shaft won't move (pull) the rod much at all. Furthermore, all it can do is pull because it's already fully extended in this configuration. We get our best transfer when the angle between the rod and the servo arm (ball to center of shaft) are at a 90 deg angle. We can push and pull equally. For this to be transferred to the carb the rod has to meet that control arm at a 90 deg angle also. This makes the arms parallel. There is a third arm, the one between the control shaft at the Tx and the throttle stick. When that stick is in the middle of its range we want the imaginary direct connection to set the throttle half open. We're bypassing the throttle curve at the moment. So we loosen the bolt and adjust the arm connection to the barrel and set the barrel half open while the arms are parallel - rod meeting arms at 90 deg. Next we have to adjust the "gear ratio" so that we don't jam the servo, but we want the stick limits to open/close the throttle fully. We want plenty servo movement to get good resolution. Around 30 deg either way gives us the 60 deg time figure specified. If that jams the servo we can move the rod closer to the servo shaft or at the engine end move it farther out. That does change the angle a little but too little to bother me.

Back in the real world we have this throttle curve to deal with. I start out setting it to 0-25-75-100, throttle hold and cut off, and trim centered, so that it's effectively not there. I get my geometry set up as above, center stick (position #3 at 50%) and 90 deg between the rod and the arms with the throttle barrel half open. To keep from bending anything I don't actually hook up the rod to the servo, I just hold the hole in the link over the ball to see how it lines up when I just lightly press the link to the ball. Check the endpoints, adjust the "gear ratio" if it's a large error, or change the endpoint setting in the Tx if it's not off by much. So now when the stick is moved from end to end the carb goes from full open to close and there's no servo binding and half stick is half throttle. The stick position now represents throttle position.

If your heli will hover at 40% throttle and you want 3/4 stick hover then if point #4 is set to 40% you're going to hover real close to 3/4 stick.

If you want to hover at 1/2 stick then set point #3 to 40%.

My box is a 9C which allows throttle cut to be on a switch. I set the throttle cut to 0% and push point #1 on the curve up enough to give a decent idle. Cut shuts it all the way off. I start off on the first run with a flat pitch curve (0 deg) so that the heli doesn't go anywhere. Once I get it running at a decent idle by messing with point #1 I wind it up looking for my rpm. When I get the right rpm I estimate the % by looking at the stick and I dial that % into point #3, and set point #2 halfway to point #1. Now I should get my running rpm at half stick.. and fiddle with the value for point #3 if not. So I have my desired rpm at half stick, zero pitch. Then I restore the pitch curve. I like to hover at 3/4 stick and keep half stick at zero pitch, so from the half stick running rpm I ease the stick up towards 3/4 and listen to the engine. By 3/4 stick I should be hovering at my rpm and I fuss with point #4 throttle curve till I get the rpm to hole up to 3/4 stick. If I reach 3/4 stick and the rpm is ok but it's not hovering then I need more pitch so point #4 on the pitch curve needs to increase, and to hold rpm the throttle value at point #4 will need to increase also. Just mess with point #4 on the 2 curves till you get your 3/4 stick hover at the rpm you want. Wherever the throttle barrel points at 3/4 stick is where it needs to point for your heli at your rpm. The manual may say 40% but they don't know what kind of heli you got or what it weighs. I use a big battery so mine is a bit heavy.

archiebald

Veralee,
I honestly didn't understand about 3/4 of that.....

The problem with this....

...is that the power output from a nitro engine is often very non-linear relative to the throttle opening position.

For example, in my case on my 9C, I started out at basics with linear throttle curve, and carb / servo arms parallel, At this setting and with endpoints set to within just a few percent of 100, I got perfect full throttle at 100% and throttle cut position (0% - idle trim) at fully closed on the carb using identical length servo and carb arms. And just to be clear - I never tweak my pitch curves once set - I run 0deg pitch at mid stick and target to hover at 3/4. I keep the mid-point to max and mid-point to min pitch linear.

Now, with this set up, due to the fact that my engine / muffler combo is producing what I estimate to be around 80% of its power at less than half stick, I am naturally going to overspeed the head.

Sure, I can get around this just by adjusting the throttle curve, but in practise (not theory), this is actually giving me an extremely flat curve that only uses a tiny percentage of the available range from the Tx / servo. Read my first post for the figures.

And, maybe I am missing something. I also use a 9C that has a 5 point curve. In your example, you say you want to have a linear translation, and if, as you say, point 1 is idle, point 5 is 100% and point 3 is 50% then how are you going to get point 4 at anything like 40%?

Now, when I check the engine manual, they describe using a ratio on the linkage, also one of the World's top governor producer's says the same AND what they are saying fits into my engine characteristics perfectly, whereas the "conventional wisdom" seems to be completely the wrong way to go.

I never saw the same level of "problem" on my previous, much softer tuned engine / muffler combination, in that case, my linkage was according to "conventional wisdom" and although the throttle curve was not anywhere linear (why should it be?) it was certainly spread over the available range quite reasonably.

Anyhow, what I am now flying is giving me a vastly improved throttle transition than I had before. Power comes in progressively, more of the throttle curve range is being used, so the resolution at lower throttle openings has been improved.

And, if I understand some of your procedures correctly, I certainly would not run my heli up to any reasonable rotor speed at 0 deg pitch on the ground. Ground resonance is not a pretty sight.

veralee

The linear throttle curve is temporary, just to get the linkage set up. The linear curve basically eliminates the throttle curve from the picture. With this arrangement, half stick is made to cause half throttle with parallel arms and 90 deg between arms and rod. Then at full stick and min stick the endpoints are set to prevent jamming the servo. Once that's done the throttle curve is set to whatever you want. If your heli will hover at 40% throttle then set 40% at point #4 to hover at 3/4 stick. The purpose of the setup I described is to get the % values at the 5 points to correlate to the actual % of throttle opening. It doesn't have to be that way of course. Some other scheme might end up opening the throttle 40% by setting a value of 80% at point #4, for example. I just prefer that the values of the 5 Tx throttle points represent actual amount of throttle opening. A value of 20% at point #2 will open the throttle 20% when the stick is at 1/4, and like that.

The balance of the rotor system has to go out of whack to get ground resonance. One blade has to lead or lag more than the other. It doesn't matter what the pitch is. When you're just starting to spool up you would wait for the blades to get into the "sweet spot" (where their CGs are in line with the hub) before continuing the spool up. Once there, what's going to knock it out? A hard landing on one skid will do the trick but that's another story. I don't understand the fear of running up.