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RE: Mechanical Advantage and servo setups - 12/28/2005 2:09 AM   
Troy Newman


 

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Status: offline 		Mike yes you want the pushrod also 90 degrees to the hinge line.

While its not needed to have the servo rotated in your picture. As shown in my picture the servo angle can change slightly but the servo wheel connection to pushrod is what needs to stay at the 90 deg mark. I don't think the servos should be turned 90degs because the servo can rock back and forth easier. With the servo long axis inline with the pushrod it will maximize your servo mounting leverage.

Since we mount servo on little rubber grommets to protect them from vibration they will move slightly If you have the long axis of the servo inline with the pushrod this longer "wheel base" makes the servo a more stable platform.

Remember ever force has a reaction force. If you push the aileron the aileron will push back. This will make the servo move very slightly on its mounts. If the short axis (width) of the servo is inline with the pushrod you can actually see the servo rock easier side to side.

Troy

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RE: Mechanical Advantage and servo setups - 12/28/2005 2:27 AM   
TOYMAKER



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Status: offline 		Mike, Troy,

This is great stuff. I wish I had this much info available to me the first time I built a pettern plane. There is so much I have learned in just this one thread.

One other point that merits bringing up is the hardware we use. Now for the most part I have used standard supply control horns and attachment points. Using the better connectors, clevis and control horns is WELL worth the investment. I am in the proccess of converting my current plane to the ball bearing clevis setup. After realizing what Troy and Bob P. has been preaching(instructing) for many years I have decided that changing control horns and clevis two or three times a year and having to re-trim is not worth it. I have gotten buy with it for several years but not anymore. Same with using a quality servo and its related componants.

Here are a few photos of my setup on my Aries and then a few of my Funtana. You can clearly see the difference between a precision setup and a 3D. It shows the off set of the control rod(not perfectly square at neutral) and when the servo is at its max throw how it comes square to the control surface. And the difference in the mechanical atvantage that Mike and Troy speak about.


Wayne Galligan

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< Message edited by TOYMAKER -- 12/28/2005 2:30 AM >

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RE: Mechanical Advantage and servo setups - 12/28/2005 3:02 AM   
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Status: offline 		oo pictures.. and drawings.. wonderful stuff, thanks a lot everyone!! I have yet to cu the aileron boxes in my wings so now i will be ready soon.

Chuck

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RE: Mechanical Advantage and servo setups - 12/28/2005 3:39 AM   
MikeEast



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Status: offline 		Wayne, those are really good illustrative pics..

It looks like the geometry setup is the same on both planes just more pronounced on the Funtana because of the increased throw or is that an optical illusion?.. If so your setup is exactly the same as how Im currently setup on my Genesis. Just like a 3D plane but a whole lot less pronounced angle at neutral to get the right geometry at full deflection. Or is your Aries setup like the pattern geometry picture and its just an optical illusion?



Im going to change my Genesis to look like the pattern setup pic when I get a chance. I think that is what Troy is driving at.
I hope I have enough room to move the Chip Hyde control horn over without getting off of the plywood triangle he preinstalled for us.

Troy, good point.. You can pretty much orient the servo in any direction you want, what matters is the servo arms relationship to the hingeline and the pushrod at neutral and then at full deflection depending on what you are wanting to achieve right?

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< Message edited by MikeEast -- 12/28/2005 4:35 AM >

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RE: Mechanical Advantage and servo setups - 12/28/2005 4:47 AM   
Edge 540


 

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Status: offline 		If you want to fly both 3D and pattern, I would set it up so that it is square at 50% of your endpoint. That way it is a compromise between both, and is not terribly askew at either neutral or full deflection.

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RE: Mechanical Advantage and servo setups - 12/28/2005 9:53 AM   
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Status: offline 		Mike and Troy,
I have no words to thank you! HOW MUCH I LEARNED!!!

If I can I would like to go deeper into the precise-and-repeatable throw measuerement tool. I was thinking about the requirements stated by Troy about this tool, and an idea I had in mind was to use long stick fixed to a surface, as we do to match elevator throw. Ok.

The most hard reqirement to meet is the 1/10 deg... so I did a little trigonometry. Let's imagine we have a ruler at the end of the stick, so we can read the 1/10 deg where the stick points on the ruler. Ok...What is the stick length required to read a 1/10 deg variation as a variation of say 1 mm (which is a difference we can easily see with a common ruler)? So, if we have:

a = stick length
b = 1 mm

=> a = b / sin (0.1)

This gives... a = 573 mm !!!!!!!! We should have a stick of half meter! A bit big don't you think ???

Besides that, there is another problem: this tool would be ok to measure surface position at about zero deg, but when we deflect it at say 15 deg then the measurement can't be read accurately, since the stick now is far from the ruler...

What do you think about that?

Thank you again!

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RE: Mechanical Advantage and servo setups - 12/28/2005 10:39 AM   
majortom-RCU


 

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Status: offline 		Mike, your second drawing is an example of what I would call 'offset geometry'. This is just a term I came up with on the spur of the moment, not anything that has entered the RC lexicon as far as I know. Its chief advantage IMHO is to get the last little degree of deflection and leverage out of an existing set-up.

Maximum deflection from an existing set-up would be for the servo to rotate from 90Ëš to 180Ëš, and for the pushrod at that point to rotate to where it is perpendicular to the hinge line. (This would happen only if the control horn was due south of the servo hub, rather than in the 'classic' geometry, due south of the servo arm connection point at neutral.) Also, on the rotation from 179Ëš to 180Ëš the deflection of the control surface would be absolute minimum, but the mechanical advantage in favor of the servo would be at its maximum. Of course servos don't rotate 90Ëš, but they will do 60 at maximum ATV/endpoint adjust, and the general rule is the further the servo rotates from neutral, the more leverage it has on the control surface (especially if the control horn is due south of the servo connection point with the arm/wheel at maximum rotation).

This is why I question TN's comment that the servo has its best mechanical advantage (= leverage) when it is at neutral, with pushrod perpendicular both to servo arm and hinge line. That is precisely the configuration where the servo has the least leverage, but the most speed, translating servo rotation speed to surface rotation speed.

On to a different topic, but still related: I am currently putting together a H9 Edge ARF (the old 78" ws size) for IMAC Basic, and using small deflections on ailerons & elevators. I am setting up for maximum 12Ëš deflections on elevator to start out with (but of course I can have more by just lengthening the servo moment arm). I could undoubtedly set it up for even less, since my currrent IMAC Basic model is an old Creek Sukhoi with 9Ëš throws on elevators, and that's plenty. (Screwing around with it this summer, at one point I pulled maximum elevator stick from straight and level, and the corner was sharp enough to cut with--so abrupt it tore my battery loose from its velcro attachment. I landed safely, but I will not try that trick again.)

Anyway, to get specific, for 12Ëš throws at 60Ëš maximum servo rotation, I want 5:1 leverage--control horn moment arm 5 times that of the servo moment arm. The shortest moment arm on the Hitec servo wheel I measure at 6.5 mm. Multiply 6.5 x5 and you get 32.5 mm for the control horn arm.

So now I make up elevator horns out of 1/16" sheet phenolic (easily workable, inexpensive, in convenient small sizes from Aircraft Spruce), cut in a stack so they're identical, and drilled in the same stack so their moment arms are identical. I cut slots in the elevators and epoxy them in. They are strong, light, rigid and durable--and best of all, they are whatever size you want.

This is a little bit of work, but not a huge chore on an ARF, and a hundred times better to my satisfaction than store-bought horns.
I do the same with aileron and rudder horns, except the rudder horn is just one sheet for pull/pull.

This being a pattern thread, I will note that I do the same with my pattern planes.

Credit to Jerry Nelson for the tip on phenolic as an RC material.

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RE: Mechanical Advantage and servo setups - 12/28/2005 11:32 AM   
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quote:

This is why I question TN's comment that the servo has its best mechanical advantage (= leverage) when it is at neutral, with pushrod perpendicular both to servo arm and hinge line. That is precisely the configuration where the servo has the least leverage, but the most speed, translating servo rotation speed to surface rotation speed.

Im very cautious when I agree with something that goes against Troys knowledge and expertise but I think from a common sense point of view you are probably right.. Weightlifters experience the same thing... Its easy to hold a 50pound dumbell straight up over your head. But from that point as you maintain a straight arm and begin to let your extended arm "boom down"(crane talk) straight out to the side it becomes increasingly difficult to hold the weight as you are rapidly losing mechanical advantage as you let your arm down. When the weight is straight out to the side and your arm is perpendicular to your body you are at the absolute minimum mechanical advantage and you are relying on sheer power to carry the load.IE servo torque. Im not sure that you gain enough advantage to make offset geometry worthwhile but I can certainly see your point looking at it from this analogy...



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RE: Mechanical Advantage and servo setups - 12/28/2005 11:43 AM   
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quote:



Anyway, to get specific, for 12Ëš throws at 60Ëš maximum servo rotation, I want 5:1 leverage--control horn moment arm 5 times that of the servo moment arm. The shortest moment arm on the Hitec servo wheel I measure at 6.5 mm. Multiply 6.5 x5 and you get 32.5 mm for the control horn arm.



A little correction...if you want to have 12° surface throw with 60° servo throw, you will not get a 5:1 leverage ratio, but about 4:1 actually. Reason is that you have to do the ratio between the sins, not between the angles. For that kind of calculations I've computed a formula that I find really helpful for those things, for example: what eight my control horn should be if I want 12° with 60° servo deflection with my favorite servo arm? Here's the formula, I've already posted it in the past but perhaps it could be useful here since we are speaking about these things... Here it is:

L_2 = L_1 * sin (a_1) / sin(a_2)

where:

L_1 := servo arm length
a_1 := servo arm angle

L_2 := control horn length (from the hinge line!)
a_2 := control surface angle

So, in the above example where you wanted to use 6,5 servo arm, we get:

L_2 = 6,5 * sin(60°) / sin(12°)

This gives L_2 = 27 mm. The leverage ratio is:

L_2 / L_1 = 4,16

So basically 4:1. Another formula that can be useful is the following, which reply to the question: with these servo arm and control horn, how much throw do I get at the surface?

a_2 = arcsin ( L_1 * sin(a_1) / L_2)

So if we want a real 5:1 leverage ratio, we get:

a_2 = arcsin ( sin(60°) / 5 )

Which is a_2 = 10°...



Hope you find those formula useful! Any thoughts on the measuring tool? Troy???????

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RE: Mechanical Advantage and servo setups - 12/28/2005 12:12 PM   
majortom-RCU


 

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Status: offline 		I have complete respect for Troy, and would certainly trade my modest stock of pattern/RC/YS knowledge for his in a flash. If I had the equipment and knowhow to set up with 1/10Ëš accuracy, I would certainly use it. However, once I have done the initial set-up on a new model (at 1Ëš precision, if I'm lucky), the only thing that matters after that is how it flies. And I do a lot of adjusting over the first hundred flights or so to get the throws where I want them... all part of trimming out, re-balancing, trimming out, re-balancing, etc. By the time it flies as well as I can make it fly, it seems to me the 1/10Ëš stuff is a long way down the river, and I don't have any need to revisit it. I don't know and don't care whether my deflections are XËš up and down within 1/10 of anything, but they are almost certainly not equal.

BTW, responding to the post asking about set-up tools, deflection meters, etc.: I have used a few of the commercial offerings, but now the only tool I use of this sort is a home-made protractor arrangement, extremely simple, which I mount to each individual servo case and use to verify end-points and centering accuracy. After that, if I know my end-points on a particular servo are 60Ëš or whatever, from that point on I go strictly by simple calculation, using moment arms for servo and control horn... until the model flies, at which point I ignore all the calculations and go strictly by flight behavior. Minute adjustments are in the TX, and if I need something more than minute, I re-link.

As to mfr recommended throws, I look at them, but prefer to trust my own judgement--at least for models of a type I am familiar with. A lot of them are way far off of what I prefer. Except maybe for 3D stuff, where more is better just about everywhere. But being as how I'm still learning to fly simple maneuvers with precision, 3D is strictly for goofing off, not for serious study.

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RE: Mechanical Advantage and servo setups - 12/28/2005 12:13 PM   
MikeEast



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Status: offline 		Im getting really dizzy........ the room wont stop spinning!!

Stek79,Man that is so far over my head its not EVEN funny.. I just barely passed college algebra .. That stuff looks really cool but Im a little ashamed to admit that I have absolutely no idea what it means!! I sure would like to learn though..

Sounds like you and I are a lot alike Majortom... once it flies I adjust to suit my liking.. However, I really do like the pattern linkage setup Troy taught us about, Im going to make that change since I can clearly see its advantage.

< Message edited by MikeEast -- 12/28/2005 12:18 PM >

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RE: Mechanical Advantage and servo setups - 12/28/2005 12:35 PM   
majortom-RCU


 

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Status: offline 		Well, now I have learned something. I always suspected my simple ratios were not completely accurate, so now I will have a look at Stek's formulas and see if I can put them to profitable use.

I remember taking it on faith back in trigonometry class (waay back, early 50's) that all these tables would be useful someday, and sonofagun, RC is where they come in real handy! Mike, I feel your dizziness. The odd thing is that this stuff is not so difficult to understand, except that the way our educational system teaches it is a horrible example of bureaucratic underperformance. Once you have a real life problem to relate all the abstract formulas to, if you sit down with pencil and paper and some reasonable text (book or website), I bet you can work it out. Much better to have a good teacher to help, but self-teaching can be very effective, if not always the most efficient.

Thanks Stek, you done good!

PS: The best thing I learned in college was from our Psych 101 grad assistant, who told us "You and you alone are responsible for your own education."

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RE: Mechanical Advantage and servo setups - 12/28/2005 12:56 PM   
stek79


 

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Status: offline 		Majordom,
thank you! I'm very glad that helped!

Mike, if there's something I can explain better, let me know! Summarizing, the formula let you compute two simple things:

1) What is the length of the control horn required to have for example 12° of surface deflection (i.e. on elevators) with 60° servo deflection with a given servo arm

2) Given a servo arm and control horn length, what surface throw do you get with, for example, 60° of servo throw.

I talk about 60° because that is the max throw of a common servo (with ATV to 140%).

It is a bit more clear? Since you used chip hyde control horns, perhaps these formulas are not really useful to you. But if you are going to make your own control horns, perhaps they can help

Regarding the protractor, I'm building something based on this idea:

http://www.rcaerobats.net/Throw_Gauge.htm

I printed a protractor from a doc file found on the net, so that I could resize it and make it big enough to clearly see .5 ° at least...

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RE: Mechanical Advantage and servo setups - 12/28/2005 8:34 PM   
MikeEast



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Status: offline 		Ok, that makes a lot more sense to me Stek,,, Im ignorant to trig formulas however, I will just have to see if I can figure it out when the times comes. Im going to save this info.

As far as the protractor, thats exactly what I make for myself. Slightly different look but the same principle.

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RE: Mechanical Advantage and servo setups - 12/29/2005 1:37 AM   
Bob Pastorello



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Status: offline 		Hello, guys! Since my name has been mentioned, and my web site referenced, thought I'd throw in my .01 or less' worth.
Coreless servos were developed to "solve" the lack of torque that our servos had available in the first few degrees of travel. Period. Look at all the market info when they were first introduced, you'll see that I'm right.

THE *REAL* reason we should set up control rods at 90 degrees to the hinge line at a STRAIGHT shot from servo takeoff to the control point attach on the surface is this...."fine resolution" of the immediate movements both sides of center. Combine that geometry with the best coreless servos, and you have the "feel" that we're all after.

It ain't about torque - anymore, anyway. Coreless servos really are the "must have" in pattern. Coreless digitals are even BETTER. The real "issue" is the "start up" of the servo around it's center/neutral point. THAT was solved completely with the coreless motor.

P.S. === The "real" solution to the rotational-geometry issues is to side mount the servos. Did that for years in several airplanes. Problems solved. But the "espurts" said that was bogus.....

We can learn a lot by trying things, too.

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RE: Mechanical Advantage and servo setups - 12/29/2005 6:57 AM   
MikeEast



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Status: offline 		Excellent and very help info...

up until this little jewel of a comment
quote:

You either KNOW what you're talking about, or you EXPLAIN so that others THINK you know.


Not that said knowledge of recognized guru is incorrect,,, that comment just degraded an otherwise VERY informative reply!...

I say there is a different way to look at the afforementioned 2 kinds of people,,,
1. those who talk about things such as this to help themselves and others by talking things out completely so that all can KNOW and UNDERSTAND the correct philosophy and facts regardless of "whos right and whos wrong" and
2. those who appear to just want to share their knowledge so they can show others just how much smarter and superior they THINK they are and how ignorant everyone else is in comparison....

If not for a ignorant statement made by "ME!" in another thread this excellent discussion might not have been started... Sometimes, OFTEN times the greatest learning comes by trial and ERROR..

This thread and RC flying in gerenal is about constant learning,, not about "Im right and you are wrong"... We are all in this together, and this RC flying bunch is the coolest brotherhood of folks I have been involved with in anything I have been a part of in my life. Its an honor to say Im part of the RC Airplane community. I cant get over what a generally honest, genuinely helpful and trustworthy the lot of us are.
Personally, when it comes to geometry,Im in it for the education ,,,,, but I do know a little bit.

Great info about coreless servos by the way,,, I didnt know that!

Also you say that side mounting solves the rotational geometry problems.. How so? Id like to know more about that...

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RE: Mechanical Advantage and servo setups - 12/29/2005 9:18 AM   
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Status: offline 		Go mock up a control surface attached to a servo laying on it's side, with the servo arm exactly in line with the control takeoff and the linkage 90* to hinge line. You will see why it solves the rotational geometry issue. Basically, think of two levers forming the "ends" of a rectangle, (parallelogram or rhombus), connected by a "fixed length" side (imaginary - it's the distance from the center of the servo shaft, through the surface to the center of the chordline of the movable surface where the control takeoff attaches). The "other" side of the rhombus is ALSO fixed (control rod length, servo takeoff to control arm takeoff).

Fore and aft movement is exactly linear, and differential travel offsets due to differences in the lengths of the "ends" are equal.

This is also the reason that the absolute most accurate elevator actuation is a side-mounted servo in the fuse, with the servo arm on the fuse longitudinal centerline.

However, it's highly likely that I am simply speculating with this so that I can be a troll to trash your thread.
Of course, there may be some that read this and know that I know, and am offering accurate and helpful insight in a straightforward manner.

Caveat Emptor.


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RE: Mechanical Advantage and servo setups - 12/29/2005 9:25 AM   
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Status: offline 		I agree Mike, all these GOOD infos that now we know is only thanks to your initial question... personally I didn't even know all that geometric stuff about torque... Here I can say that RCU has been of tremendous help for me guys!!!!!!!!!!!! I see that here there are people who have willingness to share their ideas, even if that ideas costed years of sperimentations and thought!!! This is wonderful, and hard to find: when you tipically speak with a top pilot, it is good if you got some "yes" and "no" answers... no more usually! At least, in my experience.

Good info about coreless servos too, thanks Bob! Also a huge thanks for sharing the protractor setup on your site, yesterday I built one following your setup and I say I'm very happy with the result! I adjusted all my throws as soon as I finished it! If can be of any interest, I applied two little mods to your idea, perhaps someone can find useful:

1) Instead of a plastic protractor, I printed one from a doc file. The advantage is that I scaled it to make it bigger: the radious is about 12 cm (4.8 inches), so more precise readings can be done. It weighs less also... I glued it to a 3mm depron sheet.

2) This is a nice idea, I found it on an astronomy site. Instead of using the needle as degree indicator, I put a cotton wire through the protractor hole. On the end of the wire, there is a small weight (even less that 2 gr!). This gives the advantage that the friction is pratically nonexistant!

So more accurate results can be achieved, I think... what do you think Bob?

Hope you find that useful...

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RE: Mechanical Advantage and servo setups - 12/29/2005 9:34 AM   
Bob Pastorello



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Status: offline 		I *LOVE* those improvements.... terrific ideas! Can you upload a pic or two? That is an important device, and the lighter you can make the chunk of stuff that hangs on the control surface, the better. The lighter the movable indicator/plumb weight, the more accurate, when used in conjunction with a larger protractor diameter!!! REALLY great ideas, thanks for sharing.

If you'd like me to post your mods and pics on my website, please email me that stuff direct, and I'll update my info!
Thanks for using the idea and improving it!

That's what these forums are about -

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RE: Mechanical Advantage and servo setups - 12/29/2005 9:42 AM   
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Status: offline 		I can't believe it you liked so much my ideas! My device on Bob's website???? Incredible...

I'm going to have some flights, then I'll take some pics Bob!!!!

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RE: Mechanical Advantage and servo setups - 12/29/2005 7:19 PM   
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quote:

Go mock up a control surface attached to a servo laying on it's side, with the servo arm exactly in line with the control takeoff and the linkage 90* to hinge line. You will see why it solves the rotational geometry issue. Basically, think of two levers forming the "ends" of a rectangle, (parallelogram or rhombus), connected by a "fixed length" side (imaginary - it's the distance from the center of the servo shaft, through the surface to the center of the chordline of the movable surface where the control takeoff attaches). The "other" side of the rhombus is ALSO fixed (control rod length, servo takeoff to control arm takeoff).

Fore and aft movement is exactly linear, and differential travel offsets due to differences in the lengths of the "ends" are equal.

This is also the reason that the absolute most accurate elevator actuation is a side-mounted servo in the fuse, with the servo arm on the fuse longitudinal centerline.


Thats makes good sense to me,, thanks for the insight! Im going to try it out and see next time I build!



quote:

However, it's highly likely that I am simply speculating with this so that I can be a troll to trash your thread.
Of course, there may be some that read this and know that I know, and am offering accurate and helpful insight in a straightforward manner.

I dont think you are speculating at all,,... I know you have a lot of knowledge, Ive followed and used your insightful comments for a long time and I have sat and visited with you at a couple of contests so I also know you are a really nice guy!

All I am/was just saying is that in your original post your comments appeared to put other people down to some how make your point MORE valid which is not necessary at all... There is no one here trying to
quote:

EXPLAIN so that others THINK you know.
Perhaps I misunderstood the intentions of what you said... If so I take it back but if not then I stand by what I say.

There is no question you have a lot of great knowledge and experience for us younger and less experienced people to learn from, I believe what you say and graciously accept your knowledge as truth and am glad to get it.. You have no enemy here.

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RE: Mechanical Advantage and servo setups - 12/29/2005 7:57 PM   
Bob Pastorello



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Status: offline 		It's all good, Mike. Some say "potato" and others say "tomato" and others say NOTHING.

Gonna slink back under my rock..... thanks for the interesting exchange!

Let us know how your experiments work out.

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RE: Mechanical Advantage and servo setups - 12/30/2005 1:50 AM   
MikeEast



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Looking forward to seeing you "yankees" up in temple (twice) this spring!

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RE: Mechanical Advantage and servo setups - 12/31/2005 6:13 AM   
MikeEast



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Status: offline 		I have a question,,, Is there any value whatsoever in sacrificing resolution to gain response speed on a throttle linkage setup? Im having a discussion with a person on another website and he is talking about using a long servo arm and a short throttle arm so that the throttle responds more quickly?. This is regarding a 3D setup on a gas airplane, but Im still having a hard time seeing the value in what he is suggesting. Wouldnt you conceiveably lose use of the full range of the throttle stick and end up with an oversensitive jerky throttle? On my Ultimate, we set it up with real high resolution on the throttle, and even still 1 click of throttle in a hover can cause the plane to sink or rise. Why would you want any more sensitivuty than that?

< Message edited by MikeEast -- 12/31/2005 6:15 AM >

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RE: Mechanical Advantage and servo setups - 12/31/2005 8:56 AM   
KeithB



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Status: offline 		stek79,

Very helpful formulas on the control surface deflections, thanks for doing the head scratching for us.

I've created and attached an Excel spreadsheet to calculate a few of the various deflection combinations:

#1: Calculate the required control horn length given the servo arm length, desired max servo deflection and desired max control surface deflection.

#2: Calculate the required servo arm length given the control horn length, desired max servo deflection and desired max control surface deflection.

#3: Calculate the control surface deflection given the servo arm length, control horn length and max servo deflection in degrees.

NOTE: In order to upload the file I had to rename it to a .TXT file. After you download it you'll need to rename it back to a .XLS file to use in Excel.

Keith B

Attachments
Click to see the file in new window.Attachment.txt


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