JMP Firebird servo selection help .. ??
04-09-2006 | 06:05 PM
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JMP Firebird servo selection help .. ??
I am picking out what servos to use on my JMP Firebird. I’m figuring 8411s o the ailerons, and 2721s on the flaps ( I don’t like digitals on flaps ) … As for the Rudder, will a 8611 fit in there ?? ( manual calls for a servo with the same dimensions of a 8411 which is a bit smaller)
Most importantly, how about the Elevator ? I no longer see the Multiplex Jumbo V2/stab servo specified anywhere in the Multiplex catalog. I did find a plain “jumbo” servo from multiplex on the tower hobbies site, but its rather slow at .33 transit time …. I did also find a triple bearing servo from Multiplex called the :Rhino” which has around 200 oz of torque, and a .12 transit time , and is the same size at the “jumbo” …. What are you guys using on the firebirds ? what are the available / recommended options ??
Voy
Most importantly, how about the Elevator ? I no longer see the Multiplex Jumbo V2/stab servo specified anywhere in the Multiplex catalog. I did find a plain “jumbo” servo from multiplex on the tower hobbies site, but its rather slow at .33 transit time …. I did also find a triple bearing servo from Multiplex called the :Rhino” which has around 200 oz of torque, and a .12 transit time , and is the same size at the “jumbo” …. What are you guys using on the firebirds ? what are the available / recommended options ??
Voy
04-09-2006 | 07:57 PM
#2
RE: JMP Firebird servo selection help .. ??
Why don't you like digitals on flaps, best choice ! Non use of digitals on flaps really is an old wives' tale !
Get yourself a Hangar 9 load meter, set up your digitals ACCURATELY (and just a hairs breadth away from any physical stop) and you won't have a moments trouble. Been using them on that application for years.
Regards,
David gladwin.
Get yourself a Hangar 9 load meter, set up your digitals ACCURATELY (and just a hairs breadth away from any physical stop) and you won't have a moments trouble. Been using them on that application for years.
Regards,
David gladwin.
04-09-2006 | 08:20 PM
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RE: JMP Firebird servo selection help .. ??
that’s the thing .. i don't like my flaps to be a "hairs breath" from their physical max in the up position, especially on the Firebird which i intend to fly over 300mph regularly .... By maintaining a slight pull on the flap servos in the up position, i am minimizing that as a potential flutter inducing factor. Digital servos at full torque and precise centering will pull more current, draining the battery and potentially burning something out. 2721s have worked flawlessly on flaps for my on all my planes ..
Wojtek
Wojtek
04-09-2006 | 11:56 PM
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RE: JMP Firebird servo selection help .. ??
Woj,
While I'm not sure what the multiplex servo puts out for torque, the 8611 running @ 6volts is over 300oz. Is that not enough? If not, why not gang 2 of them together like the 40% scale guys do for rudder, before the 8611 those guys were running up to 4 servo's ganged together for rudder.
While I'm not sure what the multiplex servo puts out for torque, the 8611 running @ 6volts is over 300oz. Is that not enough? If not, why not gang 2 of them together like the 40% scale guys do for rudder, before the 8611 those guys were running up to 4 servo's ganged together for rudder.
04-10-2006 | 04:08 AM
#5
RE: JMP Firebird servo selection help .. ??
Then you need to take a look at your flap servo geometry ! If you want maximum flutter resistance in the retracted position ensure that the geometry is such that the servo horn and the pushrod are in a straight line. That means that any flutter forces are trying to compress/ stretch the pushrod, moving the WHOLE sero on its mounts, which should be very solid, and the servo actually has very little work to do and has a large mechanical advantage to do what little IS neccessary ! Ideally of course in the full flap position the servo arm should have similar geometry but that would require a servo output travel of 180 degrees. This geometry also seriously considerably reduces servo current drain and, therefore, stress on the motor and associated electronics.
Of course the geometry in the intermediate flap setting is not important as speed is likely to be much lower and there fore the right servo will be able to hold it.
If thats not enough you need hydraulic screw jacks !
Regards,
David Gladwin.
Of course the geometry in the intermediate flap setting is not important as speed is likely to be much lower and there fore the right servo will be able to hold it.
If thats not enough you need hydraulic screw jacks !
Regards,
David Gladwin.
04-10-2006 | 07:21 AM
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RE: JMP Firebird servo selection help .. ??
If you want maximum flutter resistance in the retracted position ensure that the geometry is such that the servo horn and the pushrod are in a straight line.
thats only the case in the "flaps down" position. When the servo pulls the flap up, its more of a 90 deg between the arm and rod, and the servo is holding the flap up on power. ... either way, on the down or up position, you have a servo "holding" under power ... non digitals work best here. There is no need for a digital, as speed and precision are of no consequence over that of a good analog servo ..
Jeremy,
I know the 8611 is stronger than any of the multiplex servos, however the Firebird comes with a specially machined elevator rod system which also includes a special servo horn which is made for the Multiplex servos .... Im curious to see if everyone is using the recomended Multiplex servo here in the US ? I know Tom Cook says you do not need more than the 200oz torque on the elevator, and im sure thats the case as so many firebirds have had success wth it, but i would like to explore my options ... Im also concerned that the Multiplex line of servos is going away with time, along with parts support ...
Wojtek
04-10-2006 | 02:36 PM
#7
RE: JMP Firebird servo selection help .. ??
Hi Wojtek,
Multiplex no longer make the Jumbo Digi V2, but now make the Jumbo digi. It's the same servo updated a little. I must say that it is unlikely that Mpx will phase these servos out in the near future and even if they do, spares will be available for years. They have just phased out their 3030 Tx because the chips are no longer available, 18 years after launching this radio, so I doubt if this will be a worry. I can really recommend Mpx servos, I use nothing else and I have never had a failure. They are built to military specs so they are very robust.
However, I completely agree with David regarding the use of analogue servos on your flaps. I think you have your logic backwards on this one since a flap at neutral should have no load whatsoever. Whilst it is under no load, the only current draw is the quiescent current (very low). Moreover, since the real worry is flutter, provided the linkage and hinges have no slop (on a Tom Cook Model, what am I saying?), then a digital servo will provide way better flutter resistance than an analogue one.
Regards,
John
Multiplex no longer make the Jumbo Digi V2, but now make the Jumbo digi. It's the same servo updated a little. I must say that it is unlikely that Mpx will phase these servos out in the near future and even if they do, spares will be available for years. They have just phased out their 3030 Tx because the chips are no longer available, 18 years after launching this radio, so I doubt if this will be a worry. I can really recommend Mpx servos, I use nothing else and I have never had a failure. They are built to military specs so they are very robust.
However, I completely agree with David regarding the use of analogue servos on your flaps. I think you have your logic backwards on this one since a flap at neutral should have no load whatsoever. Whilst it is under no load, the only current draw is the quiescent current (very low). Moreover, since the real worry is flutter, provided the linkage and hinges have no slop (on a Tom Cook Model, what am I saying?), then a digital servo will provide way better flutter resistance than an analogue one.
Regards,
John
04-10-2006 | 03:53 PM
#8
RE: JMP Firebird servo selection help .. ??
Sorry. Woj, you've missed the point. If, in the flaps RETRACTED position, the rod and servo arm are arranged so that they are in exactly a straight line then the load on the servo is very small and the flap is held in EXACTLY the right position at very little servo load, digital servos could have been designed for exactly this application. I guaranteee that this setup gives an absolutely solid flap position and any up/down movement of the flap, as in the case of flutter, is resisted mechanically, not electronically, as the the flap movement does not translate into an angular movement of the servo arm, it just tries to rock the entire servo, which is screwed down hard thus resisting the flutter !
Regards, David Gladwin.
Regards, David Gladwin.
04-10-2006 | 04:06 PM
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RE: JMP Firebird servo selection help .. ??
04-10-2006 | 04:06 PM
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RE: JMP Firebird servo selection help .. ??
ORIGINAL: wojtek
David,
thats only the case in the "flaps down" position. When the servo pulls the flap up, its more of a 90 deg between the arm and rod, and the servo is holding the flap up on power. ... either way, on the down or up position, you have a servo "holding" under power ... non digitals work best here. There is no need for a digital, as speed and precision are of no consequence over that of a good analog servo ..
David,
thats only the case in the "flaps down" position. When the servo pulls the flap up, its more of a 90 deg between the arm and rod, and the servo is holding the flap up on power. ... either way, on the down or up position, you have a servo "holding" under power ... non digitals work best here. There is no need for a digital, as speed and precision are of no consequence over that of a good analog servo ..
Also, If I were to be in your shoes in the above "quote", I'd definitely be going digital as digital has the "Holding" power you need with deployment. The Analog servo will not have the holding power as good as digital and you will get blowback.
just my .02c
Adil
04-10-2006 | 04:15 PM
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RE: JMP Firebird servo selection help .. ??
Woj, what David is saying is exactly how I had the flaps set up on my last two Isobars. Simply program the MPX servo for about 180 degrees of throw (be CERTAIN you are not bottoming out internalyy as that is VERY bad, how do I know?) so that the pushrod is in-line with the servo arm for full down flap & full up flap. Therefore the fluttter (in the flaps up position) is resisted, as David said, mechanically, not by the servo's motion/force. The only limitation then is pushrod strength/stability or the servo case or the servo mounting. Its a REALLY solid way to do it.
04-10-2006 | 04:58 PM
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RE: JMP Firebird servo selection help .. ??
here's where the "in line " concept changes however, determining if the flap is up or down when the servo arm is in line with the rod ... if the controll horn for the flap is on the bottom of the flap, then yes, the linear set up can be of mechanical in holding the flap retracted .. the oposite is the cais in the event the linkage horn on the flap is above the flap hinge line ( Like in the case of somehting like a kingcat, bobcat, or in this case an internal set up on the Firebird) .... The only way to get aorund this would be to use a ball link and drive the servo arm to the oposite direction, and that would be especially the case if using 180 deg travel ... I do not like ball links as they do not center the force on the servo arm, but thats another issue ....
Voy
Voy
04-10-2006 | 05:00 PM
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RE: JMP Firebird servo selection help .. ??
ORIGINAL: JohnMac
Hi Wojtek,
Multiplex no longer make the Jumbo Digi V2, but now make the Jumbo digi. It's the same servo updated a little. I must say that it is unlikely that Mpx will phase these servos out in the near future and even if they do, spares will be available for years. They have just phased out their 3030 Tx because the chips are no longer available, 18 years after launching this radio, so I doubt if this will be a worry. I can really recommend Mpx servos, I use nothing else and I have never had a failure. They are built to military specs so they are very robust.
However, I completely agree with David regarding the use of analogue servos on your flaps. I think you have your logic backwards on this one since a flap at neutral should have no load whatsoever. Whilst it is under no load, the only current draw is the quiescent current (very low). Moreover, since the real worry is flutter, provided the linkage and hinges have no slop (on a Tom Cook Model, what am I saying?), then a digital servo will provide way better flutter resistance than an analogue one.
Regards,
John
Hi Wojtek,
Multiplex no longer make the Jumbo Digi V2, but now make the Jumbo digi. It's the same servo updated a little. I must say that it is unlikely that Mpx will phase these servos out in the near future and even if they do, spares will be available for years. They have just phased out their 3030 Tx because the chips are no longer available, 18 years after launching this radio, so I doubt if this will be a worry. I can really recommend Mpx servos, I use nothing else and I have never had a failure. They are built to military specs so they are very robust.
However, I completely agree with David regarding the use of analogue servos on your flaps. I think you have your logic backwards on this one since a flap at neutral should have no load whatsoever. Whilst it is under no load, the only current draw is the quiescent current (very low). Moreover, since the real worry is flutter, provided the linkage and hinges have no slop (on a Tom Cook Model, what am I saying?), then a digital servo will provide way better flutter resistance than an analogue one.
Regards,
John
thanks John, thats exactly the info I was looking for about the Multiplex Jumbo Digi .. ...
Voy
