Which servo on throttle
08-23-2011 | 10:35 AM
#1
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From: Mumbai, INDIA
Which servo on throttle
I am about to order a DLE20 and was wondering as to which servo is required on the throttle. Will a standard ball bearing servo with nylon gears such as the Futaba s3004 be sufficient or do I need to go for a metal gear servo like HS85MG or Tower TS70 to stand up to the vibrations?
Ameyam
Ameyam
08-23-2011 | 10:48 AM
#2
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RE: Which servo on throttle
Better to go the metal gears but a well set up upper end nylon gear servo will do it. Look along the lines of a standard sized servo with a minimum of 48 oz. in. of torque. The more prescise and reactive you like to fly will determine just how fast and accurate your throttle servo will need to be. A sport flyer can get away with a standard speed, standard precision servo. Similar to what is included with most radio systems. Someone flying low and wild 3d, or precision, will usually end up wanting and using a faster precision servo. They find they don't like a lag in throttle response that impacts their other control imputs during a maneuver.
The more time and care you take in setting up the engine mounts and throttle linakge/geometry the better the chance of using a nylon geared servo. Never, ever use small servos intended for low vibration electric flight with ultro low torque on a gas engine. They get shaken to death in short order. As far as servo quality is concerned, consider; Once the throttle servo dies your plane became a heavy glider with a far less than ideal glide ratio. Are you good enough to always have the altitude and position needed to make it safely to the runway once the engine dies? Base your selection on that basis and you will be off to a good start.
The more time and care you take in setting up the engine mounts and throttle linakge/geometry the better the chance of using a nylon geared servo. Never, ever use small servos intended for low vibration electric flight with ultro low torque on a gas engine. They get shaken to death in short order. As far as servo quality is concerned, consider; Once the throttle servo dies your plane became a heavy glider with a far less than ideal glide ratio. Are you good enough to always have the altitude and position needed to make it safely to the runway once the engine dies? Base your selection on that basis and you will be off to a good start.
08-23-2011 | 11:21 AM
#4
My Feedback: (19)
RE: Which servo on throttle
ORIGINAL: spaceworm
Or, if the servo fails at WOT, then you are flying until the fuel runs out with no throttle control.[
]
Or, if the servo fails at WOT, then you are flying until the fuel runs out with no throttle control.[
]
08-23-2011 | 11:59 AM
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From: Munster,
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RE: Which servo on throttle
ORIGINAL: BarracudaHockey
Three words
Optical Kill Switch
ORIGINAL: spaceworm
Or, if the servo fails at WOT, then you are flying until the fuel runs out with no throttle control.[]
Or, if the servo fails at WOT, then you are flying until the fuel runs out with no throttle control.[
]
Optical Kill Switch
I have to agree with Barracuda......it's the primary reason I put one on my plane!
Oh and I am using an HS645 on my 71" slick (mainly cause I had one) and after 20 or so flights so far, zero issues to report
08-23-2011 | 02:08 PM
#9
RE: Which servo on throttle
I have noticed a couple of folks that had servo failures in the bigger engines so far. it seemed to happen where the modeller had used a straight stiff piano wire pushrod too.
I think it is more of a problem with the stronger engine vibrations that cause the throttle servo to fail.
The engine vibrations impart a strong forward and back movement that stresses the servo gears more.
If you use a straight piano wire pushrod, then it tends to force the servo to hold its position more and thus stresses the gears and the servo output drive transistors too.
So I think it is better to use a flex cable or even nyrod for the pushrod to control the throttle. That way you have a little give or slight sponginess there to reduce the stress on the servo.
When you think about it, the bigger engine vibrates a lot more strongly than the smaller engines do. Then the fuselage itself also vibrates. Between the two you get a strong high speed movement or flex between them to occur and that can cause a stiff pushrod to push and pull on the servo arm, which forces the servo electronics to be constantly trying to fight it. So the servo gears might fail or the output driver transistors overheat and fail.
I think it is more of a problem with the stronger engine vibrations that cause the throttle servo to fail.
The engine vibrations impart a strong forward and back movement that stresses the servo gears more.
If you use a straight piano wire pushrod, then it tends to force the servo to hold its position more and thus stresses the gears and the servo output drive transistors too.
So I think it is better to use a flex cable or even nyrod for the pushrod to control the throttle. That way you have a little give or slight sponginess there to reduce the stress on the servo.
When you think about it, the bigger engine vibrates a lot more strongly than the smaller engines do. Then the fuselage itself also vibrates. Between the two you get a strong high speed movement or flex between them to occur and that can cause a stiff pushrod to push and pull on the servo arm, which forces the servo electronics to be constantly trying to fight it. So the servo gears might fail or the output driver transistors overheat and fail.
08-23-2011 | 02:26 PM
#10
My Feedback: (19)
RE: Which servo on throttle
I use quite a few of those hard, stiff, short metal throttle pushrods. But then, I don't run the throttle all the way to the full throttle stop either. I try to set up my throttles where the servo never comes even close to stalling at the extremes of its movement. If the throttle isn't banging its head against an unmoveable wall (the throttle stop) then it only has the throttle butterfly and spring for resistance which is minimal at best. Banging against a stop, the engines vibration can surely beat the servo up in short order .... even a quality servo. Its all about proper setup.
08-23-2011 | 03:13 PM
#11
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RE: Which servo on throttle
An engine generates power through rotational force, not fore/aft forces. Although a propeller does impart minor fore/aft forces throughout the combustion impulse process, those forces are negligible as far as a throttle servo and linkage are concerned if the engine and servo are secured in and on the fuselage.
Most people destroy a throttle servo though incorrect linkage travel. I have seen many throttle linkage installations where the linkage was both too long for the application with the servo driving both itself and the carb linkage hard against the stops. As mentioned before, I have seen JR 8611's, 8711's and Hitec 5975's destroyed in only a few flights by improper linkage geometry. One servo had pretty much torn itself out of the plywood it had been attached to because of excessively long linkage and a servo at more than 100% travel. That one was the epitome of stupid, and installed by a well known competitive flyer.
I ONLY use rigid linkage, generally of carbon fiber tube material, and typically using a straight shot to the carb. Flexible linkage brings with it problems associated with a creeping throttle as temperatures change throughiut a day. Ends are attached with at minimum one ball link but typically one at each end. Neither the servo or the carb linkage EVER hit the stops. There's no reason for that to happen because a gas carb achieves full power long before the throttle plate is 100% open. The last 25% of throttle plate opening does virtually nothing for RPM performance.
Excessively long linkage mulitplies the mass of the linkage times the vibration amplitiude of an engine, which is quite hard on any servo. That becomes a vertical pounding on the servo output shaft from the end of the servo arm. Under those conditions a flexible linkage could be a better choice as long as the linkage was secured for as much of its length as possible. Of note is my not having seen a plane that needed gasser throttle linkage much longer than 8". One only needs to be a little creative and not settle for using the mounting cut outs provided by kit manufacturers. Most of my linkage lengths are between 3" and 5" in length. Some as short as 1".
Most people destroy a throttle servo though incorrect linkage travel. I have seen many throttle linkage installations where the linkage was both too long for the application with the servo driving both itself and the carb linkage hard against the stops. As mentioned before, I have seen JR 8611's, 8711's and Hitec 5975's destroyed in only a few flights by improper linkage geometry. One servo had pretty much torn itself out of the plywood it had been attached to because of excessively long linkage and a servo at more than 100% travel. That one was the epitome of stupid, and installed by a well known competitive flyer.
I ONLY use rigid linkage, generally of carbon fiber tube material, and typically using a straight shot to the carb. Flexible linkage brings with it problems associated with a creeping throttle as temperatures change throughiut a day. Ends are attached with at minimum one ball link but typically one at each end. Neither the servo or the carb linkage EVER hit the stops. There's no reason for that to happen because a gas carb achieves full power long before the throttle plate is 100% open. The last 25% of throttle plate opening does virtually nothing for RPM performance.
Excessively long linkage mulitplies the mass of the linkage times the vibration amplitiude of an engine, which is quite hard on any servo. That becomes a vertical pounding on the servo output shaft from the end of the servo arm. Under those conditions a flexible linkage could be a better choice as long as the linkage was secured for as much of its length as possible. Of note is my not having seen a plane that needed gasser throttle linkage much longer than 8". One only needs to be a little creative and not settle for using the mounting cut outs provided by kit manufacturers. Most of my linkage lengths are between 3" and 5" in length. Some as short as 1".
08-23-2011 | 05:56 PM
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From: Mumbai, INDIA
RE: Which servo on throttle
Yes, but no one has recommended a specific servo. If its metal gear servo, HS85MG and s3350 are the cheapest of the lot
Ameyam
Ameyam
08-23-2011 | 06:06 PM
#13
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RE: Which servo on throttle
ORIGINAL: ameyam
Yes, but no one has recommended a specific servo. If its metal gear servo, HS85MG and s3350 are the cheapest of the lot
Ameyam
Yes, but no one has recommended a specific servo. If its metal gear servo, HS85MG and s3350 are the cheapest of the lot
Ameyam
As suggested earlier, I'd recommend a servo of the same quality and size you have on your flight surfaces. You don't need as much torque for the throttle. I have used a variety of throttle servos on gassers but all are usually high quality, coreless motor, nylon geared (never saw the need for metal here) servos ... some digital, some analog. Some are even retired control surface servos or in my case heli servos that have a lot of life left in them but no longer popular for a heli application. Lots to choose from out there. All have higher resolution than a standard sport servo would have.
08-23-2011 | 07:22 PM
#14
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RE: Which servo on throttle
Pretty much said the same thing but left the ultimate choice up to the user. The moment one suggests a specific servo the brand and type wars erupt. You can only lead them to the water...
If I had a JR radio I would use one of the 821's that came with the radio. Somewhere between $10.00 and $15.00. I normally use a JR 4721 nylon geared coreless servo but that's a lot more than most people want to pay. Once they get into the big leagues they start to understand the reasons for the higher end servos. Until then most are looking for the cheapest servo that will fill the need. A Hitec hs645 MG would be another acceptable choice in metal gear. Another Hitec mini that works for awhile is the hs225 MG. That one is as small as I would ever consider. For Futaba, Airtronics, and the other JR brand people will have to visit the servo sheets for those manufacturers to see what they have in standard sized, metal geared servos with at least 48 ounce inches of torque.
If I had a JR radio I would use one of the 821's that came with the radio. Somewhere between $10.00 and $15.00. I normally use a JR 4721 nylon geared coreless servo but that's a lot more than most people want to pay. Once they get into the big leagues they start to understand the reasons for the higher end servos. Until then most are looking for the cheapest servo that will fill the need. A Hitec hs645 MG would be another acceptable choice in metal gear. Another Hitec mini that works for awhile is the hs225 MG. That one is as small as I would ever consider. For Futaba, Airtronics, and the other JR brand people will have to visit the servo sheets for those manufacturers to see what they have in standard sized, metal geared servos with at least 48 ounce inches of torque.
08-23-2011 | 07:50 PM
#15
RE: Which servo on throttle
i have used JR 2721s, Hitec 7985s,5485s. and Hitec 5625s with good results... my next one will use a 5485
Ive had two separate incidents where an opto kill switch and a choke servo save me from flying till i ran out of gas..... 5425mg and 225mg dont make good throttle servos, even though a major giant scale company says so [8D]
ORIGINAL: BarracudaHockey
Three words
Optical Kill Switch
ORIGINAL: spaceworm
Or, if the servo fails at WOT, then you are flying until the fuel runs out with no throttle control.[]
Or, if the servo fails at WOT, then you are flying until the fuel runs out with no throttle control.[
]
Optical Kill Switch
08-23-2011 | 07:56 PM
#16
My Feedback: (19)
RE: Which servo on throttle
A favorite throttle servo is the JR DS 8231 ... mostly because I have several of them laying around from helis. These are fairly high torque, higher than average speed coreless motor digital servos with excellent centering. They seem to last forever and have an extremely free gear train. When the power is off a throttle return spring can easily close the throttle if a servo were to fail. Again, I differ from some people and fail to see the need for metal gears in a throttle servo.
08-23-2011 | 08:00 PM
#17
RE: Which servo on throttle
ORIGINAL: Tired Old Man
An engine generates power through rotational force, not fore/aft forces. Although a propeller does impart minor fore/aft forces throughout the combustion impulse process, those forces are negligible as far as a throttle servo and linkage are concerned if the engine and servo are secured in and on the fuselage.
Most people destroy a throttle servo though incorrect linkage travel. I have seen many throttle linkage installations where the linkage was both too long for the application with the servo driving both itself and the carb linkage hard against the stops. As mentioned before, I have seen JR 8611's, 8711's and Hitec 5975's destroyed in only a few flights by improper linkage geometry. One servo had pretty much torn itself out of the plywood it had been attached to because of excessively long linkage and a servo at more than 100% travel. That one was the epitome of stupid, and installed by a well known competitive flyer.
I ONLY use rigid linkage, generally of carbon fiber tube material, and typically using a straight shot to the carb. Flexible linkage brings with it problems associated with a creeping throttle as temperatures change throughiut a day. Ends are attached with at minimum one ball link but typically one at each end. Neither the servo or the carb linkage EVER hit the stops. There's no reason for that to happen because a gas carb achieves full power long before the throttle plate is 100% open. The last 25% of throttle plate opening does virtually nothing for RPM performance.
Excessively long linkage mulitplies the mass of the linkage times the vibration amplitiude of an engine, which is quite hard on any servo. That becomes a vertical pounding on the servo output shaft from the end of the servo arm. Under those conditions a flexible linkage could be a better choice as long as the linkage was secured for as much of its length as possible. Of note is my not having seen a plane that needed gasser throttle linkage much longer than 8''. One only needs to be a little creative and not settle for using the mounting cut outs provided by kit manufacturers. Most of my linkage lengths are between 3'' and 5'' in length. Some as short as 1''.
An engine generates power through rotational force, not fore/aft forces. Although a propeller does impart minor fore/aft forces throughout the combustion impulse process, those forces are negligible as far as a throttle servo and linkage are concerned if the engine and servo are secured in and on the fuselage.
Most people destroy a throttle servo though incorrect linkage travel. I have seen many throttle linkage installations where the linkage was both too long for the application with the servo driving both itself and the carb linkage hard against the stops. As mentioned before, I have seen JR 8611's, 8711's and Hitec 5975's destroyed in only a few flights by improper linkage geometry. One servo had pretty much torn itself out of the plywood it had been attached to because of excessively long linkage and a servo at more than 100% travel. That one was the epitome of stupid, and installed by a well known competitive flyer.
I ONLY use rigid linkage, generally of carbon fiber tube material, and typically using a straight shot to the carb. Flexible linkage brings with it problems associated with a creeping throttle as temperatures change throughiut a day. Ends are attached with at minimum one ball link but typically one at each end. Neither the servo or the carb linkage EVER hit the stops. There's no reason for that to happen because a gas carb achieves full power long before the throttle plate is 100% open. The last 25% of throttle plate opening does virtually nothing for RPM performance.
Excessively long linkage mulitplies the mass of the linkage times the vibration amplitiude of an engine, which is quite hard on any servo. That becomes a vertical pounding on the servo output shaft from the end of the servo arm. Under those conditions a flexible linkage could be a better choice as long as the linkage was secured for as much of its length as possible. Of note is my not having seen a plane that needed gasser throttle linkage much longer than 8''. One only needs to be a little creative and not settle for using the mounting cut outs provided by kit manufacturers. Most of my linkage lengths are between 3'' and 5'' in length. Some as short as 1''.
08-24-2011 | 04:26 AM
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From: Duluth,
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RE: Which servo on throttle
Don't get carried away with all the Einstein launch the space shuttle theories. Regardless of the engine size any standard size servo from any manufacturer will work just fine. As for the distance from servo to motor is concerned, you would be well advised not to place the throttle servo in the vicinity of any of the engine electronics. This will limit the possibility of any interference. And yes, you can get interference with 2.4 systems and electronic or magneto ignitions. Whenever possible always ensure that the linkage does not bind in any way prior to being hooked up to the servo. A tight linkage will result in poor throttle transition. try to avoid "bell crank" linkages as well, they're a pain in the butt! Good Luck!
Loopman
Loopman
08-24-2011 | 07:58 AM
#22
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RE: Which servo on throttle
My Taurus and Brison engines use bellcranks with no problems at all. In fact, 2 Brisons still have mechanical advance and work very freely and slop free. If I have ever had a problem with bellcranks on throttles, it was from trying to use cheap ones from the airplane market. Ones designed for heli use have ball bearing pivots and are very precise ... these work great for throttle bellcranks.
08-24-2011 | 08:58 AM
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From: Tacoma,
WA
RE: Which servo on throttle
Can anyone tell me why this is called "optical"....... Optical Kill Switch ? I know that the transmitter can can control it, but why the optical term.
Thanks loads,
Ernie Misner
Thanks loads,
Ernie Misner
08-24-2011 | 09:06 AM
#24
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RE: Which servo on throttle
ORIGINAL: Ernie Misner
Can anyone tell me why this is called ''optical''....... Optical Kill Switch ? I know that the transmitter can can control it, but why the optical term.
Thanks loads,
Ernie Misner
Can anyone tell me why this is called ''optical''....... Optical Kill Switch ? I know that the transmitter can can control it, but why the optical term.
Thanks loads,
Ernie Misner
http://en.wikipedia.org/wiki/Opto-isolator
There are two types of optical kill switches in common use for gas engines. In the first type, all the electronics are contained on one board so the isolation is only the small distance that can be had on that board. In another type ... made by Smart-Fly, they actually use a piece of optical fiber between two separate boards so the only connection between the receiver and the ignition is the length of fiber. This is true isolation in my opinion. Single board units can never offer this degree of isolation.
08-24-2011 | 09:13 AM
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RE: Which servo on throttle
Thanks Truckracer. The explanation is a little over my head but I think I am getting the idea that by using an optical switch, it is immune to malfunctioning (and accidentally shutting down the engine!) Is that save to say?
Thanks again,
Ernie
Thanks again,
Ernie
