Gas engine vibrations and throttle servos
04-28-2006 | 09:59 PM
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From: Melbourne, AUSTRALIA
Gas engine vibrations and throttle servos
Hi guys, I'm building a 80inch aircraft to be powered by a modified 25cc Homelite "weed whacker" gasoline engine. Work is progressing well but I need to consider my throttle servo.
Due to the position and swing of the throttle arm on the Walbro the options for mounting my servo are limited unless I go to fancy bell cranks and the like.
Looking at the engine mounted to the firewall there is plenty of room between both to fit a normal HS-422 servo. However, it's a little tight so I'm looking for a slightly smaller servo like the HS-81.
This would allow me to mount the servo in a semi-protected position behind most of the engine, with just the servo wheel hanging out into the breeze. With a simple ball jointed linkage can then get a fairly straight push/pull on the throttle.
My concerns are this:
1. While my engine runs smoothly it will vibrate. How bad would the vibrations be on the servo?
2. Which type of gear train is better suited to vibrations: nylon or metal?
3. I could use a HS-55 but will that be able to tolerate throttle control and some vibration (also noting it would live pretty much next to the engines heat - but get lots of airflow)?
Oh, the Walbro will have the return spring removed from it so it won't place any undue load on the servo.
In summary, what servo would you use for a gasoline engine and is it such a bad thing to mount it between the engine and fireall (in the open)?
Due to the position and swing of the throttle arm on the Walbro the options for mounting my servo are limited unless I go to fancy bell cranks and the like.
Looking at the engine mounted to the firewall there is plenty of room between both to fit a normal HS-422 servo. However, it's a little tight so I'm looking for a slightly smaller servo like the HS-81.
This would allow me to mount the servo in a semi-protected position behind most of the engine, with just the servo wheel hanging out into the breeze. With a simple ball jointed linkage can then get a fairly straight push/pull on the throttle.
My concerns are this:
1. While my engine runs smoothly it will vibrate. How bad would the vibrations be on the servo?
2. Which type of gear train is better suited to vibrations: nylon or metal?
3. I could use a HS-55 but will that be able to tolerate throttle control and some vibration (also noting it would live pretty much next to the engines heat - but get lots of airflow)?
Oh, the Walbro will have the return spring removed from it so it won't place any undue load on the servo.
In summary, what servo would you use for a gasoline engine and is it such a bad thing to mount it between the engine and fireall (in the open)?
04-28-2006 | 10:26 PM
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From: Bemis,
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RE: Gas engine vibrations and throttle servos
Y'all don't want to get that servo too close to the engine, or else you are going to get ignition pulses induced back into your receivers circuitry. It's always a good idea to mount the throttle servo well in back of the firewall, and connect it to your Carb with a non conductive pushrod. You can get away with it some of the time, but not all of the time. There is nothing difficult about using proper bellcranks to do the job of linking the servo to the Carb. Do it right.
> Jim
> Jim
04-28-2006 | 10:36 PM
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RE: Gas engine vibrations and throttle servos
ORIGINAL: GeeBeeJim
Y'all don't want to get that servo too close to the engine, or else you are going to get ignition pulses induced back into your receivers circuitry. It's always a good idea to mount the throtle servo well in back of the firewall, and connect it to your Carb with a non conductive pushrod. You can get away with it some of the time, but not all of the time. There is no big deal about using proper bellcranks to do the job of linking the servo to the Carb.
Y'all don't want to get that servo too close to the engine, or else you are going to get ignition pulses induced back into your receivers circuitry. It's always a good idea to mount the throtle servo well in back of the firewall, and connect it to your Carb with a non conductive pushrod. You can get away with it some of the time, but not all of the time. There is no big deal about using proper bellcranks to do the job of linking the servo to the Carb.
I've seen the use of ferrite rings to reduce interference work very well (as least on glow motors) so would that be a feasible way to minimise interference coming from a throttle servo?
At this point I've mocked a dubro ball link to the throttle arm. The pushrod then extends near vertical (within the ball links limits) and can connect to a servo mounted approx 2 inches below the carb. The servo would be mounted off the firewall in a wooden block and thus not have any direct connection with the motor.
04-28-2006 | 10:39 PM
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RE: Gas engine vibrations and throttle servos
ORIGINAL: JoeAirPort
I'd go with the metal gear version if it's a mini. Also I prefer standard size servos for throttle, especially on a gasser. A standard with nylon gears would be fine.
I'd go with the metal gear version if it's a mini. Also I prefer standard size servos for throttle, especially on a gasser. A standard with nylon gears would be fine.
I've heard it's better to use nylon gears for applications involving vibration as the nylon will better absorb these and not wear as fast as a metal geared servo. Is this true or a bit of a strecth.
04-28-2006 | 10:52 PM
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From: Bemis,
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RE: Gas engine vibrations and throttle servos
ORIGINAL: The Raven
I've seen the use of ferrite rings to reduce interference work very well (as least on glow motors) so would that be a feasible way to minimise interference coming from a throttle servo?
I've seen the use of ferrite rings to reduce interference work very well (as least on glow motors) so would that be a feasible way to minimise interference coming from a throttle servo?
Do it your way and find out.
> Jim
04-28-2006 | 11:06 PM
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From: Arlington,
TX
RE: Gas engine vibrations and throttle servos
I have posted this before but using minature servos mounted in high vibration areas can cause servo failure in a very short period of time. Sometimes less than 5 minutes. Apparently something in the motor construction or the circuit board mounting is not up to the task. I failed several before going back to a cheap standard servo. I also watched another fellow fail 2 or 3 trying to get a multi engine ready to fly at a meet last year. If you can use a standard size I would consider it first.
Take a look at the aircraft in my gallery and you can get an idea of the sizes that I am talking about.
Take a look at the aircraft in my gallery and you can get an idea of the sizes that I am talking about.
ORIGINAL: The Raven
Hi guys, I'm building a 80inch aircraft to be powered by a modified 25cc Homelite "weed whacker" gasoline engine. Work is progressing well but I need to consider my throttle servo.
Due to the position and swing of the throttle arm on the Walbro the options for mounting my servo are limited unless I go to fancy bell cranks and the like.
Looking at the engine mounted to the firewall there is plenty of room between both to fit a normal HS-422 servo. However, it's a little tight so I'm looking for a slightly smaller servo like the HS-81.
This would allow me to mount the servo in a semi-protected position behind most of the engine, with just the servo wheel hanging out into the breeze. With a simple ball jointed linkage can then get a fairly straight push/pull on the throttle.
My concerns are this:
1. While my engine runs smoothly it will vibrate. How bad would the vibrations be on the servo?
2. Which type of gear train is better suited to vibrations: nylon or metal?
3. I could use a HS-55 but will that be able to tolerate throttle control and some vibration (also noting it would live pretty much next to the engines heat - but get lots of airflow)?
Oh, the Walbro will have the return spring removed from it so it won't place any undue load on the servo.
In summary, what servo would you use for a gasoline engine and is it such a bad thing to mount it between the engine and fireall (in the open)?
Hi guys, I'm building a 80inch aircraft to be powered by a modified 25cc Homelite "weed whacker" gasoline engine. Work is progressing well but I need to consider my throttle servo.
Due to the position and swing of the throttle arm on the Walbro the options for mounting my servo are limited unless I go to fancy bell cranks and the like.
Looking at the engine mounted to the firewall there is plenty of room between both to fit a normal HS-422 servo. However, it's a little tight so I'm looking for a slightly smaller servo like the HS-81.
This would allow me to mount the servo in a semi-protected position behind most of the engine, with just the servo wheel hanging out into the breeze. With a simple ball jointed linkage can then get a fairly straight push/pull on the throttle.
My concerns are this:
1. While my engine runs smoothly it will vibrate. How bad would the vibrations be on the servo?
2. Which type of gear train is better suited to vibrations: nylon or metal?
3. I could use a HS-55 but will that be able to tolerate throttle control and some vibration (also noting it would live pretty much next to the engines heat - but get lots of airflow)?
Oh, the Walbro will have the return spring removed from it so it won't place any undue load on the servo.
In summary, what servo would you use for a gasoline engine and is it such a bad thing to mount it between the engine and fireall (in the open)?
04-29-2006 | 02:09 PM
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From: pleasant prairie,
WI
RE: Gas engine vibrations and throttle servos
I had problems with small servos also just like Gremlin says. Don't skimp or you might pay the price. Use bellcranks or whatever. I even mount some of my servos upsidedown or sideways for proper alignment. I use the standard size servos period. I even tried the 225 metal gear and that failed on me. I wouldn't even consider trying an 81......Bill
04-29-2006 | 03:31 PM
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RE: Gas engine vibrations and throttle servos
What's wrong with using a nyrod and putting the small servo way back on the CG ?
You can put a big bend in the nyrod..When G62s first came out we did it this way, no bell crank, works just fine....
It needs some support along the length somewhere to keep it from bowing....
You can put a big bend in the nyrod..When G62s first came out we did it this way, no bell crank, works just fine....
It needs some support along the length somewhere to keep it from bowing....
04-29-2006 | 10:36 PM
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RE: Gas engine vibrations and throttle servos
When I built my Giant Aeromaster, powered by a G-62, I installed two HS-81 servos right under the cockpit. One to control the throttle and one for the firewall mounted kill switch. Both used nyrod push rods. They both failed within 4 flights. Seems that the very fine wires on the servo motors could not take the vibration. I replaced them with HS-425s and never had another problem.
While at Bomber Field in September 2004 I was talking to BB Weber about the problem. Seems that he was using HS-81s and all 4 had been knocked out by the vibration of the engines on his big Bear bomber. These were mounted in the nacelles. The engines were alcohol fueled. I don't remember him flying it in 2004. By 2005 he had put standard servos in and had a beautiful flight.
While at Bomber Field in September 2004 I was talking to BB Weber about the problem. Seems that he was using HS-81s and all 4 had been knocked out by the vibration of the engines on his big Bear bomber. These were mounted in the nacelles. The engines were alcohol fueled. I don't remember him flying it in 2004. By 2005 he had put standard servos in and had a beautiful flight.
04-30-2006 | 04:42 AM
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From: Melbourne, AUSTRALIA
RE: Gas engine vibrations and throttle servos
OK, thanks for your opinions guys. Yes, I do understand that magneto or electronic ignition gasoline motors will produce more EMI than a glow motor (which has zero ignition).
I was surprised by the consensus against mini servos, even ones with reasonable ratings like the HS-81. Even ignoring EMI, it's rather surprising to hear that people think the servos won't last in what's obviously a low torque situation. Sure the vibration is a major concern but I've seen similar servos used on big Saito four strokes that had hideous vibrations.
The suggestion to use nyrod is good but it's a physical impossibility on my engine. For starters the Walbro is mounted up on the cylinder in a Homelite which makes routing a little trickier. There is also the issue of throttle arm being at an angle and requiring a push in an upwards direction.
I will reconsider using a standard servo and look at using a bellcrank setup (painful as that will be).
I was surprised by the consensus against mini servos, even ones with reasonable ratings like the HS-81. Even ignoring EMI, it's rather surprising to hear that people think the servos won't last in what's obviously a low torque situation. Sure the vibration is a major concern but I've seen similar servos used on big Saito four strokes that had hideous vibrations.
The suggestion to use nyrod is good but it's a physical impossibility on my engine. For starters the Walbro is mounted up on the cylinder in a Homelite which makes routing a little trickier. There is also the issue of throttle arm being at an angle and requiring a push in an upwards direction.
I will reconsider using a standard servo and look at using a bellcrank setup (painful as that will be).
04-30-2006 | 05:27 AM
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RE: Gas engine vibrations and throttle servos
As everyone has already said, skip the mini or micro and go with standard size.
I use a HS-425BB right next to my engine in front of the firewall on a little "diving-board". I use a [link=http://forgues-research.com]Forgues Research[/link] fiber-optic extension to keep the Rx clean. Same thing with a firewall-mounted choke servo.
The fiber-optic extensions give you the flexibility to do some really effective linkages and they are very reliable - going strong for 520 flights.
I use a HS-425BB right next to my engine in front of the firewall on a little "diving-board". I use a [link=http://forgues-research.com]Forgues Research[/link] fiber-optic extension to keep the Rx clean. Same thing with a firewall-mounted choke servo.
The fiber-optic extensions give you the flexibility to do some really effective linkages and they are very reliable - going strong for 520 flights.
04-30-2006 | 09:17 AM
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RE: Gas engine vibrations and throttle servos
ORIGINAL: The Raven
I was surprised by the consensus against mini servos, even ones with reasonable ratings like the HS-81. Even ignoring EMI, it's rather surprising to hear that people think the servos won't last in what's obviously a low torque situation. Sure the vibration is a major concern but I've seen similar servos used on big Saito four strokes that had hideous vibrations.
I was surprised by the consensus against mini servos, even ones with reasonable ratings like the HS-81. Even ignoring EMI, it's rather surprising to hear that people think the servos won't last in what's obviously a low torque situation. Sure the vibration is a major concern but I've seen similar servos used on big Saito four strokes that had hideous vibrations.
Good luck
04-30-2006 | 04:26 PM
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From: San Antonio,
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RE: Gas engine vibrations and throttle servos
Hello,
Here is a solution which hasn't been offered. Order a twister heatdam (manifold) from Homelite. Part number PS04357. This will give you a streight shot to a servo mounted in the fusalage. This will solve all of the issues mention above. If you choose to use a mini in the cowl, do a very though range check with the engine at full throttle. Make sure that you use a resister plug. The radio manufactures don't recommend having a conductive path between the engine and the radio equipment. Fautaba recommends at least one foot (0.3 meters). I attached a picture of both standard and twister heatdams. Good luck.
Dave
Here is a solution which hasn't been offered. Order a twister heatdam (manifold) from Homelite. Part number PS04357. This will give you a streight shot to a servo mounted in the fusalage. This will solve all of the issues mention above. If you choose to use a mini in the cowl, do a very though range check with the engine at full throttle. Make sure that you use a resister plug. The radio manufactures don't recommend having a conductive path between the engine and the radio equipment. Fautaba recommends at least one foot (0.3 meters). I attached a picture of both standard and twister heatdams. Good luck.
Dave
05-01-2006 | 04:34 AM
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From: Melbourne, AUSTRALIA
RE: Gas engine vibrations and throttle servos
ORIGINAL: Big_Bird
It seems that you don't really believe our comments on the HS-81 based on your comment about the big Saito. My suggestion is for you to go ahead and use a HS-81 on your throttle and report back to us how long it lasts.
It seems that you don't really believe our comments on the HS-81 based on your comment about the big Saito. My suggestion is for you to go ahead and use a HS-81 on your throttle and report back to us how long it lasts.
05-01-2006 | 04:38 AM
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From: Melbourne, AUSTRALIA
RE: Gas engine vibrations and throttle servos
ORIGINAL: davewallace
Hello,
Here is a solution which hasn't been offered. Order a twister heatdam (manifold) from Homelite. Part number PS04357. This will give you a streight shot to a servo mounted in the fusalage. This will solve all of the issues mention above. If you choose to use a mini in the cowl, do a very though range check with the engine at full throttle. Make sure that you use a resister plug. The radio manufactures don't recommend having a conductive path between the engine and the radio equipment. Fautaba recommends at least one foot (0.3 meters). I attached a picture of both standard and twister heatdams. Good luck.
Dave
Hello,
Here is a solution which hasn't been offered. Order a twister heatdam (manifold) from Homelite. Part number PS04357. This will give you a streight shot to a servo mounted in the fusalage. This will solve all of the issues mention above. If you choose to use a mini in the cowl, do a very though range check with the engine at full throttle. Make sure that you use a resister plug. The radio manufactures don't recommend having a conductive path between the engine and the radio equipment. Fautaba recommends at least one foot (0.3 meters). I attached a picture of both standard and twister heatdams. Good luck.
Dave
Thanks for the info, I will keep my eyes open for a supplier of these manifolds.
05-01-2006 | 09:33 AM
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RE: Gas engine vibrations and throttle servos
ORIGINAL: The Raven
I'm not implying I don't believe you but I was surprised at how quickly everyone condemned the idea. I thought the mini servo, noting this one is 2Kg rated, would be more than adequate for a simple throttle setup.
ORIGINAL: Big_Bird
It seems that you don't really believe our comments on the HS-81 based on your comment about the big Saito. My suggestion is for you to go ahead and use a HS-81 on your throttle and report back to us how long it lasts.
It seems that you don't really believe our comments on the HS-81 based on your comment about the big Saito. My suggestion is for you to go ahead and use a HS-81 on your throttle and report back to us how long it lasts.
I am not surprised at how quickly everyone condemned the idea. Most of these people probably thought that you were asking an honest question and wanted an honest answer based on experience. It seems to me that you really were wanting validation for something that you were going to do anyway regardless of the safety aspects.
05-02-2006 | 06:06 PM
#21
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RE: Gas engine vibrations and throttle servos
I'm not implying I don't believe you but I was surprised at how quickly everyone condemned the idea. I thought the mini servo, noting this one is 2Kg rated, would be more than adequate for a simple throttle setup.
Just saving you the hassle of rebuilding servo mounts like I had to when the vibes killed the 81.
05-02-2006 | 08:21 PM
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From: , FL, VENEZUELA
RE: Gas engine vibrations and throttle servos
Hello guys, I´m glad to see this subject, because I almost crashed my 33% toc yak this past weekend do to a HS-225 servo failure on the throttle, I was hovering and all of the sudden I didn´t have power control no more, the servo failed about 1/4 to 1/2 of power, afortunately I got out of the situation and had to wait until the engine ran out of fuel and landed dead stick. The worst thing is that I went home and puted another HS-225 in the same place and went flying the next day thinking that the servo failed for another reason other than what you guys are talking about in this forum. My is mounted about 10 inches behind the carb with a metal pushrod. NOW I KNOW WHY MY SERVO FAILED! And I´m lucky the newone didn´t failed the next day I went Flying. Now I will remove the HS-225 miny servo from there and will use an standard futaba 148 or 3003 with a plastic rod in it. So MR RAVEN I hope you read my Story and do what this friends are telling you. DONT USE A MINY ON YOUR THROTTLE FOR A GASER!!!!!!!!!! BIG PROBABILITIS THAT IT WILL FAIL:::::::::::::::
05-02-2006 | 08:24 PM
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From: , FL, VENEZUELA
RE: Gas engine vibrations and throttle servos
I thougth just the same, I said throttles dont demand any torque, so a miny will do just fine, BUT EVERY DAY WE LEARN SOMETHING NEW!!!!!!!!!! Thanks for the INfo guys........
05-02-2006 | 10:38 PM
#24
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RE: Gas engine vibrations and throttle servos
I hear ya. I think this is a big misunderstanding about throttle servos. Everyone thinks, no torque so I will use an HS 55. True, no torque but gobs of vibration, especially gassers. Glad you got 'er down all right. I like to hear lessons learned without total losses.
ORIGINAL: raimondi
I thougth just the same, I said throttles dont demand any torque, so a miny will do just fine, BUT EVERY DAY WE LEARN SOMETHING NEW!!!!!!!!!! Thanks for the INfo guys........
I thougth just the same, I said throttles dont demand any torque, so a miny will do just fine, BUT EVERY DAY WE LEARN SOMETHING NEW!!!!!!!!!! Thanks for the INfo guys........
05-02-2006 | 11:15 PM
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RE: Gas engine vibrations and throttle servos
ORIGINAL: raimondi
I thougth just the same, I said throttles dont demand any torque, so a miny will do just fine, BUT EVERY DAY WE LEARN SOMETHING NEW!!!!!!!!!! Thanks for the INfo guys........
I thougth just the same, I said throttles dont demand any torque, so a miny will do just fine, BUT EVERY DAY WE LEARN SOMETHING NEW!!!!!!!!!! Thanks for the INfo guys........
Glad you dropped by.
