Servo Help
07-25-2015, 10:46 AM
#1
Thread Starter
Join Date: Aug 2014
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
Servo Help
Aloha fellow RCU flyers,
I am having some problems installing/operating standard ball bearing Futaba servos in the fuselage of my Great Planes .61 Escapade. When I give close to max aileron and rudder input in either direction the servos make the dreaded buzzing sound and the control surfaces have an unequal distance of travel (to far in one direction and not enough in the other). When I unscrew the servo from the servo tray it wants to move forward and up out of the tray.
To try correcting the problem I repositioned the servos by sliding them left and right in tray, switching to Dubro EZ connectors so that I can adjust the length of the push rods, and repositioning the servo arms themselves. I have built two ARFS before this one and have never had this stubborn of a problem with servos. What can I try next? Any help is much appreciated.
Thanks!
I am having some problems installing/operating standard ball bearing Futaba servos in the fuselage of my Great Planes .61 Escapade. When I give close to max aileron and rudder input in either direction the servos make the dreaded buzzing sound and the control surfaces have an unequal distance of travel (to far in one direction and not enough in the other). When I unscrew the servo from the servo tray it wants to move forward and up out of the tray.
To try correcting the problem I repositioned the servos by sliding them left and right in tray, switching to Dubro EZ connectors so that I can adjust the length of the push rods, and repositioning the servo arms themselves. I have built two ARFS before this one and have never had this stubborn of a problem with servos. What can I try next? Any help is much appreciated.
Thanks!
07-25-2015, 12:16 PM
#2
Senior Member
Most probably you have the push rods binding when they move to the farthest positions. If, with nothing connected to the servo, the servos move properly, it has to be caused by binding of the push rods in there sleeves or the surfaces binding as they reach maximum throw. Sounds like a mechanical or structural problem, not a servo problem.
07-25-2015, 12:29 PM
#3
OK two different issues as far as I can tell from your description: First excessive travel of the control surface and binding, second differential travel of the control surface (traveling further in one direction than the other).
I will address the excessive travel first. Since you posted this in the beginners forum I will respond with the suggestion that with you first airplanes it is best to always use the hole on the servos arm closest to the center of the arm and on the control surface horn that you use the hole that furthest out from the control surface. This will give you the least mechanical throw and any further reductions/fine tuning can be done electronically with the transmitter if available.
Now to the differential, the servo horns must be (in the case of the fuselage servos) must be ninety degrees to the fuselage centerline. Next and here is where folks tend to screw up when they assemble an ARF is to position the control horns improperly on the control surface which induces a mechanical differential. The control surfaces horn must be positioned when installed with the hole that is to be used for the pushrods clevis or S bend directly even (fore and aft) with the hingeline of the surface. This is a very common mistake and will introduce a differential every time.
John
I will address the excessive travel first. Since you posted this in the beginners forum I will respond with the suggestion that with you first airplanes it is best to always use the hole on the servos arm closest to the center of the arm and on the control surface horn that you use the hole that furthest out from the control surface. This will give you the least mechanical throw and any further reductions/fine tuning can be done electronically with the transmitter if available.
Now to the differential, the servo horns must be (in the case of the fuselage servos) must be ninety degrees to the fuselage centerline. Next and here is where folks tend to screw up when they assemble an ARF is to position the control horns improperly on the control surface which induces a mechanical differential. The control surfaces horn must be positioned when installed with the hole that is to be used for the pushrods clevis or S bend directly even (fore and aft) with the hingeline of the surface. This is a very common mistake and will introduce a differential every time.
John
07-28-2015, 12:49 AM
#5
Thread Starter
Join Date: Aug 2014
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
OK two different issues as far as I can tell from your description: First excessive travel of the control surface and binding, second differential travel of the control surface (traveling further in one direction than the other).
I will address the excessive travel first. Since you posted this in the beginners forum I will respond with the suggestion that with you first airplanes it is best to always use the hole on the servos arm closest to the center of the arm and on the control surface horn that you use the hole that furthest out from the control surface. This will give you the least mechanical throw and any further reductions/fine tuning can be done electronically with the transmitter if available.
Now to the differential, the servo horns must be (in the case of the fuselage servos) must be ninety degrees to the fuselage centerline. Next and here is where folks tend to screw up when they assemble an ARF is to position the control horns improperly on the control surface which induces a mechanical differential. The control surfaces horn must be positioned when installed with the hole that is to be used for the pushrods clevis or S bend directly even (fore and aft) with the hingeline of the surface. This is a very common mistake and will introduce a differential every time.
John
I will address the excessive travel first. Since you posted this in the beginners forum I will respond with the suggestion that with you first airplanes it is best to always use the hole on the servos arm closest to the center of the arm and on the control surface horn that you use the hole that furthest out from the control surface. This will give you the least mechanical throw and any further reductions/fine tuning can be done electronically with the transmitter if available.
Now to the differential, the servo horns must be (in the case of the fuselage servos) must be ninety degrees to the fuselage centerline. Next and here is where folks tend to screw up when they assemble an ARF is to position the control horns improperly on the control surface which induces a mechanical differential. The control surfaces horn must be positioned when installed with the hole that is to be used for the pushrods clevis or S bend directly even (fore and aft) with the hingeline of the surface. This is a very common mistake and will introduce a differential every time.
John
Is there anyway to compensate for this or should I replace the rudder?
08-04-2015, 04:03 AM
#6
Senior Member
Join Date: Aug 2003
Location: hingham, MA
Posts: 731
Likes: 0
Received 0 Likes
on
0 Posts
we are now at the point where we need picures of the problem to determine the best course of action. try to photograph where the bind is or what is getting wedged into the fuselage like control horns
08-04-2015, 09:51 AM
#8
Thread Starter
Join Date: Aug 2014
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
https://www.youtube.com/watch?v=r38ObOWeLc8
08-04-2015, 11:08 AM
#9
OK first off screw that darn servo down otherwise all you're doing is twisting your knickers and every thing you are doing is inconclusive. Now return to the second paragraph in my post above #3 Your pushrods need to be in the closest hole to the screw on the servos output arm. Using the hole furthest out on the elevator which goes to those double pushrods which are really to close to the servo will never work and bind every time. You are demanding far to much travel of the servo and pushrod.
Now if the rudder truly goes further one way than the other with no pushrod connected the reason is very simple: here is what happened.. Who ever assembled and Ca'd the rudder pushed the rudder to tight aginst the fin period. The fix is real simple and a no brainer, stop amping about it. You really do not have a problem and you really do not need two and half inchs throw, this airplane is never going to be a 3d airplane.
John
Now if the rudder truly goes further one way than the other with no pushrod connected the reason is very simple: here is what happened.. Who ever assembled and Ca'd the rudder pushed the rudder to tight aginst the fin period. The fix is real simple and a no brainer, stop amping about it. You really do not have a problem and you really do not need two and half inchs throw, this airplane is never going to be a 3d airplane.
John
08-04-2015, 05:24 PM
#10
Senior Member
Join Date: Aug 2003
Location: hingham, MA
Posts: 731
Likes: 0
Received 0 Likes
on
0 Posts
I can see the two pushrods binding with each other. they are tied close together but the two pushrod guides try to separate them when they are pushed which is causing a lot of friction and binding as they are entering the guides. you have no problem when it pulls back because the separation get greater. the loose end pushrod guides are going to cause trouble because the guides can move front and back which can cause a sag in the pushrod so they bend more then push in the space between the ends.
why do you need two push rods? with out knowing the whole setup you need to keep the two push rods rigidly fixed with the proper spacing so they can enter the guides freely. disconnect the push rod from both the servo and the rudder and see how tight the pushrods bind up when you push them by hand with nothing connected. I have seen spacing maintained by using a round dowel. three holes are drilled in the sides. two are drilled in the sides at the horizontal. the two rudder push rods are bent 90 to go into the holes and the rest of the pushrod follows the length of the dowel this provides spacing. the other hole is drilled on the top or bottom and has a 90 bent pushrod inserted but this rod goes forward and attaches to the servo. the dowel is covered in shrink wrap to hold the rods in and keep it together
why do you need two push rods? with out knowing the whole setup you need to keep the two push rods rigidly fixed with the proper spacing so they can enter the guides freely. disconnect the push rod from both the servo and the rudder and see how tight the pushrods bind up when you push them by hand with nothing connected. I have seen spacing maintained by using a round dowel. three holes are drilled in the sides. two are drilled in the sides at the horizontal. the two rudder push rods are bent 90 to go into the holes and the rest of the pushrod follows the length of the dowel this provides spacing. the other hole is drilled on the top or bottom and has a 90 bent pushrod inserted but this rod goes forward and attaches to the servo. the dowel is covered in shrink wrap to hold the rods in and keep it together
08-04-2015, 05:32 PM
#11
Senior Member
Join Date: Aug 2003
Location: hingham, MA
Posts: 731
Likes: 0
Received 0 Likes
on
0 Posts
I can see the two pushrods binding with each other. they are tied close together but the two pushrod guides try to separate them when they are pushed which is causing a lot of friction and binding as they are entering the guides. you have no problem when it pulls back because the separation get greater. the loose end pushrod guides are going to cause trouble because the guides can move front and back which can cause a sag in the pushrod so they bend more then push in the space between the ends.
why do you need two push rods? with out knowing the whole setup you need to keep the two push rods rigidly fixed with the proper spacing so they can enter the guides freely. disconnect the push rod from both the servo and the rudder and see how tight the pushrods bind up when you push them by hand with nothing connected. I have seen spacing maintained by using a round dowel. three holes are drilled in the sides. two are drilled in the sides at the horizontal. the two rudder push rods are bent 90 to go into the holes and the rest of the pushrod follows the length of the dowel this provides spacing. the other hole is drilled on the top or bottom and has a 90 bent pushrod inserted but this rod goes forward and attaches to the servo. the dowel is covered in shrink wrap to hold the rods in and keep it together
ok split elevator that why two pushrods but they are binding getting into the guides.
looks like control horn from rudder will impact side of aircraft when the rudder is pulled. you might have to trim the bottom of the horn to allow movement of the rudder
why do you need two push rods? with out knowing the whole setup you need to keep the two push rods rigidly fixed with the proper spacing so they can enter the guides freely. disconnect the push rod from both the servo and the rudder and see how tight the pushrods bind up when you push them by hand with nothing connected. I have seen spacing maintained by using a round dowel. three holes are drilled in the sides. two are drilled in the sides at the horizontal. the two rudder push rods are bent 90 to go into the holes and the rest of the pushrod follows the length of the dowel this provides spacing. the other hole is drilled on the top or bottom and has a 90 bent pushrod inserted but this rod goes forward and attaches to the servo. the dowel is covered in shrink wrap to hold the rods in and keep it together
ok split elevator that why two pushrods but they are binding getting into the guides.
looks like control horn from rudder will impact side of aircraft when the rudder is pulled. you might have to trim the bottom of the horn to allow movement of the rudder
08-05-2015, 12:33 AM
#12
Join Date: Jul 2014
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
Champstarr
I would suggest the following steps be taken to solve your problem(s).
1. Disconnect all the elevator and rudder pushrods at the servo end, screw the elevator servo down, make sure that you don't have any trim or throw limits set in the transmitter.
2. Turn your system on and check that the two servo horns are set at 90 degrees to the for/aft axis of the servo as shown on page 6 of the assembly instructions. There should be no buzzing at this point.
3. Move the elevator and rudder sticks full travel up/down and left/right. You should see about 60 degrees of travel at the servo on each side of center and no buzzing. This is about twice the travel that you will need to get the recommended high rate throws called for, but that will be adjusted later on.
At this point you will have proven that the servos are OK.
4. Turn off the radio and measure the control surface travel as shown on pages 23 and 24 of the assembly manual by operating the pushrods by hand one at a time. If you can't easily get the travels specified, find out what is binding and fix it.
At this point you have the control surfaces proven.
5. Now, for the rudder only, reconnect the pushrod as suggested in the instructions. Turn on the radio equipment and move the stick to it's limits. The manual is showing the starting position as being the outer hole. If you get the buzzing at the end of travel, you have more servo rotation than the mechanical travel of the rudder will allow. You could probably adjust the travel limits in the transmitter but I would save that for fine tuning later. Move the pushrod in one hole on the servo and try it again. Moving the pushrod toward center reduces the linear travel of the pushrod as the servo rotates. Just keep going until the servo is quiet over its entire travel
.
At this point you should have a rudder that is operating properly.
6. Go back to page 10 of the manual. Starting with step 12 and continuing through step 15 read the instructions out loud and study the illustrations. Reading the instructions out loud helps you to focus on what you're reading, not what you think you're reading. Onlookers might think you're nuts, but you have already proven that thought because you have spent a bunch of money setting up a little airplane that flys because you wiggle a couple of little sticks! Yup, you're nuts, just like all the rest of us. In step 14 note the offset bend in the one pushrod wire. It's there so that the two wires are moving parallel to each other when clamped together. If you leave that step out, like you did in the video, it's going to bind. After you get the wires properly bent and clamped, make sure you can move them by hand smoothly through full travel.
7. Now hook up the elevator pushrod assembly as you did for the rudder and test. Keep moving in towards center one hole at a time until you get full travel and no buzzing.
I hope this helps some.
Diggr
I would suggest the following steps be taken to solve your problem(s).
1. Disconnect all the elevator and rudder pushrods at the servo end, screw the elevator servo down, make sure that you don't have any trim or throw limits set in the transmitter.
2. Turn your system on and check that the two servo horns are set at 90 degrees to the for/aft axis of the servo as shown on page 6 of the assembly instructions. There should be no buzzing at this point.
3. Move the elevator and rudder sticks full travel up/down and left/right. You should see about 60 degrees of travel at the servo on each side of center and no buzzing. This is about twice the travel that you will need to get the recommended high rate throws called for, but that will be adjusted later on.
At this point you will have proven that the servos are OK.
4. Turn off the radio and measure the control surface travel as shown on pages 23 and 24 of the assembly manual by operating the pushrods by hand one at a time. If you can't easily get the travels specified, find out what is binding and fix it.
At this point you have the control surfaces proven.
5. Now, for the rudder only, reconnect the pushrod as suggested in the instructions. Turn on the radio equipment and move the stick to it's limits. The manual is showing the starting position as being the outer hole. If you get the buzzing at the end of travel, you have more servo rotation than the mechanical travel of the rudder will allow. You could probably adjust the travel limits in the transmitter but I would save that for fine tuning later. Move the pushrod in one hole on the servo and try it again. Moving the pushrod toward center reduces the linear travel of the pushrod as the servo rotates. Just keep going until the servo is quiet over its entire travel
.
At this point you should have a rudder that is operating properly.
6. Go back to page 10 of the manual. Starting with step 12 and continuing through step 15 read the instructions out loud and study the illustrations. Reading the instructions out loud helps you to focus on what you're reading, not what you think you're reading. Onlookers might think you're nuts, but you have already proven that thought because you have spent a bunch of money setting up a little airplane that flys because you wiggle a couple of little sticks! Yup, you're nuts, just like all the rest of us. In step 14 note the offset bend in the one pushrod wire. It's there so that the two wires are moving parallel to each other when clamped together. If you leave that step out, like you did in the video, it's going to bind. After you get the wires properly bent and clamped, make sure you can move them by hand smoothly through full travel.
7. Now hook up the elevator pushrod assembly as you did for the rudder and test. Keep moving in towards center one hole at a time until you get full travel and no buzzing.
I hope this helps some.
Diggr
