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Servo Buzzing

Old 04-10-2006, 11:53 AM
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dasintex
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Default Servo Buzzing

I am using a servo to open and close Landing gear doors; when the doors are closed the Servo buzz; I know it's because the servo is pushing the door against the gear opening frame; is this a big problem; I suspect when it is buzzing it is drawing power, is this a big drain on the battery?
Old 04-10-2006, 12:02 PM
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tadracket
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Default RE: Servo Buzzing

To answer your questions, yes and yes. Well, the last question could be up for debate. It would definatly be a bigger drain but I don't know how big of a drain. You will want to fix this to make your servo and your battery last longer. Depending on your radio, it could as easy as lowering your travel percentage.
Old 04-10-2006, 08:30 PM
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redfox435cat
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Default RE: Servo Buzzing

this is a serious problem that needs to be dealt with. you'll kill a battery quicker than anything. Try adjusting the ATV's first to stop the buzz. if it doean't stop or the door starts opening you'll either have to rework the retracts or put a hole in the door to alleviate the stress
Old 04-11-2006, 08:30 AM
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mcarleno
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Default RE: Servo Buzzing

I agree with all of the answers. This is a big problem that must be address. I had similar problems with my retracts but mine where buzing when open. I thought that I could leave them as is, get the plane started and get it up in the air quick. Took about 2 minutes to prep and get her airborne. I took off and the gear wouldn't go up and the plane was hard to control. I landed after one lap only to find that my reciever battery was now so weak it couldn't even close the retracts upside down on the bench. I got lucky that day! If you fly with this condition you will loose this aircraft (maybe not today but soon).
Old 04-11-2006, 06:03 PM
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Default RE: Servo Buzzing

I'm using Hitec 635 servos in an 11 lbs plane and they buzz a little but if you bump the stick they will quit. I made many flights with this plane and the battery stays up just fine.
Old 04-11-2006, 06:43 PM
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Default RE: Servo Buzzing

Try taking just a half turn on your linkage one way or another to relieve the end pressure on the clevis. You can sometimes check this by using the trim button to see if the buzzing stops or sometimes just bumping the stick will tell you. In your case I assume it's on a switch so it will be a little harder to find. GOOD LUCK !! ENJOY !!! RED
Old 04-11-2006, 07:25 PM
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redfox435cat
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Default RE: Servo Buzzing

I'm using 635 servos in an 11 lbs plane and they buzz a little but if you bump the stick they will quit. I made many flights with this plane and the battery stays up just fine.
thins kinda thing is fine. and almost expected. in the air that buzz will alleviate with the vibration of the engine and air flowing over the planes surfaces. a door or retract or flap well split flap anyway and recessed spoiler that is constantly holding and forcing a function is going to drain the battery and dangerously quick
Old 04-12-2006, 11:09 AM
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dasintex
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Default RE: Servo Buzzing

I appreciate the answers; let me clarify; The Plane is a P-47, the retracts are Robarts Pnuematic, and the servo controlling the valve is alright never binds, no buzzing, the gear door is mechanical, servo articulated; does not buzz on the ground when doors are open , gear down; its when the gear is retracted and the door is closed the servo buzzes and probably still buzzes while in flight. If I adjust the EPA, trim or the linkage to stop the buzzing, the gear door does not close completely; allowing the winsdtream to enter the gear compartment; if the flights were about 15 mins, do you think the drain on the 1600 Mah battery from the servo buzzing be significant, I thought of putting some thin foam tape around the door edges to seal off the door so I wouildn't have to close the door as tight to possible stop the buzzing; or to solve the problem completly, use small air cylinders and another servo/valve to open/close the gear door. What do others use to operate gear doors?

Doug.
Old 04-12-2006, 01:47 PM
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mcarleno
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Default RE: Servo Buzzing

To close all of the way, set it up like we setup servos for retracts. So that when the servo has it most force, it goes just past the zero point so that the force is against the servo past maximum. Retracts are 180 only so there is drain when extended or retracted where as standard servos have no drain at the center point (unless with force on them).

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Old 04-12-2006, 02:19 PM
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dasintex
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Default RE: Servo Buzzing

MCARLENO;

I like your suggestion, it would save me from having to re-work the whole thing; to get it clear in my mind, and correct me if I am wrong, the following: since the buzzing occurs when the Servo is underload/binding when pushing the gear door closed, set the servo arms in such a manner that the door is pushed snug where I want it, adjusting the linkage, etc and the servo arm is placed at the zero point on the Servo that is not engergized but stopped at zero; then set servo at normal or reverse accordingly to allow rotating in the right direction that will open the doors; am I on track?
Old 04-12-2006, 02:25 PM
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mcarleno
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Default RE: Servo Buzzing

You are correct sir! Put the servo so that instead of having to apply force to keep the door shut, it applies the force at 95% of the servos revolution and then allows for the servo to go beyond the apex of the curve so that the force of the door is pushing past the apex. This method works with retract servos. If you are using a standard servo, you will need to adjust your end points to maximum (120%) at the "closed" end so that the servos will not try to back off as standard servos are energized at the extents rather than the center point which is just opposite of a retract which is 180 degrees. I would just keep trying to get it adjusted. You might also want to look at adjustable arms as you can really fine tune how much travel you will need rather than just trying to figure out where to put holes in your standard servo arm.
Old 04-12-2006, 02:46 PM
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dasintex
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Default RE: Servo Buzzing

You mentioned 'Adjustable Arms' I didn't know they exist; can you shed some info in this regard; the servo I am using is a Low Profile Standard HiTec Servo because of space constraints, here is the link

http://www2.towerhobbies.com/cgi-bin/WTI0001P?&I=LXN620

now I noticed what may well be an adjustable arm; my project uses one servo with a double arm pulling/pushing the both doors open/close at the same time.

Is that what you mean by adjustable servo arms

http://www2.towerhobbies.com/cgi-bin...?&I=LXFAH0&P=7

Thanks.
Old 04-12-2006, 03:06 PM
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mcarleno
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Default RE: Servo Buzzing

Hitec comes with a single arm adjustable. If I need both arms on a hitec but need to figure out for each side where the hole needs to be, I use the adjustable arm and do one side at a time. I get the top arm working just the way I want and then measure with a caliper the radius needed and mark it on the double arm that I am going to use. Do the same with the bottom arm. Then drill new holes in the double arm so that the top and bottom are percise for each movement. Hitec servos also come with a "wheel" that has no arms. You can use this and then remove the sections not needed so that you turn the wheel into arms.
Old 04-12-2006, 04:22 PM
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dasintex
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Default RE: Servo Buzzing

Marc;

You have been great help, you seem to know this stuff pretty good where I need some help; the setting the servo arms at zero with doors closed makes all the sence in the world; but what about keeping the doors open as is the case on a P-47 when the gear is down; there is no load on the open doors other than keeping them open; would this be a big drain on the battery, although when the plane is parked you have the battery turned off, I would think the only drain would be when you turned it on to fly and doors would stay open till a point when you retract the gear upon being airborne?

Doug.
Old 04-12-2006, 04:51 PM
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mcarleno
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Default RE: Servo Buzzing

Servos don't use a lot of current to keep their position even when energized except under load. So when the doors are open the servo will be energized but there should be minimal load so that it will not draw a lot of current. A good example of this are Flaps. When have flaps, the neutral position is usually with the dial on your radio centered. This means that the flaps are deployed at 50% of their travel. When all of the way closed, the servo is drawing power to get the flap to close (servos end point) but the current is used to run the potentiometer controlled moter to move the servo to its position. Once there, it will draw very little current unless under load. So, when flaps are up, though the servo must keep them there, the load is minimal espcecially when flying. When they are lowered, the go to the other end point (fully extended). The servo must keep the flap open which now has a lot more force because of the load of the airstream; however, this will not cause a huge drain because this force as compared to a servo that can't move to its end point is minimal. Where you get the drain is when a servo must use as much current as it can draw to keep the servo in the position.

In the case of your doors, if you adjust the endpoint so that the servo is not buzing then the doors are shut. But if you get enough force to shut the doors, that strain on that the servo must overcome is provided by pulling a lot of current to keep the "Pot" engergized and the specified restance level and keeps the servo motor pushing the door shut. So if you adjust the servo so that it gets little force directly on the servo motor when the door is shut (which is where it appears the most force is), I wouldn't worry about the servo being energized to keep the doors open with the landing gear deployed as that force will be very low.

Another recommendation is that on those pushrods that may be under a fair amount of stress such as your doors, you can put a single or double coil in the push rod to allow for a little stress relief. Most park flyers run with a "V" bend in the push rods. I use either flexible cable or the coil mechanism for throttle linkage.
Old 04-12-2006, 05:50 PM
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dasintex
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Default RE: Servo Buzzing

Marc;

Again, some great advice; I will have to mess with it some more to get it right; I will be using this neat Gear/Door sequencer from Canada, that uses your Computer and measures the travel the servo makes to open the doors and activate the airvalve, remembers it, then you dowload into the memory of the sequencer, then when you flip an on/off switch assigned to the retract channel it will only allow the servos to travel the distance that was inputed into the memory; when you first set this up you use a variable slider switch like a flap switch to articulate the gear doors and valve servo to the end points you want; after all the endpoints are keyed in and the time delay between functions, you dowload into sequencer and change the switch assignment to an on/off switch.

When you flip the switch the Sequencer does the rest.

So from what you have told me, this should all work well with the sequencer I have told you about here is the link to this sequencer; let me know what you think of it?

http://www.gccustomelectronics.ca/gdc1.html
Old 04-13-2006, 09:04 AM
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mcarleno
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Default RE: Servo Buzzing

Looks cool! Interesting concept -- I've seen a number of sequencers but a programable one at this cost is pretty good.

All I can say is I watched the video and with the retracts they are using I would make sure to keep my fingers a way from the gear during operation (LOL).

Good luck and share some pictures as you go!

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