Paul Cataldo

My Feedback: (10)

Guys,
I have two Hitec 5645mg digitals operating my two elevator halves, and one is faster than the other. This really shows up when I loop the plane. It pulls to the right, due to the right elevator having more throw at certain stick inputs.
I have the endpoints set up the same. I am using Airwild Heavy Duty 24" servo extensions. 2400mah 6v Rx pack.
Hitec told me today to use a "booster buffered extension"
Where do I get one of these, and will it work? How exactly is it set up?
Any advice would be appreciated. Thanks.

Lynx

How are they connected to the receiver? Are they on two different channels of the RX and mixing them on the radio itself? If you're doing radio mixing that's your problem because each channel's signal is sent about 1ms later than the last. A buffered extension removes this problem by delaying the signal that's sent to the servo by the required amount. FMA direct sells them in the 'other electronics' section for 16.95 It's just a short pigtail extension you place in between the receiver channel and the servo of the lower channel. How far spaced apart are the two elevator channels, because you may need to delay it more if they're not adjacent.

Paul Cataldo

My Feedback: (10)

Lynx,
I have one on channel 2 and the other is on channel 8. Using the "ailevator" function on my Futaba 9C. Would you recommend going with the FMA booster? What exaclty do you mean by "placing the booster between the receiver and the servo of the LOWER channel?"
Which one are you referring to as the LOWER channel? Channel 8?

ml3456

Look and see if they are matched completely through all motion. Go slow and stop and multiple locations. If they do not match up at any point, its probably a linkage problem. Its easy to set the center and endpoints, but do they match inbetween! To make it easier and more accurate, take some long sticks ( 12") and tape them to the elevator at the neutral so they line up and are close to each other. Then make sure the line up through the whole travel envelope.

Mark

Paul Cataldo

My Feedback: (10)

Yeah,
Just got through doing that as a matter of fact. They are close the whole way, but there is a slight difference in between. This is due to not having a Hitec servo programmer, to adjust the neutrals. The metal servo arms fit on PRETTY close, but not exactly at the same position. Guess I'll have to find one to borrow. Thanks guys.

FLYBOY

My Feedback: (11)

I am guessing it is more a missmatch of surface than speed. The micro second miss match wouldn't cause what you are explaining. A surface not in the exact same place as the other, twist in the wing, heavy wing or a multitude of other things will cause it to do that too. I pretty sure that a milisecond will cause it to pull to one side. If it is pulling to that side through the whole loop, there is no way it can be the speed of the servo. Also make sure your wing and stab are lined up propperly.

causeitflies

You can swap the servo plugs at the RX and see if the problem is reversed to the other servo. If not, swap the servos themselves to see if it is a surface problem.

ec121k

Before you start trying to correct this problem with servos, make sure that the airplane is balanced. Suspend it along the centerline and make sure you don't have a wing heavy condition. That will do it for sure. Also make sure you don't have any warps.

Another thing to try is to deflect the elevators in the up direction and pre load them with the same force. Could be a spring scale or weight. You might have one linkage that is flexing more than the other under load. You need to be rather precise with the load from side to side.

Then go to the servo swapping like in the previous post.

Remember, the more "G's" you pull, the more the wing heavy condition will be apparent.

Lynx

Flyboy it's not a micro it's milli seconds that's three orders of magnitude higher.. If one is on channel 2 and the other is on channel 8 You have (using standard throws) a minimum of a 6ms and a max of 12ms variable delay. With high speed digital servo's you WILL notice a difference in your control surfaces if one elevator reacts 12ms before the other to control inputs. You can either try to mix it out or get a servo delay to help even things out a bit. Thing is I don't know if the delay can make up for a full 6 channel difference.

Geistware

My Feedback: (16)

I have found that with analog servos, that this difference only shows up when I move the controls fast. When I move it slow, it does not exist!

I have seen where the center to down movement is consistant and the cetner to up movement does not track but matches at the center and endpoint.

Lynx

It happens with all servo's at all speeds. The pulses sent to a servo are about 50 times per second so you need a fairly large degree of lag for a human eye to see it visably. Check the output on a scope though and the pulses wouldn't even show up on the same screen at 6 channels difference. You will see a degree of variability though because as the info to the other channels change the pulse spacing changes as well

FLYBOY

My Feedback: (11)

Lynx, I understand that, but as he stated, he notices it more during loops when the stick is at a certain deflection. This tells me that there is something else going on.

Lynx

In a loop the control surfaces are at a significant load, and minor differences in control surface orientation will show up where they won't at slower speeds because the load differential isn't high enough.

Geistware

My Feedback: (16)

I must have good eyes.
I can see the lag easily!

rajul

My Feedback: (58)

This thread has made me consider whether to go for two servos on separate channel, or hook up two servos on the same channel with a synchronizer in between. I think Futaba has one at the same price of a servo

FLYBOY

My Feedback: (11)

Exactly, if the surfaces are not deflecting the same, the loop will be a clover leaf. It is the amount of deflection, not the speed of the servo. Thats what I was getting at. The deflection has to be right. if it were the speed of the servo, you would only notice it for a second. If it were the amount of deflection of one surface being more than the other, the loop would not be round, the plane would turn in the loop. That is what I was trying to say. The speed of the servo wouldn't cause what he said was the problem.

Paul Cataldo

My Feedback: (10)

Thanks for all the info fellas.
I believe the cause is that the metal Airwild MLP servo arms will not fit on the exact same on each servo. I need the Hitec servo programmer to adjust the neutrals to make them the same.

FLYBOY

My Feedback: (11)

There you go. Hope that works out. If one is pushing more than the other, the surface won't move the same amount and you will get a rolling effect.

RJConnet

Paul,

Doesn't your 9C have a sub-trim function on both channel 2 & 8 that will allow you to set the neutrals on both servos to an identical and exact neutral? Then you can make your end-point adjustments to give you equal throws. Even my ancient Prism 7 allows me to do this.

RJ

Paul Cataldo

My Feedback: (10)

RJ,
Yes, it does. However, I experimented last night, and the sub trim would have to go to about 35 or 40, which PHYSICALLY isn't much of a distance to move, BUT it ended up taking away somewhere in between 5-10 degrees of throw from my elevator half. This was unacceptable. Anytime I can avoid using sub trims, I do, as I want as much throw as possible. As you probably know, ANY time you adjust the sub trim, you are taking away from the servos max endpoints.

Dave763

My Feedback: (1)

Get the programmer, set the center , end point and check the speed to be sure they are the same. My SWB arms did not fit on the same when they(5645s and 5735s) were new.After setting the center to 0, all my SWB arms fit perfectly! 90 degrees to the servo case!

RJConnet

Paul,

You might take a look at my post on Pg. 3 of the Radio Manufacturers Sub-Forum. Somewhat of a hassle but without buying the programmer I don't know what else to do.

RJ