What does a poor potentiometer look like?

[woodsta888]

Some of you may know that I have in other threads, been chasing a servo judder on my 800.

I have changed the servos, removed all unnessesary electronics, tested wiring for continuity. Changed sats and sat extentions from by BD3SX FBL.

The judder still happens when servos are removed from the swash linkages. THIS ONLY happens when elevator (3 servo operation) is input and is fine and smooth on aileron (2 servos).

The judder creates large power draw from the servos dropping the available voltage to my FBL....with sats plugged in.....= brownout.

WIth the FBL enabled I can lift the heli and tilt through all direction including pitch and the servo movement is fine. Until yesterday I thought I had nailed it down to the FBL unit giving a bad elevator signal. But after thinking about it, when I tilt the heli the movement is smooth where the FBL (without tx input) is running a elevator signal to counter act the tilt then it dawned that maybe it could be a poor tx signal and I'd forgotten about the Tx and I dont have a spare.

What does a bad Tx signal/pot'gimbal look like? Can I see this in the servos will it be evident maybe as a judder?

It's a DX8

Thanks in advance

[GIXERMAN]

have you checked to monitor screen and see any movement there , also you can re-calibrate the dx8

[woodsta888]

Hi Gixerman,

I did look at the monitor screen and the movement looks OK. The servos have a fast judder.crunchyness to them that I wouldnt expect to see on the monitor. I can move the elevator and catch every %age on the monitor.

Re calibrate! Awesome I'll check the manual thanks!

[Ice-Man]

hi Woodsta888 you have just nailed it i have just put your fbl unit in the google search and guess what it came up with yes what is the voltage issue if I use Sats?The downloadable BD3SX instructions say if you use Sats you should have at least 5.5V on your control power. They also say 4S NiMh is not sufficient. So it seems reasonable to just set your BEC for 6V, use 5S NiMh, 2S LiFe, or 2S Lipo. Some people have posted that some BECs that are built in to ESC’s (internal BEC’s) do not supply enough current. If the control voltage gets pulled down too low when loaded, the Sats will “brown-out” i.e. lose connection with the TX. This is obviously something you don’t want to happen. Spektrum RX’s (even with Sats) are rated down to 3.6V and the BD3SX is rated down to 4V. So I think it’s fair to say that using a full RX buys you 1.5V of safety margin over using Sats. I’ll share with you that I have a Trex 550E running two Sats. My power system is a Castle BEC Pro along with a 5S NiMh buffer battery. I have never had a Sat brown-out

[Ice-Man]

How do I power my 3SX?This is covered in the instructions to some degree but still comes up a lot. The 3SX has a port labeled Servo4/Batt. This is where most people connect their control power. However, if you are running Sats you still need to get the Throttle signal to your ESC. If your ESC has an internal BEC, you can just plug the BEC cable into Output1. This both powers the 3SX and applies the Throttle signal to the ESC. As mentioned above, some people have claimed Sat brown-outs with underpowered internal BECs. If you use an external BEC, LiFe battery or LiPo battery, plug the power into Servo4 and plug the ESC cable into Output1. Cut the red wire only if your ESC has an internal BEC AND you have something else feeding power on Servo4. If you want to divide the power into two plugs, you can Y-cable into Output1, Servo1,2,3, or even the USB port. If you are using a full RX, the RX will get power through the cable loom but you can also plug a power cable into the RX as a second power input. The 3SX should have at least one direct connection to power. If you have a full RX, the ESC cable goes directly to the RX but if you are only using an internal BEC, you should use a Y cable so that power goes directly to the 3SX. In this case, cut the signal wire on the leg that connects to the 3SX Servo 4. You don’t want the Throttle signal applied to the signal pin on that port.

[woodsta888]

Cheers Iceman,

I have been down this route.

I have tried an external RX and whilst that may give me the room for voltage drop for no brown out it wont stop the judder through my servos and the associated large power draw and the wear on the servos. I didnt have this problem when I built the heli and it has manifested itself since. I have been running a 6.6v LiFe direct into the FBl and I dont use a BEC. My electronics are seperate from the Lipos that power the motor. I wanted to remove as many components as possible. I have 2 conections into the FBL from my (1) LiFe, one into teh Batt and 2nd into USB connection.

I thought it was the servos so I have swapped those out for v expensive futaba HV servos and I just don't want the judder to draw that much power as it is an unessessary overload on the servos gears and faster wear. I may have already ruined my cheaper align 615 & 655.

I tookmy heli into my local RC model shop and some Jet guys who are very fussy looked at it and said that the judder was unacceptable. This isn't jitter I'm on about where a servo hunts for it's centre. This is judder on the movement when applying only elevator from the Tx and these guys helped me nail it down to the FBL. But no0 one yesterday thought of the signal from the TX.

Just been out and recalibrated and it still judders but Elevator will only centre on the monitor at -2% or 2%....Never 0%

My goal here is to eliminate the judder and it's either the signal from the FBL or the Tx as I dont want to wear out my lovely new futabas (thanks Maxw)

[Ice-Man]

have you got 2 helis that you could swap them over to see if it moves from heli to heli or have you got a spare that you can swap it and see

[Guest]

Remove the fbl controller, setup a good old fashioned 3 servo swash in your TX and hook servos up to your receiver. Wiggle and pitch pump and see what happens.

MJ

[Ice-Man]

potentiometer you can get a switch cleaner but you could move it back and forth a few times to clean it to try as they just get dust inbetween and that in its self causes bad supply but thats norm over years

[woodsta888]

Tried the 450x and that seems OK though has a differnt swash setup.

I don't have my own seperate Rx they let me try it in the shop. Good idea though. Wonder if I can get the FBL off the 450 and servo plugs are the same size. I'll try that thanks.

[Ice-Man]

all the plugs should be the same size because that would narrow it down pos the fbl controler has gone faulty

Tried the 450x and that seems OK though has a differnt swash setup.

I don't have my own seperate Rx they let me try it in the shop. Good idea though. Wonder if I can get the FBL off the 450 and servo plugs are the same size. I'll try that thanks.

[woodsta888]

Thanks guys,

Plugged the 800's cyclics into the AR7200 from my 450x and the elevator input doesn't judder so it's the FBL.

Got there in the end - Some HV servos later and alot of help from Whipton Models Exeter and of course you knowledgable lot on here.

I have to say that the guys at Bavarian Demon Captron have been very helpful and their replies have been within hours. But I think I have eliminated everything now to definately send my BD3SX backto CAptron.

Thanks again.

Woodsta

[woodsta888]

Quick Update:

I emailed Bavarian Demon yesterday and I had a reply within the hour.

They said they would like to test my unit and even if they find nothing wrong they will send me a new unit so that if my issue remains they know it is not their system.

The support and service I have had from Bavarian Demon is second to none. They have given me lots of help and very very quickly too.

Well done Bavarian Demon and thanks to Joachim

[Ice-Man]

sounds like it is a fault on the unit but fair play to them mate it will be intresting what they say about it though