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Dx6i Servos blip to full travel at switch on

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Chris Bott - Moderator23/12/2008 16:38:00
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I'm very very pleased with my Dx6i system and the various Rx's I've bought to go with it. I just have one niggle, on Rx switch on, all servos except throttle usually go to one end of travel and then back to center. Does anyone else's do this? On one model this pushes the servo beyond the max throw of the surface. more worryingly, I just completed a Conversion of a YT 3Demon to a twin (maybe another thread??) I used a mix of throttle to Aux to give me a second throttle output. Trouble is, I'm using a UBEC so motor power is available as soon as the power is applied. A quik blip of Aux to one end arms the ESC then dropping back to centre the motor starts at half throttle. As soon as the Tx and Rx "connect" throttle stops again but thats not the point. My fix has been to use a Y lead instead of the mix.
Tim Mackey23/12/2008 18:51:00
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Hi Chris...have you done the correct failsafe settings as per the spekky manual?

Also, ensure that you switch the TX on first, and LEAVE IT ALONE for at least 15 seconds BEFORE arming the receiver with power. If the Rx is powered up before the Tx has acquired the necessary 2 x signals then the rx acts as if its in failsafe. Sometimes the Tx ( especially the DX6i ) takes a while to find a clean channel. Also, certain receivers are notoriously slow to lock in to the Tx ( ar500 being one example )

Try that and let us know how it goes.

Frank Skilbeck23/12/2008 20:39:00
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I find it does it with some servo's and not others. What I think happens is that when you put power to the Rx power is applied to the servos but no signal, some servo's won't move until they get the position signal other go to the end of their travel. As it takes the RX 0.5s or so to boot up they move to end of travel and then back to correct position when signal is sent.

Doesn't happen with throttle because this is the only channel on failsafe on the DX6i

Chris Bott - Moderator23/12/2008 21:52:00
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Thanks Timbo, I'll give those a good try tomorrow. Many thanks.

I don't think it will be the failsafe positions, they certainly need setting up if they are!

I'll let you know what happens.

Frank you are probably right too. Different servos etc... 

I thought the throttle channel gave out no pulses at all untill the correct Tx was received.   I thought I'd seen servos sit at dead centre before, and then move to their correct trim position once the signal is established.

This twitch to one end must have been the Rx output however. It was enough to arm the speed controller, which requires a "low" throttle before it will "arm"

Eric Bray24/12/2008 13:01:00
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I thought the throttle channel gave out no pulses at all untill the correct Tx was received.   I thought I'd seen servos sit at dead centre before, and then move to their correct trim position once the signal is established.

Chris, I think you are confusing the throttle o/p of the receiver with the motor output of a speedo! The speedo (usually) will not give any output to the motor until it hears the correct low-throttle setting data from the rx.

Chris Bott - Moderator24/12/2008 13:48:00
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OK, just did a test or two on the twin.

Currently: Throttle OP from the Rx goes via Y lead to the two ESC's

1. Switch Tx on for 20 seconds, then Rx (UBEC Powered). Servos twitch, 1 aileron goes to full travel. A second or so later they all go to fully trimmed centre. ESC's Beep "Armed"

2. With Rx on and working from Tx., Switch Tx off.  Nothing moves, motors stay stopped.

3. Switch Tx back on, Rx lights come back on quite quick. Absolutely no movement from anything until a stick is moved.

Both Aileron servos are the same, they are in different chanels, so why does one go to full travel in test 1?

Thanks for your interest
Seasons Greetings
Chris

Frank Skilbeck24/12/2008 14:40:00
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Chris, I think it's as I thought earlier, apart from throttle (which has a signal because it's the only channel with failsafe) the others have no position signal (it's a voltage I think) until the Rx has booted up, but the power rail is energised immediately, some servo's see 0v as a signal and move to that end of the travel, wjereas others wait until they see a position signal.

If somebody had an oscilloscope that would be a good way to check it.

Chris Bott - Moderator24/12/2008 14:45:00
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Thanks Frank.

I have a 'scope (but no time this side of the new year now)
I'll have a good look when I have a minute.

Danny has suggested a difference between a UBEC coming up and using a Rx battery with its steady voltage. So I'll test that too.

I'll report back, but it won't be for a week or two. (Family stuff from now 'till Sat, then off to Scotland for a week over new year

Happy Christmas everyone
Chris

Brian Lambert24/12/2008 18:47:00
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Chris, now you have the new setup try re binding the rx and see if anything changes.

Brian

Doug Ireland26/12/2008 12:15:00
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Hi Chris,

I had the same problem with my DSX9 but it affected both aileron servos. The bad bit about mine was the servos would go past the end points. The two aileron servos were a different make to the others and you could clearly hear them "binding" until the tx/rx link was established.

See here

(the link thingy took a bit of sussing out but I got there in the end!)

Chris Bott - Moderator26/12/2008 13:37:00
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Thanks Doug

Well done with the link   Yes very useful, I'll let you know what the Rx does in the new year when I have time to check with a 'scope.

If the Rx puts supply volts out and no pulses until the Signal is locked, that could explain why some servos react differently to others.

Still not sure it answers why my 2 ailerons act differently? They are identical servos but plugged into Ail and Aux channels. Could the 2 channels do different things?

Doug Ireland26/12/2008 13:59:00
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I was that concerned with the possibility of damaging something that I've gone back to 35meg for this model. But another model has the new 2.4G gear and all JR servos and they only twitch on power-up, hardly noticeable. I'm waiting for the postie to deliver a new 2.4G nini rx (AR500) and I'll try that in the twitchy model.

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