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Old Sep 27, 2012, 12:16 AM
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United States, OH, Galena
Joined Jul 2003
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I tried two different servo types, with different results:
- Four older Hitec servos (purchased in 1994)
- Two HXT900 servo (purchased in 2010)
When connected to different receivers:
- Futaba FP-R114H (Single conversion 72 MHz)
- ACE Pro 810 (Double conversion 72 MHz)
- Hitec Micro 05 (Single conversion 72 MHz, DSP)
- JR R720UL (Synthesized 72 MHz, DSP)
- FSky V8R4 (2.4 GHz)
- FrSky D6FR (2.4 Ghz, telemetry),
both servo types twitched a switch-on.
If the signal wire was pulled from the connector, the older Hitec servos did not twitch at all at switch-on, but the HXT900's twitched as before.
I then tried to connect the signal wire of the HXT900's to ground, they still twitched at switch-on.
Conclusion: disconnecting the signal wire will prevent some servos (maybe of older technology) from twitching at switch-on, but some others will not stop twitching, signal wire connected or not, or even grounded.
Twitching is greatly reduced with the older receivers (Futaba FP-R114H and Ace Pro 810) if the transmitter is on before switching receiver on. These receivers use a simple shift register decoder which requires a very short initialising time and bring the servo back to the intended position almost instantaneously.
For the other receivers (DSP or 2.4 GHz), having the transmitter on before the receiver does not really reduce the twitching.
Solution looks like applying power to servos after transmitter and receiver.
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Last edited by JMP_blackfoot; Sep 27, 2012 at 12:24 AM.
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Old Sep 27, 2012, 12:31 AM
Dean
A10FLYR's Avatar
USA, CO, Littleton
Joined Apr 2005
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I tried this out tonite. If reciever was only bound, servos would jump on switch on. After setting failsafe they would not jump when switched on...you might try that.......
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Old Sep 27, 2012, 12:53 AM
|Taranis|>|All other Tx's|
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United States, WA, Richland
Joined May 2009
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Quote:
Originally Posted by A10FLYR View Post
I tried this out tonite. If reciever was only bound, servos would jump on switch on. After setting failsafe they would not jump when switched on...you might try that.......
Well Played!
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Old Sep 27, 2012, 01:21 AM
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Joined Dec 2002
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Just tried setting f/s......... no difference .
I'm going to independantly power the flap servos at least, as these linkages are at most risk, being bottom hinged, not able to move up.
I have plenty of 2mm gold connex, so no pbm.
Makes me wonder what battering my throttle linkages are getting in my ic models, ramming against the end stops!
-
Many thanks for your interest, steve
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Old Sep 27, 2012, 01:22 AM
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Whoops...double post!
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Last edited by SteveM; Sep 27, 2012 at 02:36 AM.
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Old Sep 27, 2012, 01:55 AM
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United Arab Emirates, Dubai
Joined Sep 2006
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Quote:
Originally Posted by SteveM View Post
It is not consistent.....there is a very brief delay in tx/rx synching, during which all servos will move to a random position away from neutral, then immediatly back.
D8R II plus rx.....does it every time.
All my flavours of frsky receivers do this. (9 in all)
It is not good, Steve
Never seen that on any of my frsky RXs. Not even if I power the rx up before the radio. I'd check the servos indeed.
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Old Sep 27, 2012, 02:27 AM
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Twitching

Kilrah,

".. I'd check the servos indeed."
-
In what way?......as above, happens on Futaba, GWS,Hitec,HXT,Corona, Turnigy,JR etc.
-
Same regardless of D8R, D8R-II, D8R-II plus.
-
What concerns me, is that I am yet to convert my Sceadu Heli over to Frsky in the near future, and that has very powerful expensive Futaba digitals on the swash!!
-
Better stock up on connectors/solder etc, otherwise I will be flinching every time I switch on
-
Steve
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Old Sep 27, 2012, 02:48 AM
Happy FPV flyer
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United Arab Emirates, Dubai
Joined Sep 2006
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Sorry, hadn't seen your post with the tests, wasn't present in my email notification...
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Old Sep 27, 2012, 02:56 AM
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Joined Dec 2002
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Servo Twitch on power-on

That's OK.......as a last resort, have just emailed Eva to comment on what exists on the signal wires during this brief sync period......I guess there is nothing, and that the servos don't have anything meaningful to work with, so "throw a brief wobbly" (technical term!).
-
Will put this issue to bed, as there are far more interesting things to discuss than this "feature".
-
Rgds, Steve
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Old Sep 27, 2012, 03:28 AM
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Quote:
Originally Posted by SteveM View Post
Kilrah,

".. I'd check the servos indeed."
-
In what way?......as above, happens on Futaba, GWS,Hitec,HXT,Corona, Turnigy,JR etc.
-
Same regardless of D8R, D8R-II, D8R-II plus.
-
What concerns me, is that I am yet to convert my Sceadu Heli over to Frsky in the near future, and that has very powerful expensive Futaba digitals on the swash!!
-
Better stock up on connectors/solder etc, otherwise I will be flinching every time I switch on
-
Steve
Hi Steve,

When you power-up your receiver, there will be a "reboot time". During this period, receiver will output nothing. Some of the clutter may cause analogue servo move to "random position".

When reboot is finished, the receiver start to output normal signal (or failsafe in case the Tx is power off). That's the "move back".

This is nothing to do with the Rx. Because all the receivers do have the reboot time.

For analogue servo it's very normal, because they are more sensitive to these clutter; but on digital servo, you won't see this happen.

e.g. in video you use Corona CS239, which jitters, if you try Corona DS239 (the digital version of the same servo), you will see no jitter at all.

So, your problem might be solved by replace those "jitter" with digital servo.

Just my $.02

Regards,

K
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Old Sep 27, 2012, 03:31 AM
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Romania, Dolj, Craiova
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Hitec HS55/81, Robbe FS550 / BMS380 / MG16 / here, in various gliders, all flavors on D8R, since alpha pre-production to current II Plus, no jumping, I can post video.
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Old Sep 27, 2012, 03:55 AM
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Bedfordshire, UK
Joined Feb 2006
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I have never seen this problem with a variety of analogue servos and FrSky Rx's.

It occurs to me that I power everything from a BEC on my ESC which gives a soft power on. A glider would presumably use direct battery power which would give a sudden, and possibly noisy, power on. A digital servo would wait until the supply is stable before attempting to move whereas an analogue would move as soon as it gets power.
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Old Sep 27, 2012, 04:07 AM
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Zeeland,

YOU'VE HIT THE NAIL ON THE HEAD!!!!!

Just tried a couple of Corona digitals......all well-behaved at switch on, only once was the VERY slightest twitch observed.

Its funny....I was actually after digital slims for wings.....hk were out of stock for DS-239MG, so bought CS's instead.

Will keep these and pwr on after rx.

Many tks again for all your interest.....I think I have now worn this subject out.

Rgds , Steve
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Old Sep 27, 2012, 04:11 AM
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Trevor....just seen this...just looking for small electrolytic............
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Old Sep 27, 2012, 04:22 AM
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Only have 10 uf......no change
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