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[SwedishProjectBuilder]

Could not find a thread about it. If there is, please redirect me.


X-tail rudder with 4 servos using 2 channel signals.
It's possible to do by first mixing the signals with an single V-tail mixer and then duplicate the resulting signals. ending up with 4.
If connecting the servos correctly its possible to get the desired signal combinations.


Problem is, when doing this the servos "twitch" a lot (they turn the right way but spin a few degrees back and forward) like it seems to not getting "enough" power.
Is this correct? or is there someone who knows why they are twitching and if its possible to correct this?


Is there any other good way to make an x-rudder control?




Old picture. Submarine seen from the aft. Translation: Up, Down, Right and Left

[Martin (Admin)]

First thing to try, disconnect ALL mechanical linkages to the servos and try again.
( Also, some modellers have reported problems if a florescent light fitting is near the work bench. )

[Netleyned]

First thing to try, disconnect ALL mechanical linkages to the servos and try again.
( Also, some modellers have reported problems if a florescent light fitting is near the work bench. )

If using 2.4GHz for testing in close proximity to a Wireless Router (Same Frequency)
strange things have been known to happen


Ned

[Subculture]

I've experienced this problem with mixers. I think you will find the issue is the way a lot of modern receivers work, especially 2.4ghz ones. They output all channel pulses simultneously, whereas older receivers squirt out the channels in a sequential fashion, one after the other at a 50hz (20ms) frame rate.

The x or v-tail mixer usually has just one microprocessor built in to do the mixing, and it's programmed to read one channel, then the next, mix the two together and output to the servos.
With the newer receivers, the two channels arrive at the same time, and the microprocessor can't read the pulses accurately, hence the twitching.

Some manufacturers have realised this and modified the designs of the mixers to suit (e.g. fitting twin processors, or using devices which can read more than one input at the same time), but you need to ensure you have a mixer that conforms to this.

Either that or just use the mixer with an older receiver.

Other methods of mixing? Use an inbuilt v-tail mixer in the TX (many have them) or make a mechanical mixer on the boat, which is quite involved.

[Circlip]

And if using 2.4 gigglies, you're going to loose control when dropping it into the water.
 
  Regards  Ian.

[SwedishProjectBuilder]

I've experienced this problem with mixers. I think you will find the issue is the way a lot of modern receivers work, especially 2.4ghz ones. They output all channel pulses simultneously, whereas older receivers squirt out the channels in a sequential fashion, one after the other at a 50hz (20ms) frame rate.

The x or v-tail mixer usually has just one microprocessor built in to do the mixing, and it's programmed to read one channel, then the next, mix the two together and output to the servos.
With the newer receivers, the two channels arrive at the same time, and the microprocessor can't read the pulses accurately, hence the twitching.

Some manufacturers have realised this and modified the designs of the mixers to suit (e.g. fitting twin processors, or using devices which can read more than one input at the same time), but you need to ensure you have a mixer that conforms to this.

Either that or just use the mixer with an older receiver.

Other methods of mixing? Use an inbuilt v-tail mixer in the TX (many have them) or make a mechanical mixer on the boat, which is quite involved.

Well, when I experienced this twitching-issue I were using 35MHz radio. The thing is that it worked rather well when inserting the V-tail mixer to the receiver and then connecting two servos to the V-tail mixer.
The twitching got ridiculous when connecting "split cables", duplicating each signal into two cables, to connect to 4 servos.
Can this issue be because of insufficient power? Do I need to use a booster of some sort?
Also, had have thoughts on connecting 2 duplicator cables to the receiver making 2 cables into 4 cables. And then connecting 2 V-tail mixers to these 4 cables and then 4 servos to the v-tail mixers.


I would love to make the mixer mechanical but am not sure if I can spare the room in the sub..

And if using 2.4 gigglies, you're going to loose control when dropping it into the water.
 
  Regards  Ian.

Yeap, am aware of that. Therefor will be using 35MHz..




Cheers

[Subculture]

Okay. Think Ned threw a red herring into the mix by mentioning 2.4ghz.

If the mixer works well with two servos connected, but gets erratic when you double the servos, then this does indeed sound like a power supply issue.

What are you using to power the receiver and servos. Are you using a BEC of some description?

[SwedishProjectBuilder]

What are you using to power the receiver and servos. Are you using a BEC of some description?

If I've understood the specification of BEC correctly, then no.
Forgot to mention that these "experiments" where undertaken 2 years ago when I, together with a friend, built our very first submarine for a school project. (http://www.modelboatmayhem.co.uk/forum/index.php?topic=26858.0) Thus the old receiver not accessible at the moment, but I believe it was this sort of receiver:
Feigao 35MHz 6 Channels FM Mini Receiver
http://www.himodel.com/radios/Feigao_35MHz_6_Channels_FM_Mini_Receiver.html
With 6V I believe.

I even found a video of it, which I had forgot about:
http://www.youtube.com/watch?v=bDl90i1YcAw

So no, because we only used 4-channels on the receiver and the outputs was only for servos. (The ballast tank and propeller motor were controlled via mechanical switches, controlled by two of the servos. The black servos in the youtube-clip.)


Cheers! 

[malcolmfrary]

Servos do need a very stable power supply because the use a voltage derived from their supply as a reference for timing the pulse length that determines the position that they take up.  Voltage varying due to load changes can be caused by other devices powered down the same lead working and drawing power. 
This is a possible downside of Y leads and anything being used like one.  The answer is probably to make a distribution panel to allow the signal to fan out as wanted, but have all the servos powered direct from the battery, rather than via the receiver.  The mixer will be adding to the confusion because it too will probably require a stable voltage.  In either case, extra connections between source and destination don't help.  The info on the RX gives a surprisingly wide voltage range - it might have an internal BEC for its own circuit, but probably not for anything else.
Here in the UK, using 35MHz is illegal for anything other than aircraft, don't know what the rules are in Sweden.

[SwedishProjectBuilder]

I suspected something similar..
Fortunately we have a course about electronics at university the next autumn.
Therefor most of the electronics for my sub will be onhold for a while.

Thanks for the help! 

And yes, I believe that 35MHz is only for heli and aircraft in Sweden too.
Wont be using 35Mhz for the new sub.

Cheers