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EFI..RFI..ETC

R/C Submarine modelers

EFI..RFI..ETC

Postby Kerry Addington » Wed Sep 01, 2010 7:32 am

Gents,
I am using a Seeker-6 receiver with a Polks Tracker III and had no problems in a previous boat. Just assembled new WTC and despite "triangle" capacitors on motors,when they are running I am getting severe servo chatter. Funny thing is that it seems mainly confined to whatever servo is connected to the Ch-1 port. Servo chatter on ch-2 is minimal. I havent plugged servos into the other ports yet but wanted to send this shout-out in the meantime.
Thanks for any comment/suggestions,
Kerry
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Re: EFI..RFI..ETC

Postby Skip Asay » Wed Sep 01, 2010 8:30 am

The first thing to try is plug a servo into your other channels to determine if the problem is limited to ch 1 or is systemic. Then connect a wire between the motor case(s) and battery ground. I remember pulling my hair out a bunch of years ago while helping Bud Lederer with one of his big boats. We tried everything until finally using a jumper as stated above. Problem solved!

Hope this helps.

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Re: EFI..RFI..ETC

Postby Kerry Addington » Wed Sep 01, 2010 8:35 am

Thanks Skip!
I'll do that tonite!
check your PM for a quick followup question.
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Re: EFI..RFI..ETC

Postby Kerry Addington » Wed Sep 01, 2010 8:59 am

I will check the other receiver ports tonight.
Question- when you say run a jumper wire from the motors to 'battery ground", do you mean a 12 or 14 gauge ( power type ) wire from the motor case to the negative terminal on the battery?
Or, a wire from the motor case(s) to the negative terminal bus on the WTC endcap?
Major thanks here...
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Re: EFI..RFI..ETC

Postby PaulC » Wed Sep 01, 2010 10:22 am

Just as an aside, low transmitter or receive batteries will cause servos to jitter if you are testing the system before they actually go flat. I was tricked by this early on. :D
Warm regards,

Paul Crozier
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Re: EFI..RFI..ETC

Postby Kerry Addington » Wed Sep 01, 2010 10:35 am

Excellent point Paul!
I did notice my transmitter was down to 9.8 in the LCD window and believe my battery is good but will check/charge both tonight.
What kind of meter reading do you Tracker III guys optimally like to see?
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Re: EFI..RFI..ETC

Postby Skip Asay » Thu Sep 02, 2010 5:57 pm

"Question- when you say run a jumper wire from the motors to 'battery ground", do you mean a 12 or 14 gauge ( power type ) wire from the motor case to the negative terminal on the battery?
Or, a wire from the motor case(s) to the negative terminal bus on the WTC endcap?"

Either way should work as long as wherever you attach that wire is connected directly to the battery ground/negative terminal.

There are a couple of other things to check -
1. Make sure the wires that carry the current to the motor, both from the battery to the speed control and from the speed control to the motors, are twisted around each other.
2. Make sure these wires mentioned above are kept on the opposite side of the boat relative to the signal/servo wires.
3. The receiver itself should also be kept as far away as possible from the power wires, too.

Hope this helps.

Skip Asay
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Re: EFI..RFI..ETC

Postby Al Nuci » Fri Sep 03, 2010 10:51 am

Kerry, I find that the tracker charged up can get a reading anywhere from 10.75 to close to 11. I wanted to touch base with you about another matter and will PM you on that. Hope the info helps. Al,
Last edited by Al Nuci on Fri Sep 03, 2010 6:39 pm, edited 1 time in total.
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Re: EFI..RFI..ETC

Postby Kerry Addington » Fri Sep 03, 2010 11:13 am

Thanks very much Skip and Al.
I will use all the above input this weekend and post results.
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Re: EFI..RFI..ETC

Postby Kerry Addington » Fri Sep 03, 2010 10:05 pm

DISCOVERY- The SubTech APC-4 is the cause. Any servo with the pitch controller inline will chatter proportionately with throttle/motors.
All servos plugged directly into receiver are rock solid at any speed.
The APC-4 functions normally when motors are stopped. I have moved the APC unit a good four inches away from the ESC and no improvement.
Thoughts?
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Re: EFI..RFI..ETC

Postby Kerry Addington » Thu Sep 09, 2010 8:16 am

To update, I had a frayed wire on the ribbon from my ESC which has been repaired. I am told that levellers like the APC-4 that use an accellerometer can be more susceptible to interference although I had not experienced it in the past.
This new 'engine room' has 600 motors instead of 500's, and my wiring paths were different and 'wrong.'
I have re-routed the servo wires away from the motor/12V lines and moved the APC-4 further away from the SubViper ESC.
Glitching almost gone and tolerable at this point of construction. Increasing the distance between the APC and ESC eliminates the glitching totally. Many thanks to all who responded/replied and kept me in a positive mode that led to a fix and continuation of progress.
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Re: EFI..RFI..ETC

Postby roedj » Thu Sep 09, 2010 9:39 am

Can someone please explain to me why the cautionary advice on running power wires separate from servo wires or twisting the wires is necessary. I ask this because for over two years now I have been running my SWM Blueback with the power wires and all the servo wires jammed together into a small plastic tube that connects the front of the WTC, where the battery and receiver is, to the rear of the WTC where the motors, servos, ESC and other electronics are. All the wires are running completely parallel to each other for over eight inches. I set up this parts arrangement to separate the receiver from the other electronics, especially the ESC, as far as possible. The motor has the appropriate capacitors across the leads.

To date, I have not seen so much as a hint of servo glitching or other electronic malfunctioning. Perhaps I've just been dumb lucky. Perhaps there's something else going on here. Is there a scientific/engineering explanation for the cautions or is most of this anecdotal at best?

Dan
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Re: EFI..RFI..ETC

Postby Sub culture » Thu Sep 09, 2010 2:47 pm

When you pass electric current through a conductor/cable it creates a magnetic field. This magnetic field can induce a voltage in conductors/cables running adjacent to then, this is how transformers work. Heavier currents induce larger magnetic fields.

This effect can be particularly bad when the current is pulsed e.g like the output of an ESC or the signal wires from servos.

By twisting cables together, induced magnetic fields tend to work out of phase with one another and thus (hopefully) cancel themselves out.

These days a lot of equipment is very good at rejecting stray patterns of interference, so it's less of a problem, however it's still good practice to separate power and signal wires and twist cables together where possible, especially for submarines where everything is against us with a sub optimum operating environment and tight installations.

I find older 27mhz AM equipment to be far more fussy about noise of this type than my 40mhz FM kit, and modern 2.4ghz kit appears to be totally impervious to it, unfortunately not at all suitable for sub aquatic models.
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Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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Re: EFI..RFI..ETC

Postby roedj » Thu Sep 09, 2010 3:10 pm

Subculture,

Thanks for the reply. I am aware of the effects of coupling between wires, both inductive and capacitive especially with square waves (the servo signals) running through them. If there ever was a situation prone to that happening, it's my layout in the Blueback. All of the servos and the battery leads to the ESC are packed together very tightly and run parallel to each other. I use a Sombra FM receiver which is very good at selectivity. But still, all in all, I guess I've just been lucky. If I had the room I probably would have separated them but my greater concern was in separating the receiver and its antenna lead from all else as much as possible.

IMHO, 27MHz vs. 75MHz is more a case of AM vs. FM, FM being far superior at noise rejection.

Dan
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Re: EFI..RFI..ETC

Postby Sub culture » Fri Sep 10, 2010 1:59 pm

Some companies supply their kit with wires twisted others don't e.g. Hitec do, Futaba don't

It's a bit like the old dual conversion versus single conversion receiver debate. In practice its been found that in good fresh water the difference between the two is marginal. In swimming pools however glitching and signal loss is far superior with the dual conversion.
'Why are you staring at an empty pond?'

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