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Author Topic: interference protection  (Read 2169 times)

hopeitfloats

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interference protection
« on: May 31, 2009, 11:00:16 AM »

i read somewhere in the forums that you can cut down electrical interference through servos by wrapping the leads in i think it was aluminium foil.  the rudder servo lead on my new build will run close to the motor (50mm from it). i'm not at the stage of running it yet but it would be a bit easier to wrap it now than later. any thoughts as to whether it would likely be of any benefit.  call it preventative maintanence. dont know if length of lead would have a bearing on it but its about 500mm long
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stallspeed

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Re: interference protection
« Reply #1 on: May 31, 2009, 11:05:14 AM »

It would be of no benefit at all to wrap it in foil.
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cos918

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Re: interference protection
« Reply #2 on: May 31, 2009, 11:34:27 AM »

Hi there. The main cause of interference is electrical noise cause by the motors , this is fixed by 3 suppression capacitors on the motor. If you are using a high power motor and your servo lead ran a long side it for a reasonable length you can get back E.M.F . the easiest way to fix this is to use a graphite core and run your servo lead through in once or twice. This core breaks down the magnetic field made by the back E.M.F.

John
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hopeitfloats

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Re: interference protection
« Reply #3 on: May 31, 2009, 12:13:41 PM »

is a 'toroid ring' the sort of thing you are talking about
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wombat

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Re: interference protection
« Reply #4 on: May 31, 2009, 01:26:56 PM »

Probably this is what COS is thinking of - but these will probably not make a lot of difference to the sort of noise you get off a motor - normally they are good for 10MHz or more unless you have a big one with a lot of turns. Most of the interefeence you get from motors is below that sort of level.

Wrapping the servo cable will not harm things but will not really do much - most of the noise will be coming up the motor power cables and into the rest of the system by that route.
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malcolmfrary

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Re: interference protection
« Reply #5 on: May 31, 2009, 04:03:52 PM »

Wrapping with foil and grounding to the battery -ve might stop interference, but if that level of interference was being passed into a servo lead, you wouldn't know because the radio would not be working - the aerial would do a much better job of picking up the unwanted signal..  The ali foil might, if you were unlucky, move and short out something important.
If interference is suspected, it needs to be killed at source.
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hopeitfloats

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Re: interference protection
« Reply #6 on: June 01, 2009, 11:46:36 AM »

i have done a temporary hook up of the rudder and tested today without covering lead. slight twitching in servo  only when in neutral position but motor isnt suppressed so hopefully when i do it will solve that.  just as a side issue.  1 motor is turning 2 x 40mm props and at full throttle is pulling 1 amp. :-) steering isnt brilliant but i will put up with it for now.  main problem i think is rudder is too far from prop and losing its effect. twin rudders or maybe a bow thruster might solve it if required. then again it is a container ship so dont expect to turn too quick.
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kiwimodeller

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Re: interference protection
« Reply #7 on: June 01, 2009, 12:18:42 PM »

As has been mentioned in other postings on this subject the best article written abot suppression (at least for brush type motors) is on the website of one of the shops in the Traders Directory on the Mayhem home page. I think they are called Model Solutions Canada. I followed their suggestion and solved problems I had struggled with. They say you need capacitors and resistors from the motor terminals to the case and between the terminals but the thing that made the most difference for me was putting Ferrites on all the leads. I bought a pack of ten from my local radio shop for just a few dollars and they worked wonders even on my forty year old Taycol motor which makes heaps of RF interference. Hope this helps. Cheers, Ian.
Found the page, go to http://modelsolutions.ca/articles.htm and look at the article "Radio Interference Suppression in Model Boats". There are several other interesting articles too.
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flashtwo

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Re: interference protection
« Reply #8 on: June 01, 2009, 12:19:11 PM »

Hi,

If any electrical gear is mounted on a metal chassis , it is worth taking a chassis earth wire connection back to a common point, e.g. battery negative.

I had a case of some earth leakage from an ESC driven motor and, without the earth wire, you could see, with an oscilloscope, the chassis voltage spiking with the ESC signal. The interference  caused other servos to "twitch" badly. With the earth wire the problem went away.

Always run the wires individually to the common earth and not looped otherwise a resistance can build up and the interference may occur again.


A STRANGE EFFECT!
During the development of my flash steam boiler, the computer based controller had some very erratic behaviour, which I assumed was software related, but which only occured when steam was issuing from a test pipe. I combed through the software, wrote filtering programs for the incoming signals, all to no avail.

After some research, I found an artical about William Armstrong and his discovery of steam generated static electricity (1840s) about which he corresponded with Michael Faraday. Well I earthed down the copper steam pipe and the problem went away! Well, for all the years I spent in industry, I had never heard of that effect.


Ian.
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hopeitfloats

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Re: interference protection
« Reply #9 on: June 01, 2009, 12:57:03 PM »

 :-))thanks guys. i will try both those suggestions :-))
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