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Radio frequency noise question?

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Radio frequency noise question?

Postby Pirate » Mon Jan 11, 2010 7:48 pm

Will metal gears in a reduction unit cause radio frequency interference?

I used metal reduction gears in my Ohio motor set up, and they are audibly noisy, but will that cause radio noise? Something is freaking out my radio, and I wonder if that is playing a part.

Any advice is appreciated.

Pete
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Re: Radio frequency noise question?

Postby TMSmalley » Mon Jan 11, 2010 11:18 pm

Try grounding it.
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Re: Radio frequency noise question?

Postby Pirate » Mon Jan 11, 2010 11:23 pm

Grounding what? The motor ground terminal goes to ground. Should I hook a ground wire to the motor case, or the reduction gear case, or what?
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Re: Radio frequency noise question?

Postby Tommydeen » Tue Jan 12, 2010 2:13 am

I belive that if the gears are of the same material than the gears "can" generate R/F interfearance. can you change the drive gears with a good quality plastic gear?
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Re: Radio frequency noise question?

Postby TMSmalley » Tue Jan 12, 2010 8:07 am

On the workbench, try grounding the motor to the gearbox.
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Re: Radio frequency noise question?

Postby Bigdave » Tue Jan 12, 2010 10:28 am

The gears will cause RF noise. I had metal U-joints in a sub once and it was very bad as well.
I would say swap out for plastic as Tom said. BD.
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Re: Radio frequency noise question?

Postby TMSmalley » Tue Jan 12, 2010 12:28 pm

Have you run it with the gears unconnected - just to ensure it isn't some other gremlin?
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Re: Radio frequency noise question?

Postby Sub culture » Tue Jan 12, 2010 1:48 pm

You need to ground the case of the motor.

Have a look at the article 'Beat RFI' by David Harrison in the December 2007 SCR.

Plastic gears would help too, or at least one plastic gear. They wear better too.

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Re: Radio frequency noise question?

Postby Pirate » Wed Jan 13, 2010 2:04 am

So I should solder a wire to the metal motor case and connect it to the negative pole on the motor? Or should it connect to somewhere else that's ground? Also, the gear box is aluminum. Any thoughts on how to connect a ground wire to that?

Any suggestions on where to find plastic gears to replace the metal ones?

I did find that I had too small of capacitors on the motor. I got .1M and it helped a lot, but I still get quite a bit of twitching out of the pitch control, or at least that servo. That servo is right next to the motor. Is there a way to shield that?

I also realized I didn't put any capacitors on the blood pressure pump motors I'm using for the ballast. So I hooked those up too.

One other thing that's happening. There's a micro-switch sitting next to the bow planes servo. The bow planes servo is connected to a SubTech depth control. The micro-switch activates 12V that runs to a solenoid valve in the ballast system. Whenever it goes on, the depth control seems to deactivate, and the servo goes back to manual control. It's like it's blocking the switch signal that turns on the depth control. I know it's not a cross in the wires to the receiver to a different switch which really does turn the depth control on and off, because all I need to do is activate the micro-switch with my finger and not the radio for it to happen.

Is there a way to put capacitors on that micro-switch to possibly prevent this interference?

Thanks for your guys help.

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Re: Radio frequency noise question?

Postby Ramius-II » Wed Jan 13, 2010 12:09 pm

Hi Pirate,
A few things that may assist you. First each and every motor should have a "triangle" of .01 mfd disc capacitors. One capacitor from the + terminal to the - terminal, then a capacitor from the + terminal to the motor case and one capacitor from the - terminal to the motor case at the same location on the motor case. Motor cases are often plated so it may be necessary to file off the plating in the area on the motor case where you wish to solder. Remember to include a HEAVY "ground" wire that connects the motor case to the negative (-) side of your power battery. The reason for a heavy wire is that you wish the wire to have the minimum of resistance so any stray signals see a solid low resistance path to ground. It is recommended to use a single sepreate ground wire for each motor and not "daisy chaining" the grounds. This is referred to as "Home running" the grounds. As for your gear box, you will have to drill and tap a hole so you can attach a "soldering lug". You may choose to use the type where the "ring" of the terminal has teeth. Another "technique" when dealing with most power connections is to take the leads and twist them together. This provides a couple of advantages. First, it makes you wiring neater and easier and by twisting the wires you reduce the tendancy for the wires to become transmitting antennas for RF interference and Electro-Mechanical interference. You can easily take the wires and put them in a drill chuck to perform the twisting. About solenoids, relays, etc. it is a common practice to use a diode across the coil. When a coil is activated it creates a magnetic field around the coil. When power is removed and the magnetic field colapses it puts voltage back into the circuit. A diode will short out this back voltage. Using a twisted servo cable may help with the servo and you can always make a brass box to surround the servo, or use 2" copper tape. Don't forget to ground the box or tape! :wink: Hope all this is easy to understand and solves the issues.

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Re: Radio frequency noise question?

Postby Ramius-II » Wed Jan 13, 2010 12:11 pm

Sorry, :( capacitors should be .1 mfd not .01 mfd.
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Re: Radio frequency noise question?

Postby Sub culture » Wed Jan 13, 2010 1:00 pm

These people are good for gears, belts etc.-

http://www.sdp-si.com/
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Re: Radio frequency noise question?

Postby roedj » Wed Jan 13, 2010 5:42 pm

To All,

This is very interesting hearing that metal gears, in and of themselves, can cause Radio Frequency Interference (RFI). I can see the metal shafts out of a electric motor, especially brushed, and their attached gears acting as a kind of antenna to carry the RF energy out of the metal motor casing to the outside world but I'm having trouble seeing how metal gears can generate RFI. Are there sparks involved? Can someone please explain that RFI generation mechanism?
Thanks for your time,

Dan
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Re: Radio frequency noise question?

Postby Pirate » Wed Jan 13, 2010 9:10 pm

Ed,
Thanks for all of that info. I do know about the capacitors, and have installed those. And I started with all the wires twisted. It has made a huge difference, but am still getting the glitching with the servos. I'm sure others will benefit from this info.

THe antenna wire does run past a positive buss terminal I've set up in the hull. Instead of running umpteen number of wires all to the battery terminal, I set up a brass buss with a screw and nut for both the positive and negative leads. The positive is on the side the antenna goes down, and the negative is on the other side of the hull. Could this arrangement be causing me trouble too?

What I didn't know about was the solenoid diode. Can you tell me what size or description of diode I should get, and where exactly to mount it? I've attached a schematic drawing of the valve I am using.

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So basically all these parts you list, motor casings, gear box casing, any shields around the servos, need to be grounded? Is it ok to run the ground wires to the same negative lead that comes into my WTC that the motor is connected to? Or does it have to be it's own separate wire going straight to the battery?

Oh, any idea where to get copper tape?

Thanks for the gear lead Subculture. Are you Andrew?

Thanks again.
Pete
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Re: Radio frequency noise question?

Postby RickNelson » Wed Jan 13, 2010 9:33 pm

Use a 1N914 or equivalent diode. Connect the cathode or banded end to the +, Plus, Positive side of the coil. Always mount RFI filtering components as close to the source as possible. In the case of the diode mount it right on the soleniod terminals. Any farther away just puts wire resistance into the filter which is not good.
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