Gerula

As I mentioned on another topic, the Rx18 in the Panzer III is making the motors "sing" realy loud. And I mean loud, if I turn the sound down to zero I can hear the intereference (or whatever it is) screaming behind a closed door .

On certain Left-Right trim positions it would scream nonstop after first hitting the stick. On other trim positions it will scream only on some parts of the right stick's travel.

Anyone knows what's causing this and how can I get read of it?

Panther G

See if the internal antenna wire is near the motors. If it is then move it as far as possible away from them.

Pah co chu puk

My stug has a hum when it is sitting still that I can affect by tapping the right stick. The hum goes away when it is moving.

I put in a internal coil antenna myself so I know the wire and antenna are as far as possable from the motors, boards etc... and it did it withthe stock antenna. Mine is not as loud as you describe yours as being.

Gerula

Nope, the antenna wire doesn't have anything to do with the motors (motors are in the front, wire is routed in the back). I even unscrewed the small rx board and placed it on the floor, far from the Rx18. speakers and so on, and it still does it.

Pah co chu puk, did you tried to remove the tracks, mute the speaker and check if the sound really goes away when you send some input to the motors?

YHR

The high pitched frequecy comes from the power Fets. When you get a little older your hearing at this frequency will fail, and you will be unaware of it!!!!!!!!!!!!. Seriously I was able to improve this by keeping the motor leads very short, and placing the RX 18 close to the motors. I did this on the JAGD, and it did improve, but I don't think you can eliminate it. It seems worse when the stick is just off of neutral, and levels out as the tank goes into motion.

Pah co chu puk

The sound does not bother me enough to go to much trouble to fix it. I have turned the sound all the way down and the noise is still there. It goes away when tank is moving so I just keep moving.

Gerula

I think my english is failing me here, what are the power Fets?

RodgerB

Put a Ferrite Bead on the power wires to the unit that should end it? Pass the leads through the Bead, around it once and back out. The Bead will block any AC from travelling down the power pair.

Pah co chu puk

Ferrite Bead? Is that something I buy or something I make?

Gerula

I think I have a a ferite bead somewhere in my den.

Problem is that in my case the harmonics can be heared even with both motors unplugged and with the speaker muted. It's not that loud as in the motors, but I can still hear the buzzing in the speaker.

YHR

Darkith explained one time that these Power transistors switch on and off in the process of regulating power to the motor. This causes a high frequency pitch.

Gerula

At the moment I have in the house 3 Rx13 and 3 older boards (no S&S version ). Got them in bulk with the Pantiger, except for a Rx 13 and a old non S&S board all were considered broken to some degree. Replaced some leaked capacitors, re-soldered some of the wires, changed a few fried resistorsand now 2 Rx13 work flawlessly, one Rx13 cannot move forward the right motor (otherwise working fine) and all 3 non S&S boards work as intended. NONE of these 6 boards is doing the high pitch screaming when paired with the two motors in the panzer III.And I mean no screaming, no whining, nothing.

Now, I wonder why the hell would the damn Rx18 keep screaming? Is this a design flaw of the Rx18 or it's something that can be actually fixed?

darkith

The older boards used a more irregular and slower switching frequency/pattern, which wasn't as audible or irritating.

Chances are that the electrical noise is weaseling it's way into the amp chip, either through the power supply lines, or the signal lines. Try to keep the motor wires as far away from the "sound" end of the RX18. Try to keep the volume control wires away from the board and motor wires. If that doesn't work, try adding ceramic capacitors to the motors and the supply pins on the amp chip. I'd try it myself, but I don't have one with those symptoms.

D.

YHR

I was able to reduce the noise on my Jagd by relocating the wires. What pins on the amp need the capicator??? I wouldn't mind giving this a try on one that is especailly loud.

Gerula

What specs would you recommend for the ceramic capacitors to be added to the motors? (instead of the stock ones, I suppose)

darkith

Pin 2 is +'ve. Pin 4 is -'ve.

Exact value would depend on the frequenc(y/ies). 0.1uF, 0.01uF, and 0.001uF in parallel should cover most bases.

D.

Gerula

Thanks.

I still think (since there are both "screaming" and non-screaming Rx18's of exactly the same design) that this problem can be traced to a faulty component. Unfortunatelly my electronics skills aren't up to the task.

YHR

OK

I will give this a try on my bad actors.

darkith

You could be right. The noise could be the result of a failed cap in a band-pass filter further up the chain, or a failed bypass (DC noise filter) cap on a the sound circuitry.
Really need to get an oscilloscope on two RX18s (good and bad) and compare the signals to trace it to the origin, then find the countermeasure.

D.