Building a Ziroli B-25(CONDENSED VERSION)  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> RC Airplanes >> RC Warbirds and Warplanes >> Building a Ziroli B-25(CONDENSED VERSION)
Page: <<   < prev  1 2 [3] 4 5 6 7 8 9 10   next >   >>  

Login
Message << Older Topic   Newer Topic >>
Building a Ziroli B-25(CONDENSED VERSION) - 2/4/2002 1:06:57 PM   
mselby



Posts: 372
Joined: 12/29/2001
From: Bangkok, THAILAND
Status: offline 		Dave,
we are in agreement that the aluminum tubing on the wings should not present a problem. The issue on aluminum tubing such as yagis being susceptible to RF noise is due to joints such as where the aluminum telescopes. RF induced atmospheric noise and corona discharge is another issue with yagi's, thats what triggered Moore to design the quad which was a full wave length closed loop and less prone to these problems.
RF noise issues in model airplanes are more complex. They range from resonant pickup on servo and battery leads to gremlins in metallic joints. In some cases lead extensions with cold solder joints are the problem. Other cases can be as simple as a bad rf environment including harmonic breakthrough or front end over load on a receiver. Model airplane receivers are not exactly heavily filtered or front end protected.The reason it seems like a black art is that most people are not geared to directly track down the reason for a given case of rf interference. With the right instruments there would always be a clear answer.
Mike

(in reply to badigital)
       Post #: 51

WOW - 2/4/2002 10:30:23 PM   
badigital


 

Posts: 20
Joined: 1/18/2002
From: Jefferson City, MO,
Status: offline 		What is all this stuff about aluminum. Man, when I started this thread I had a few questions about the proven way to build this B-25. Now we are into metal to metal RF interference! I wonder, if using metallic coverings can cause any interfence? Any comments. I have heard this but never experienced it.
Sorry you guys have not heard from me in awhile but, I had a pretty busy weekend. I am really excited that a thread I started has grown to this level.

On the Fly-in here in Jefferson City, MO. see it here [url]www.jcrc.com/extravaganza[/url] for info on the show email me at [email]info@jcrc.com[/email] it is also scheduled on the RCU calendar.


_____________________________

President
Jefferson City Radio Control

(in reply to badigital)
       Post #: 52

wing tubes - 2/5/2002 5:15:43 AM   
1wolf-RCU



Posts: 190
Joined: 1/4/2002
From: camdenton, MO, USA
Status: offline 		Brian to catch you up to speed... We are using an 8" piece of tubing in the main wing and a 12" piece in the outer wing. I was afraid that just sliding the tubes in and out of the holes in the wing ribs would eventually cause wear and that added strength of the tubes would be a plus. It was mentioned somewhere along the line that two pieces of metal together could cause RF. I hadn't worried about the tubes because I had seen this done in other planes but for the sake of caution (and possibly to see a cool debate ) I threw it out here to see if anyone had comments. To summarize most everyone seems to think it will work fine even though technically and theroretically the possibility for rf could exist ( thougt I worded that nicely without committing to either side don't ya think) None in this forum have encountered any difficulties with our usage of the tubing in this aplication. (Boy being politically correct takes a lot of words) So there you have it!!! Gentleman Please continue.....

(in reply to badigital)
       Post #: 53

Building a Ziroli B-25(CONDENSED VERSION) - 2/5/2002 6:21:34 AM   
mselby



Posts: 372
Joined: 12/29/2001
From: Bangkok, THAILAND
Status: offline 		Sorry guys the RFI explanation was perhaps overly expository. Brian metalized fuses create signal shielding. If you use a lot of metal covering use a whip.
Mike

(in reply to badigital)
       Post #: 54

Building a Ziroli B-25(CONDENSED VERSION) - 2/5/2002 8:42:21 AM   
pantherjetf9f2


 

Posts: 9
Joined: 1/19/2002
From: jefferson city, MO, USA
Status: offline 		As for the J.C. B-25 we are using a cardboard tube that you can get with the tubes when you order from some companys. I have used the cardboard tubes in all the airplanes that i have used alu. tubes. Gordon

(in reply to badigital)
       Post #: 55

Valuable information! - 2/5/2002 9:50:06 AM   
Dave McDonald



Posts: 1326
Joined: 1/4/2002
From: Eldon, MO, USA
Status: offline 		Mike! Don't go just yet!

Just so you know, I REALLY appreciate both of you and Gibb chiming in about the Skunkworks B-25 projects! The way I see it, the more minds involved here, the better the chances are that these B-25s will have a long life.

As far as the RF interference issue, you have far more knowledge of antenna theory than I do......and I'm really glad to hear that we both agree that the aluminum wing tubes shouldn't cause any problems.

Steve, Glenn, TJ and myself have already discussed some other potential RF interference problems with their B-25s, and they have already made some changes based on my advice. But since you guys are here, I would REALLY appreciate hearing your opinions!

My first concern was that each engines ignition kill switch was going to be located in the fuselage, with the ignition kill wiring within inches of the receiver. Plus with a throttle servo located in each nacelle, the ignition kill wiring would have been running parallel to the throttle servo leads. As soon as I saw this, alarm bells, sirens, and flashing lights started going off in my head as a MAJOR source of RF interference! Since then, they have relocated the kill switches into the nacelles, but I'd still like to hear your thoughts on whether or not you agree that this could have caused interference problems.

My second concern was that originally they were going to run individual servos into each nacelle for throttle control, with the servos very close to the engine. Because of the close proximity of the servos and wiring to the ignition engines, I suggested that they install optical isolaters to minimize the ignition RF noise from being induced into the the throttle servo wiring. I would think the closer these optical isolators are to the receiver, the more effective they would be. Do you know of a better way of doing this? Or am I being paranoid here based on your experiences?

My third concern was the length and the amount of servo extenisons that are being run throughout these planes. All of the servo extension that they have run are homemade of twisted wire. I think using the twisted wire is a good idea, but I dont' know the optimum number of twists per foot to minimize interference. Do you know? Do you think that these wires should also be optically isolated from the receiver? Or am I being paranoid again?

My fourth concern was the use of PPM receivers in these B-25s. I agree that the PPM receivers will work fine if all of the potential RF sources are eliminated. But unfortunately, you only get one chance that way. Therefore I have strongly suggested that the Skunkworks guys use PCM receivers (JR). Are you flying PCM? Or PPM? And again, am I being paranoid here?

Even if we don't agree on this stuff, make no mistake that the Skunkworks guys and myself value your opinion on these things!

_____________________________

McDDD
ProBro 415

(in reply to badigital)
       Post #: 56

Building a Ziroli B-25(CONDENSED VERSION) - 2/5/2002 9:58:41 AM   
mselby



Posts: 372
Joined: 12/29/2001
From: Bangkok, THAILAND
Status: offline 		Hi Dave,
I think you are spot on. I always use optical isolation on the kill switch and the throttle. On the receiver I prefer PCM also. For twisted servo leads you are creating inductance which gives a slight choking effect. You could use some ferrite beads. They may be available at radio shack otherwise Amidon sells them. I don't know their web site but they advertise in QST. Something around a number 71 or slightly higher would be about right. Around 3 to four beads at the end of each wire. Some people are starting to use carbon tubes for routing wires, this should give some rf blockage but is probably over kill.
Mike

(in reply to badigital)
       Post #: 57

optic isolators - 2/5/2002 10:06:29 AM   
1wolf-RCU



Posts: 190
Joined: 1/4/2002
From: camdenton, MO, USA
Status: offline 		Hi Mike
What type of optic isolators are you using?? We are using the same chip ace used in their y buffer amps but it's not really an isolator. We were going to use rf chokes in the servo leads from the throttles. Are ferrite beads better??

(in reply to badigital)
       Post #: 58

Thanks Mike! - 2/5/2002 10:58:26 AM   
Dave McDonald



Posts: 1326
Joined: 1/4/2002
From: Eldon, MO, USA
Status: offline 		Mike,
Thanks for sticking around! And thanks for the vote of confidence about my radio installation concerns!

I believe the isolator that Glenn is talking about is the old Ace "Noise Trap". I just happened to find my old assembly instructions from the Noise Trap that I built and tried many years ago. It uses a 74C04 CMOS Hex inverter for isolation.

I bought and built my Noise Trap for the dual ailerons in my Byron Christen Eagle. Back in 1988 I was flying it with an Ace Silver Seven on AM. With high speed coreless Futaba S-131SH servos on the ailerons, I was getting glitched. But even with the Noise Trap installed, I was still getting glitched at about the same rate. I ended up nearly eliminating the glitches by swapping out the high speed coreless for standard Futaba S-28 servos. Switching to a PPM receiver years later further reduced the glitching. The final glitches weren't completely cured (masked?) until I switched to a PCM receiver. Although I don't fly it very often, it's still alive 14 years later!

I'm not going to bet my life on this, but I don't believe that the Noise Trap CMOS chip uses optical isolation. Any ideas on this Mike? If the Noise Traps aren't optical isolated, where is a good source for the Skunkworks guys to get them? I REALLY believe they need OPTICAL isolators....especially on the throttle servos.

_____________________________

McDDD
ProBro 415

(in reply to badigital)
       Post #: 59

Building a Ziroli B-25(CONDENSED VERSION) - 2/5/2002 11:31:05 AM   
mselby



Posts: 372
Joined: 12/29/2001
From: Bangkok, THAILAND
Status: offline 		Hi Dave,
The cmos circuit is a buffer amp, it isolates the signal line from variance and spikes but is not an optical device. Andy Low makes an optical isolator. I don't have his company name here in the office, I will look it up at home and post it from there.
Mike

(in reply to badigital)
       Post #: 60

Building a Ziroli B-25(CONDENSED VERSION) - 2/5/2002 12:12:21 PM   
mselby



Posts: 372
Joined: 12/29/2001
From: Bangkok, THAILAND
Status: offline 		Andy's company is electrodynamics. The web site is:
http://www.electrodynam.com/
Mike

(in reply to badigital)
       Post #: 61

Shielded wire - 2/5/2002 7:24:35 PM   
gibb


 

Posts: 108
Joined: 1/26/2002
From: Livonia, MI, USA
Status: offline 		Mike, If I can ask one further question: I have been using shielded wire for some time to help with the long leads we typically see. Of course, only grounding on the battery side. In your opinion, is this an acceptable solution, or is the ferrite beads, a better way, etc...?

(in reply to badigital)
       Post #: 62

servo's - 2/6/2002 9:39:18 AM   
1wolf-RCU



Posts: 190
Joined: 1/4/2002
From: camdenton, MO, USA
Status: offline 		I think we are good on the wing tubes were going to leave those with the 2 aluminum tubes it a nice tight fit and very strong.Randy I apreciate knowing that yours has worked so good it's a morale booster. Anyone have a wescraft B-17 before??? I am really leaning towards going with Andy's isolator I think it would be a good move and then we will probably run the battery backup system on the isolator because of the 13 servo's it will have on it.

(in reply to badigital)
       Post #: 63

Radio interference thread on RC Universe - 2/6/2002 9:51:04 AM