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KeithLuneau

A little help with EMI/RF noise?

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It seems I've got a problem with one of my planes (a GWS Slowstick), the video gear is reducing the range of the R/C gear, resulting in twitchy servos! I've got great range on the ground and in the air with the video gear off, but when I switch it on, the problems are back.

Here's the tests I did so far...

I powered up the plane, video gear, and R/C transmitter. I laid the r/c transmitter on a table, with the antenna collapsed, and walked away holding the plane in my hands, and get about 120 feet before the servos start to jump around. With the video gear off, I can walk the full length of my runway (400 feet) without a single glitch.

This was with a new set up I'm working on, so I thought it was kinda short on range. I cleaned up the wiring and routing as best I could, and retested, with the same results. At that point I did the same test, same day, same conditions, with my Easy Star that I've got a number of flights on, nothing changed. I got the same results, same range within a few feet. I haven't pushed this plane to it's limits yet, but I've been pretty far out without a single glitch. Just for fun, I swapped video transmitters on the planes, and retested, with the same results on each.

Now for some detains on the planes and equipment...

Easy Star is using HXT900 servos on rudder, elevator, and pan, with a GWS PicoBB on tilt. Receiver is a Corona RP8D1. Video transmitter is a 1W 2.4GHz, with a Panasonic CX-161 camera, amplified mic. Main battery is a 2100mAh 3-cell lipo, battery for video gear is a 3-cell 800mAh lipo fed to the transmitter and mic, and using a LM7805 regulator for the camera.

Slowstick is using servos from a Venom helicopter on rudder and elevator, HXT900 on pan, no-name servo on tilt. Receiver is a Hitec Electron 6. Video transmitter is a 700mW 1.3GHz. Camera is a Panasonic board cam from Electromavin. Main battery is a 1800mAh 3-cell lipo. Battery for video gear is a 3-cell lipo fed straight to the transmitter and camera. Mic is built into camera.

So, I posted this on RCGroups as well and got some helpful tips, and went out to do some more testing, here's what I found that time...

I pulled all the FPV gear of the plane, then walked with the plane away from the transmitter until I started getting glitches, had lots of range as expected. So at that point, I powered up the video gear, still off the plane, and moved it closer and closer to the plane, got no glitches at all. Even with the video transmitter/antenna nearly touching the servos, wires, and R/C receiver, everything was solid. So, I moved just the camera closer to the servos, and they started jumping around. I found that it seems the closer the camera itself, or the wiring between it and the transmitter are to the R/C parts, the worse it is. The video transmitter itself doesn't seem to cause a problem at all.

Now, I've used the camera in the past with no problems at all, but had a shielded cable on it. When I started setting this up, that shielded cable was too short, so I soldered a twisted lead to the camera and to the end of the shielded cable, getting rid of the connector on the camera. Could that be my problem? I do have enough shielded cable to re-wire it with if you think it'll help solve the problem.

Attached is a picture of the current wiring for the FPV gear. If it will help, I'll put the gear back on the plane and post a picture of that as well, though I've tried various ways of mounting things, keeping it all separated as best I can, to no avail...

Thanks in advance for any help! I know this is usually a hard problem to solve, and a methodical approach is usually best, I was just hoping some of the experts here might see a big mistake I'm making, or at least offer some kind of "game plan" to approach the problem with. I don't mind making new mounts, rewiring things, etc., just need some guidance on what to look at and in what order! ;)

post-646-125685642764_thumb.jpg

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Also, to add to my questions...

All my servo leads are twisted. If I wanted to add a toroid ring to the leads, would it be ok if I left them twisted? My ESC has a kinda long lead, plus a short extension on it, it's the longest lead in the R/C gear. I wanted to add a ring to it as a start. Would I add it next the the ESC or the Receiver?

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I got a little lost in the background details. Are you saying that both your Slowstick and EZ Star have the same problem? Or, is the problem just on the Slowstick with the Electromavin camera?

Before we toss a solution at you, there's some tests to do:

Re-install the video gear back into the Slowstick.

Confirm the range test is poor with video system on. What is the range?

Repeat with video system off. What is the range?

Repeat with video Tx on, video cam off (leave wiring in place). What is the range?

Repeat with video Tx off, video cam on (leave wiring in place). What is the range?

For the new range tests I suggest you leave the model on a wooden park bench and then walk away with the Tx. Have someone that is more than ten feet from the model call out the jitter status. The reason for this is when your body is close to the video Tx it can skew the results, at least more so than when tested the other way around. If you are doing this alone then just go back to your original test methods.

Most of the servos you mentioned are economy imports. These often have EMI/RFI susceptibility issues. Do you have any quality Hitec/JR/Futaba that you can use as subs, just for the jitter test?

Do you have any small Toroids in your tool box, like the dpcav.com #TOR-001?

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I've got a couple toroids like that I can use. I bet I can find a few more if I rummage through some old electronics I scavenge parts from too.

As for the Easy Star, I see there may have been some loss of continuity there, a lot of my post was copy/paste from the thread I started on RCGroups. I had mentioned the ES since my original question was how much range should I see, and is it ok to have a reduction in range, is it normal. I only ask because I've only done simple range checks before, and when it seemed ok, I flew, and haven't had any problems so far. I've flown the Easy Star a number of times without problems, though it does seem to have reduced range with the FPV gear powered up as well. That said, I haven't flown in more than a half mile or so away. For now, I'm focusing on the Slow Stick only.

I don't have any small high quality name brand servos on hand, thought I've got plenty of Futaba standard sized ones if that's relevant. They won't fit in the plane, but I could plug them up and lay them next to the small servos is that's a valid comparison.

As for the range with the video gear powered on, I was getting around 115-120 feet before it started jittering, and another 20-25 feet things got really bad, servos moving around at full throw! With just the R/C gear working, I was able to walk the full 400 feet to the other end of my runway with no jittering.

If it matters, my R/C transmitter is a Futaba 9CAP (not a Super) on 72MHz channel 28. I should also mention that my video transmitters are both "cheap Chinese imports". The one in question on the Slow Stick is the one listed here: http://www.bestofferbuy.com/av-wireless-transmission-combo-p-15758.html I do have a 500mW 2.4GHz Lawmate transmitter and receiver ordered though, so if it is something with this cheap gear I've been using I'll be able to compare with known good products.

I'll do those other tests and record my results to post either tomorrow, or Saturday, depending on the weather. Supposed to rain tomorrow.

One more thing, would shielded cables for the servos be worth a shot? I've got some CD-Rom audio cables that have two wires plus the outer shield for ground. Can it hurt?

Edited by KeithLuneau

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I've flown the Easy Star a number of times without problems, though it does seem to have reduced range with the FPV gear powered up as well.

Ok, so you have two models that have reduced range when the video gear is on. Just be aware that the exact fix for one installation may not at all be the one that solves another.

I've got plenty of Futaba standard sized ones if that's relevant. They won't fit in the plane, but I could plug them up and lay them next to the small servos is that's a valid comparison.

It would be helpful to try them. Honestly, some economy servos (those China types that are often under $10) have given a lot of folks grief in their FPV model. The "bad" ones can make your job of solving servo jitter issues a lot harder (sometimes impossible) because they have little immunity to EMI/RFI noise and some even contribute to the background noise.

As for the range with the video gear powered on, I was getting around 115-120 feet before it started jittering, and another 20-25 feet things got really bad, servos moving around at full throw! With just the R/C gear working, I was able to walk the full 400 feet to the other end of my runway with no jittering.

As a wild guess, I would say your effective R/C range in a noise free environment has been reduced from 2 miles to about 1/2 mile. Still plenty range for flying at the local club field, but even so you have reduced safety margins. I recommend that you work on getting the range difference between video-gear-on / video-gear-off to be less than 20% (aim for ~0% if you intend to fly extremely long range). You have a long way to go for that.

would shielded cables for the servos be worth a shot? I've got some CD-Rom audio cables that have two wires plus the outer shield for ground. Can it hurt?

Before modifying anything please perform the tests mentioned earlier. Let's establish a baseline and then proceed with a plan of action.

Please post photos of your video gear installation.

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You seemed to indicate that you thought it was the camera it self causing the problem, have you tried connecting a battery to just the camera and bringing it near the receiver?

I don't want to disrupt the logical process of pinpointing the problem but one leap in the dark won't hurt ;)

Terry

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That is a good test and should be tried too. But I also think it would be very informative to leave all the wiring in place and just remove DC power from the camera itself (this is one of the tests suggested earlier).

From my past dealings with similar troublesome installations, stuff like camera noise is conducted into the attached cables, then re-radiated off the wiring. Any temporary changes to the wiring can affect the tests; so for the baseline measurements it is helpful to keep as true to the original setup as possible before implementing the fixes and/or alternative troubleshooting tricks. That is why I recommended just removing camera power to establish the noise contributor sources.

There are video cameras that are hideous EMI/RFI generators. It's usually the DC-DC switcher on them, but things like its oscillator can contribute too. Some of these just aren't practical for typical FPV applications due to their refusal to be tamed with practical EMI/RFI solutions. Could be the situation here, but hopefully not.

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I'll certainly try all the suggested tests, record results, and report pack here. I was hoping to do it this evening, but it's been raining all day, and even if it stops, the field is under water! lol

I'm not going to jump right to a conclusion just yet, but I think you're onto something with the cable from the camera itself radiating noise. Like i said I've used this particular camera on two planes before with no issues, but always had a shielded cable on it. (three wires inside, plus an outer shield which I used for ground, with the three wires being +12V, video, and audio) When I did this installation, I needed a longer cable, so I used a twisted 4 wire cable, and soldered it directly to the camera board. Now I wish I had left the connector, gonna have to de-solder it to remove power and leave the wiring... lol

I'll do all the tests and report my results as soon as I get a change! I cannot thank you all enough for the help!

-Keith

Edited by KeithLuneau

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The shielded wiring might have been the silver bullet in your earlier installations that worked. But I am more satisfied with common-mode filters using Toroids since they can suppress the noise at the source rather than just bottle it up.

If you haven't see the dpcav.com white paper on EMI/RFI then I recommend you read it:

http://www.dpcav.com...tepaper_RFI.pdf

Although the paper discusses 900MHz and its impact to GPS and R/C receivers, the information is just as appropriate for your situation too.

Here's a tip: Carefully read the paper, set it aside for a day, then read it again; The information that is provided could fill a book, so when it is condensed into five pages it is important to recognize all the important little details. Honestly, I've talked with folks with persistent noise problems that claim to have followed the paper's guidelines to the letter. But later when I see photos of what they did it becomes obvious they did not understand the information at all. So several readings are recommended!

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Ok, rain stopped last night, I was able to do the tests today, with some telling results... ;)

Confirm the range test is poor with video system on. What is the range? 42 feet

Repeat with video system off. What is the range? +/- 400 feet, hard to say exactly, minor twitching around 300-400, sudden major deflection around 400

Repeat with video Tx on, video cam off (leave wiring in place). What is the range? Same as before, minor twitching started around 300, sudden loss around 380 this time.

Repeat with video Tx off, video cam on (leave wiring in place). What is the range? 45 feet

We're probably all thinking the same thing at this point... It's the camera! ;) Having used this camera before on this same plane, very similar setup, but with the shielded cable, I'm thinking it's probably noise in the cable, and not from the camera board itself. So my question is, should I replace the wires with shielded cable again, or use a toroid close to the camera? I will need to change the cable either way, the one on there isn't long enough to get more than one or two wraps, I know I'll need more than that. A shielded cable would be easier, I've already got it.

For the camera only test, I simply unplugged the 4-wire connector at the transmitter. For the transmitter only test, I clipped just the +12v wire at the camera, leaving the ground, video, and audio connected.

I'll add a picture of the whole setup in a little while, waiting for the camera batteries to charge right now.

Edited by KeithLuneau

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Thanks for the update, I for one would like to see how the torroid works before you replace the cable.

Terry

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I'm thinking it's probably noise in the cable, and not from the camera board itself.

That is what I usually find. The camera's EMI/RFI noise is driven into the cable, where it is conducted to the other components. Even more troubling, it is often radiated from the cable too. For this reason it's best to stop the noise at the cable.

I would recommend a Toroid on the camera cable. It should be similar (size and material) to the dpcav #TOR-001. Get 10+ tight wraps on it and have it positioned on the cable about one inch from the camera. I would also install another Toroid on the 4-wire cable at the video Tx, one to two inches from the video Tx.

Even if these don't fully solve it, there is no real downside to installing them. So try them first and report the results.

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Ok, toroid rings it is then! lol

Before I start rewiring it, I just want to make sure I'm doing it right. I've got two rings floating around my parts bin, attached picture below. They are about 1/2" diameter each. I don't know what material they are, is there a way to tell?

The wiring I have to use is individual wires, not connected like servo wiring. Will that be ok? Do I need to keep them laying flat on the rings, or is it not so critical?

I'll try getting it all wired up with them tonight. I promise I'll get a picture of the setup on the plane too, I never did get a chance to yesterday.

Thanks again for all the help!

-Keith

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I've got two rings floating around my parts bin, attached picture below. They are about 1/2" diameter each. I don't know what material they are, is there a way to tell?

Without a data sheet I don't have a clue on how you can tell what material they are.

The wiring I have to use is individual wires, not connected like servo wiring. Will that be ok?

That is fine.

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Ok, so I'll try it with the rings I have, and if they work good, of not I order the TOR-001s and try those. I may also try the shielded cable in the mean time if it doesn't work with these toroids I have.

Here's the pictures that show the plane and gear, and how it's laid out. I did previously have the receiver on the boom behind the wing, but moved it down lower to try to get it farther from the video transmitter when I first started troubleshooting this. The video transmitter and battery are just in place temporarily to get it all working then I'll make a proper mount to hold them. Ideally I'd like to make a little wood platform that fits the top of the wing and is held on with the rubber bands, then the video transmitter and battery can mount properly to that. If anything, it'll raise the transmitter a little, which can't hurt.

So on to the picture, this is my "Slowstick Ultralight" :)

1.jpg

2.jpg

3.jpg

4.jpg

I'm also planning to paint all the exposed wood parts black too, just not a major concern just yet... ;)

Edited by KeithLuneau

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Because of the close proximity of the tilt servo to the noisy camera, it may need a Toroid on its cable too (located 1-2 inches from servo). Keep it in mind if you continue to have issues.

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Just a quick update and final verdict. I put only one of the toroids on the camera wires, about an inch from the camera with 10 wraps as specified. (Didn't have long enough wires at hand to do both toroids, figured I'd give it a shot with what I had.) I ranged checked it this evening and was getting full range on the ground, great! So I sneaked in a flight at sunset while the winds were calmed down, and flew to the end of my video range with no glitches. Success! Granted, I was only able to go about 3/4 of a mile out before the video was getting really fuzzy and dropping off, but I'm using the stock omni antenna on the receiver for the 1.3GHz Chinese set.

On a related note, I'm kinda impressed with this particular tx/rx set from China, range is not bad for the stock antennas. I will put one of my other transmitters on and use a patch antenna on 2.4GHz and fly farther, but for now I think the noise issue is solved. :)

Thanks so much for you help!

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Thanks for the update. Glad to hear you killed the noise beast.

Even though the R/C Rx range issue is solved, I highly recommend you put another toroid on the Tx too. I've run into many folks that didn't do that and had other EMI/RFI problems later on.

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