RF shielding for Electric Senior Telemaster + UNAV2R + CPD4

[Brio3]

Hi all,
I just finished my project and have a few questions about RF shielding. Based on the location of the components and proximity of the PicoPilot, RX, and FMA co-pilot to the wireless tx (200mw), is shielding necessary? What side effects occur when there is interference? In other words, what should I be on the look out for?
Thanks in advance for your expertise.
Steve Morris

Specs:
Airframe: Senior Telemaster (Hobby Lobby)
Wing Span: 93"
Wing Area: 1330 sq."
Wing Loading: 21.7 oz./sq.'

Motor: AXI 4130/16
Prop: 16" x 10" APC-E
Battery: EVO7400 6s2p
ESC: Jeti 77-O

Autopilot: PICOPILOT NAV2R, ALTE
FMA CPD4 Co-Pilot on the ailerons.

[d_wheel]

Have never used shielding so can't be of any help in that area. Just wanted to say that it looks like you have spent a great deal of time getting the wiring to look so neat. Also, I am amazed that you were able to get the Picopilot and Copilot working with a Futaba PCM receiver... I had to use PPM on my last 2 projects for just that reason. Care to share you secrets?

Later;

D.W.

[hihptsi]

Have never used shielding so can't be of any help in that area. Just wanted to say that it looks like you have spent a great deal of time getting the wiring to look so neat. Also, I am amazed that you were able to get the Picopilot and Copilot working with a Futaba PCM receiver... I had to use PPM on my last 2 projects for just that reason. Care to share you secrets?

Later;

D.W.


id be very interested in everyones ideas as far as sheilding for the Receiver.i have a similar setup that id like to do this to for that extra saftey margin :).

thanks
walter

[workshop]

I used copper lined RF boxes. Check out the Catalina Project thread to see photos and descriptions.

Jeff

[Mr.RC-CAM]

There certainly is a lot of equipment packed in there. Are you getting acceptable ground range tests with all the electronics turned on and motor running at various RPM's? That will tell you a lot. BTW, I see an Inspire OSD tucked away in there! :)

[Brio3]

Mr. RC Cam,
You have a very good eye for spotting the OSD tucked in there. I really don't have any range problems due to my RF filters and my base loaded Revolution whip - which I have mounted behind the "component compartment".

D.W.,
I had to use a servo buffer (from FMA) on on the aileron function to make PCM work, otherwise the servo action was "herky-jerky" and erratic

Thanks for your ideas guys. Work shop, I love your Catalina plane!

[dalbert02]

My answer? It all depends. I have a Kadet Senior with almost the identical setup you have (AP4 instead of Pico & FMA Rx) and I had all kinds of twitching and glitching. I used copper foil, ferrite beads, opto isolators, Rx counterpoise, etc. and I still get some problems. On the other hand, I have a Sig Cloud Ranger, no shielding and everything works fine even in closer proximity to eachother. I don't get it. The Rf gobblins sure are tricky!
-dave

[d_wheel]

D.W.,
I had to use a servo buffer (from FMA) on on the aileron function to make PCM work, otherwise the servo action was "herky-jerky" and erratic


Interesting! I tried the same thing and could never get rid of the "twitchies"... Where in the circuit did you install the buffer? Everything works normally with a ppm receiver, but have to use extra circuitry to attain failsafe. With all of the other wiring, this made the rats nest even worse.

On a side note, I installed a Spektrum system in one of my birds and everything works great. The only problem now is that with a Spektrum AR7000, the only channel that actually goes into failsafe is throttle. Everything else holds last good data position. Makes it impossible to set up an automatic return to home in the case it gets out of range or what -not. The AR9000 receiver is supposed to have a normal failsafe setup (all channels, that is) so maybe then I will be happy....

Later;

D.W.

[clolson]

Hi all,
I just finished my project and have a few questions about RF shielding. Based on the location of the components and proximity of the PicoPilot, RX, and FMA co-pilot to the wireless tx (200mw), is shielding necessary? What side effects occur when there is interference? In other words, what should I be on the look out for?


Hi,

I notice from your pictures that you mounted your elevator/rudder servos in the tail of your senior telemaster. I'm working on a senior telemaster right now and doing the same thing. Did you have any balance issues with moving servos back there or were you able to get a good balance with suitable battery placement?

Thanks,

Curt.

[Brio3]

Curt,

I'm using an "industrial sized brick" for a battery, which I thought would enable me to put the servos in the rear to counter balance. As luck would have it, it balanced perfectly w/o any lead or battery shifting. I have the bat. pushed clear up against the firewall.

D.W.,
My buffer is attached between the Co-pilot aileron lead and the receiver.
BTW, I really like the new Spektrum modules coming out for the Futaba/JR radios. These will give my the 8 channels needed + the added 2.4mhz protection + no need for a full size antenna or whip. Hopefully it will be compatible with the picopilot and not have the problems you mentioned??

Steve

[kd7ost]

It looks like your usual great work Steve. Can't wait for the flight results.

Dan

[kd7ost]

Interesting! I tried the same thing and could never get rid of the "twitchies"... Where in the circuit did you install the buffer? Everything works normally with a ppm receiver, but have to use extra circuitry to attain failsafe. With all of the other wiring, this made the rats nest even worse.

On a side note, I installed a Spektrum system in one of my birds and everything works great. The only problem now is that with a Spektrum AR7000, the only channel that actually goes into failsafe is throttle. Everything else holds last good data position. Makes it impossible to set up an automatic return to home in the case it gets out of range or what -not. The AR9000 receiver is supposed to have a normal failsafe setup (all channels, that is) so maybe then I will be happy....

Later;

D.W.


D.W.

I don't want to hijack Steve's thread but heres a down a dirty of the Futaba PCM interface.

When connecting to the FMA Co-pilot here's the issue. The Futaba processor puts out four pairs of parallel pulses. First goes 1 and 2 together, then 7 and 8, then 3 and 4 and finally 5 and 6. This is not an issue to a single ended device like a servo. But the Co-pilot has a different processor. It can only handle one pulse coming in at a time. It processes that then looks for the other pulse, processes that and goes back to the first one and on and on.

Elevator and Aileron are on pulse 1 and 2. So, they both hit the co-pilot simultaneously. If you put a buffer between the receiver and the copilot on one and only one of those servo channels, it will delay that pulse as it goes through the chip. Then 1 servo pulse gets there first then the other. It doesn’t matter which one you delay, but you can only delay just one.

The enable line is a separate function though so you don’t have to delay that in any way.

Dan

[Brio3]

Thanks Dan,

I (as always) appreciate your expertise and insight in these areas that I know little about.
Test flight went well. I'd like to get together for my maiden with everything in full function mode. ;)
Steve

[kd7ost]

Thanks Dan,

I (as always) appreciate your expertise and insight in these areas that I know little about.
Test flight went well. I'd like to get together for my maiden with everything in full function mode. ;)
Steve

That would be great. I just spent the last 9 days working in New Mexico. Is the Lakebed dry enough to fly from?

Dan

[Wmacky]

D.W.

I don't want to hijack Steve's thread but heres a down a dirty of the Futaba PCM interface.

When connecting to the FMA Co-pilot here's the issue. The Futaba processor puts out four pairs of parallel pulses. First goes 1 and 2 together, then 7 and 8, then 3 and 4 and finally 5 and 6. This is not an issue to a single ended device like a servo. But the Co-pilot has a different processor. It can only handle one pulse coming in at a time. It processes that then looks for the other pulse, processes that and goes back to the first one and on and on.

Elevator and Aileron are on pulse 1 and 2. So, they both hit the co-pilot simultaneously. If you put a buffer between the receiver and the copilot on one and only one of those servo channels, it will delay that pulse as it goes through the chip. Then 1 servo pulse gets there first then the other. It doesn’t matter which one you delay, but you can only delay just one.

The enable line is a separate function though so you don’t have to delay that in any way.

Dan

Is it also true that the futaba puts out the wrong voltage to drive devices like the co pilot and RCAP?

[kd7ost]

Is it also true that the futaba puts out the wrong voltage to drive devices like the co pilot and RCAP?

That is true in some cases.

Futaba uses a 3.3 vdc processor. The amplitude of the pulse doesn't matter to a servo. Only the frequency and pulse duration. But, when you need to use a shorter or longer pulse to enable a device that uses 5 vdc TTL logic, you need to level shift the Futaba pulses to 5 vdc to make them work. 3.3 vdc is ambiguous as a TTL level.

Coincidentally, the FMA FS8 receiver uses the same levels. That’s OK to do in the electronic world. 3.3 volt processors are newer and take less power and can operate with lower voltages. But it does pose certain interface issues.

Anyhow, using the 3.3 vdc pulses to a co-pilot is a non issue. The co-pilot will work with larger range of pulse amplitude inputs. . Devices like the RCAP use a 5 volt PIC chip and you need to shift the voltage from the 3.3 volt receiver to 5 volts for the PIC chip in the RCAP. (Generally battery voltage is what you shift to. 4.8 to 6 volts is OK).

Some of these servo buffers will do the job. Some don’t. It depends on what chip they used to do the buffering. (This shouldn’t be confused with delay we spoke of above. Any one of them will do that) the component in the buffer is a single IC chip. It needs to be something like a CD4049, 74HC4049 or things that end in 49. If it’s a CD4069, etc then it will buffer but not level shift. I don’t know if this helps. Maybe if you roll your own. I build my own so don’t know which manufacturers of those buffers use what chips.

I did a quick search of the FMA site and found this. If you’re just connecting to Co-pilot from Futaba PCM receiver, any buffer on one line should do you. This looks like it would be the best choice. http://www.fmadirect.com/detail.htm?item=1762&section=52

If you’re connecting the Futaba PCM receiver to something like an RCAP, you will need at least two buffers that level shift. It would need to go between rudder on the receiver and the line you’re using to enable. Here, delay is not an issue but voltage pulse level is.

Hope this is clearer than mud.

Dan

[Wmacky]

OK, it just so happens that the buffer you just listed is the one I was going to get for use with a RCAP, (I'm also buying the CPilot and an additional buffer for it). Can anyone confirm that the FMA buffer shown will shift voltage "up" as required by the RCAP?

[kd7ost]

I would email FMA and ask them. They've always been pretty quick to get back to me. http://www.fmadirect.com/contact_us.htm

Dan

[icebear]

OK, it just so happens that the buffer you just listed is the one I was going to get for use with a RCAP, (I'm also buying the CPilot and an additional buffer for it). Can anyone confirm that the FMA buffer shown will shift voltage "up" as required by the RCAP?

Hi,

No, unfortunately it doesn't - I bought a FMA buffer for my FS-8 and it didn't work out, but then I tried ServoCity boosters and Cermark boosters and they both worked fine!

Thanks Dan for explaining to me why the FMA unit didn't level shift - I didn't know why, just that it didn't work!

/Icebear

[Brio3]

That would be great. I just spent the last 9 days working in New Mexico. Is the Lakebed dry enough to fly from?

Dan

If not, it will be this weekend; 67degrees by Sun :D
Steve

[kd7ost]

Yay Bjorn, I may not know a lot but I'm happy I know that. I pulled hair out once getting it all figured out.

Steve,

Drop me an e-mail when you get an idea when you'll be out there. I did some shop adjustments on my Dragonfly and need to flight test them so would be glad for a chance to tag along. I want to see that new Telemaster up close and watch it fly.

Dan

[Brio3]

...

[jludwick]

Dan the Man,

This was exactly the answer I was looking for. I'm going to PM you with a followup question. Thanks!

--Jon

When connecting to the FMA Co-pilot here's the issue. The Futaba processor puts out four pairs of parallel pulses. First goes 1 and 2 together, then 7 and 8, then 3 and 4 and finally 5 and 6. This is not an issue to a single ended device like a servo. But the Co-pilot has a different processor. It can only handle one pulse coming in at a time. It processes that then looks for the other pulse, processes that and goes back to the first one and on and on.

Elevator and Aileron are on pulse 1 and 2. So, they both hit the co-pilot simultaneously. If you put a buffer between the receiver and the copilot on one and only one of those servo channels, it will delay that pulse as it goes through the chip. Then 1 servo pulse gets there first then the other. It doesn’t matter which one you delay, but you can only delay just one.

[d_wheel]

If you put a buffer between the receiver and the copilot on one and only one of those servo channels, it will delay that pulse as it goes through the chip. Then 1 servo pulse gets there first then the other. It doesn’t matter which one you delay, but you can only delay just one.

Dan

Evidently, the one I have is defective. I have a drawer full of buffers I have tried, including ones I purchased from FMA, and none made the slightest difference. When used with a ppm receiver, it works fine. When used with PCM, it goes berserk. The only exception is when it is used with a PCM3 receiver where it operates normally except for a small jerk in one of the servos at one particular position.

It is an older unit, bought when they were first introduced. It has left me with bad feelings about the product so I have been attempting to figure out ways to make everything work without it. I think I will order a new one and see how it compares.

Later;

D.W.

[kd7ost]

Evidently, the one I have is defective. I have a drawer full of buffers I have tried, including ones I purchased from FMA, and none made the slightest difference. When used with a ppm receiver, it works fine. When used with PCM, it goes berserk. The only exception is when it is used with a PCM3 receiver where it operates normally except for a small jerk in one of the servos at one particular position. D.W.

There are a few possible answers. If you can connect it up to a receiver channel, either PPM or PCM, and connect it up to a servo and it works, it is most likely operating as it was manufactured.

In stock form, it's a servo buffer for long leads. If the RC system picks up noise, or that nice square wave servo pulse begins to decay a little, the buffer shapes it back up. Remember, the servo doesn't care if it's a 3.3 volt pulse at .5 to 1.5 ms in duration or a 5 to 6 volt pulse at .5 to 1.5 ms. The amplitude of the pulse is not critical to the servo. Only the .5 to 1.5 ms length is important. The buffer helps keep noise from RF off the leads to the servo. It also acts like a block to RF noise going the other direction. Unwanted RF or noise spikes being generated by a straining or bad servo won't feed back down the servo lead and get through the buffer to the receiver. This keeps it from transferring those pulses to other systems and keeps it isolated beyond that one buffer to the servo or servos that are on line beyond that buffer. In essence, the buffer is designed to isolate a servo or set of servo's that are sharing a work load from the receiver and the rest of the system.

But, there are different ways to do it so one buffer may not act like another buffer if you're looking for other qualities.

The one I mentioned above is level shifting. The chip needs to be a 4049 or similar to shift the pulse to the rated battery voltage.

Something I left out above is how many gates they may use in one of these chips to do the job. All the discreet chips we're talking about are Hex gate units with a total of 6 individual gates in there. If it's an inverting chip, you have to use at least two gates to replicate the input. One gate takes a low in and gives a high out. The next one takes the high out and gives the original low back out. Then it's not inverted at the output and it meets the servo needs again. It also shapes the pulse and gives the other buffer qualities.

However, propagation delay in going through two gates is not very long. If the company that sells your buffer only uses two gates of those six it might not allow enough delay. FMA used to state that if one buffer doesn't work, put a second one in line with the first one. The reason is just to further increase the delay. If, the unit you use goes through all 6 gates of that one chip, it will provide enough delay to do the job. I don't know of any comprehensive listing of units that do or don't do the job. That’s why I've always just soldered up my own. I use the buffers for either level shifting or delay. That's why I pick the chip I use and roll my own.

It sounds like icebear using the servo city or cermark buffers, (boosters) will do the job. If you guys want a how to on making your own I'll do one up and take some pictures. for posting.

Dan

[d_wheel]

FMA used to state that if one buffer doesn't work, put a second one in line with the first one. The reason is just to further increase the delay.

Dan

Last night, I had 5 buffers in series and it made absolutely no difference. I ordered another CoPilot to see if a newer one is any different.

Later;

D.W.

[kd7ost]

Yep, that's too much. Put enough buffers in and the propagation delay will align the pulses back up with each other. Thats probably not happening.

Can you describe your set up in detail?

Type of receiver? Manufacturer and model number.

Goes to a CPD4 co-pilot?

Goes to any PIC chip devices? Like any UNAV guidance parts?

Goes to any other electronic devices?

Battery voltage used? 4 cell? 5 cell? Lipo with regulator etc.

What channel are the buffers connected up to on the receiver side and what input's to the co-pilot etc are they going in to? Aileron, Elevator, Enable?

Always throw a servo on the end of those chains of parts to ensure you still get servo good action.

Also, if you can peel off any heat shrink and read the part numbers off the chip, we would know what it's doing or not doing.

Dan