specialFX

Bob, maybe i was not exact enough, but the ACT diversity system is a receiver system. You are right that ECU´s can´t make a decision which signals are correct and which are bad. but what all(?) actual ECU are able of is determinign if a signal is within acceptable range. And Failsafe programming with ACT diversity works like with other PCM RX´s. Teach the ECU a acceptable range and program your failsafe value far out of this, as done with PCM. No differencies here. And the diversity system eliminates any(!) glitches on servo signals within acceptable range. Like hold on PCM´s.

Thomas

SJN

I think ill try the ACT 2 x DSL-8 Diversity-Set 16 Servo outputs.

The features seem VERY neat with this dual RX setup.



http://www.acteurope.com/html/start_english.html

Woketman

My Feedback: (6)

I think this Diversity system sounds very promising. I sent them an e-mail, a few months ago, asking for some info, but never got any reply at all. Anybody have a contact that will actually reply?

siclick33

What failures are possible with this system? What happens if one of the receivers fail?

What about this 'diversity computer'? Are there any failure modes that would cause the other receiver to get confused?

I can see where the benefits may lie, but is not a 'redundant system' as they are interconnected.

SJN

though connected, it seems even if one rx fails, the other can still controle all 16 outputs.

http://www.acteurope.com/html/divers..._it_works.html

SJN

Also the neat servo programming features for all 16 servos by a palm pilot or PC
signal monito for the last 20 minutes
battery voltage monitor also

specialFX

I think, the interconnection of both systems gives the huge andvantage. Only if both systems are able to decide which signal is ok, the benefits of a dual receiver system come into play. As the redundant systems in e.g the space shuttle, the system is interconnected TO DECIDE which signal is ok. (OK, the shuttle my be not the best example tist days, but you get the message;-))

Thomas

mikehannah

Hi
Sorry to nit pick but when you start talking about dual rx you are into a whole different ball game to just comparing PPM versus PCM rx. Such a system would work just as well if not better with PCM.

Plus Unless the two RX where operating on different frequencies then the ambient signal to noise ratio would bomb both rx out at the same time. ( regardless off antenna orientation)

But interesting all the same.

The true answer is spread spectrum as it would jump to find an less crampy frequency.

Mike

rpmtech

My Feedback: (6)

Ahhh, this subject once more, im bored so I'll have to give my 2 cents

I will have to say that some of my models like my submarines, my tank etc, I absolutley cannot use PPM. Too much electrical noise from stuff to ever be able to solve for a PPM Receiver. The LINK with PCM is much more secure.

Like what was said, PCM can and will HIDE a potential problem, and it will rear it's head at the most unfortunate time.

Setup with and range check with a PPM, drive the damn thing around on the ground for an hour, make sure you are getting no BS with your signal or jitters.

Use logic when installing electrical components. install toroids on long leads etc.

Buy a frequency scanner! the $200 is a piss in the ocean compared to the consequences of flying on a channel with some type of interference from somewhere.

PCM is waaaay ahead of std PPM in link quality.

erbroens

Rpmtech: The common mistake in modelers thinking that a PCM link is far superior to a PPM system is the lack of servo jittering when installed in a noisy environment ... but they are rudely awakened to reality when they feel the lack of instantaneous servo response! not such the case with a relatively slow moving model like a sub or a tank... but disastrous when it happens in a helicopter or a fast plane.

Another real field data I observed in my years of r/c modeling is this kind of situation: a guy buys a giant scale gas bird or helicopter and initially installs a PPM receiver.. he got pissed by the glitches in his aircraft that almost lead to crash more than once. Then, instead of searching for the origin of the radio noise he buys a PCM receiver. the glitches disappears and the plane too
after entering in failsafe for too much time.

SJN & Thomas: that system look pretty good!

JohnMac

Hi Mike,
I think that you are misunderstanding what IPD is and does. Personally I think that the phrase "post processing" is a little misleading. To all intents and purposes IPD does the same as PCM. PCM filters each frame before passing it to the decoder. If it sees a dodgy frame then that frame is blocked. The difference is simply that PCM and IPD use a different set of papameters to determine if the frame is good or not. The pertinent word in IPD is the first one-"Intelligent". Rather than encode the signal in a numeric format, modern processers can be programmed to recognise a good signal from a bad one, on a number of different parameters, do this in real time and offer slightly more than PCM. For example, one of the points detractors of pCM make in this debate is that PCM will mask any problems until it is too late. They have a point. With the latest generation of MPX IPD Synth Rx's you can turn off the IPD filter to perform a range check. Swith off and on again and the filter is restored. Now you can do another range check. If there is big discrepacy between the range with the filter on or off then you need to take a closer look because something is wrong. There also seems to be a slightly "softer" regime ragarding failsafe, where the reciever finds itself in the grey area between a good signal and an entirely bad one. What the IPD one does during this short period is follow the trend of the previos pulses and "fill in the gaps" as it were. However this slows the servos down whilst it is doing this. The effect in practice is that you get ( n these particular circumstances, or on the edge of radio range) a few moments of sluggish response, which warns you of a problem.
In my experience with IPD recievers ( I was amongst the first people to use these in the UK) there is little to choose between these and PCM in practice, except for a slightly faster servo respnse from IPD. (which is why I use IPD in my jets and keep my PCM for my big scale gliders) They do exactly what its says on the tin.
One further point. I have done some impirical testing of PCM vs PPM rx's in the past regarding there interference rejection capabilities. Here I agree with your earlier post. I break down the test into 3 catagories: 1) light interference, 2) moderate interference, 3) major intereference. Results were 1) PPM = Glitches, PCM = no effect at all. 2) PPM =Serious glitches, probally would result in a crash with most models, PCM = momentary failsafe followed by periods of control, you have a chance of controling the model. 3) PPM = Servos fully locked over, the model is doomed, PCM Rx in failsafe.
The same test with IPD has proved more or less the same results. The point is that these tests give the lie to the idea that with a straight PPM reciever that the flyer will fight through the interference, but a PCM RX will enter a lockout condition. IMO, from these tests, whilst they PCM/IPD equipped plane may be cruising gently to oblivion, the equalilent PPM equipped plane has already rekitted itself on the runway. Whilever your model is flying there is a chance that the interference will cease and you can recover. I speak from experience, this has happened to me with a D/F model.
Regards,

John

Big feet

This is getting interesting.

I have a few observations,

1 PCM and the MPX IPD systems seem closely matched from the tests carried out by John above. ( No experience of IPD myself)

2 The Diversity system looks like you get Rx failure backup more that interference defense.

3 Where the Diversity system would provide a huge step forward in signal integrity would indeed be if they both were on different frequency's as Mike said above. My question is, How do we transmit on two different frequencies at the same time from the same Tx?

specialFX

Yes, I think so! My buddy is about to try it out with his 2,5m Katana, If things work out as expected, I´ll try it with my Su-27. The system solves many problems at once, as there are many servos, programmable as the needs are, if there are 4 or 6 servos on channel X, failsafe position of servo x but not y and so on. looks pretty promising! As I read you like Hitec servos, same on this side of the pond, never had any problems with them, no matter if airplanes or one of my helis.

regards
Thomas

specialFX

The Diversity systems offers this option too.
They sell a dual-frequency-TX-module. Then you transmit on two frequencies, receive with two frequencies and each receiver is able to reconstruct the whole RX-signal if some frames are lost. I think it´s the most perfect system availible nowadays! If you fly a JR/Graupner MC-24 you can buy their dual-TX-module and replace it without further modification to your transmitter and use dual frequency/dual receiver technology. Really promising!

Thomas

SJN

Please tell us how it goes with your freind.

specialFX

Sonnich, he just ordered the system. I´m eagerly awaiting it for myself;-)!! The palm is already at home, we are just waiting for the RX´s! Can you read German? If not, I´ll gonna try to translate, if some problems occure. And No, I´m no Rep. Maybe, if you guys are interested, I can get the developer of this system to step in here. I don´t know him, but I know the forum he writes in.
Immediately if I get some results I´ll let you know!

Thomas

JohnMac

It is no problem at all. The diversity system has a dual module to replace the original TX module, so it can transmit on two frequencies at the same time.
Regards,

John

robert

So how do we make sure that a PCM receiver is not hiding a problem? I've heard several times that you can do all the checks with PPM and when everything is ok change to PCM. However I find that most of my incidents come from messing with my models by changing stuff around that was just fine to begin with.

specialFX

Yeah!
Thats it. It seems to be a really well thought out system.

Thomas

specialFX

The most easy way to be sure PCM doesn´t spoil your results is NO TO USE PCM;-)
Don´t be fooled, up to now I use PCM, but I think some other solutions are on the horizon!

Thomas

Big feet

Now this is looking better than any other system I have seen to date, unless the noise is a very wide band and blocks every channel. [:-]

But then the original question PPM/PCM would be useless as well, so fair enough.

Is there any price for this system?


Peter