modelcrasher

Searching the forum IPD seems to please everybody who uses. A few mention that they will never go back to PCM.
So, are there any real disadvantages to IPD? Multiplex stopped there pcm range long ago so it must "good enough".
I don't really want to switch to pcm as it mean having to upgrade transmitter, not something that I really want to do. But I really need the extra glitch protection plus the fail safe is a bonus.
I only fly sports models (80 inch max) but i hate the idea of a model go ing out of control as a few have on our field, and glitching is common. BTW I tried a futaba D/C ppm which improved things but since the price for a IPD is simler I thought it would be better to go straight to IPD or PCM


thx

dirtybird

My Feedback: (5)

IPD is an improvement on the old standard PPM. In my opinion its not as good as PCM. But for you its the most economical solution. Go for it.

anthonymio

I fly gas ignition engines using both multiplex IPD and JR dual conversion PCM receivers. To be honest, I don’t see a difference in performance between the two. Theoretically, IPD will warn you (soft control) if there are signal problems, while PCM will go into lockout until a good signal is restored. The only plane I have lost in the last four years was to a PCM lockout on a JR Single conversion PCM receiver. So far, I am sold on the multiplex IPD receivers, particularly the RX-9 receiver and plan to continue using it in the future. FYI- it is not advertised, but, the RX-9 is shift selectable and will work with negative shift transmitters, i.e. Futaba, making it versatile as well as reliable.

Tony M.

JohnMac

I still use some very old Multiplex PCM Rx's in my large scale gliders. They work just fine and absolutely bullet proof. I also use IPD and IPD synth Rx's. Equally they work just fine.
There are theoretical advantages and disadvantages both ways, but even in theory these are slight. I practice I can not tell the difference, except the extra range with the synth Rx's, but then that has nothing to do with IPD.
Regards,

John

modelcrasher

Thanks.

looks like IPD is the way to go...

BillS

Is IPD yet another name for non-error checked FM or is there something unique about it?

Bill

modelcrasher

IPD is basicly a ppm reciver that has a built in signal proceser. this mean that gliches are alot rarer. it also has a failsafe built in that provides the same function as one in a standard PCM reciver, the advantage is that you get more warning(such as mild gliches) before a total lock out

JohnMac

Hi Modelcrasher,
Nearly right but not quite. Neither PCM or IPD let glitches through to the servos. In different ways they filter out interference on a frame by frame basis. If someone switches on on your channel both will go into failsafe. However, in the case of reaching the edge of range, apparently PCM is all or nothing, one minute you are in range the next you're not, and it goes into failsafe. IPD works differently. As the error rate starts to increase it slows down your servos, which would make most of us want to bring the model back, so in that way you get some warning.
Regards,

John

rmw00

I hesitate to get into these discussions because everyone is so passionate about their views, but here goes...

All of my experiences are with JR PCM-10 equipment.

First, while I was flying my plane began to respond slower and slower. I thought my receiver battery was dying and landed immediately. I then discovered and a new pilot about 20 feet away who didn’t know better had turned his transmitter on the same channel. His radio was PPM and as expected was responding very erratically. My PCM setup continued to provide reliable control, just slightly slower response. At no time did it go into “failsafe�.

Second, I was flying a large electric with a home made speed control. At certain distances and aspects my power would go to low and stay there until I cycled the throttle. Turns out that the speed control was putting out massive amounts of RF interference and my “failsafe� setting was to leave all control surfaces as they were, but go to low throttle. When I solved the RF issue, I never had another problem. Here is an example of PCM indicating (not covering up) RF problems, yet maintaining control.

Finally after I got a lot of grief for relating the incidents above I did some testing. I put two JR receivers, same channel (19 if I recall) , one PCM and one PPM about 6� apart on my front porch. I then turned on the respective transmitters, both PCM-10’s (one on PCM, one on PPM) and had a friend walk down the street, moving the sticks, while I watched the servos.

0-10 feet from the receivers, PPM jittery, PCM no movement
10-30 feet from the receivers, PPM jittery, PCM sluggish but working
30-100 feet from receivers, PPM jittery, PCM appears to be working fine ( I suspect it was somewhat sluggish)

Try it your self.

BillS

Do you know how or what the signal processor might be filtering?

Bill

stek79

Guys,
I just did some few searches on the net to discover what is IPD tecnology. Check this page, for example:

http://www.hobbyhorse.com/ipd_technology.shtml

As we can read, the only criteria used by an IPD receiver to decide if a frame is good or not is by analyzing its time length...

DONT even compare such a device with the PCM technology!!! PCM is an order of magnitude better in design and safety, IMO.

IPD will declare a good signal if it is contained in the time windows stated above, so ANY signal with that feature can go through and get sent to the servo.

With PCM servo position is encoded in digital and error checked, so :

1) it is very hard to corrupt a frame (this is one of the main digital modulation advantages)
2) in case of a corrupt frame it can be detected with a given probability - usually very high and choosen in the design process - thanks to a checksum sent by the TX at the end of every frame

BillS

stek79,

Thanks for the information. At least some manufacturers are starting to reject completely bogus signals. A TX turn on that produces servo hard over on an in flight aircraft seems totally ridiculous and unnecessarily dangerous.

Bill

sillyness

My Feedback: (25)

Maybe I'm the exception here, but I am happier with IPD than I was with PCM. I use my JR 10X to run Multiplex 9 ch Synth RXs in my 35% aerobats.

The reasons I like IPD:
-Signal is lost gradually, as stated above. If your ignition shielding is breaking down it eventually overpowers the PCM and lcan ock it out. IPD will warn you.
-IPD Synth memorizes the traits of your particular radio when programming the frequency... i.e. it remembers that my radio has 10 channels. I can turn on my 8 channel 8103 (also in PPM mode) either at the same time as my 10X, or even by itself, and the RXs completey ignore it!!! Sweet!
-The IPD RXs let me turn the IPD off for periodic filterless range checks to make sure that the ignition shielding and all wiring is still working without generating interference. PCM guys usually range check with a PPM RX once at initial setup to check the same thing. I just have to push a button and can do it whenever I want.
-Futaba boasts about 2048 resolution with their new systems. IPD is infinite resolution!
-I get UNBELIEVABLE range checks with my IPD synth RXs and JR Synth TX module!!!!

FWIW... I do think that FM (PPM) tech is developing to the point where it is surpassing PCM. I don't believe that passing digital info packets is the best way to do things... sure sounds neat, but it shares the inherent fragility of all digital signals... they must be heard perfectly to work. I'd rather a half-heard signal partly work than not work at all. The most bulletproof RXs I've ever seen are BERG RXs... they will ignore anything that is not your TX... and they take a fresh "imprint" EVERY TIME they are turned on. I wish BERG would make RXs for Giant Scale.

Just my .02.

XJet

Sorry to disappoint you but IPD *doesn't* offer infinite resolution for several reasons.

Firstly, all computerized transmitters have a finite resolution (regardless of whether they're operating in PPM or PCM modes). This is because the voltage across the control stick's potentiometer has to be converted to a digital value by the transmitter's processor. Because it's digital, this means the value must be represented by a finite number of bits, and therefore has a finite level of resolution.

Now most transmitters use A/D (analog to digital) converters with a 10-bit resolution (1024 positions) so no matter what type of carrier encoding is used (PPM/PCM), that's the best they can do.

And, to make matters a little worse for the IPD receivers, they have to convert the received pulse-width (essentially an analog value) into a digital value (again with a fixed resolution) before it can be processed. That digital value is then used to re-create the pulse that was received -- but with the limitation that only a fixed resolution is again possible due to the fact that it has been stored as a digital value.

Then there's the issue of servo resolution. Right now, even the best servos are hard-pushed to keep up with the resolution of a 10-bit transmitter so 11 bits (aka: 2048 positions) is really quite a waste of money until we can get servos with deadbands of less than 0.5uS. Right now, most analog servos have a deadband of around 8uS and even the best digitals are pushing the boundaries if set for 1uS (1024 positions).

So, although IPD does offer some benefits over PCM (and some disadvantages), infinite resolution is *not* one of them. If you really want that, you'll have to go back to a pre-computer transmitter and a straight FM (or AM) receiver -- but personally, I'll take the resolution hit of modern RC gear in return for the imperceptible effect that any immeasurable resolution reduction might produce.

sillyness

My Feedback: (25)

I stand corrected. I guess I was thinking of pure PPM, and I wasn't sure how computer radios did the mixing... I thought the signal reamined analogue for mixing.

I completely agree. I think this 2048 stuff is a total gimmick. At best, 5955s have 600 steps of resolution (the 1:1 setting on deadband makes them sensitive to about 2us signal changes... assuming 2 us this gives you 600 steps). The 8611s are a little tighter (I can repeat 1 us resolution) but what you gain in resolution you lose in gear slop. I think the 5955s actually feel a little better in the air, but they should have less resolution... hmmm....

HarryC

My Feedback: (1)

In reality, it isn't an order of magnitude better than IPD. I have used IPD and nothing else for about 6 years including in my jet models and it has been excellent. PPM error detection can detect tiny levels of errors.

H

outssider

My Feedback: (23)

after reading your post, i tried this !! didn't work for me ! have evo 12 synthetic tx and multiplex synthetic 9 ch ipd rx. using channels 1,2,3,4,7,8 turned on airtronics 6 ch tx on same frequency. the ipd rx did not block out the other transmitter.....also tried a 4 ch tx and also didn't block.....how come mine doesn't block out the signal from the other radios ??

BillS

I am curious to know if the IPD RX went to fail-safe and if any of the servos did a hard over.

Bill

JohnMac

Please Explain. Why is it PCM better by an order of magnitude. Please exand on you assertion.
Regards,

John

sillyness

My Feedback: (25)

How close was the second TX? If it's too close you can swamp the RX with energy. When I got my 2nd TX really close it started to cause issues, but it did not listen to the controls of the second TX. I just got delayed and intermittant control from the primary TX.

Also, are you sure the IPD was turned on?

When I turned the primary TX off the RX completely ignored the 2nd TX no matter how close or far. I reprogrammed the RX to to listen to the secondary TX and it now ignored the Primary TX... pretty sweet.

There were never any hard-overs or other extreme outputs in any case.

This is total speculation, but I know there are different software versions of the IPD Synth RXs out there... it may be possible that the TX ID function is a recent upgrade. Both of my IPD Synth RXs are fairly new.

causeitflies

When I first got my MPX Rx I locked it on to my JR 783. I then turned on my Polk 8 channel and the Rx totally ignored the Polk on the same frequency. I reversed the sequence and it totally ignored the JR. The Rx and two Txs were within two feet of each other. This was in my shop and not out in the field. I only tried this once but if I remember I'll try it again including the Evo.

sillyness

My Feedback: (25)

OK... I did a little "research". I downloaded the 9 CH IPD Synth manual off the Multiplex website and compared it to my manual.

The one off the website is for Software V 1.0. My manual (and RXs) are Software V 1.2X (if I remember right the RXs are V1.24, but I'm not pulling them out to look).

The V 1.2X manual, bullet 11.1, discusses "Automatic servo channel count detection". The V1.0 has no mention of this feature anywhere.

Check your Software version... mystery may be solved.

outssider

My Feedback: (23)

my rx is only several months old and is the version 1.2. it does say in the instructions that the receiver counts the number of channels being used. I do remember when setting up the plane having a problem when i set up only a couple channels then later plugging in all 6 channels. I then had to reset the rx. IPD comes on automatically when receiver is powered up so IPD should have been engaged. both transmitters were about 4 feet away from the rx antenna and the tx antennas were completely collapsed. The rx did not go into fail-safe ! nether tx could control any of the channels consistently. The servos did not go nuts however. rx was definitely not blocking out the foreign tx.

sillyness

My Feedback: (25)

Hmmm... wierd. 4 feet with 2 TXs on the same channel is a still a lot of energy hitting the RX. When I got the second TX really close to the RX it acted in much the same way you are saying yours is.

Plugging in more servos shouldn't matter... only the number of channels the TX is sending out should matter.

You said you weren't going into failsafe... you also said you had intermittant control. The IPD holds the last good signals position for 0.5s before going into failsafe... maybe you were getting good signals at least every 0.5s?

Failsafe on all mine (2 synth and 1 non-synth) work great!

I'm going to get a couple more (to replace my non-synth IPD and a HITEC RX in another 35%) sometime in the near future! Love 'em! Gotta love the dual conversion too!

outssider

My Feedback: (23)

when I was setting up for first time was using multiplex 12 evo tx. I may have only had set a couple of channels up when i first tried the plane and started setting up. If you set only 2 channels up with a particular plane i think this tx only transmits 2 channels. with multiplex evo tx you designate each channel and what it does. channels not being used default to off.


I am going to do a more detailed test tomorrow and I will post exact results here....I will also add an additional channel to the transmitter (go from 6 to 7) and see if the multiplex rx activates when i turn the transmitter on for the first time using 7 channels instead of 6.