Very interesting topic!
While reading this I realised something. I have a MPX failsafe PPM RX in a PicoJet, a small speed400 powered plane (don't remenber the exact type RX, I'm at work now). Until now I didn't know that it should not be possible to to have any glitching, it should "hold" when something interferes. When I switch off the TX is goes into failsafe like it should.
Thing is, it almost CONSTANTLY glitches when I turn on the motor! How is this possible??
Eelco
Because the RX has no way of knowing which is a valid pulse if the "valid" pulse is within the margins specified. Even if it does go outside there is no way to know if the previous "good" pulse was valid either, so the failsafe hold hold could be anywhere... It is beyond me that R/C mnf can ignore the many years of theory and practice on this subject. PCM is the only way to have a reliable failsafe. PERIOD.
Having said that it is quite possible to under bench conditions demonstrate to the uninformed that the two systems are equal, which is probably why there are a few believers.
If you had to make PPM more "failsafe" ( the bandwith issue is a good reason to do this) there are a few schemes that would do a better job than the what the IPD claims. I have had experience with Multiplex in years past and their RF design is nowhere near as good as any other brand. They may have improved since but at jet meets we have a few crashes locally. And the R/C systems were....
Andre Baird