04-29-2022, 11:14 AM
The maximum number of channels that you can have in PPM mode, per the official specification is 8 channels.
However, you can have more PPM channels if you increased the frame rate. This is what Graupner and Multiplex do with their radio systems. The PPM specification calls for 2.2ms x Number of channels + at least 4.9ms. With a typical 8 channel radio that gives you a frame time of 22.5ms, which is a frame rate of 44.4 times per second. 32 channels would require more than 75ms, which is ~13 frames per second, making it too slow really for controlling a RC model - especially if dropped frames occur. XPS transmitter modules support up to 32 channels in PPM mode.
Long frame times means a lot of latency, which iis why protocols like Xtreme, XBUS, SBUS, XJT, etc. exist. The Xtreme protocol supports up to 256 channels, and a frame rate as low as 3ms with 4 channels.
However, you can have more PPM channels if you increased the frame rate. This is what Graupner and Multiplex do with their radio systems. The PPM specification calls for 2.2ms x Number of channels + at least 4.9ms. With a typical 8 channel radio that gives you a frame time of 22.5ms, which is a frame rate of 44.4 times per second. 32 channels would require more than 75ms, which is ~13 frames per second, making it too slow really for controlling a RC model - especially if dropped frames occur. XPS transmitter modules support up to 32 channels in PPM mode.
Long frame times means a lot of latency, which iis why protocols like Xtreme, XBUS, SBUS, XJT, etc. exist. The Xtreme protocol supports up to 256 channels, and a frame rate as low as 3ms with 4 channels.