Nano outputting 16 ch in CPPM mode? - Page 2 - RC Groups
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Sep 13, 2012, 11:50 AM
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GoFaster's Avatar
Originally Posted by JimDrew
I should probably calculate the frame rate and divide that by 2.250 to determine the maximum number of channels that can be allowed and use that for a cap with the PPM output for our receivers.
What did you decide on Jim?
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Sep 13, 2012, 05:42 PM
I am not sure. Some people want all of their channels with radios that will deliver 12 channels or more in a valid PPM frame length.

I wonder if it would be best to have two PPM modes, one where 8 channels are output or ALL channels are output. How many channels do you need?
Sep 13, 2012, 06:08 PM
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Right now, I need 8 channels. But tomorrow, who knows.
Perhaps default to 9 from the factory, but give people the choice to change it via XDP. Increasing PPM frame length would decrease the refresh rate but as long as people are aware of it.

Also if you could take a look to make sure PPM pulses/frames are legit when the Evo (with 3.41 firmware) channels are set to -110%/+110% endpoints. I recall seeing something weird happening with the Nano's PPM output especially when channel endpoint are set less than -100%...950us or so if I recall correctly.

Here the msg with a capture when a channel min endpoint is set to less than -100%

- Felix
Last edited by GoFaster; Sep 13, 2012 at 06:13 PM.
Sep 14, 2012, 10:07 AM
What you are seeing has to do with 16 channels being output in a longer time frame than what is available, so there is an overlap and a spike when you have the channel pulse set to less than 900us. The only way to fix this is by limiting the number of output channels to what can fit within a frame, plus some headroom to handle the widest pulse width that can be achieved for all channels.

The PPM output routine currently uses the number of input channels to define the number of channels being output. I will have to see if it is possible to use another RAM location to handle that, but I seem to recall that I am completely out of variables (some are shared with the binding routine already). I could hard code a set value of output channels, but that would be something that could not be changed. However, the problem with hard coding the number of channels to say 9 is that if you used a transmitter with 8 or fewer channels, the unused channels would not be defined.

The reason why the PPM output is set to use the number of input channels was so that people did not need to have the XDP in order to get this feature.

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