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Old Jan 24, 2016, 03:46 PM
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Yes, the 400us pulse width is to verify the host and is one of those JR things we inherited.

The pulse for the servo is still measured from leading edge to leading edge.

Andy
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Old Jan 24, 2016, 03:46 PM
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Originally Posted by AndyKunz View Post
Phil did you say that Spektrum uses non-standard or hi does? The correct timed is measured from leading edge to leading edge. That means if the line is normally low that the pulse sixth to be sent to the servo is from the time the pulse starts to go high until the pulse starts to go high again. Using this technique means that the time the pulse is high is immaterial. Back in the old days we used pulses that ranged from about 130us to about 375us. It didn't matter so long as the electronics were set up to handle pulses properly. Some RF decks needed different widths.

Andy
Thats exactly as it should be Andy - edge to edge - traditional PPM does not depend on the precise width of the PPM pulses, only the time between matching edges. But as we've discussed before - the DM9 does in fact need its PPM pulses to be 400uS or the channel timing is out by the difference between the actual PPM pulse width, and 400uS. All my project stuff has used 250uS so I have to do a specific 'Spekky version' with a 150uS fudge

Cheers
Phil
EDIT: I should add, its not a problem once you're aware... heres my Spektrum DM9 transmitter:
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Old Jan 24, 2016, 03:56 PM
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Actually, I think it was supposed to be rejecting you completely if you were too far away from 400. Kinda late now to fix that bug though!

Andy
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Old Jan 24, 2016, 04:06 PM
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Part of my test setup is a ppm generator with all parameters variable including channel count, polarity, pulse width - the DM9 works fine with all (reasonable) widths, but the channel timings only coincide at 400uS. But as I said, its not a problem once you're aware
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Old Jan 24, 2016, 04:34 PM
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Originally Posted by pmackenzie View Post
It is possible that the DM9 is doing something a bit different.



I can take a model from an XP9303 with an FrSKy module and copy it over to an X9503 using a DSMX receiver and not even have to touch the trims.



But many have said that when using the DM9 unless you set the PPM width to 400 usec the trims will be off. Other modules don't have this problem.
I can verify all of that. I just checked with a DM9 in my Taranis. With Protocol set to 300us the neutral is at 1600, at 350 it's at 1550 and at 400 it's at the desired 1500.
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Old Jan 24, 2016, 06:22 PM
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I can verify all of that. I just checked with a DM9 in my Taranis. With Protocol set to 300us the neutral is at 1600, at 350 it's at 1550 and at 400 it's at the desired 1500.
Same here with my own PPM generator (stick encoder) - the DM8/DM9 does not measure the complete pulse (rising edge to rising edge which includes the "start" pulse) but the length of the low portion of the pulse for the DM9 and the high portion for the DM8. I can vary all aspects of the PPM and the DM8/9 will work fine with a start pulse anywhere between 250us to 450us simply ignoring it.

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Old Jan 24, 2016, 06:44 PM
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Sorry Ivan that doesnt quite tally with my findings. That would put the channel timings miles out, and in the opposite direction. If the DM9 did only use the 'low' portion of the pulse then a 1500uS neutral with 250uS pulses would give 1250uS neutrals whereas I measure 1650.
My own unsubstantiated belief is that they measure the low portion and add 400uS. This would give perfect timing on 400uS pulses and also the exact offsets we have witnessed when using other pulse widths.
Cheers
Phil
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Old Jan 24, 2016, 09:40 PM
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Originally Posted by phil_g View Post
Sorry Ivan that doesnt quite tally with my findings. That would put the channel timings miles out, and in the opposite direction. If the DM9 did only use the 'low' portion of the pulse then a 1500uS neutral with 250uS pulses would give 1250uS neutrals whereas I measure 1650.
My own unsubstantiated belief is that they measure the low portion and add 400uS. This would give perfect timing on 400uS pulses and also the exact offsets we have witnessed when using other pulse widths.
Cheers
Phil
Same thing said in different way. The DM8/9 ignores the start pulse and assumes it is 400us. So it considers 1100us of what it actually measures as neutral and goes from there. Whether it adds a fixed 400us value to the measured value and uses 1500us as neutral or uses the measured value only with 1100us as neutral reference is immaterial. The final result is the same - it ignores the actual length of the start pulse so for the module to generate correct servo output at the receiver the PPM fed to it must have exactly 400us start pulse.

I don't have a problem with that peculiarity of the DM8/9 as I can easily get the needed pulse duration on my designs or modify the timing circuit in the old trannies so they generate a 400us pulse.

Ivan
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Old Feb 07, 2016, 11:35 AM
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A quick history of the modules

Things were fairly simple for a couple of years:

1. Original DSM2/DSMX module was released in fall 2012. First batch had a firmware fault ("channel 2 error"). Detected and fixed within a few days by HK, who sent out a fixed one free to all affected. It did DSMX but the box originally said DSM2.

2. Revised version produced in 2014 was different only in the physical layout and antenna mounting.

Then in early 2015, two new versions were issued using a new DSMX implementation:

A. Basic with no switches.

B. "Walkera Switchable", which has DIP switches and does Walkera and DSM protocols and TAER or AETR channel order (given TAER input).


That's where things stand now.

In functional terms, the original and 2014 modules worked well with all DSM2/DSMX receivers, including the integrated types. Receiver mode was learned at bind time but could also be changed manually by pressing the bind button three times in quick succession. The mode was indicated by the number of flashes of the LED: 0, 1, 2, 3.

The 2015 Basic and Switchable share two main differences from what came before: (1) they don't support manual mode change so must be rebound if the class of receiver changes (e.g., from DSM2 22ms to DSMX 11ms); (2) they just don't work properly with any of the receivers that are integrated with any kind of FC, such as the UMX AS3X bricks, the SAFE receivers in BNF models, or the various quads like 180QX (one specific issue is that channel 1 is dead or erratic).

In some cases, the switchable can be useful. By setting it on DSM2 22ms you get a module that doesn't need to be rebound when changing receiver classes. Unfortunately, it still doesn't work with lots of the most popular receivers.

The Walkera mode is supposed to work but I have no direct experience. The ability to switch channel order is of very limited interest since most people using one of these would have that ability in transmitter firmware (ErSky9x or OpenTX).

It's now nearly 12 months since the faults in these modules became clear but no response from HK.

EDIT

There's also the Telemetry module for 9XR Pro only. Uses the built-in antenna in the 9XR and requires different module protocol provided by ErSky9x firmware.
I just had some struggle with my Blade Nano CPS and the "A" and "B" versions. Binds OK as it seems but no throttle. Is the "1" or "2" versions still available at HK? Are there any other soloutions! Still want to use my Taranis though.
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Old Feb 07, 2016, 11:46 AM
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Originally Posted by pernstig View Post
I just had some struggle with my Blade Nano CPS and the "A" and "B" versions. Binds OK as it seems but no throttle. Is the "1" or "2" versions still available at HK? Are there any other soloutions! Still want to use my Taranis though.
Hack module
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Old Feb 07, 2016, 12:26 PM
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Do you have any specific module in mind?
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Old Feb 07, 2016, 12:30 PM
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Do you have any specific module in mind?
The "hack" module". There's a link in that thread to John Prikkel's site. Pat has contributed to the module as well.

Ivan
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Old Feb 07, 2016, 12:38 PM
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Originally worked out the details for using it with the 9X. Same thing works for the Taranis of course and some of the er9X code is still used there.

You can do it without the PCB, but it is probably easier with it.

Lots of details on line for it:

https://www.google.ca/#q=spektrum+hack+module

The only real limitation is that you are limited to 6 channels. Other than that it is arguably the best way to do DSM2/DSMX in a radio using er9X or Opentx.
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Old Feb 07, 2016, 12:45 PM
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Orange DSM TX Module problems

Yes. A hack module is the way to go if six channels will meet your needs. HK have had nearly a year to fix the Orange modules and have yet to even acknowledge the problem.

The module comes from a DX4e, DX5e or DX6i. If the original transmitter did DSMX the module will too. There are also lots of old DSM2 transmitters that will yield a usable module if you don't absolutely need DSMX. Avoid any of the low power transmitters as a source unless you fly only very small models at close range.

How to build a true Spektrum DSMX module for Taranis (25 min 36 sec)
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Old Feb 07, 2016, 03:05 PM
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Thanks guys!
/Leif
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