[NSRCA-discussion] 2.4 Ghz

[Ed Alt]

Hi Jim:
I thought JR SPCM was about a 44 ms frame rate for a complete interlaced pair of frames transmit.  Futaba PCM 1024 is 23 or 24 ms for a full data frame if I'm not mistaken.  No idea about Airtronics though.

Too bad about the trim resolution being so wide on the DX7, but I would assume and hope that as long as you go back and re-adjust things through some servo centering option, you ought to be able to re-center the trims and avoid that sloppiness?

Ed
  ----- Original Message ----- 
  From: J.Oddino 
  To: NSRCA Mailing List 
  Sent: Sunday, December 17, 2006 5:52 PM
  Subject: [NSRCA-discussion] 2.4 Ghz


  I flew the Dx7 on Thursday and it felt pretty good.  It was in a Dog House Extreme with marginal servos but still had a very nice feel.  I took it way up and out so we could barely see it and had no problems.

  Today I ran a few tests.  Following are some results and my comments:

  1) The update rate, that is, the rate at which the servos get new information was about 45 Hz or every 22 milleseconds.  This is a little slower than most modern day systems.

  2) The resolution less the servo, that is, the minimum change in the pulse width to the servo, was 1.0 microsecond.  This is better than any system I have measured. When I connected one of my elevators with a good JR digital servo it was extremely accurate and neutralized perfectly as far as I could see.  This was confirmed by measuring the pulse width on a scope scaled to one microsecond per cm.  This also says the mechanics of the transmitter gimbal are not creating an error in commanding neutral.

  3) The change in pulse width per click of the digital trim was 3 to 4 microseconds which is not good.  The basic system is a 1024, 1024 steps from lock to lock, but you can only trim it as if it were a 256.  To me it is setting the trim that requires the best resolution.  We could fly with a 256 system as long as we could trim to 1 in 1024. 

  4) An interesting thing was the dither on the pulse width of .4 to .8 microseconds.  I assume this was done on purpose because there should be no pulse jitter in a digital system.  I'm wondering if this can contribute to the good feel when flying.  Any opinions out there?

  This system looks like a very good value and the big boys better get a spread spectrum system out if they want to sell systems in this price range.

  Jim O




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