SOLVED (I THINK) Spektrum DX8 Throttle Anomolies

Hi All,

I'm running the APM2.5+ with Arducopter 2.8.? (The version before 2.9)

My Radio is a Spektrum DX8.

All of the radio calibration went fine, but I noticed at the time of calibration that the throttle 'green bar' would randomly blip up to half throttle (or if it was at half it would blip up to full).

At the time i thought maybe it was just because i was inside and usb tethered.

Motor testing without props though verified that occasionally the motors would briefly double speed then drop back to idle or half speed. this was random again, no pattern, once every 5 to 15 seconds.

Fool that I am i thought maybe somehow attaching props would solve this issue, but again, at idle the motors would pulse enough to just lift frame, or if I was almost at takeoff speed the frame would jump up and flip.

I've noticed one issue of uneven thrust front to rear which I think is due to different quality props (front coloured ones appear stronger).

But the throttle pulse/blip thing is my primary concern.

Has anyone else experienced this?

I saw a thread somewhere about flashing the 32u chip to help it keep up with the high speed of futaba 8 channel sets, would the same fix help me?  I am only skeptical about that fix due to my board being so new surely it has the latest file in the 32u chip? (The post about the flashing was from 2011).

I've ruled out the tx or rx being the issue as the motor speed is completely stable and constant when powered directly by RX,


Changed data rate to 11ms instead of 22ms, the throttle blips have disappeared in the 5 min test i did in the workshop, more tests tomorrow to get conclusive results, but it's looking great so far.  

Many thanks to J B for suggesting this fix.

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  • I think I am seeing the same issue with different Spektrum gear. It popped up when I connected the gear channel to the Ardupilot:

  • I have experienced this very exact problem very clearly with the DX8 using AR8000. I sent the DX8 back for repair but to no avail. So I bought a new second DX8 with a brand new AR8000. The problem remained.

    So here is the one thing that I have found common and consistent between both my first DX8/AR8000 and the second exact set:


    The moment you connect the GEAR signal (From AR8000) for any function  (Even if there is no configured  function on the APM) you will immediately see the THROTTLE randomly Jump up! In fact if you arm (Without propellers please!) you will hear and see the motors blip every now and then randomly ! Unplug the gear signal live and the problem disappears!

    So now I am thinking that it could be the onboard pwm to ppm converter with all 8 signals coming in. The fact that you observed a change by reducing the speed on the data rate may actually indicate that the onboard PWM to PPM mux may not be fast enough or has a bug.

    I ordered the external PWM to PPM mux from DYIDrones and will see if that makes a difference. I want to feed the APM PPM from a different mux to see if that makes a difference. Will keep you updated.

    I Just wanted to be more specific: This problem occurs only when connecting the GEAR signal. This is very disconcerting because it still could indicate a DX8/AR8000 combination problem and not the PWM to PPM mux.

  • I was so excited to get my DX8. All those flight modes. Same problem. Here is avideo Mark Harrison shot of the tuning graph you can access on the "flight Data " page by checking the "tuning" box at the bottom of the map. It shows the "blipp" you are describing at about 35 secs.. It seems to jump to around 1500 for abot .5 seconds. Very random. When I bind the DX8 back to a 6 problem.

  • I experienced the exact same problem that you are describing. I was able to make mine go away by changing my receiver to operate at 11ms. (It was set to 22ms for some reason to start.) I also experienced the same glitches on other channels. (3, 5 and 7 to be precise.)

    I found that if I moved my inputs around the glitches followed so it is definitely something associated with the receiver.

  • i have been able to flash the ppm firmware now... will test soon

  • i just bought my apm from 3dr andd tried flashing chip but cant get usb to connect to chip like wiki says so im stuck with the blips....

    anyone help?

    seems this issue is ignored?

    mabye bad batch?

    cant believe 3dr would not flash these to work with a super popular futaba t8j radio?

  • T3
    I had the same problem. It turned out to be a faulty receiver. I had another receiver which did not give the throttle problem. I contacted Spektrum and they replaced the receiver. I really like the level of support from Spektrum.
  • Hi Charlie,

    The blips during calibration might suggest an issue with the transmitter or receiver...

    Have you checked the channel monitor on your DX8 to see if the transmitter is sending out a faulty signal?

    I have the DX8 as well. After unspoken headaches and a couple of crashes, I found that my transmitter was occasionally sending erratic values on the elevator and aileron channels (-70%!). Luckily, my controller was still under warranty and Spektrum replaced it promptly.

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