Servo jump after few minutes

  • Richard new problem and I noticed this before the telemetry lead was connected to Cockpit so makes no difference.

    I have two tailplane matched servos in Hawk and this is in done on ‘B’ channel the settings are still perfect after software update with servos perfectly matched, no noise no current fighting each other etc

    I leave Core Tx alone well away from Jet 4m at least even put Tx in house whilst I am in workshop and every now and then I hear the tailplane servos ‘jump’ or a small thud noise also sometimes I see a quick 2mm-3mm deflection on tailplane (I am nowhere near the Tx stick.

    Also the low loss Jetronic brake valve is in ‘C’ and suddenly I hear quick two pulses of brake valve

    The Tx / Rx has been switched on around 35min and just as I am writing this I have just had tailplane blip again!

    Just for info in ten years of having Cockpit > FASST never had this happen so is it problem with output of Expander going to servo Cockpit inputs?

    Time it’s taken to write this the tailplane has just blipped twice more....Rudder perfectly still JR8911 also tailplane JR8911 x2

    Sometimes servos you can hear a jump noise but small so you see no movement other times it happens you can see deflection...

    Battery supply to Cockpit fully charged 2 x A123 2.5A


  • Richard

    This is a non SRS Cockpit it does not have Rx1/Rx2 for connection of the 26ch Rx that’s why I was using the Power Expander?

    I have removed the telemetry lead from Cockpit and also the CTU to see if servos still twitch


  • Richard managed to capture on video, ok like picture shows just Cockpit, Expander and 2 x 26ch Rx

    Upon powering on I heard three blips at servos with one actual movement I then got iPad and managed to get 4th blip which was movement on tailplane, note: this can be up or down

    I have also tried going back to FASST/MX24 Tx with tailplane plugged in and no problems

    So looks like Power Expander combination with Cockpit or problem with Expander and 26ch Rx’s ?

    Might do test with servo plugged in Expander output #5 and see if ok not going through Cockpit

    I will send video on messenger as cannot post here

    Edit: You now have video


  • Hi Richard ok Cockpit obviously V19 as you have just done it. The expander and both PBR26 latest software (always keep everything latest) the strange thing is after the blip in video that was the last blip for over 2hrs!

  • Richard after some more tests ?

    I have taken out the ‘Elevator’ output away from output #5 of expander so the two tailplane servos are locked by Cockpit in middle position etc

    In expander output #5 I have placed single servo.

    I have just had tailplane jump! The elevator single servo plugged in #5 of expander remained still

    I still have all the other leads from Expander to Cockpit in place

    My next test is to power the Cockpit on its own no connection to Expander to see if it jumps on its own whilst holding the two matched tailplane servos on ‘B’


  • Yes ? you have just updated it to V19 as I could not as I brought it in 2010!

    Ok with elevator removed and B channel locked in centre by Cockpit for 1.5 hrs it has not jumped at all.

    It only happens when leads are present from Cockpit to Expander!

    Have you got Cockpit SRS in stock looks like I might need to purchase one off you and get rid of Expander and run the PBR26 x 2 straight into Rx1 and Rx4 of new Cockpit SRS?


  • Richard

    Have found something, Cockpit was on 15ms frame rate also I set Expander to 15ms. For the last 4.5 hrs and a recharge of A123 I have had the frame rate set to 12ms on Cockpit and Expander.

    I have had not one jump, zero nothing....also done around 6 power off and back on and left on etc but this has definitely made a difference

    I have not moved from this Hawk and is quiet so I know when it jumps etc and since both on 12ms so far ?