Radian issue - looking for some help

Discussion in 'Radian' started by Cris Olariu, Jun 3, 2013.

  1. Cris Olariu

    Cris Olariu Member

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    Hello!

    I just recently upgraded to the CS 360 gimbal with Radians and having some issues that hopefully one of you will be able to help me sort thru. Thank you in advance!

    System Specs:

    Aircraft Type: Cinestar 8
    Gimbal Type: CS 3-axis
    Radian Type ( 1, 2 , 3 axis): 3 axis
    Gimbal Power source: 3S Zippy 1300mA
    Gimbal Radio Type: GR-12
    Radian Communication Protocol (S.Bus, PPM, PWM, Spektrum): PPM

    Connections:
    Roll Sensor:
    Port
    1. From Pan Sensor
    2.
    3. To Tilt sensor
    4. To Roll Servo

    Tilt Sensor:
    Port
    1. From Roll Sensor
    2.
    3.
    4. To Tilt Servo

    Pan Sensor:
    Port
    1. GR-12 receiver and power.
    2.
    3. To Roll Sensor
    4. To Pan Servo

    Symptoms:
    Shaky at times on the pan axis, along with jitter on the same axis. I believe I see a tad of jitter on the roll axis as well, but it's minor compared to the pan axis.
    I should say also that I am only using a GoPro Hero2 at the moment, so maybe the very little weight on the gimbal has something to do with it. Also, and I feel this is pretty important, I have installed a quick release system from Allied Drones (the Echo model).

    Steps taken to resolve:
    I have lowered the gain on the Pan Radian all the way to 25%, while keeping the Roll and Tilt Radians at 80%. From what I'm seeing on the forums, it looks like 25% is very low. It seems that above 50% it starts to jitter very very bad for my setup, just not sure I should go lower than 25%.
    All my other settings on the Radians are from the default Pan-1, Roll-1, and Tilt-1 configs.

    Please see the attached video example and photos of my settings. In the video, at about 27-28 seconds in, you can see the weird left/right shake (which was not sent by the camera op).



    RadianPAN 060313.JPG RadianROLL 060313.JPG RadianTILT 060313.JPG
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Cris:
    Thanks for the very complete trouble report. The wiring of the Radians looks fine.
    I see what you mean in the video.....

    You don't mention whether you've checked all of the pulleys and belts for tightness (check the small pulleys on the servos too). The belts should be sufficiently tight that if you press your finger into the belt midway between the small pulley and the large one, that the deflection should be about 3 - 4 mm. The reason I suspect that pan servo/belt is that that waggle looks to be right at the natural frequency of the gimbal...

    With such a light payload, I think you may find that you have to back the gains way down -- it's all about the mass-in-motion and the physics of that.

    As an experiment, could you fly with the Radians turned off -- do you still see the same issues or not?

    One odd thing I note: The Tilt Radian is showing that it has a valid Sbus signal. I would also expect the Roll sensor is also showing S.bus valid, but it is not. With the configuration you describe, the sensor connected to the receiver will reflect the signal from the receiver, but the other Radians that are connected in the daisy chain should show S.bus valid. That points to a possible wiring issue -- could you double check that the Roll sensor is not somehow connected to the receiver? I'm just grasping at straws here.

    Thanks
    Andy.
     
  3. Cris Olariu

    Cris Olariu Member

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    Andy -

    Thank you for your quick response!
    As usual, you are a genius (and turns out I'm not even close). I should've learned my lesson but didn't. I had a similar problem when I was running the 2-axis gimbal: on the Tilt axis, the belt was not tight enough and it was skipping; once I got that tightened, it worked great. Now, when the new parts for the 3-axis gimbal arrived, I of course forgot to check for tightness on the pan axis. I just went in the garage and indeed I found out it was a bit loose, so I tightened it. Pretty late now for a flight, but I'll fly first thing in the morning and report back.
    I also lowered the pan gain to 15%. I'll try it like that first, then adjust accordingly.
    When you say to fly with the Radians off, do you mean with the 3-way switch in the OFF position? Or is there something else I need to do to it?
    Now, on the Sbus vs PPM signal. I currently run all the software for the Radians and MK Tools thru VMWare on my MacBook, and sometimes it acts funky when I connect the USB cable to it (sometimes it believes I'm adding a USB mouse, LOL). It's a tad annoying, but not enough for me to bother finding a solution. Anyway, I have noticed something similar to what you did, and it seems to be consistent (except for the time I took the picture apparently): the PAN radian shows a PPM signal (that's the one connected to the GR-12), while the ROLL and TILT show a Sbus connection. To tell you the truth, when I saw that it made me pause for a second and say "huh... weird". But when I saw everything was working properly, I didn't give it any importance (why mess with a thing that's working, right?)

    I hope this answers some of your questions, and I will report back tomorrow after the morning flight. Let me know if you think of anything else. Thank you again!
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I wish I were a genius... :) But thanks for the thought.

    Glad that you found something that needed tweaking. Always satisfying when that happens.

    As to flying with the Radians off -- just use the Mode switch to turn them off. The intent is to see whether the issues are coming from having the Radians running or whether they're coming from the mechanical aspects of the gimbal.

    Andy.
     
  5. Cris Olariu

    Cris Olariu Member

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    Copy that. I'll report back tomorrow. Thanks again!
     
  6. Cris Olariu

    Cris Olariu Member

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    Andy -
    Thank you for your help! Between tightening the belt and dropping the gain on the pan axis to 15%, I got rid of pretty much all the jitter, and definitely got rid of those shakes. I think I'll also drop the gain a bit more on the roll axis now.
    Thanks again!
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I find that the sweet spot on the gains can be only +/- 1% -- so if you move from, say, 25% to 20% you might miss it.

    Also, if you go too low you may find that the gimbal lags behind the copter's movements -- but you can bench test that just by having a camera on and feeding the video to a monitor -- point the camera at a fixed position (I have a piece of paper with a cross hair printed on it) and then deliberately move the copter around by hand and observe whether you the gimbal stays centered. Beats having to get caught in the "charge-fly-video--watch video" cycle... :)

    Andy.
     

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