Question for Graupner guru's

Discussion in 'Electronics' started by Dave King, May 4, 2015.

  1. Dave King

    Dave King Well-Known Member

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    I am using my Graupner MX20 not only for my MK rigs but also my Wookong rig. I have a question about fail safe. I have fail safe setup correctly in the Wookong so that if the radio turns off it will go into fail safe mode but I have a question about the fail safe setup in the Graupner. Using Sumo12 is it possible to setup fail safe for channel 1 throttle so that I can program throttle to be 40% if fail safe is engaged? I have downloaded the MX20 manual and have read the part on failsafe and I see how I can set the position for a particular channel like channel 1 but to me its unclear how this would work in SUMO mode or if fail safe is even possible with SUMO.

    I have down a lot of internet searching and it appears that there is a chance that if the throttle position is not setup correctly in the radio it might default to a throttle of 0 if fail safe is activated which I am trying to avoid :D
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Dave (and anyone else who might have the same question):

    SUMO 12 tells the MX-20 to use channel 8 as a combined channel for channels 1-12 -- that is, if you imagine that all 12 channels have different servo values, then they will be transmitted one after the other out via channel 8, channel 1, 2, .... 12, and then repeating 1, 2, 3, ....12.

    This is what I understand is called Partial Pulse Modulation (PPM), as distinct from Pulse Width Modulation (PWM). However, quite a few folks misunderstand what PPM is and actually refer to PWM and PPM (which it is not!) See http://www.endurance-rc.com/ppmtut.php for graphical illustration. For example MK says that their individual ESCs respond to PPM. They do not. I wasted weeks trying to get that to work (thinking that I had programmed an Arduino incorrectly) -- turns out they only respond to PWM. Sigh.

    The Graupner Fail Safe feature is completely independent of SUMO. It allows you to determine what happens if the Receiver loses contact with the Transmitter. Options (for each channel) are: 1) Hold at the last known value, or 2) Move to a preset value.

    Fail Safe does its thing whether you're using SUMO or not.

    What was it you read that leads you to believe that Fail Safe and SUMO might not work together? I've not seen anything to suggest the two features are related or cannot be used together -- but what do I know? :)

    The other thing you can do (with the props off), is configure Fail Safe, and actually test it by turning off the transmitter -- so you could, for example, have channel 1 (throttle) go to 50% or whatever on Fail Safe, then fire up the motor (sans props!), have the motors spinning at just above idle, then turn the transmitter off. What should happen is then Fail Safe will kick in and you should hear the motors spin up to 50%.

    Hope this helps.

    Andy.
     
  3. Dave King

    Dave King Well-Known Member

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    HI Andy

    Very helpful as usual! I didn't read anything about failsafe and PPM necessarily I just read a lot about how you need to set failsafe for each individual channel. Since I knew that all channel commands come out of channel 8 into the Wookong I wasn't sure if fail safe would work based on on the fact that all the channels output on one channel. It's more of me not knowing how it worked and wanting to be sure.

    Great idea by the way, I will at least be able to see what the motors do and if they cut off. :)
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    When you are using SUMO, it's a different set of rules, Dave. All channels come out of channel 8. Ignore what the internal channels 1-12 are doing.

    Now that said, I have a faint memory that with SUMO 12, you still *can* get PWM out of channels 1-7, 9-12 -- but I'd need to stick a scope on the receiver output to prove that point.

    I would proceed with caution and do a ground-based test because if I'm wrong (and I often am (but rarely uncertain)), Really Bad Things will happen! :)

    Andy.
     
  5. Dave King

    Dave King Well-Known Member

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    Yes and that's why I wasn't sure. I guess I don't understand how fail safe can work and keep a stored value for a servo when they are all being modulated through channel 8. When you are setting the fail safe position of the throttle for example is it storing it in the RX so that if the RX loses communication with the TX it knows to tell the flight controller what value to use? If not how else would the flight controller know to use a specific value?
     
  6. Gary McCready

    Gary McCready Active Member

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    With DJI A2 and the MX-20 you want to turn Failsafe Mode "off" (vs. Hold or Failsafe) on your Tx so the A2 will control the Heli. It is the same with the MK. You don't really want your Tx controlling the Heli when it looses signal. The A2, and I assume the WK, will take control, and return home.

    " All channels come out of channel 8"......You can still use the PWM, I use two of them on the GR-24 (9 and 12 I think) for my gimbal control. Not going through the channel 8 connector PPM, but separate servo cables.

    The Graupner tech support is very active on RC Groups if you need something "specialized".
    http://www.rcgroups.com/forums/showthread.php?t=2035316&page=119

    FYI: The lastest Graupner Tx updates (including MX-20 and MZ-24) has a binding feature very similar to the Spektrum Model Match, You do need to rebind after you update.
    http://www.rcgroups.com/forums/showpost.php?p=31229336&postcount=1642
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think you may have answered your own question there, Dave! :)

    I don't see how it could work if only the transmitter knows what it should do if it loses contact with the Receiver.

    Andy.
     
  8. Dave King

    Dave King Well-Known Member

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    I thought fail safe work pretty much the same for the Wookong and A2?
    For the Wookong you have to enable fail safe to get the Wookong to go into fail safe mode. I followed these instructions and was able to get it to work.
    http://www.mikrokopter.us/the-wooko...on-dji-products-and-how-to-set-failsafe-4964/

    The Wookong doesn't auto detect like Mikrocopter does.
     
  9. Gary McCready

    Gary McCready Active Member

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    That was the "old" way, it has changed, confused me too. Graupner updated the Rx firmware:
    From Lothar Freudenberg at MK tech support May 2014
    "Graupner did change the FailSafe function in the receivers. If you use the latest Software on your receiver you have to go into the Menu"
    ""Setting & Data view".
    There go to the window "RX Fail Safe Vx.xx" and change the "MODE" of channel 1 to "OFF". Now the copter will again receive the lost signal."

    I got a similar message from DJI for the A2.


    My vid:

    Confirmed turning the Tx off = loss of signal = FS
    You turn Failsafe mode "off" just like the MK
     
  10. Dave King

    Dave King Well-Known Member

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    Hi Gary

    This is confusing to say the least. I have been researching this for most of a day. Have you tried the fail safe procedure all the way through landing? If you haven't I believe what you will see is that the copter will do what you tell it to but I believe it needs a landing throttle value. To get the flight controller to recognize "loss of signal", Either way works as far as Ziggy's or your method. I followed Ziggy's way and the U channel goes to fail safe if I turn the radio off. However the important part is that the flight controller is looking for a gas value to land. When it goes into fail safe the Wookong will do one of three options that you can select. I chose altitude go come home and set the altitude to 50 meters(sorta like MK's fail safe). After the copter flies back to over the come home area for 15 seconds if it doesn't see the radio signal it will start to descend. This is where DJI and and Mikrokopter differ. MK uses all predetermined data (emergency gas settings, landing values, and vario or not vario) to determine the deacceleration to land. DJI looks for a stored gas value that you program via the radio. I read that if you don't store a value it defaults 0 gas. If you use Specktrum for a radio the position of the throttle stick on bind is the value that it uses for fail safe. For Graupner I believe it uses the stick position in the fail safe menu when you hit store. But I have not confirmed this.

    This is where I found this
    http://www.djiwookong.co.uk/dji-wookong-m-multi-rotor-flight-controller.php
    NOTE: For Failsafe Mode to work your radio needs to support Failsafe on multiple channels, in this case your main 3-way mode switch for the above modes and your throttle, and you need to bind your radio so that when you switch it off it puts the throttle to around 48%

    The above is assuming that you are using a radio where the value is stored by binding the receiver. Graupner's way I think is just storing the value when you hit store. It's also assuming 48% thinking that your throttle to hover is 50%.


    I also found this on DJI's site
    WooKong-H Enhanced Fail-Safe Precautions

    1 The Fail-Safe (AutoHover or Level) will not be activated, until you’ve correctly Pre-set Transmitter Command Stick Center Position.

    I also see a post of a guy that crashed because he didn't set a throttle value
    http://www.rcgroups.com/forums/showpost.php?p=21510638&postcount=21

    If you are telling me something different please let me know.
     
  11. Gary McCready

    Gary McCready Active Member

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    s900 with A2:
    I've not tried the A2 all the way through landing but very close, done it at least 3 times. I did try the switch operated Failsafe, just not switching off the Tx entirely. I did confirm in the A2 software it does go into Failsafe (Shows ""RC Lost" ) when I turn off the Graupner, but not tried while flying. You DO have to setup failsafe on the "U" channle.
    When I initiated Failsafe/Come Home via the switch the s900 climbed to 30m (as I had set up), came back to the place where it took off, and slowly descended. I set NO Failsafe throttle values, and had Graupner Failsafe MODE = Off. I stopped it at about 3m, on it's way down from 30m. DJI tech support assured me that the A2 takes "complete control" when FS is initiated.
    I have 2 Naza mulitrotors and they do it the same way. A few years back it wasn't that way, you had to FS your throttle values. (your link was fromn 2012) With my FPV Naza, also on my MX-20, I've lost orientation dozens of times and use the come home/failsafe option. Comes down right in front of me except the one time it tried to climb through tree branches on it's way up.
    DJI Tech support (Blade Strike): "No need to worry about throttle or any other channel."
    Also if your FS is from signal loss you can NOT gain control back if it is on GPS mode, you need to go back into Atti or manual mode. I have turned off the Tx (MX-20) on my Phantom, to test FS.

    but like I said you do need to correctly setup the "U" channel so it goes into FS when you turn off the Tx.

    As I said I turned the MX-20 FS Off, just like the MK. Works fine, and realizes there is no signal.
    Tested it on the MZ-24 too. (Had to send my MX-20 for repair)
    http://www.rcgroups.com/forums/showpost.php?p=29593926&postcount=1960
    http://www.rcgroups.com/forums/showpost.php?p=30002926&postcount=1629
    http://www.rcgroups.com/forums/showpost.php?p=30098220&postcount=6521

    That said this is for the A2, which I have, not sure about the WK but I'd guess it is the same.
     
  12. Dave King

    Dave King Well-Known Member

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    Hi Gary

    I don't dispute that it will come home, and hover at come home. I do question the landing gas setting in fail safe. How else would the Wookong or A2 know how much throttle to give to land X copter if X copter takes Y throttle value to hover. A copter could need 65% throttle to hover or it could need 40% throttle every copter is different. My copter is a flat 8 with KDE 4014's and a payload of 10.8KG. At 50% throttle it just goes straight up in manual mode and hovers around 45%. I need a value of 30-40% to descend or it will just go straight up and just thinking about that happening gives me chills.

    My Wookong is running an old reliable update too and the release notes really don't state what changes to fail safe (if any) were done. I was going to go ahead and due the power off test with the copter strapped down with sand bags outside as it needs a GPS signal. If that test passes and the motors just dont cut off I plan on setting up come home altitude to a lower altitude and just confirm it comes home.

    Thanks for the tip about fail safe needing ATT or manual mode to disengage. I'll make sure I do the test in ATT mode.
     
  13. Gary McCready

    Gary McCready Active Member

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    Like I said, I've never set my Throttle failsafe, it lands itself. I've done it more than once. It knows the same way the MK does, barometer and GPS. The MK Does an Auto land and Take off with no Throttle failsafe. You used to have to set the value, but not anymore. Vario..

    It knows how control the throttle to land the same way it knows how to hover. As I've said, it does Autolanding, after "Coming Home", adn then hovering above start point for a few seconds. It comes down from 30 m to land. I take control just before it touches down because it looks a little fast for me. I haven't setup a throttle Failsafe on the A2 ever. Failsafe mode = off
    With the MK you used to have to set "emergency gas" as a little less than your hovering throttle, but you don't have to anymore.
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    In the case of the MK it chooses a descent rate for autoland -- not a throttle setting. So it simply adjusts the throttle to whatever it needs for a particular descent rate.

    Andy.
     
  15. Dave King

    Dave King Well-Known Member

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    OK did some testing today.

    Both ways of engaging fail safe work. You can either set the U channel to fail safe or simply turn channel 1 failsafe off in the menu. Both engage fail safe mode in flight controller. Next up I found out what happens to each channel during fail safe. If you don't set each channel's fail safe, it will store the last command before fail safe is engaged. In my case I was yawing slightly and turned off the radio and it continued to yaw. So I set Channels 1 to 4 to 50% in failsafe and it then resorts to the stored center position when fail safe is engaged. I tested this by monitoring the channels and turning the radio off. SO it is very important to center all 4 channels and store the centered value into fail safe or it will continue with the stick commands you were doing if radio communication is lost.
     
  16. Gary McCready

    Gary McCready Active Member

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    Interesting: I've only used the FS/Come Home and Land switch.
    Is this with Failsafe mode = Off? I was told by Graupner that if you turn Failsafe Mode = Off then no values are stored, and there is no output on the Receiver, so you will get a "lost signal" on the A2.
    I don't have the cojones to turn off my Transmitter completely....lol
    The MZ-24 also takes longer to boot up......
     
  17. Dave King

    Dave King Well-Known Member

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    HI Gary

    Here's what happens.
    Method #1 - In Fail safe adjust menu keep the Fail safe value of Channel 1 to on. Go to servo adjust menu and adjust the U channel till the cursor moves into one of the two fail safe areas on the indicator. Go to Fail safe adjust menu and change your U channel to the up position. Then hit store. Go back into servo adjust and adjust U channel switch so that it works as normal.

    Method #2 - Go to Fail safe adjust menu and change channel 1 to off.

    I tested both methods and verified Channels 1 through 4 resort to the stored values. But it only resorts to the "STORED" stick values if you store them when the U channel is in fail safe. If you don't do this fail safe will resort to the last command it sees before the radio communication is lost.

    So essentially you have two methods to engage fail safe. You can do it one of two ways.
    1. Store the value of the U channel to the up position in the fail safe menu of the graupner when the U indicator shows fail safe.
    2. Turn Channel one to off in the RX fail safe menu of telemetry.

    Either way works to engage fail safe and both ways will engage the stored values if they are programmed correctly.

    To store Channels 1 through 4 to a centered position when fail safe occurs you need to do the following.
    1. Go to servo adjust, manually change the value of the up or down position of U channel so that it goes into the fail safe area.
    2. Go into Fail safe adjust menu and turn Channels 1 through 4 to the up position. Make sure all 4 channels are centered and then hit store.
    3. Go back to the servo adjust menu, and Configure the U channel so that it reads normal (Manual - ATTI - GPS)
     
  18. Dave King

    Dave King Well-Known Member

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    FYI: I did not test auto land, I just tested it see if the copter would go into the fail safe method I chose which is altitude come home and it did that fine. I am just worried about a momentary losss of radio communication where I can re-establish it. With the Graupner radio I will occassionally temporarily lose signal if I am 100 to 115 meters high. It doesn't happen often but I want to make sure the safety features did work to prevent a flyaway.
     
  19. Gary McCready

    Gary McCready Active Member

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    Interesting. I was assure by DJI that if I turned off the failsafe on channel one throttle (Failsafe Mode = Off) on the Graupner then the A2 would take compete control, if there was loss of signal, as long as you setup channel U correctly.
    They said if it said "signal lost" in the software then the A2 has determined it is in Failsafe, and do as it was setup to do. ie come home and land.
    I'll ask again to make sure!
     
  20. Dave King

    Dave King Well-Known Member

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    Gary don't trust DJI. They have already told me incorrect information about the inspire. You can easily verify this yourself by doing the test and seeing if the stick values hold to their last position. I did the test last night and the channel indicators showed it kept the last known stick position of channels 1 through 4. I did this test with both the old way and the new way you describe. After I turned channel one off in RX fail safe I had both left and right sticks to the lower right position and then turned the radio off. The Wookong kept all 4 channel positions until the radio reconnected.
     

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