Home Forums Everything about everything else Tricopter build with yaw concept

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  • #60381
    Fosch
    Participant

    Hi all,

    I’m almost new here and happy to share the design of my tricopter (in progress…).

    It will be a light 260mm tricopter, for LOS acro.

    Flight Controller : MATEK F405 STD (with dRonin, also new for me)
    Motors : old Cobra 2204 2300kV (24g!) / 4S Lipo
    Servo : EMAX ES3352 (12.4g / 6V / Metal Gear / Digital)

    Yaw concept :
    The servo is integrated into the frame, direct-mounted to the tail. The main risk is a misalignment between the servo axis and the tail axis that could block or overheat the servo. Thus I will soft-mount the servo on the frame to avoid to over-constrain it, using small pieces of rubber between servo and plates (like a sandwich). I have added a feedback wire based on Jihlein and Kevin_Erik recommandations.

    Here is a test of the partial assembly :

    For more reactivity, I plan to run the servo at 7V later on. That’s why I drilled the servo case for a better cooling.

    For sure I will come back later with questions about dRonin settings, especially for fine tuning 🙂

    • This topic was modified 4 years, 1 month ago by Fosch.
    #60574
    Fosch
    Participant

    Some progress of the build here :

    Servo runs @7V instead of 6V… using a LDO Regulator (ROHM BA07CC0T / 25V input max / 1A output) + a Capacitor on output to get a smooth constant output voltage of 7 volts. That gives 375 deg/s in dRonin System. I will tell you later if the servo burns @7V ^^

    Special thanks to Jihlein & Kevin_Erik for their help regarding dRonin settings 🙂

    • This reply was modified 4 years, 1 month ago by Fosch.
    #60578
    Kevin_Erik
    Moderator

    Your build looks very clean, I’m assuming that your FC is mounted under the frame? (Didn’t see it from your pictures) Biggest issue i see is that your Servo would be difficult to replace if later it was found to be faulty.

    Note: I could recomend that you use large Zip-Tie off the Tricopter arms to act as landing supports. The great thing is that they bend rather than break, while being very easy to install.

    Anyways, I have wanted to redo the Tri-Mini frame using a 3rd party FC and PDB, while keeping everything internal. With some of the smaller FC’s this should be possible. Yet alas i may need to wait to the summer to start the project.

    #60579
    Fosch
    Participant

    You’re right, it will be a nightmare to change the servo, especially once the frame will be fully glued 🙂 This build is design for testing the yaw concept, I just hope to be able to fly several Lipos before the servo die 😉

    Correct, the 4-in-1 ESC and the FC are below the frame. Good idea for the Zip-ties, I will look at it.

    #60581
    Kevin_Erik
    Moderator

    Something i was thinking of a moment ago…

    Extending the Nose of the frame, turning the Y-Tricopter into an T-Tricopter. This should give you more room to mount critical things internally (FC) and have folding arms. While maintaining the same Motor spacing. Furthermore, having a cutout section on the or bottom top carbon frame would allow you to hot-swap the Servo. This also assumes that you’d use header pins from you PDB to attach it.

    #60716
    Fosch
    Participant

    Hello & Happy New Year ! 🙂

    My tricopter build is completed. I did the first tests and autotune today following the steps from the dRonin video.

    It flies very well for cruising and I did some “slow motion” flips…
    However as soon as I push the throttle hard or compensate too much with throttle after a hard flip, I have a very bad yaw behavior for a second (big servo displacement from left to right several times) and the tricopter makes a 1/4 turn at the end which is hard to handle !

    For information :
    -The FC is soft-mounted and the motors too
    -I use a 1000uF/25V capacitor (4S lipo)
    -I put Yaw Dterm at Zero immediately after tuning as mentioned in the video (I didn’t test the D value given by Autotune). Could it be the reason ?
    -I run inverted motor direction…

    I had no more time to make additional test today. Any ideas how to solve it ?

    • This reply was modified 4 years, 1 month ago by Fosch. Reason: add pictures
    #60723
    Fosch
    Participant

    OK, I’ve just seen that the tail tune did not work (MotorThrustFactor is still 13.8).
    Let’s try again tomorrow !

    #60736
    Fosch
    Participant

    I still have a huge yaw twitching issue, during fast motor accelerations only (not at constant full speed)

    Please have a look to video here (description below the video) :

    I re-ran the autotune
    I tried to set Yaw D-Term to 0
    I also tried to reduce “DynamicYawMaxThrottle” to 0.25 instead of 1 without success

    #60749
    Kevin_Erik
    Moderator

    Did your tail tune complete correctly? If your still seeing values of 13.5 or 13.8 then it did not. If your having tail tune issues i suggest rebuilding the tail assemblely and pay specific attention to the slop and smoothness of the tail mech. Idealy, the tail shouldn’t have any wiggle room, yet move freely when commanded.

    Edit: Looking at the values you have posted, this appears to be exactly your problem. Make sure that your servo limits are spot on otherwise it will perform poorly. I tyipically set my max yaw values for 35 degrees vs 40 and set the Servo range amd system settings to reflect this.

    #60752
    Fosch
    Participant

    As you suggested, I did again the manual servo calibration.
    Do you mean that you manually setup the servo at 40° and then set the ServoMaxAngle value to 35° ?

    PS : On the video, the tail tune was re-done just before (my MotorThrustFactor is now 8.82)

    #60753
    Kevin_Erik
    Moderator

    With those figures, you should be good then. Keep in mind that the Tribaby would normally see around 5-6, thus the 8 for your Tri-Mini sounds about right. (larger props vs baby tri)

    Now as for the +/- 35 degree i use, its simple. I’ve never encountered a situation in Acro flight yet that required the full 40 degree Yaw. However, having the larger range doesincrease the time it takes to get from one end of the span to the other. Making the total span shorter, just worked for me as it was easier for me to setup as I’m not using the stock Tilt-Mechanism.

    #60755
    Kevin_Erik
    Moderator

    Forgot to mention that you should redo your auto-tune now that your tail-tune is good.
    Beyond this look into the Dynamic-Yaw-Min / Max-Throttle. Normally thtese figures are set to 1.0 but you can alter this to increase / decress your Yaw torque. Obviously one figure is for high throttle Yaw and the other low. David had a write up on it here in forums.

    Edit, Here it is…

    “DynamicYawMinThrottle:
    Dynamic yaw gain when the tail motor is spinning at min throttle. The default is 290 (%).

    Example values:
    1.00: Dynamic gain disabled. Yaw output is same as in mid throttle.
    1.50: Yaw output at min throttle is 50% greater than on mid throttle.
    3.00: Yaw output at min throttle is 300% (3 times) greater than on mid throttle.
    Values between mid and min throttle are linearly interpolated.

    Tuning tips:
    To gain more low throttle authority, increase the value. Remember that there’s a limit on how much yaw can be produced at min throttle. Extremely high values reduce the resolution of PID output and cause oscillations.

    DynamicYawMaxThrottle:
    Dynamic yaw gain when the tail motor is spinning at max throttle. The default is 100 (%). This is the opposite of tri_dynamic_yaw_minthrottle, it reduces the yaw output at high tail motor speeds. It’s possible to increase it, but usually not preferred. By default, this parameter has no effect as the value is 100 %.

    Example values:
    1.00: Dynamic gain disabled. Yaw output is same as in mid throttle.
    0.75: Yaw output at max throttle is 25% lower than on mid throttle.
    0.50: Yaw output at max throttle is 50% lower than on mid throttle.
    0.25: Yaw output at max throttle is 75% lower than on mid throttle.
    0: 100% reduction of yaw output at max throttle. This means no yaw output at all.

    Values between mid and max throttle are linearly interpolated.

    Tuning tips:
    Reduce the value if you are experiencing yaw oscillation at higher throttle values.”

    Based on what I’ve seen from your video and Davids expanation above, I suggest you adjust the DynamicYawMaxThrottle down using increments of 0.05. Till Either the problem goes away or the Copter starts spinning under high throttle with no stick input (Yaw).

    #60761
    Fosch
    Participant

    Well, not good news…

    I tried to re-autotune. The twitching during autotune was very very violent, until the 3 motors stopped and tricopter falls on the floor. Motors were so hot that I couldn’t touch them. Then I waited for the motors to cool down and when I tried to take off again, magic smoke appears… 🙁
    I don’t know yet if it is the 4-in-1 ESC or one motor.

    #60762
    Kevin_Erik
    Moderator

    Ohm them outbefore reapplying power.

    #60766
    Fosch
    Participant

    It seems at least one motor is Burt.

    If the 4-in1 ESC is safe, I will probably try to tune it again, but how to deal with the auto-tune to avoid to burn something again?
    As I said, sometime the auto-tune is very violent (high frequency oscillation), causing motor overheat…

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