Home Forums Everything about the Bicopter RCE BiCopter with sOAT Control

This topic contains 32 replies, has 6 voices, and was last updated by  LitterBug 6 months ago.

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  • #59271

    jihlein
    Participant

    The main issue with a BiCopter is lack of good pitch control, in the typical configuration the titling motors simply do not produce a strong enough pitching moment for good stability and control.

    Oblique Active Tilting (OAT) attempts to solve this problem by rotating the motor tilt axis, and then using the gyroscopic forces generated when the motors are tilted to supplement, actually enhance, the vehicle pitching response.

    This is not a new idea, I found it in a technical paper while searching for ways to improve the control of a BiCopter. The paper can be found at:

    “http://www.academia.edu/27851369/Lift_Fans_as_Gyroscopes_for_Controlling_Compact_VTOL_Air_Vehicles_”

    It requires some info to download, so I felt it wasn’t correct to post a copy on an open forum. For those so inclined to read it, all of the equations describing the OAT control are derived, so we should be able to make quantitative changes and based on the equations predict the resulting changes in flight.

    So this thread will detail the successes and/or failures of applying OAT to the RCE BiCopter. It should be noted that there are two types of OAT control, sOAT and dOAT, single axis and dual axis respectively. sOAT will be used on the RCE BiCopter because of it’s simplicity and applicability to smaller vehicles. I may in the future try converting my Trex 450 SE to dOAT and explore it’s full capabilities.

    The attached photos show the wiring, top view of the motor mounts, neutral pitch position, forward pitch position, and aft pitch position. The direction of the prop rotation is critical to get the gyroscopic forces aligned correctly. I will be using dRonin flight firmware on the F3Fc, although I think BetaFlight would work okay too.

    Unfortunately first flights will be delayed some, as the left tilt servo failed while setting things up on the bench……

    #59281

    I’m so excited to see how this works!
    Makes the copter look even weirder 🙂

    #59285

    jstremmler
    Participant

    What do you think of mounting the sOAT controls upside down keeping the CG as low as possible?

    But for that we would of course need different side plates of the frame allowing approximately 40mm space below the tube. But a modified drawing of the side plate could then include a 30mm landing gear as well….

    #59287

    Kevin_Erik
    Moderator

    I’ve had an inverted copter. They’re more stable and appear to be more efficent as well. The big down-side isn’t the props possibly contacting the ground but the fact its alot harder to build a frame inverted thats intended to be upright.

    For the Bicopter, it maybe advisable to raise the carbon arm higher. Just above the FC would work if the motors / sOAT were inverted.

    BTW The Simple-Ducts will work inverted!

    • This reply was modified 10 months, 2 weeks ago by  Kevin_Erik.
    • This reply was modified 10 months, 2 weeks ago by  Kevin_Erik.
    #59290

    jihlein
    Participant

    I won’t go into the gory math details, but there’s evidence in the equations that describe OAT that the higher the rotational plane of the motors is above the CG, the quicker the pitch response is going to be.

    It’s something we can certainly experiment with, but I don’t think it’s going to change things that much.

    #59447

    jstremmler
    Participant

    Printed the sOAT motor mounts. It’s a tight fit!

    • This reply was modified 10 months, 1 week ago by  jstremmler.
    Attachments:
    #59449

    jstremmler
    Participant

    My old-fashioned PDB… bringing as little weight to the front of the bicopter as possible for improved pitch control. Btw. servo power supply will be an external 6V BEC with 7A located below the FC in the center of gravity.

    Attachments:
    #59471

    LitterBug
    Participant

    Have a sOAT Impossible tilt mount in the works, and have completed initial testing on whats left of EZbi#2 and with one of @kevin_erik‘s ducts.

    https://www.thingiverse.com/thing:3098210

    Cheers!
    LitterBug

    #59486

    jstremmler
    Participant

    Still waiting for my 7A BEC and my new SBUS RX (Hitec Optima D)… but with the rest I am almost there.

    (Pls note my different servo installation in comparison to jihlein. Purpose is to support the servo industry…)

    Attachments:
    #59489

    Kevin_Erik
    Moderator

    @jstemmler

    Just get the Matek FCHUB-W instead of the 7A BEC. It can produce 5, 10, (Both 3 Amps) and manually selctable Servo voltages 5, 6 & 7.2 volts (5 Amps). While taking up aprox the same area and having a similar weight. Sure it’s only 5A for the Servo’s but what are you going to run that will draw more than 2 amps?

    http://www.mateksys.com/?portfolio=fchub-w

    #59491

    jstremmler
    Participant

    @kevin_erik,

    my FC has already a 2A 5V BEC! If it would be like that I wouldn’t need any additional BEC.

    But did you once measure how many amperes e.g. a blocked servo can draw? My 7A BEC will allow my 2 servos being totally blocked and it will not smoke in case of an emergency. Price is only $6 and it is safe to use it.
    And I will only use it for the power supply of my servos and it will not have any connection (except GND) to my FC.
    Juergen

    #59492

    Kevin_Erik
    Moderator

    @jstemmler

    That’s assuming the Servo isn’t capable of self regulating via feedback. Unfortunately our Servos suck in the fact that they’re not sophisticated enough to do such on their own. Now as sorta a work-around, I’ve found that using the highest Voltage the Servo is rated for helps a lot during excessive current draw. Reason being, is that our BMS-210 servos run fine with 5 or 6 volts. Hence using a 6 Volt supply allows for some flexibility when max current is reached causing the Voltage to sag under load. In that situation, even when the Voltage sags to 5 Volts the Servo can still function a bit longer before smoke-checking itself. However with a 5 Volt supply, the Servo will burn up almost instantly.

    Regardless, IMO if you’ve got a blocked Servo, then that’s the least of your problems.

    Edit: This looks promising… https://www.radio-electronics.com/info/circuits/diode_current_limiter/power_supply_current_limiter.php

    #59529

    Hmm interesting thought about using the servo feedback wire to prevent burning of servos. Hmmm hummily hum hum hum. That shouldn’t be too hard to figure out.
    If the FC is trying to move the servo but the feedback is reading the same value for say 3 seconds it stops giving PWM pulses altogether. That would stop the servo from trying to move, making it go “limp” so to say.
    With the caveat that if the feedback is at 0V, which it never is unless it’s disconnected, the output should continue to work as usual. That would prevent the copter from crashing in case the feedback wire is disconnected during flight or if you don’t use servos with a feedback wire.

    Could potentially save some servos.

    #59777

    Cshep70
    Participant

    David, since I’ve been sitting on my as of yet unbuilt bicopter waiting for my 3d PRINTED sOAT arm extenders…

    Have you gotten anywhere with the feedback wire? Even just as far as where I should preemptively solder them for future use?

    #59779

    jihlein
    Participant

    Alright, close to being back in business. Everything is wired except the receiver. I’ve checkout the KakuteF4V2 dRonin target a little further.

    1)Both FDBK signals work, although there is nothing using them at the moment for the BiCopter. FDBK1/FDBK2 are RSSI/UART4 RX respectively.
    2)BLHeli 32 pass through works. First time for me playing with BLHeli 32.
    3)BiCopter mixing working (Custom Vehicle mix table).
    4)Motors and servos calibrated.

    I should go back to the shop and get the RX wired in. But it’s too dark to fly already tonight……

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