V-22 Osprey Project - Prototype 2 Control Tests
To start on the second prototype of the V-22 Osprey, I took the pair of KDS 450 helicopters and stripped them of everything but the main shaft housings and landing skids. Each rotor disc is 28" (711.2mm) in diameter. If I compare that to the full-scale rotor disk of the V-22 of 11.61m, I get a scale factor of 16.87:1. In Fusion360, I scaled a 3-view drawing of the V-22 to the full size of the model and measured the distance between the rotor shafts and came up with a scale value of 33.2". I modeled a connecting block in Fusion360 that utilizes the original bolts and pattern of the KDS helicopter to attach to each side. The connecting boom is a piece of 1/2" x 5/8" C-channel aluminum that is 1/16" wall thickness.
I moved the control electronics over from the first prototype but redid the Arduino mixing code. I found some other PWM reading code that implements Pin Change Interrupts instead of the dedicated external interrupt pins which are very limited on most Arduino models. Using this code, I'm able to almost immediately detect any change on the input pins coming from the SPRacing F3 flight controller and mix them to control the 6 cyclic servos. The reduction in the delay is noticeable, and I was able to switch from the Arduino micro board to an Arduino nano and shave a few grams of weight. (https://create.arduino.cc/projecthu...-rc-receiver-input-and-apply-fail-safe-6b90eb)
The first suspended control tests went pretty well, but it became apparent that many flight controllers don't implement a heading hold gyro in their code. Despite enabling the HEADING_HOLD mode in iNAV, the copter would begin to rotate one way or another on its own. The flybarless "eBar" control module from the original helicopter does implement this, so my next try will be to pass only the rudder output from the flight controller through the KDS eBar box to keep the copter heading hold locked. If this succeeds, I will likely swap out the flight controller for a FrSky S8R stabilized receiver and pass the yaw control through the eBar. This will potentially simplify the control stack.
The eBar did try to keep the heading on track, but the response was too slow and rather violent. I was concerned it would twist the aluminum bar as it tried to correct for yaw. I tried just using the FrSky S8R stabilized receiver and immediately had a couple of successful, and more importantly, stable flights as shown below:
The next steps are to draw up some foamboard shaps to make it look more like an airplane. After additional flights with a static hover config, I will start developing the tilt mechanism. I have a few thoughts on this, but nothing definite for now.
I moved the control electronics over from the first prototype but redid the Arduino mixing code. I found some other PWM reading code that implements Pin Change Interrupts instead of the dedicated external interrupt pins which are very limited on most Arduino models. Using this code, I'm able to almost immediately detect any change on the input pins coming from the SPRacing F3 flight controller and mix them to control the 6 cyclic servos. The reduction in the delay is noticeable, and I was able to switch from the Arduino micro board to an Arduino nano and shave a few grams of weight. (https://create.arduino.cc/projecthu...-rc-receiver-input-and-apply-fail-safe-6b90eb)
The first suspended control tests went pretty well, but it became apparent that many flight controllers don't implement a heading hold gyro in their code. Despite enabling the HEADING_HOLD mode in iNAV, the copter would begin to rotate one way or another on its own. The flybarless "eBar" control module from the original helicopter does implement this, so my next try will be to pass only the rudder output from the flight controller through the KDS eBar box to keep the copter heading hold locked. If this succeeds, I will likely swap out the flight controller for a FrSky S8R stabilized receiver and pass the yaw control through the eBar. This will potentially simplify the control stack.
The eBar did try to keep the heading on track, but the response was too slow and rather violent. I was concerned it would twist the aluminum bar as it tried to correct for yaw. I tried just using the FrSky S8R stabilized receiver and immediately had a couple of successful, and more importantly, stable flights as shown below:
The next steps are to draw up some foamboard shaps to make it look more like an airplane. After additional flights with a static hover config, I will start developing the tilt mechanism. I have a few thoughts on this, but nothing definite for now.
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