ethicalhacker
Junior Member
I scratch built an FT Kraken, but I cannot get it to taxi right. It turns so sharply on the ground that there’s no way it could sustain flight for more than three seconds before crashing. Yes, I know that from experience. I’ve rebuilt this thing four times now without a single flight lasting longer.
I’m running dual SunnySky X2820 920kv motors with counter rotating 11x6 APC props on an 8000mA 3S battery. I’m also using dual HobbyKing 40A YEP ESCs. I’ve setup a differential thrust configuration through an EzUHF 8 channel Lite receiver and a Taranis Plus transmitter as described in the build videos, and everything seems to work in my living room floor.
I had to make modifications to the stock landing gear design to support the weight of these motors. The original design flexed side-to-side 45 degrees when taxing (which induced undesirable ground steer). I went with a heavier gauge steel rod to stiffen things up. Likewise, the tail fins required modification. The ground chewed them up way too quickly, so I put some curved, ridged steel wire on the underside of the tail fins to slow the process down. It travels over pavement better now.
My current problem is that even after setting the endpoints on both ESCs and monkeying with the rudder trim, I still cannot get the plane to taxi anywhere close to straight on asphalt. It will taxi in a 10’ diameter circle even with the trim set all the way in either direction.
I thought that maybe one of my motors or speed controllers was out of speck, so I ordered two more of each. Then I measured the thrust of each changing one variable at a time (motors, ESCs, and props). In the most extreme case, there was a 5% difference. I would think trim could overcome something as small as that. I did notice that the ESCs were different from each other at fixed points along the throttle curve, but again, it didn’t seem like any of them was off by a lot. Putting a new prop on one side while leaving a beat up prop that’s missing a 1/16” from both tips on the other side would make more difference than swapping a motor or an ESC.
I also modified my trim via the Taranis such that it would not raise one motor’s RPM while reducing another. It will now only reduce the RPM of one motor at a time. I don’t expect this to work since trimming didn’t work before and the ESCs are not perfectly matched along the throttle curve.
Does anyone have any ideas? I’m willing to post my Taranis config. I can also post a diagram of my prop directions and motor rotation directions if that would help.
I’m running dual SunnySky X2820 920kv motors with counter rotating 11x6 APC props on an 8000mA 3S battery. I’m also using dual HobbyKing 40A YEP ESCs. I’ve setup a differential thrust configuration through an EzUHF 8 channel Lite receiver and a Taranis Plus transmitter as described in the build videos, and everything seems to work in my living room floor.
I had to make modifications to the stock landing gear design to support the weight of these motors. The original design flexed side-to-side 45 degrees when taxing (which induced undesirable ground steer). I went with a heavier gauge steel rod to stiffen things up. Likewise, the tail fins required modification. The ground chewed them up way too quickly, so I put some curved, ridged steel wire on the underside of the tail fins to slow the process down. It travels over pavement better now.
My current problem is that even after setting the endpoints on both ESCs and monkeying with the rudder trim, I still cannot get the plane to taxi anywhere close to straight on asphalt. It will taxi in a 10’ diameter circle even with the trim set all the way in either direction.
I thought that maybe one of my motors or speed controllers was out of speck, so I ordered two more of each. Then I measured the thrust of each changing one variable at a time (motors, ESCs, and props). In the most extreme case, there was a 5% difference. I would think trim could overcome something as small as that. I did notice that the ESCs were different from each other at fixed points along the throttle curve, but again, it didn’t seem like any of them was off by a lot. Putting a new prop on one side while leaving a beat up prop that’s missing a 1/16” from both tips on the other side would make more difference than swapping a motor or an ESC.
I also modified my trim via the Taranis such that it would not raise one motor’s RPM while reducing another. It will now only reduce the RPM of one motor at a time. I don’t expect this to work since trimming didn’t work before and the ESCs are not perfectly matched along the throttle curve.
Does anyone have any ideas? I’m willing to post my Taranis config. I can also post a diagram of my prop directions and motor rotation directions if that would help.