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simple boat keeps turning for no reason

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simple boat keeps turning for no reason

Old 05-06-2020, 05:14 PM
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Default simple boat keeps turning for no reason


Just for fun, I designed and 3d printed a very basic airboat. I was hoping that I could just have some fun with it in the swimming pool, but for some reason, it just keeps turning in one direction whatever I do.

All seems to be working fine, motor spins and there is a relatively good airflow coming out of the prop and the rudder works fine, but even with rudder in full opposite direction, it keeps turning in one side only. I can slow it down a bit with full opposite rudder, but it will never go straight, (pool pump is turned off and water is pretty calm)

I understand that it could have a tendency to one side or another, but I was hoping I could manage to get it going somehow straight...

I'm a complete newbie to rc boats so there must be something basic I didn't account for, like motor spin inducing some side force or I dont know what, but I'm a bit desperate here.

So if anyone has any idea of what might be wrong, I would appreciate some help!

I attached a few pics if it can help anyone understand my problem


Old 05-13-2020, 11:06 PM
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I can see a couple of issues with your boat:
1) Unless that rudder servo is in a water resistant enclosure, it's going to get wet and that will cause you major issues
2) I'm assuming your prop was printed as well. If the blades are flat and not like an airfoil or wing shape, it may be causing the air to spiral more than a commercially made prop would and that may be causing issues as the spiraling air is putting a turning force on the rudder, pushing it to one side and turning the boat
3) You said the boat is constantly turning, but not which way. It is possible that the boat, which is very tall for it's width, is trying to "torque roll" on you. If that is the case, motor torque is pushing one side down and that's pulling the boat to that side due to increased drag from the water.
4) Your thrust angle may be causing your problems as well. On an airplane, the engine is usually turned a few degrees to one side and slightly down to account for aerodynamic forces against the plane's structure as the prop "pulls" it through the air. Since your prop is pushing your boat, the direction the prop needs to push may need to be changed to account for this as well
Good Luck
Old 05-15-2020, 12:06 AM
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This appears on another forum - I believe the problems have been sorted. Redesigned prop to prevent it acting as a paddle/centrifuge and the big slot at the bottom of the shroud designed out. It was probably air escaping through the slot with its direction biased by the rotating paddle blade that was pushing the back of the boat sideways.

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