How does the quad or any other multicopter motor arm/strut lenght and flexibility affect to the flight performance or stability if u keep the motor size same all the time? How would for example a quad copter with 1m arm lenght fly? Or how would a cuad copter fly if the arms were made of very flexible fishing rods or something like that? Any experience?


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  • I was using H beam shaped pvc arms, motor to motor length of about 80cm. However I had the arms orientated differently. Two arms were in the H configuration and the other two were in an configuration. The second configuration was very liable to lateral vibrations, where as the first (H) was much more stable. I did not look at vertical vibrations because it was only an observance of the motors shafts moving. However as I had designed the frame myself I had no problem in shortening the arms. So once the arms were reduced to approx 56cm motor to motor, the vibration was noticeably reduced.

    So I guess the lesson is that if you do want the longer arms you will need more rigidity. However if you are going for a very rigid frame it most likely will be more brittle and therefore more liable to breaking/snapping on impacts.

    Having said that the 70cm frame seemed to fly alright, I just didn't want to chance flying it much with cheap motors as it could do damage

  • flex would have a bearing on the stability of the craft. I would not use fishing rods as they are heavier then the carbon rods you can buy from online, and also more flexible. The more length you put on the arm, the more stresses on the arm come into play. You would need to reinforce the arms to handle the weight of the motors, and the load. Think of the old tail booms on the helicopters that were open and built in the shape of a triangle and reinforced with spars. The trade off is survivability in a crash. The more rigid designs will sustain more damage. I'm just rambling here as the ideas come to me, so bear with me :).

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