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  1. #1
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    Quad arm length?

    I was wondering if there is a preset (required) or optimum distance (based on the IMU software) between the center of the copter and the center of the motor at the end of the arm. A longer arm is going to create more intertia when rolling or banking and thus increasing the response time. Perhaps the software doesn't care since it just looks at the groscope input until the desired roll angle has been achieved? Or is this an input parameter of the configurator that I missed?

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    It'll work with any arm length as long as you tune the PID settings right, but the default PIDs work best with 20-24" motor to motor (so 10-12" center to motor), 1.5kg AUW (all up weight) quads.

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    But what are the benefits and against of a long and short arms?

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    Longer arms means your craft is more stable but at the sacrifice of agility. Conversely, short arms mean a nimble craft but you sacrifice some stability.

    I would guess wind would affect a craft with longer arms more than one with shorter arms if everything else was the same (weight, motors, props, etc.).

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    And one more thing can u give an idea of how to define the propellers and motor size?
    Thanks for everything

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    It depends on the weight of your quad and the type of flying you're looking to do. If you want a more nimble quad, smaller propellors will do you good - the smaller the mass of the prop, the less energy it takes to change its speed. Wind also affects smaller props less than larger ones. Motor size is tougher to define, but in general you'll want a motor that draws the smallest amount of current possible while still providing enough thrust to make the quad/hexa/octo/etc. easy to fly.

    Generally, the whole weight of your quad should be less than half of the total thrust provided by all your motors combined. So, if you have four motors that provide 800g of thrust each (or 3200g = 3.2kg total thrust), you want your quad to weigh less than 1.6kg. If your tri/quad/hexa/octo weighs less than half of the total thrust, you'll lift off and hover at less than 50% throttle which leaves plenty of room for maneuvering quickly and arresting quick descents without becoming unstable.

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    Thanks man, this information will help a lot to get started.

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    Quote Originally Posted by alexprata View Post
    But what are the benefits and against of a long and short arms?
    go for something between 35cm and 50cm m2m for your first quad. a small quad is harder to pid tune.

    Quote Originally Posted by alexprata View Post
    And one more thing can u give an idea of how to define the propellers and motor size?
    Thanks for everything
    http://www.ecalc.ch/xcoptercalc_e.htm?ecalc


 

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