Geared / Direct prop selection?
04-23-2003, 06:03 PM
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Geared / Direct prop selection?
Hi Guys,
I'm getting into the electric world and need a little help. From all the reading I've done the general statement is that you a geared drive allows you to turn a larger propeller than a direct drive.
My problem is that I have no idea how to translate it into: For drive X you can use props between Y and Z sizes. If drive X is geared at R then you can use props S and T..
You get the idea.
For example, Let's say I have a Graupner speed 300 6V (#3306) motor. This motor has a free running RPM of around 31k; and, I "believe" is a candidate for gearing due to it's high RPM. So, how do I figure out which props it can comfortably turn at a particular ratio?
Motocalc will run the numbers for a given prop range / gearing ratio and give a whole system view, but I'd like to know how to determine a starting point. IE: for this motor should I start in the 4x2 and work up to a 6x5 prop?
When I plug in various numbers I'm just shooting in the dark and would rather understand the math behind it anyway (even if it is to just get an idea of where to start plugging info into a motor calculator.
Thanks!
I'm getting into the electric world and need a little help. From all the reading I've done the general statement is that you a geared drive allows you to turn a larger propeller than a direct drive.
My problem is that I have no idea how to translate it into: For drive X you can use props between Y and Z sizes. If drive X is geared at R then you can use props S and T..
You get the idea.
For example, Let's say I have a Graupner speed 300 6V (#3306) motor. This motor has a free running RPM of around 31k; and, I "believe" is a candidate for gearing due to it's high RPM. So, how do I figure out which props it can comfortably turn at a particular ratio?
Motocalc will run the numbers for a given prop range / gearing ratio and give a whole system view, but I'd like to know how to determine a starting point. IE: for this motor should I start in the 4x2 and work up to a 6x5 prop?
When I plug in various numbers I'm just shooting in the dark and would rather understand the math behind it anyway (even if it is to just get an idea of where to start plugging info into a motor calculator.
Thanks!
04-24-2003, 05:35 PM
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Geared / Direct prop selection?
Unfortunately, there isn't any (easy) mathematical way to come up with a starting point. Most of the existing combinations were determined using trial-and-error (many motors bravely sacrificed their lives), or by measuring the current with an ammeter.
What you don't want to do is exceed the physical limitations of the motor. As you put larger and larger propellers on a motor, you draw more and more Amps. Eventually you cross a threshold where the motor can no longer handle the current, and begins to get really HOT! When the motor gets hot enough, the windings start to melt, and the motor is ruined.
Use the Wizard in Motocalc, if you have a plane in mind. Simply limit the motor choice to the Speed 300, and Motocalc will do what it can to find a solution.
What you don't want to do is exceed the physical limitations of the motor. As you put larger and larger propellers on a motor, you draw more and more Amps. Eventually you cross a threshold where the motor can no longer handle the current, and begins to get really HOT! When the motor gets hot enough, the windings start to melt, and the motor is ruined.
Use the Wizard in Motocalc, if you have a plane in mind. Simply limit the motor choice to the Speed 300, and Motocalc will do what it can to find a solution.
