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« on: January 03, 2013, 10:23:57 AM »
lastRites
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I have 7x4 props. But I need to run them on a motor that needs a 5x4. What precautions should I take if I trim them down to 5 inches and balance them carefully.
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« Reply #1 on: January 03, 2013, 10:27:05 AM »
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The motor is Turnigy 2826-6 2200kV. The ESC I am using is HobbyKing Brushless Car ESC 30A w/ Reverse. So need to keep the amperage below 25A. And I have no time to get new props.
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It is the pervading law of all things organic and inorganic,
Of all things physical and metaphysical,
Of all things human and all things super-human,
Of all true manifestations of the head,
Of the heart, of the soul,
That the life is recognizable in its expression,
That form ever follows function. This is the law.
 

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« Reply #2 on: January 03, 2013, 03:47:37 PM »
atulrajguru9
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Balance the prop horizontally and vertically.

Make sure that both blades are exactly symmetric.
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« Reply #3 on: January 03, 2013, 05:06:10 PM »
sbajare
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hi,

cutting down props is not a better solution. weight of the prop also has to be considered.

a 5x4 prop will be lighter than the 7x4.

always use recommended props by the manufacturer.

regds
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« Reply #4 on: January 03, 2013, 05:38:05 PM »
sanjayrai55
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« Reply #5 on: January 03, 2013, 06:19:16 PM »
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I think u should go ahead with what u have planned.
If u balance the prop correctly.  it will work properly.

I have even used a Half broken blade fixed with araldite. U just have to balance the prop correctly.

All the best
Rgds
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« Reply #6 on: January 03, 2013, 08:35:50 PM »
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go for it - not such a big deal - one thing.. if you cut down
a 7X4 to 5" - effective pitch will change i.e you will not get
a true 5X4 prop - however it will serve your purpose.

do it like this ... cut the proposed
prop shape in duplicate on thick paper  and stick one to each blade then cut around the shape.

or center the prop hub and use a divider to score a line where you want the cut

Sand and final balance.
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« Reply #7 on: January 03, 2013, 11:34:56 PM »
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I agree with Saikat. Make sure you get the balance correct at the end of the exercise. This is most important.
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« Reply #8 on: January 04, 2013, 10:00:37 AM »
sanjayrai55
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Don't wake a Tiger until you've factored the teeth
I don't want to get overly technical, but suffice to say that what we do is static balancing. A prop which is static balanced is not necessarily dynamically balanced. At higher RPMs this effect is more.

Further, when you trim down a prop to a very different size, the dynamic balance gets affected more than in the original condition. The Prop characteristics also change viz. thrust and speed.

Sure, you can use a trimmed down prop, it will work. But it is unlikely you will get the desired performance.
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« Reply #9 on: January 04, 2013, 11:28:00 AM »
lastRites
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Thank you for the suggestions everyone! I am making an amphibious boat. So weight and efficiency are not that important at this stage. What is dynamic balance?
And performance is not much of an issue as the boat will have a power to weight ratio of more than 2:1  >Cheesy
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It is the pervading law of all things organic and inorganic,
Of all things physical and metaphysical,
Of all things human and all things super-human,
Of all true manifestations of the head,
Of the heart, of the soul,
That the life is recognizable in its expression,
That form ever follows function. This is the law.
 

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