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.

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.

Balance the prop horizontally and vertically.

Make sure that both blades are exactly symmetric.

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

Sandeep: I couldn't agree with you more. Never try such "jugaads"

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

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.

I agree with Saikat. Make sure you get the balance correct at the end of the exercise. This is most important.

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.

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