When flying any aerial vehicle make sure to check local regulations before flying. Always check battery levels, frame stability, and the strength of any connections before flying to prevent catastrophic failure. Most areas now require a permit or written consent of landowners to fly in an area and have height requirements. For US users check http://knowbeforeyoufly.org for information.
The balance of props refers to whether or not each half of the prop weighs the same amount. If they are not equally weighted the propeller will not spin flat, but instead have up and down movement. This decreases the efficiency and will lead to wobble in the flight. To fix this you need to make the blades of the prop balanced.
GeneralThe balancing of props is performed by adding or subtracting mass to one side of the prop until they are balanced. Mass can be added with tape, epoxy or removed by sanding it down (except on carbon props).
Each time you test for balance you either add material to the lighter blade or subtract from the heavier blade. After the blades have been balanced if you are not using self-tightening props you need to also balance the hubs.
Also, whenever you are balancing make sure your balancer is on a level surface.
Balancing Normal PropsNormal Props are the easiest to balance and there are many balancing stands available online. The problem is that the device used to secure the props in these is sometimes unbalanced itself and needs to be balanced via sanding first.
If you want to make your own balancer it is very simple. First you need is a object with a flat top which is wider than 1" or so. The other parts you need are a threaded dowel (not much thinner than the hole in the prop) and two nuts of the same size. To attach your prop start by putting a nut on one end. Twist it over 1" from the end. Then, put the prop on. Follow it with the other nut which should only just be screwed on. Lastly, bring the first nut closer so that it grips the prop and holds it in place.
To balance the prop place it into your balancer. If you are using the homemade one just lay the dowel perpendicular to the front edge of the object you chose so that the prop is less than 1/2" away from the edge.
Bring it to center (so that the blades form a line parallel to the ground) and once it begins to fall wait until it comes to a rest. The blade pointing towards the ground in the heavier. Either sand it down or add tape to the other blade. If sanding sand near the center and avoid the edge. If adding tape or other material do not add it to the underside of the blade. Make sure it is as smooth as possible. If using a glue or epoxy be careful to keep the layer thin. No matter the method you choose, only make small changes. It does not take much to balance a prop most times, and you do not want to over do it. You will know the prop is balanced when you bring it to center and it remains in that position.
Finally, to balance the hubs test if it will stay in place at non center positions. If it does, the hubs are unbalanced. Try placing the prop so that one blade is lower than the other. If the lower blade moves upward when it comes to a rest the side of the hub on the bottom is heavier. If it moves downward then the hub that started on top is heavier. Balance the hub by adding or subtracting material on the outside in the same way as before.
Balancing Self-Tightening PropsSelf-Tightening props are harder to balance because they screw on and do not have a hole all the way through.
You can either buy a balancing rod online and use the process above to balance them or build a balancer in the way described below for self-balancing props.
Building a balancer for these props requires a large board and two screws or nails of the same length. First one nail or screw into the board from the bottom. Be careful that it sticks straight up. Insert the second about 1" farther that the radius of your props away from the first. If using a screw sand it so it has a bit of a point.
When spinning the prop if it is not balanced one blade will spin above the second screw and the other will be below it. The blade above is lighter and below is heavier. Balance the blades in the same method as for normal props with an additive or subtractive method. Continue balancing until the blade remains flat while spinning.
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