Propellers are to a multirotor what tyres are to a car - a key component. Because of this, it pays to get good quality props especially for those who are into aerial video.
That being said, you can't beat carbon fiber props for rigidity, and you can't beat RCTimer propellers for price.
Prop balancing may sound like a simple exercise, however there is a bit of technique involved if you want to ensure a reliable result.
Below details my experiences and lessons learned while balancing and finishing 8 x 12x4.7" carbon fiber propellers.
Here is a picture to help understand terms used below...
Things you need:
- A prop balancer
- Metal sand paper: 500, 800 and 1000 grit.
- Pure Beeswax
- Lint free cloth (an old t-shirt works)
- Rubber gloves
Carbon fiber dust is dangerous and does not break down inside of your body! Take all prautions! Also, the blades can be sharp so please be very careful at all times, not just when they are spinning.
Things to be aware of:
- The first thought I had of sanding I my new carbon fiber props was painful. I thought I would ruin the prop completely! However after much research I saw that many professionals were using the sanding method. Sanding is a much more permanent, simple and effective method than using tape or dealing with clear spray paints... so lets get that mental block out of the way!
- Get a balanced prop balancer, as silly as this may sound there is nothing more frustrating then using an unbalanced prop balancer. A brand I hear recommended more often than most is the DuBro balancer.
- Check your propellers 'track'. That means checking whether your prop tips follow the same path while they are spinning. You can do this by marking here the blade as it spins and seeing how close the other blade is to that mark. Ideally the two blades should pass at exactly the same mark.
- Don't bother being a perfectionist. Absolute balance is not critical because static props (such as are used on multirotors) no matter how balanced, all suffer from vibrations in forward flight. That includes maintaining a hover in the wind, perfect balance and near perfect balance will make negligible difference.
Take a carbon fiber prop and put it into your balancer of choice. Note the direction that the prop tends toward. The heavy side needs sanding... our aim is to get the prop sitting horizontal.
Note that the faster the prop falls the more it needs to be sanded.
Using your roughest grit metal sand paper, sand either the front or back of the blade toward the tip. Taking off material here will have a better effect than near the hub.
Put the blade back on the balancer and see if there has been any improvement.
Depending on how much material needs to be removed, work your way up the grits until you finish at 1000 grit. At this point your props should be perfectly horizontal.
Time to balance the hubs... hold your prop vertical and note which side of the hub the prop falls toward.
There are two ways you can balance the hub...
- By adding some weight to the light side of the hub using glue.
- By sanding the trailing or leading edges of your prop until a balance is achieved.
Please note when using method two not to change the airfoil too much. You can do this by sanding with the shape of the blade edge.
Wash off any carbon dust from your props under a running tap.
Take your balanced props and rub beeswax over the entire surface area. Using a lint free cloth, polish the prop to a mirror finish. It may take some effort to get the wax moving under the cloth.
Here is a before shot:
If you have any tips of your own please share them below!