TLDR; …I made a video.
While I’m a bit new to the multicopter world, I’m no stranger to aerodynamics, physics, and mechanical concepts. While building my first quadcopter, I delved into prop balancing and discovered that I hated the common techniques for doing so.
The most common technique seemed to be adding some kind of tape to the light side of the prop. I’ve used reflective tape for measuring machine tool spindle rpm and masking tape to mark a depth stop. Both methods are extremely temporary, and the higher the rpm, the more temporary. Props at 4,000+ RPM make the tape solution seem extremely temporary.
Since tape is out, how about sanding the back of the heavy blade or trimming the blade tip? I’ve found that it takes a lot more sanding than I really want to do in order to achieve balance, and the (Master Airscrew) multirotor props have a sharp upsweep at their tips that I don’t want to disturb by trimming.
Well, that leaves CA glue (superglue) which can be difficult control. You can’t brush it on, lest the brush get permanently adhered to the blades, so you have to apply it carefully and then spray a catalyst onto it to make it set, and then it’s quite permanent, though very brittle.
Instead, I prefer clear nail polish, applied thinly on the back of the blades wherever weight is necessary. It brushes on easily and can be controlled vs CA+kicker that sets instantaneously and must be sanded off if mis-applied. The disadvantage of nail polish is that it contains a significant amount of solvent (weight) that evaporates while curing, so it may be necessary to reapply it after the first attempt.
Also, it seems that a common perception is that one must balance the blades independently from the hub. The hub on any RC model prop has very little mass. When one orients a prop in the vertical direction, the observed imbalance is highly likely to result from an imbalance in the blades rather than the hub itself. So there is little merit to balancing the “hub.” Instead, weight should be added to the leading/trailing edges of the blades in the lighter direction.
What we are really trying to accomplish is a dynamic blade balance in a statically measured environment. Without sophisticated equipment, true dynamic balancing is impossible. But I contend that with a little knowledge, one can approximate a dynamic balance using a static balancing tool. The key is to understand that it isn’t likely the hub that contributes imbalance, but rather the blades themselves, so offsetting the nail polish toward the leading or trailing edge can accomplish balance in multiple orientations with just a single application.