RE: Low Cost 120mm EDF Power System Possibility
Just a small point, yes Wemotec rotors are dynamically balanced, IE they are put on a balancer and balanced for motion, they use an epoxy putty in them. Same with HET but the problem with HET is the inserts in the front and rear of the rotor can be pressed in badly if you are unlucky, and the collet can be a real pain to get running true with the rotor, take a lot of work to get the HET running perfect whereas the wemo adapters are incredibly well made and everything just fits together.
Lander on the other hand are not dynamically balanced at all, they are harmonically balanced, Lander takes a rotor out of the bin and fits it, tests it, adjusts the position relative to the shaft adapter until its running as smooth as they can get it, then they add the spinner cap and rotate it until the parts are all harmonically together. If they cannot get it perfect they try another spinner and so on and so on.
This is not proper balancing, and if you move the spinner cap the fan will vibrate instantly...Also the lander rotors are not as efficient as a wemo, they started out with wemo clones but something went down legally and they stopped with the clones and went with a chinese design. The chinese rotor is similar on the bench in tests but in the air its slower.
Static balancing comes down to quality of your gear, I have dynamic balancing equipment and I have very specialised precision ground tooling for static balancing, I can balance a rotor statically and then assemble a fan that runs so smooth you wouldnt bother checking it dynamically. Your biggest issue with static balancing is holding your parts dead centre, most magnetic balancers are junk, the shafts that come with them are never straight and the tips are never ground 100% dead centre. You need to make your own shafts or have a machine shop make what you need.