Can anyone help? I have no clue how to balance the rotor with spinner of an EDF.

There is a difference between static and dynamic balance. Dynamic blance is very important for EDFS because of the huge RPM range (ie some turn ~50K RPM or more) as compared with most prop planes (~10K to 20K).

A good place to start is to statically balance just the rotor on a precision balancer. Be very careful the rotating parts of the balancer itself don't skew your results. Small rotors will appear to lose balance simply cause you turned the shaft or cones even on the magnetic balancers.

What I do for static balancing of a small rotor is to use the magnets that came with the top flite balancer, put them in a vise, and then use a drill bit of the correct diameter as the shaft. Space the vise with the magnets on either jaw so the point of the drill bit touches one magnet and the other floats (with the rotor on the bit). If you get the jaws too close, the bit will jump to the other side. You can do this without a vise, using something else to hold the magnets, but the screw action adjust is nice if you have a big enough vise.

Static balance alone often isn't good enough for a smooth running fan. A lot of advice will boil down to trial and error combinations in re positioning the rotor in small increments when installing the rotor/fan assembly to get any small runouts of the rotor mount (ie collet assembly and motor shaft itself) and imperfections of balance for the rotating parts of the motor to "play together" at certain speeds. The discriminator is the amount of VIBRATION you feel (or don't feel) with each combination. With small fans, people often hold the fan in their hands to feel this vibration, but I don't recommend that approach for safety reasons. It's better to make a test stand with a soft mount from a U shaped piece of plywood or similar and gage the vibration by the sound and feel without using your hand to hold it. Guys who have actual equipment and precision fans will add weight to the inside of the fan near one of the blade supports in the form of clay, or glue or tape until they get a smooth run.

Do some searches on RC Groups. You'll see it's a topic most choose to avoid, so having the pre-balanced fans (dynamic) from wemotec, HET or the larger names is a big plus. Still knowing what is going on will help you maintain a smooth running fan.

Joe

Also, try to avoid large plastic spinners. They're usually mounted far away from the motor and any small run out (bend away from straight) will make the spinner "wobble" and that is a huge source of vibration. The "Hyperflo" fans from Great Planes are notorious for this trait. If at all possible avoid spinners, or seek small aluminm ones, or small spinner nuts.

Let us know how you make out. I'm curious which fan you're using.

I have a 70mm shroud, and 2600kv inrunner. The rotor should be a 5 blade for 4 cells, or 5 cells. I'm going to try a wemotech mini. All the 4 I've tried can't run, and at 11,000 rpm hit the duct...then the resononance goes away, and they will run up. This is obviously not the way to get a good effiecient fan unit. So I've decided on letting a pro balance them, either the HET 6904 or the Wemotech mini...and if I find another, maybe Lander. I asked Extreme RC about it.

One other thing I didn't mention is a motor shaft which has a pronounced flat spot makes it very difficult to get a true rotor mount unless the collet/screw arrangement is machined expressly for that motor shaft. I had real headaches trying to adapt the "ammo" line of inrunners to grub screw type mounts because they simply wouldn't run true in any configuration I tried. If you're a machinist, you can deal with stuff like that by making custom shims or collets, but most people can't.

I don't blame you for passing. Unless you really love tinkering with these things, and want to squeeze every last drop of performance out of them, home grown dynamic balancing isn't worth the effort IMO.