Freewing 12 blade 80mm and 90mm EDF dynamic balancing tips. - RCCanada - Canada Radio Controlled Hobby Forum
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Old 01-15-2016, 11:45 AM   #1
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I am: Eric K.
Join Date: Feb 2007
Location: Burlington ON

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Freewing 12 blade 80mm and 90mm EDF dynamic balancing tips.

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For those interested here is my basic process to dynamically balance the FW 80mm and 90mm fans.
First take the back cone off to remove the 4 screws holding the motor in. Make a mark in the shroud to note where the wires exited the shroud for replacement later.
Now is a good time to add a drop of Triflow oil to both motor bearings.
I removed the two small set screws holding the motor shaft to add locktite to the threads and did the same with the spinner screw. No need to remove the fan, just get some locktite on the threads and tighten the screw well. The fan can twist slightly within the detent so I made sure it was where torque would naturally want it to go to under load before tightening the spinner screw. The screw must be secure or the fan blades will slip within its retaining cones under high power and will throw any balancing work off. Reinstall the motor/fan assembly into the shroud using locktite on the motor screws. Replace the cone using locktite on the two set screws and install the fan into a test stand. I use a simple foam stand made from old styrofoam packaging. Nice to have a spare ESC and receiver for this to save time.
Wearing eye protection you can run the fan and note the vibration level at under 1/4 throttle (no need for high power). Add a 1cm square of duct tape on the spinner and run it again. Now position this piece at each of the blade positions on the spinner noting the vibration at each. It will become very obvious where it is worse and where it is better (always the opposite side of the worst). If the original vibration was very little without this trial weight, you might have to use a piece half the size and if it was strong add a larger piece or double it up. It helps if you clean the spinner with alcohol first and use a knife to remove and replace this piece of trial tape. Fingers tend to reduce adhesion. It is important to find the most exact spot where this trial weight runs the smoothest as it determines where weight will be removed on the opposite side of the spinner cone (with the 1/8" drill).
I make marks with felt pen where the tape was and where the opposite side is then begin drilling away alloy material with a 1/8" drill.
Naturally you want to remove a little at a time. After your first dimple add the trial weight to its original position and then the side where you drilled. This will show if you have removed enough weight as the trial weight will show a higher vibration on one side of the spinner or the other. Drill more and use a smaller trial weight of tape as you get closer to perfection. I have had to use larger drill sizes to remove more material when the initial vibration has higher. When the small trial weight gives equal vibration (should be very little with a small piece of tape) the fan is done! You will be amazed how much smoother it runs! This same basic process is how I balance outrunners using a piece of stiff wire wrapped around the exposed motor bell twisted a couple turns and cut short. This outrunner balancing isn't necessary on the FW 80mm setup but here is a link for those who have exposed outrunners and want it smoother.
Here are some pictures of the 80mm final balancing.
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Zen thinking * It's rebuildable till it fits back in the box. **

Last edited by 4stripes; 01-15-2016 at 03:27 PM.
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