• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Freewing 90mm EDF fan (rotor hub ID)


Posting Elsewhere
As my project jet is a Freewing 90mm F-16 sold with a 6 cell outrunner EDF system I'm posting here under "Warbirds". This is because I can't find a dedicated forum for EDFs here on the FT form site.

What I’m looking for some information on the Freewing/Changesun 90mm 12 bladed rotor. What is the inside diameter of the 90mm EDF rotor (inrunner and outrunner rotors)?

Some background, I’ve recently come back to the EDF part of the hobby. When I left the WeMoTec was the standard by which all other EDF units were measured. We were also using round cells (NiCads). Shocked It looks like in the last 8 or so years the efficiency of the fan units has dropped noticeably in an effort to get that swish sound. Combined with the generally less efficient outrunner motor, I’m finding that the EDF systems sold in the entry level foamy jet market are rather poor performers. I define performance as power in vs power out.

While I too like the swoosh sound of the modern EDF rotor, to get any power out of the Freewing/Changesun 90mm 12 bladed rotor takes a huge amount of watts. Unfortunately for us we are limited in the EDF entry market by the cost of the transistors used in the ESC. The cost of transistors that can handle more than 20 volts to 22 volts triple. This is why most entry level EDF are limited to 6cell (22.2v nominal). As a result of this limitation the 6 cell 12 bladed 90mm EDF model needs to have a battery cooking 110 plus amp draw.

Unlike the OEM (Freewing) which in mainly interested in the cost of entry. I’m mainly interested in the cost of operation. Cooking a $100 set of batteries for 30 3 minute flights in not my idea of a practical EDF set up. The best way I know to extend the battery life is to cut down on the amp draw. To that end I feel that the 10 cell battery set up is the proper voltage for the 90 mm edf.

As of late I’ve been using the WeMoTec EVO and Jet fan 90mm units to great effect. These rotors have a much lower rotor load (power) than the Freewing/Changesun 12 bladed rotor and are also noticeably more efficient. Plus they don't whine!

The idea was to use the stock EDF unit and re-motor it for 10 cell operation. Here is where we hit our snags. The Freewing 90mm rotor used a questionable non standard proprietary rotor mounting system. And the outrunner EDF housing uses a rear motor mounting system. Because of the poor motor mounting with the rear cantilevered mount that introduces an overhang ratio of 2.5:1 (or more), the fan housing* has to go into the trash bin. While I don’t like the Freewing rotor mounting system, it allows for mis centering of the rotor with its inherent clearances (a collet system is far superior). It should be safe to at least 2.5 Kilo watts of power.

Wanting to use as many parts as I already had, I was on the Freewing USA importer’s site (MotionRC) looking for a rotor adaptors to use the Freewing/Changesun
proprietary rotors with higher end motors.

Much to my surprise I find that the rotors are listed as being engine type specific.

Here is where I made my first real mistake. I called MotionRC and asked to talk to a Customer Service Representative (CSR) that was familiar with the 90mm fan units.

At first the CSR tried to sell me on the idea that the inrunner was a much more powerful system. I tried to correct him in saying I wasn’t interested in the EDF system but rather the differences in the rotors. Why had Freewing assigned two different SKU# P9020 and P9021? He came back saying the the inrunner rotor had much stronger blades to harness the power of the inrunner motor. This is blatantly false!

After some digging on my part, I found the difference in the 90mm rotors in the ID mounting bore. The outrunner rotor had a much smaller ID bore as it pilots on the extended 5mm motor shaft. The inrunner rotor uses a much larger ID bore to allow the mounting adaptor from the inrunner motor to have sufficient wall thickness. The fan blade are identical between both rotors.

This brings to light a problem with this product SKU# P09023
This hardware looks to be only applicable to the motors (rotors) that use the adaptor (grub screwed onto the inrunner motor).
It would also be nice to know what size motor shaft (5mm, 6mm or 8mm) the fan adaptor fits.

I suggested that MotionRC might want to consider a rewrite of their descriptions, as I can only hope there is translation issue between chinese and english. The EDF housing are really defined as front or rear motor mounting. (I’m using a lot of Hyperion/Scorpion outrunners in the Freewing inrunner housings). MotionRC might also want to give the dimension for the bores in the fan rotors, this is what I’m asking for.

As it stands now MotionRC is leaving a lot of sales opportunities on the table for lack of accurate data, conscientious and technically accurate customer service.

I know, just be done with the Freewing EDF unit and run a WeMoTec or JetFan 90mm EDF unit. After cooking your first set of batteries one would be money ahead with the WeMoTec or JetFan!

All the best,

*Freewing/Changesun aren’t stupid. The cantilevered rear mount for the cheap outrunner was done to try to get some effective cooling for outrunners in EDF applications. The outrunner rotor is by nature fighting the natural cooling airflow found in the standard EDF housing.
Last edited: