Hip Pocket Builders' Forum

Radio Control Forum => Jets => Topic started by: Konrad on October 19, 2017, 04:16:05 PM

Post by: Konrad on October 19, 2017, 04:16:05 PM
I purchased this set of FreeWing 70mm metal EDF units from MotionRC when it was looking like they were going out of business*. I think I got both the clockwise and counter clockwise units for about $30. I thought that these would be a great upgrade for my Me 262 or Su-35. And at about 28% the cost of the great WeMoTec units how could I go wrong. ::)  :o

I quick runs and a look at the numbers and it was clear that the discrete 12 blade rotor was a distant second to the 11 bladed WeMoTec rotor.  So these sat on the shelf for about 4 years. Then I saw that Tam Jets was having a sale on the HET 2W30-2200KV motors. This looked like it might be a good fit for 6 cells and an altitude of 6K feet (Denver area). So this is where the good money comes from I spent something like $120 to motor these fan units.

Now this is my real beaf with Freeewing, their documentation is atrocious!  >:( In the case of these EDF units there was none. :-\ I guess this is an improvement from what the misinformation we often get from Freewing (read some of my other threads here on HIP). There is no indication as to how Freewing intended to cool the motor, be it an outrunner or the much preferred inrunner, in my case the HET Typhoon inrunner.

As is the case with most high quality inrunners the air gap between the rotor and windings is far too small to allow for any effective cooling airflow through the motor. With inrunners the heat of the winding is transferred to the outer motor cace and dissipated there, ether by direct airflow or heat sinks. The Freewing 70mm metal housing does allow for the proper flow of air over the inrunner housing, moving from the high pressure area in the back of the motor (EDF unit) forward to the low pressure are just aft of the rotor (fan). The nice red fairing cone even maintains this cooling path. But, again there is no mention of the cooling paths anywhere from Freewing.

Now HET does supply a manual for the motor and a heat sink for the motor. The manual states to use a heat sink. What is nice about the heat sink it that it includes a pilot diameter to support the rear of the EDF housing and the rear of the motor. Unfortunately these heat sinks block any airflow going down the motor case when used with the FreeWing 70mm metal housing.

The solution is to machine groves into the heat sink to allow cooling air to enter between the motor case and the Freewing 70mm metal housing ahead of the heat sink fins. Since I was having to machine the heat sinks I decided to add a second piloting diameter to the heat sing to pilot the rear fairing.

With the cooling under control I hit my next snag! There is no mention as to where the rotor adaptor is to be placed on the motor shaft. Normally I like to place adaptors as close to the bearing as possible, this is just good mechanics. Then I recalled that WeMoTec had you place the adaptor 1.0mm away from the motor mounting plate. This was to allow air to flow from the center of the EDF housing up towards the rear of the EDF rotor. It also helps with reducing the EDF whine.

So lacking any other guidance I place the rotor adaptor 1.0mm out on the motor shaft.

Some details that should be supplied by the OEM but isn’t;

Motor Housing diameter 30.0mm nominal (30.1 actual)
Can accept 16mm and 19mm motor mount spacing (will not accept 3 bolt hole motor patterns)
Adaptor 4mm grub screw type, with FW proprietary drive (8.6mm O.D. with two drive flats 6.7mm apart).

All is not lost for those nice HET 2W30-2200KV motors. They should make a real nice power system with the 68mm Evo WeMoTec on 8 cells.

All the best,

* As MotionRC does not have to publish their financial records I don’t know the true condition of the firm. For all I know they just had a cash flow issue and put a lot of their products on a clearance sale to generate some much needed cash.

Post by: Konrad on October 20, 2017, 12:14:48 PM
Just some clean up of the cartoon. I hope it makes the cooling path issues and their solutions a little bit clearer.

I need to state that I have no data showing that what I think was Freewing's intended cooling scheme is any worse or better than my solution.

All the best,

Post by: fred on November 07, 2017, 03:04:12 PM
Interesting adventure.
 Although IMO :-) I'd  be looking at solidly connecting the Motors' outer shell to the fan shrouds motor tube.  A Tight fitting ali tube over the motor would do the trick.
 Giving a direct clear path for heat to transfer from windings to the Force cooled ali shroud... unobstructed by a 1mm air insulation  layer.
Then Hoping some reverse airflow thru the  motor holes  and said teeny air space etc., will cool much at all.
 If you are more enamoured of the Wemo rotor? It's possible to buy one  and fit it to this shroud. Mettham does sell them

Post by: Konrad on November 07, 2017, 04:35:35 PM
Thank you Fred.

The WeMoTec is a 68mm rotor and does not fit the 70mm Freewing housing. Please see this thread about that error!

As I think I said the Freewing four stator metal housing has the motor bore being 30.1mm. Most inrunners sized for the 70mm Nominal rotor are 28mm so there really is no practical way to use the housing as a heat sink other than what we get from the mounting face.

Adding an aluminum tube to make up the difference is not effective as there is now another joint to break the thermal path (motor to spacer, spacer to EDF housing). It also adds a lot of weight to the EDF unit. In the short run time of the EDF it more than likely will increase the winding's temperature.

I think I went into some detail about the different thermal paths in this thread.

I will say that allowing air to flow in the 1mm space has a marked effect in the reduction of motor temp. I have verified this with thermal couplers and in flight telemetry. I may not have been clear but there is little air flow going down the inside of the motor. In high quality motors where the air gap is small between the motor rotor and motor winding there is little benefit from air flowing inside the motor. In my last cartoon and photos I’m trying to show that I have machined large “holes” in the heat sink to allow air to enter the 1mm air space ahead of the heatsink’s fins. This is similar to what we see in some of the Tam EDF housings.

All the best,