Author Topic: Embarrassingly stupid question!  (Read 1201 times)

Offline Allen Smithee

  • Full Member
  • ****
  • Posts: 867
  • Mordor, Middle Earth
Re: Embarrassingly stupid question!
« Reply #15 on: January 27, 2019, 03:32:14 PM »
I could buy one as per the photo, but the problem is that they make fan removal difficult. The motor is installed (with adaptor fitted) into the fan stator/housing from behind with screws into the front of the motor casing. The fan is then put on the adaptor and retained with the nut and washer, and then the spinner cap. This is the sort of thing, although the one I'm using has an alloy fan which will be running at around 2kW:



The problem is when I want to remove the fan. If I want to remove a prop from a model motor (IC or electric) I hold the prop with one hand and the spanner with the other. But I can't do that here because the fan blades themselves aren't stiff enough and get damaged if you try. Some of the fans have adaptors which include a screwdriver slot across the front or a cross-hole for a tommy bar, but these are larger units (like the one in the above photo) and the adaptors are more substantial. I've tried both approaches with the standard adaptors for this unit and the material isn't strong enough - the slot soon "spreads" and the tommy bar hole just breaks out. So I thought I'd try making one from steel to see if it could take a tommy-bar hole without leaving the shaft too weak. Hence the questions!

My only other thought was to cut a screwdriver slot at the front of the shaft (as I've done before) but make a tubular retaining nut with a collar that extended up the full length of the thread to support  the slotted bit and stop it spreading/cracking. There is room inside the spinner dome to do this, but I don't happen to have any dural or bronze hex bar stock to hand to try it.

AS
Quidquid latine dictum sit altum sonatur

Offline dieselpilot

  • Full Member
  • ****
  • Posts: 267
Re: Embarrassingly stupid question!
« Reply #16 on: January 27, 2019, 04:44:19 PM »
I'm familiar with all this, though I haven't kept up with EDF for quite a while now. 140kRPM sounds unrealistic, maybe 70k? The torque on the running fan isn't tremendous, why are the adapters being tightened with so much torque? Which fan unit exactly is this? Specifics help understand the underlying cause. If it's a common problem why hasn't the manufacturer remedied it?

Offline Allen Smithee

  • Full Member
  • ****
  • Posts: 867
  • Mordor, Middle Earth
Re: Embarrassingly stupid question!
« Reply #17 on: January 27, 2019, 05:36:11 PM »
The actual application is using the Wemotoc minifan housing with a chinese alloy rotor and a 3500rpm/v motor on 12s to get the revs. This setup produces around 40kN of thrust at 25-30A, which allows four 3s2200 packs to be distributed around the airframe rather than a single brick right in the middle where the intake duct should be! The high nut torque to because the metal fan boss has minimal compressibility so it needs to be nipped up tightly to prevent the fan coming loose if the ESC stutters (which it sometimes does on trailing throttle because of the timings used to maximise the revs - on an EDF you're not really bothered about smooth low-throttle/idle running).

AS
Quidquid latine dictum sit altum sonatur

Online sco

  • Full Member
  • ****
  • Posts: 1566
  • Location: Northants UK
Re: Embarrassingly stupid question!
« Reply #18 on: January 27, 2019, 06:19:16 PM »
40kN of thrust - should make it into orbit!!!   ;D

Simon.
Ars longa, vita brevis.

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10100
  • Central Massachusetts, USA
Re: Embarrassingly stupid question!
« Reply #19 on: January 27, 2019, 06:23:19 PM »
8900 pounds.....perhaps that should be 40 N?
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Noitoen

  • Full Member
  • ****
  • Posts: 102
  • Setúbal - Portugal
Re: Embarrassingly stupid question!
« Reply #20 on: January 27, 2019, 06:24:17 PM »
Sacrifice a reamer and cut the taper part? >:D

Offline Allen Smithee

  • Full Member
  • ****
  • Posts: 867
  • Mordor, Middle Earth
Re: Embarrassingly stupid question!
« Reply #21 on: January 27, 2019, 06:26:10 PM »
40kN of thrust - should make it into orbit!!!   ;D

Damn keyboard threw in the 'k' - I'll have to give it a serious talking to!

It's about 9lbs of thrust in old money...

AS
Quidquid latine dictum sit altum sonatur

Offline Allen Smithee

  • Full Member
  • ****
  • Posts: 867
  • Mordor, Middle Earth
Re: Embarrassingly stupid question!
« Reply #22 on: January 27, 2019, 06:28:37 PM »
Sacrifice a reamer and cut the taper part? >:D

I did wonder about that - could I cut it with a carborundum disk in a dremel?

AS
Quidquid latine dictum sit altum sonatur

Offline Noitoen

  • Full Member
  • ****
  • Posts: 102
  • Setúbal - Portugal
Re: Embarrassingly stupid question!
« Reply #23 on: January 27, 2019, 06:58:49 PM »
Sacrifice a reamer and cut the taper part? >:D

I did wonder about that - could I cut it with a carborundum disk in a dremel?

AS

I would think so

Offline Vixen

  • Full Member
  • ****
  • Posts: 1077
  • Hampshire UK
Re: Embarrassingly stupid question!
« Reply #24 on: January 27, 2019, 06:59:18 PM »
Sacrifice a reamer and cut the taper part? >:D

I did wonder about that - could I cut it with a carborundum disk in a dremel?

AS
A Dremel disk would do it. You will probably break a few

But, you need the taper part to start a hand reamer. 

Try a 4mm end mill down the hand reamed hole to see if the final hole size is good enough.

Cheers

Mike
It is the journey that matters, not the destination

Offline Noitoen

  • Full Member
  • ****
  • Posts: 102
  • Setúbal - Portugal
Re: Embarrassingly stupid question!
« Reply #25 on: January 27, 2019, 07:03:00 PM »
Can still use the taper part. Just like a 3 piece tap :thinking: