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OT: Running a pedestal fan in reverse - failed - a rant of s

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John Larkin
Guest

Wed Dec 27, 2017 9:25 pm   



On Wed, 27 Dec 2017 18:11:23 +1100, Sylvia Else
<sylvia_at_not.at.this.address> wrote:

Quote:
On 27/12/2017 3:02 PM, Sylvia Else wrote:
On 26/12/2017 5:54 PM, Sylvia Else wrote:

I decided I was unwilling to be defeated, and a fair amount of
soldering, heatshrinking and hot gluing later, I got it to work.

https://www.youtube.com/watch?v=GWB9I33k-Rs

Sylvia.

One issue I haven't addressed is that the fan is held on by a left-hand
threaded nut, because a right-hand threaded nut will tend to undo itself
in this application. Since I've reverse the direction, I really need the
nut to be right-hand threaded, but there's no way I can change the
threadedness of the shaft.

May need to use some more hot glue - we'll see.

Sylvia.


I used nine of the big glue sticks yesterday to fix a really dumb
bathroom light fixture. Hot-melt is interesting; it seems more like an
epoxy reaction than just melting stuff. If it just melted, you
couldn't get anything positioned before it cooled.

I suppose I could look that up.


--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

rickman
Guest

Thu Dec 28, 2017 12:59 am   



Steve Wilson wrote on 12/27/2017 7:34 AM:
Quote:
FMurtz <haggisz_at_hotmail.com> wrote:

The original discussion was about reversing the propeller don't know
where the pitch comes in (missed that)
you would not be likely to reverse the pitch on a simple fan.

Requires new fan blades with reversed pitch.


That's not the topic of conversation. The OP wishes to reverse the entire
propeller on the shaft. That rotates the pitch by 180 degrees which is only
a change at all if the blades are not symmetrical which they likely aren't.
It does not actually change the pitch, it changes the shape of the blades
compared to the rotation.

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998

Sylvia Else
Guest

Thu Dec 28, 2017 3:36 am   



On 28/12/2017 3:45 AM, amdx wrote:
Quote:
On 12/27/2017 1:12 AM, Steve Wilson wrote:
FMurtz <haggisz_at_hotmail.com> wrote:

Steve Wilson wrote:
John Larkin <jjlarkin_at_highlandtechnology.com> wrote:
On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia_at_not.at.this.address> wrote:
For reasons I need not go into, I wanted to make a cheap pedestal fan
blow backwards, by putting the fan on backwards, and running the
motor in reverse.
Wouldn't those two things cancel?
Many turbine propeller aircraft can reduce their landing roll by
placing the propellers in reverse pitch. The blades are still turning
in the same direction, but the thrust vector is reversed. They are not
very efficient in this mode, but are still able to slow the aircraft.
To visualize what would happen in a pedestal fan, imagine turning it
around 180 degrees. The motor is still spinning the propeller in the
same direction, but the thrust vector is reversed in relation to the
floor.
In order to reverse the thrust vector, either the propeller pitch has
to be reversed, or the motor has to be reversed.
John is right. Doing both would cancel.
Wrong,reversing motor would reverse air flow, reversing the propeller
would be same air direction but would put the leading edge in the right
position for efficiency.

Wrong. Think about it. Reversing the propeller pitch reverses the thrust
vector. This is how turbine aircraft shorten their landing roll.


OK I took the cover off a 3 blade fan that turns clockwise. I removed
the blade put it on backwards. The fan still blows air in the same
direction. It doesn't blow very much air though.
Certainly is some design consideration in the way the blade is curved.
Mikek


Ah, the scientific method. I hadn't actually tried it, since I knew the
efficiency would be reduced and I was starting with a new unassembled
fan. Interesting that the difference is significant.

Sylvia.

FMurtz
Guest

Thu Dec 28, 2017 5:49 am   



amdx wrote:
Quote:
On 12/26/2017 10:02 PM, Sylvia Else wrote:
On 26/12/2017 5:54 PM, Sylvia Else wrote:

I decided I was unwilling to be defeated, and a fair amount of
soldering, heatshrinking and hot gluing later, I got it to work.

https://www.youtube.com/watch?v=GWB9I33k-Rs

Sylvia.

 Is this just to confuse one of your coworkers?
                        Mikek


I made this clock for that.
https://imgur.com/a/gwPXM

Jasen Betts
Guest

Thu Dec 28, 2017 8:20 am   



On 2017-12-27, John Larkin <jjlarkin_at_highlandtechnology.com> wrote:
Quote:

One issue I haven't addressed is that the fan is held on by a left-hand
threaded nut, because a right-hand threaded nut will tend to undo itself
in this application. Since I've reverse the direction, I really need the
nut to be right-hand threaded, but there's no way I can change the
threadedness of the shaft.

May need to use some more hot glue - we'll see.

Sylvia.

I used nine of the big glue sticks yesterday to fix a really dumb
bathroom light fixture. Hot-melt is interesting; it seems more like an
epoxy reaction than just melting stuff. If it just melted, you
couldn't get anything positioned before it cooled.


heat-activiated thermoset formulations seem like a good idea, but
wouldn't that clog the gun?

--
This email has not been checked by half-arsed antivirus software

Jasen Betts
Guest

Thu Dec 28, 2017 8:36 am   



On 2017-12-27, Steve Wilson <no_at_spam.com> wrote:
Quote:
FMurtz <haggisz_at_hotmail.com> wrote:

Steve Wilson wrote:
John Larkin <jjlarkin_at_highlandtechnology.com> wrote:

On Tue, 26 Dec 2017 17:54:51 +1100, Sylvia Else
sylvia_at_not.at.this.address> wrote:

For reasons I need not go into, I wanted to make a cheap pedestal fan
blow backwards, by putting the fan on backwards, and running the
motor in reverse.

Wouldn't those two things cancel?

Many turbine propeller aircraft can reduce their landing roll by
placing the propellers in reverse pitch. The blades are still turning
in the same direction, but the thrust vector is reversed. They are not
very efficient in this mode, but are still able to slow the aircraft.

To visualize what would happen in a pedestal fan, imagine turning it
around 180 degrees. The motor is still spinning the propeller in the
same direction, but the thrust vector is reversed in relation to the
floor.

In order to reverse the thrust vector, either the propeller pitch has
to be reversed, or the motor has to be reversed.

John is right. Doing both would cancel.

Wrong,reversing motor would reverse air flow, reversing the propeller
would be same air direction but would put the leading edge in the right
position for efficiency.

Wrong. Think about it. Reversing the propeller pitch reverses the thrust
vector. This is how turbine aircraft shorten their landing roll.


No, it is not!

reversesing the proprellor changes the blade pitch by 180 degrees,

Aircraft make smaller changes to the pitch so that the slope of the
blades reverses,

180 degrees gets you approximately back where you started.

--
This email has not been checked by half-arsed antivirus software

FMurtz
Guest

Fri Dec 29, 2017 2:34 am   



FMurtz wrote:
Quote:
amdx wrote:
On 12/26/2017 10:02 PM, Sylvia Else wrote:
On 26/12/2017 5:54 PM, Sylvia Else wrote:

I decided I was unwilling to be defeated, and a fair amount of
soldering, heatshrinking and hot gluing later, I got it to work.

https://www.youtube.com/watch?v=GWB9I33k-Rs

Sylvia.

  Is this just to confuse one of your coworkers?
                         Mikek


I made this clock for that.
https://imgur.com/a/gwPXM

Get one of these,
https://www.klockit.com/reverse-time-quartz-clock-movement-bundle.html

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