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

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Sylvia Else
Guest

Wed Dec 27, 2017 6:02 am   



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.

FMurtz
Guest

Wed Dec 27, 2017 6:57 am   



John S wrote:
Quote:
On 12/26/2017 12:21 PM, John Larkin 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?


It seems to me that they would. Reversing the motor makes it blow in the
opposite direction. Reversing the blades makes it blow in the opposite
direction.

If you reversed the motor, you would also reverse the blades because
although the blades would pass air either way ,they work more efficiently

Steve Wilson
Guest

Wed Dec 27, 2017 7:40 am   



John Larkin <jjlarkin_at_highlandtechnology.com> wrote:

Quote:
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.

FMurtz
Guest

Wed Dec 27, 2017 8:24 am   



Steve Wilson wrote:
Quote:
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.

Sylvia Else
Guest

Wed Dec 27, 2017 9:11 am   



On 27/12/2017 3:02 PM, Sylvia Else wrote:
Quote:
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.

Steve Wilson
Guest

Wed Dec 27, 2017 9:12 am   



FMurtz <haggisz_at_hotmail.com> wrote:

Quote:
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.

FMurtz
Guest

Wed Dec 27, 2017 9:40 am   



Steve Wilson 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.


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.

FMurtz
Guest

Wed Dec 27, 2017 9:42 am   



Sylvia Else 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.


Thread seal or drill and tap propeller boss for a grub screw.

P E Schoen
Guest

Wed Dec 27, 2017 10:17 am   



"Sylvia Else" wrote in message news:fagvcuFe9alU1_at_mid.individual.net...

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

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.


I don't think hot glue will be strong enough. It might be possible to cut
right-hand threads over the left hand threads, but that would probably
result in severe loss of strength. It might work for a very coarse thread
with high helix angle, like the level wind mechanism on a fishing reel:

https://www.youtube.com/watch?v=lIfGcMkP408

If there is enough length of thread on the shaft, you might be able to put a
second nut on it and lock it in position once it's tight. Loc-tite on the
threads might also work. Another method is to use a lock-nut, or create the
equivalent by deforming the threads in the nut or on the shaft.

Paul

Steve Wilson
Guest

Wed Dec 27, 2017 2:34 pm   



FMurtz <haggisz_at_hotmail.com> wrote:

Quote:
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.

FMurtz
Guest

Wed Dec 27, 2017 3:36 pm   



Steve Wilson wrote:
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.

???? If you reversed the motor the air would blow the other way with the
same blade except that the leading edge would be on the wrong side, so
you would reverse the blade without altering pitch to rectify that,IE
take it off shaft reverse it and pit it back.


Guest

Wed Dec 27, 2017 4:39 pm   



On Wed, 27 Dec 2017 07:12:07 GMT, 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, as others have pointed out, a right-hand screw is still a
right-hand screw if you insert it the other end of a nut. Reversing
the pitch of a propeller changes it from a right-hand screw to a
left-hand screw.


Guest

Wed Dec 27, 2017 4:43 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.


Loc-Tite. If you never want to restore the fan, Epoxe.

amdx
Guest

Wed Dec 27, 2017 6:45 pm   



On 12/27/2017 1:12 AM, Steve Wilson 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.


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

amdx
Guest

Wed Dec 27, 2017 6:50 pm   



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

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