Date: Mon, 13 Dec 2010 21:41:44

Author: Urs Lauterburg

Subject: Re: Simple Rail Gun

Post:

--============_-919849585==_ma============
Content-Type: text/plain; charset="us-ascii" ; format="flowed"

Dave,

It might depend on how you line up the setup in respect to the earth
magnetic field. The two parallel rails should be in line with the
north to south longitude. It may have an impact if it is indeed the
driving field.

Regards

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland

>The last time I took this out for the video I posted, it always
>moved the same direction regardless of polarity.
>
>I vaguely remember doing this in class and talking about reversing
>the polarity and explaining that the rod should roll the other way.
>I then reversed the leads and thought that the rod did go the other
>way. But it is a vague recollection and when I try it now it only
>goes one way.
>
>I will try it again, the current setup is on the tabletop and the
>tables here have steel bases. I used to do it with the rods
>extending off the end of the table. I will try that again and see
>what happens
>
>dave
>
>On Mon, Dec 13, 2010 at 9:59 AM, Paul Nord
> wrote:
>
>Urs,
>
>So it could be some variety of shaded pole motor?
><'"http://books.google.com/books?id=r8I1gyNNKnoC&pg=PT296&lpg=PT296&dq=shaded+pole+motor+demonstrator+physics&source=bl&ots=qOqF15sG4m&sig=niU_pbC_PxycXtWtNXpDEL0UUzw&hl=en&ei=Y08GTcjsFdTNnAetj8nlDQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CB0Q6AEwAQ#v=>New
>understanding physics for ... - Google Books
>I never understood that! :)
>
>It's likely that there is something going on with the intermittent
>electrical contact between the rods.
>
>Paul
>
>
>On Dec 13, 2010, at 1:16 AM, Urs Lauterburg wrote:
>
>>Paul,
>>
>>I assume that what really counts is the direction it will start
>>rolling without any implied external mechanical force. If it does
>>not start rolling then the external B-field is simply not strong
>>enough. Once you have the rod rolling then I would guess that some
>>rather subtile and nonlinear eddy currents could also have a
>>significant impact.
>>
>It would be interesting to know if Dave Kardellis's arrangement
>would move the other way when he changes the current's polarity. If
>his rod does indeed move in the other direction then it should be
>the interaction of the current's B-field with the one of the earth.
>
>Rolling rod motors are kind of mysterious. In fact I have an
>arrangement that only consists of a rather thick and short metal
>cylinder with both ends inserted in the inner diameters of two ball
>bearings. Now, if I apply a rather large current from one outer ring
>of a ball bearing to the other then I observe the same behavior as
>you do. The metal cylinder and the inner parts of the bearings would
>begin to rotate rather fast much like an electric motor would. In
>this case it is indeed the way you describe: It would rotate in the
>direction you initially kick it. I always wondered about the reason
>of this behavior.
>
>I find the things which cannot be simply explained intriguing.
>
>Regards from over here
>
>Urs
>
>Urs Lauterburg
>Physics demonstrator
>Physikalisches Institut
>University of Bern
>Switzerland
>
>>Thanks Urs. That would surely be more dramatic.
>>
>
>But I still don't understand why Dave Kardelis' setup can roll both
>ways? I thought this was just the interaction of the field produced
>by the current in the rails with the field produced by the current
>in the cross bar. But that should only move in one direction. My
>setup moves in the direction I start it rolling in.
>
>
>Paul
>
>
>
>On Dec 12, 2010, at 3:24 PM, Urs Lauterburg wrote:
>
>
>>Paul,
>>
>If you make the whole arrangement smaller to fit within a B-field
>produced by a horseshoe magnet you get much better results. In fact
>that's our traditional arrangement to demonstrate the Lorentz force
>on charges that move along a rolling rod on a rail. You can show the
>effect of changing both of the polarities of the current as well as
>of the B-field by flipping the magnet.
>
>
>Regards form over here
>
>Urs
>
>Urs Lauterburg
>Physics demonstrator
>Physikalisches Institut
>University of Bern
>
>Switzerland
>
>
>>Ok Dave,
>>
>
>I just tried it.
>
>
>My little battery charger trips off after a few seconds. And it
>doesn't have enough power to get the roller started by itself.
>
>
>Here's the curious feature... The rod will continue rolling if
>given a small nudge. And it might even accelerate just a bit. It
>doesn't keep rolling if the power is off. But the thing about that
>is... it works it both directions. And it works in both directions
>regardless of the polarity of the power.
>
>
>Does this bother anyone else? Or can I choose to use either a
>left-hand rule or a right-hand rule depending on my mood?
>
>
>Paul
>
>
>
>On Nov 17, 2010, at 11:51 AM, david kardelis wrote:
>
>
>>Adam asked about my rail gun.
>>
>>Simple setup, 2 3/4" aluminum rods on the table about 1/2 meter
>>apart, Third aluminum rod laid on top. B field comes from the earth.
>>
>>The power supply is a emergency jumper battery , one lead hooked to
>>each rod on the table, see the thread on power supplies.
>>
>>Flip the switch and the rod rolls.
>>
>>I find I need to sand the aluminum rods before doing this as the
>>oxidation prevents good electrical contact. The rods do get pitted
>>along the contact points
>>
>>Here is a video on Photobucket I took quickly this morning
>>
>>
>>http://s366.photobucket.com/albums/oo108/dkardelis/Rail%20Gun/?action=viewĄt=003.mp4
>>
>>
>>
>>I tried using conduit this morning, to see if could get a
>>longer run, and a lighter "bullet". The conduit just welded itself
>>together when I flipped the switch,
>>
>>dave

--============_-919849585==_ma============
Content-Type: text/html; charset="us-ascii"



Dave,

It might depend on how you line up the setup in respect to the
earth magnetic field. The two parallel rails should be in line with
the north to south longitude. It may have an impact if it is indeed
the driving field.

Regards

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland

The last time I took this out for the
video I posted, it always moved the same direction regardless of
polarity.

I vaguely remember doing this in class and talking about reversing the
polarity and explaining that the rod should roll the other way. I then
reversed the leads and thought that the rod did go the other way. But
it is a vague recollection and when I try it now it only goes one
way.

I will try it again, the current setup is on the tabletop and the
tables here have steel bases. I used to do it with the rods extending
off the end of the table. I will try that again and see what
happens

dave

On Mon, Dec 13, 2010 at 9:59 AM, Paul
Nord
wrote:
Urs,

So it could be some variety of shaded pole
motor?
New understanding physics for ... - Google
Books
I never understood that! :)

It's likely that there is something going on with the
intermittent electrical contact between the rods.

Paul


On Dec 13, 2010, at 1:16 AM, Urs Lauterburg
wrote:

Paul,

I assume that what really counts is the direction it will start
rolling without any implied external mechanical force. If it does not
start rolling then the external B-field is simply not strong enough.
Once you have the rod rolling then I would guess that some rather
subtile and nonlinear eddy currents could also have a significant
impact.



It would be interesting to know if Dave Kardellis's
arrangement would move the other way when he changes the current's
polarity. If his rod does indeed move in the other direction then it
should be the interaction of the current's B-field with the one of the
earth.

Rolling rod motors are kind of mysterious. In fact I have an
arrangement that only consists of a rather thick and short metal
cylinder with both ends inserted in the inner diameters of two ball
bearings. Now, if I apply a rather large current from one outer ring
of a ball bearing to the other then I observe the same behavior as you
do. The metal cylinder and the inner parts of the bearings would begin
to rotate rather fast much like an electric motor would. In this case
it is indeed the way you describe: It would rotate in the direction
you initially kick it. I always wondered about the reason of this
behavior.

I find the things which cannot be simply explained intriguing.

Regards from over here

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern
Switzerland
Thanks Urs. That would surely be
more dramatic.






But I still don't understand why Dave Kardelis' setup can
roll both ways? I thought this was just the interaction of the
field produced by the current in the rails with the field produced by
the current in the cross bar. But that should only move in one
direction. My setup moves in the direction I start it rolling
in.


Paul



On Dec 12, 2010, at 3:24 PM, Urs Lauterburg wrote:


Paul,







If you make the whole arrangement smaller to fit within a
B-field produced by a horseshoe magnet you get much better results. In
fact that's our traditional arrangement to demonstrate the Lorentz
force on charges that move along a rolling rod on a rail. You can show
the effect of changing both of the polarities of the current as well
as of the B-field by flipping the magnet.


Regards form over here

Urs

Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern

Switzerland


Ok Dave,










I just tried it.


My little battery charger trips off after a few seconds.
And it doesn't have enough power to get the roller started by
itself.


Here's the curious feature... The rod will continue
rolling if given a small nudge. And it might even accelerate
just a bit. It doesn't keep rolling if the power is off.
But the thing about that is... it works it both directions.
And it works in both directions regardless of the polarity of
the power.


Does this bother anyone else? Or can I choose to use
either a left-hand rule or a right-hand rule depending on my mood?


Paul



On Nov 17, 2010, at 11:51 AM, david kardelis wrote:


Adam asked about my rail gun.

Simple setup, 2 3/4" aluminum rods on the table about 1/2 meter
apart, Third aluminum rod laid on top. B field comes from the
earth.

The power supply is a emergency jumper battery , one lead hooked to
each rod on the table, see the thread on power supplies.

Flip the switch and the rod rolls.

I find I need to sand the aluminum rods before doing this as the
oxidation prevents good electrical contact. The rods do get pitted
along the contact points

Here is a video on Photobucket I took quickly this morning


http://s366.photobucket.com/albums/oo108/dkardelis/Rail%20Gun/?action=view¤t=003.mp4



I tried using conduit this morning, to see if could get
a longer run, and a lighter "bullet". The
conduit just welded itself together when I flipped the switch,

dave









--============_-919849585==_ma============--

Back