scratchbuilding a working turntable
Brian Smith
I am unable to afford the larger turntables that I require to turn my
Northern, and was wondering if anyone had tried to build their own?
I believe that I have the skill to build a mechanically sound unit but am
not certain on how to gear it for slow smooth operation. Looking through the
walthers catalog on pages 748/749 leads me to believe that I can build a
reduction gear system to turn the unit. I'm uncertain though if I can get
the turntable to rotate smoothly at low speed using the brass gears.
As I recall worm drives are very 'inefficient compared to direct drive
gears, but very suitable for low speed operations. Does anyone have any
practical experience building a gearbox, and how did you mount it to drive
the turntable?
I was thinking of putting a old Tyco can motor unit in the turntable bridge
itself, and having it simply turn a old loco driver that runs on the rail
around the base of the turntable bridge. Assuming I put some reduction gears
in place, and maybe some slip on the wheel to track it would turn without
flinging my loco around like a merry-go-round. Eyeballing the stops would
have to do, as I have no clue how to 'step' the motor exactly to each stall.
Ideas and comments are welcome! Especially any good construction notes, or
diagrams!!!
Brian
larsso
What some people do is pick up a cheap turntable from a larger scale and
build a new deck structure for it. For example, I am in N, so I could buy a
small HO turntable and put a N scale platform on the mechanism and hide the
HO one underneath.
--
Alan Larsson KC2GOC / NYSING-305
http://way.to/alstown
Webmaster, Genesee & Ontario N-Gineers N-Trak
http://www.ggw.org/gno
"Brian Smith" <smit...@home.com> wrote in message
news:FrU16.33054$36.9...@news1.rdc1.il.home.com...
Brian Smith
I had though of buying a hand cranked turntable (12") from Atlas, but im
still stuck with the problem of powering it. Also from the box picture it
did not appear that the unit was anything more than a simple deck with a
large plastic hand crank just off center. Still now that you mention it I
will have to go take another look. Mahaps the dealer will allow me to open
the box, and peek under the hood to see how it works. :)
"larsso" <all.n...@rochester.spam.rr.com> wrote in message
news:rwU16.56277$7I.64...@typhoon.nyroc.rr.com...
larsso
--
Alan Larsson KC2GOC / NYSING-305
http://way.to/alstown
Webmaster, Genesee & Ontario N-Gineers N-Trak
http://www.ggw.org/gno
"Brian Smith" <smit...@home.com> wrote in message
news:BJU16.33059$36.9...@news1.rdc1.il.home.com...
Gerry Leone
First, the disclaimer: I am by no means anywhere near an expert at this. In
fact, I was at a total loss for everything you said *until* your last
sentence, about stepping the motor for lining up each stall.
Many years ago I built a optical circuit that sounds like it would do what
you want it to. I'd turn a rotary switch to indicate the stall track I
wanted -- this lit a grain of wheat bulb under the layout, then hit a button
to start the turntable. When the optical circuit sensed the grain of wheat
bulb, it cut the power to the motor AND triggered a twin coil switch
machine, which would lock the turntable in place. It worked like a charm.
In the very first installment of MR's "Electronics Symposium in November of
'80, I wrote a [rather lengthy] explanation of the circuit. Included with
the article were some great drawings by the MR staff. I have this entire
article, the circuit, and the MR drawings, on my website at
http://home.earthlink.net/~gerryleone/ar-indicator.htm . I've recently
built this same circuit and found that all parts are still available at
Radio Shack.
As far as lining up roundhouse stalls, perhaps this is what you're looking
for!
--
- Gerry Leone
http://home.earthlink.net/~gerryleone/trains.htm
"Brian Smith" <smit...@home.com> wrote in message
news:FrU16.33054$36.9...@news1.rdc1.il.home.com...
Ernie Fisch
2000
> flinging my loco around like a merry-go-round. Eyeballing the stops would
> have to do, as I have no clue how to 'step' the motor exactly to each stall.
There is nothing wrong with this. I operated on a layout where the
breakin job
for the new guy was the hostler job. The turntable was aligned
manually. My
problem was that the alignment points were out of focus. Too far for
the reading
part of my bifocals and too close for the distance correction.
The system used a two speed motor setup and the motor speed was
adjust-
able to a crawl. Alignment was quite accurate. It was sure a lot
simpler than
setting up stops.
--
ernie fisch
Jim Guthrie
wrote:
Brian,
>I believe that I have the skill to build a mechanically sound unit but am
>not certain on how to gear it for slow smooth operation. Looking through the
>walthers catalog on pages 748/749 leads me to believe that I can build a
>reduction gear system to turn the unit. I'm uncertain though if I can get
>the turntable to rotate smoothly at low speed using the brass gears.
>
>As I recall worm drives are very 'inefficient compared to direct drive
>gears, but very suitable for low speed operations. Does anyone have any
>practical experience building a gearbox, and how did you mount it to drive
>the turntable?
You can use a model locomotive motor and worm gearbox, then use a
pulley drive to the turntable. You could use a geared drive as well,
but the main point is to get the diameter of the final pulley or gear
as large as possible (with a small diameter driving pulley or gear) to
minimise any play or backlash as well as giving you an overall
reduction gear which gives good slow movement. If you use small
diameter gearing on the final drive to the turntable deck, you can
find that the small amount of play in the gearing is amplified many
times at the ends of the turntable deck which can make alignment of
the rails a bit difficult.
>
>I was thinking of putting a old Tyco can motor unit in the turntable bridge
>itself, and having it simply turn a old loco driver that runs on the rail
>around the base of the turntable bridge. Assuming I put some reduction gears
>in place, and maybe some slip on the wheel to track it would turn without
>flinging my loco around like a merry-go-round. Eyeballing the stops would
>have to do, as I have no clue how to 'step' the motor exactly to each stall.
That idea might work in model form, but you might run into problems
getting sufficient traction from one or two small wheels with a heavy
load on the bridge. You might get a better system using a rubber
wheel driving on the wall of your turntable pit, with the assembly
sprung in some way to provide a constant pressure against the wall and
give allowance for inaccuracies in concentricity. The drawback to
this type of setup might be disguising the motor/gearbox on the
turntable deck.
One of the ways I have found to get accurate indexing is to have a
large diameter circular plate on the turntable shaft and cut wedge
shaped notches in that plate. A armature of a spring loaded solenoid
bears in the slots. A small micro switch is arranged to work from the
armature. To operate, power is applied to the solenoid when its
armature is pulled out of the slot and the microswitch is operated to
apply power to the turntable motor. Once the turntable is moving,
the voltage to the solenoid can be broken since the plate stops the
solenoid going fully back to the engaged position and the microswitch
is kept closed keeping the turntable motor turning. When the next
notch comes round, the armature drops into the slot and the
microswitch opens, cutting off power to the turntable motor, and the
turntable stops in position, held there by the solenoid armature with
its wedge shaped end.
The problem with the simple version of this arrangement is that it is
sequential and will only move to the next available position. If you
have several roads leading off the turntable, you would have to power
the solenoid at each road position until the correct road was reached.
You can get over this by introducing a more complex indexing setup
using something like a PCB disk with tracks which maintains power to
the solenoid across unwanted roads until the required road is reached.
You might also want to make this even more sophisticated and use
semiconductor logic and some form of positional sensing like photo
diodes to do the work. The main point is that the locating of the
table is done by a solid mechanical wedge on a large diameter plate
which overcomes any backlash in drive gearing.
Instead of a solenoid, you can modify an appropriate relay by
sticking an arm to its armature with the wedge on the end of the arm,
and use the contacts of the relay instead of the microswitch.
The reason for the wedge shape is to prevent the system seizing up in
use. If you use a square shaped notch, it's possible for the
locking part to seize in the slot since some over-run in the turntable
driving motor can do cause this to happen when it drops in the slot.
Jim.
--
Jim Guthrie
S7 Dabbling at www.netcomuk.co.uk/~sprocket/index.html
Phillip Dimond
indexed electronically. I have a total of 22 positions on the turntable (11
entrances/exits, and I want to be able to specify the direction, so a assume
a certain direction on the platform to be 'forward' and thus count the
entrances).
Mine uses a commercial indexing mechanism, and like one of the posters I
used a small Atlas HO turntable and motor and scratchbuilt the platform (it
looks a little wrong, but it's not really noticeable). I model in N scale so
this gave me a huge turntable.
Anyway, to index it I built a large circular card, and cut a sequence of
holes in it. The card is mounted below the turntable and is quite a bit
larger than it, allowing accurate indexing. The card does NOT have to be
perfectly circular .. I cut mine with scissors and make it out of thick
styrene sheet.
Marked on the card are radial lines from the centre which correspond with
the exits. Also marked are 5 concentric circles. Where each circle and
radius intersect, I drill a *really* small hole (I made a jig using the
sensing mechanism I'll describe in a second).
There are five LEDs and five optosensors mounted into tubes that are on the
circular positions. The LEDs shine through the plate onto the optos mounted
under the plate. The optos are connected to a simple digital 'comparator'
circuit. The other input of the comparator is fed from a pair of digital
rotary switches. The comparator output drives the turntable. Whenever the
comparator shows the control switches and the index card to be not equal,
the turntable starts and runs until it is equal. It has the disadvantage
that if the turntable has to simply turn to the next exit in the direction
opposite to that in which it is set to turn it will go all the way around to
get to it, but a slightly more creative circuit for the controller would fix
this .. I just haven't had time.
Thus, all I have to do to drive the turntable is set the selector switches
to the exit I want (numbered to give both exit number and direction) and the
turntable automatically slews to the appropriate exit. As the sensor card is
almost double the diameter of the turntable (it looks funny under the bench!
:) and the holes used for the optos are 0.6mm diameter, I get about 0.3mm
positioning accuracy, which is better than my eyeball can make.
In actual fact the positional accuracy is better than that, as I the LED and
optosensor assembly is easy to remove. To drill the index holes in the
indexing card I just set the turntable manually and drilled through the
holes in the assembly, so the card is dead accurate.
This may be all a little excessive for the average layout, but mine is
large-ish and growing, and I want to automate as much of it as possible, so
I can have a couple of trains going on automation while I run one manually
or operate the yard or one of th switching industries.
If I ever get the direction control implemented I'll write this up into an
article and put it into one of the mags if anyone is interested.
Phil
> I am unable to afford the larger turntables that I require to turn my
> Northern, and was wondering if anyone had tried to build their own?
Maycop
bldg. a large TT by Gordon Odegard. Worth searching for.
Don
Ken Bessler
Try this URL:
http://users.50megs.com/kg0wx/turntable.html
--
---------------------------------------------------------
Ken Bessler, Ham callsign KG0WX
Design Services Company
Model railroad design services
http://users.50megs.com/kg0wx
Smoke free since 9/30/96
ICQ #63379650
---------------------------------------------------------
Donald Lodge
(Maycop) wrote:
You can order copies direct from Kalmbach Publishing.
Don Lodge
Michael McIntyre
>
>I had though of buying a hand cranked turntable (12") from Atlas, but im
>still stuck with the problem of powering it. Also from the box picture it
>did not appear that the unit was anything more than a simple deck with a
>large plastic hand crank just off center. Still now that you mention it I
>will have to go take another look. Mahaps the dealer will allow me to open
>the box, and peek under the hood to see how it works. :)
I don't have the links handy, but there are a couple different pages
out there explaining how to use an Atlas turntable to power a
scratchbuilt one, or to power a Walthers turntable. You can get a
motor assembly for the thing, though the combination costs around $40
and the tables rotates in a most unrealistic nothing nothing nothing
nothing SNAP nothing nothing nothing nothing SNAP fashion that I find
irritating.
Basically you mount the Atlas turntable under your scratch built one
and make a driveshaft to transfer the rotational power. You can also
put in a geartrain to reduce the spacing between stops to get your
engine tracks closer together. You'll need to do this to make it work
with almost any roundhouse kit on the market.
You DON'T want to hand crank an Atlas turntable. You have to rotate
the crank something like 10-20 times before the track moves once.
Maybe it's not really that bad (been a long time) but it's definitely
really annoying. Get the motor drive.
---
D. Michael McIntyre | mmci...@swva.net | USDA zone 6a in sw VA
http://www.geocities.com/Paris/Rue/5407/index.html
mcb...@my-deja.com
Ken Bessler <kg...@yahoo.com> wrote:
> Brian-
>
> Try this URL:
>
> http://users.50megs.com/kg0wx/turntable.html
-----------------------------------------------
Very impressive.
Questions:
1. How does the Atlas motor drive know to stop at each index?
2. How do you attach the Atlas motor drive to the Atlas manual table?
3. How does the Atlas turntable actually reverse polarity automatically?
4. How do you actually connect the Atlas motor drive to a source of
power and operate the turntable?
Thanks!
Sent via Deja.com
http://www.deja.com/
mcb...@my-deja.com
mcb...@my-deja.com wrote:
> Questions:
Just two more ...
5. Do you power the *Enter* and *Exit* tracks coming to and from the
electrified, Atlas turntable with the same transformer/wiring to allow
for the automatic polarity reversing to occur?
6. How do you actualy wire all of these tracks to have this happen?
Thanks very much!
Mark Smith
a great idea and by adding a second track to the bridge, the fifteen
degree index will accomodate twice as many tracks.
The walthers turntable is a joke for operation.
A friend nearby has a world class layout, and the only piece of junk is
the walthers turntable located near a junction yard.
I'm sorry I sold it to him. I also wish I had no more in stock.
Diamond scale makes a dandy, and by changing some gears around to
eliminate the angles of the driveline, makes a VERY smooth running unit,
and looks great too.
They are certainly not overpriced when you consider the need for
alignment and looks together.
--
Mark Smith
Tri-State Kite Sales http://www.trikite.com
1121 N Locust St
Mt Vernon, IN 47620 mailto:ma...@trikite.com
ChromeDome
>
> In the very first installment of MR's "Electronics Symposium in November of
> '80, I wrote a [rather lengthy] explanation of the circuit. Included with
> the article were some great drawings by the MR staff. I have this entire
> article, the circuit, and the MR drawings, on my website at
> http://home.earthlink.net/~gerryleone/ar-indicator.htm . I've recently
> built this same circuit and found that all parts are still available at
> Radio Shack.
>
Now that's a useful link! Thanks, Gerry. I'm building a new layout and
that detection circuit will serve a lot of needs.
--
Homo Sapiens is a goal, not a description.
Ken Bessler
mcb...@my-deja.com wrote:
> In article <3A48AE01...@yahoo.com>,
> Ken Bessler <kg...@yahoo.com> wrote:
> > Brian-
> >
> > Try this URL:
> >
> > http://users.50megs.com/kg0wx/turntable.html
> -----------------------------------------------
>
> Very impressive.
>
> Questions:
>
> 1. How does the Atlas motor drive know to stop at each index?
It dosen't. It keeps running while a mechanical system pauses the rotation
of the deck.
>
>
> 2. How do you attach the Atlas motor drive to the Atlas manual table?
The components are designed to work together so attaching the motor is easy.
>
>
> 3. How does the Atlas turntable actually reverse polarity automatically?
Through a rather clever system of internal wipers.
>
>
> 4. How do you actually connect the Atlas motor drive to a source of
> power and operate the turntable?
I ran mine from a LM7806 regulator (6 volts). I used a DPDT momentary
center off switch (radio shack #275-709)
5. Do you power the *Enter* and *Exit* tracks coming to and from the
electrified, Atlas turntable with the same transformer/wiring to allow
for the automatic polarity reversing to occur?
Just hook them up like any other block - the Atlas turntable will alter
it's polarity to match them automatically.
6. How do you actualy wire all of these tracks to have this happen?
See the instructions that come with the atlas turntable - it's pretty easy.
>
>
> Thanks!
>
> Sent via Deja.com
> http://www.deja.com/
--
Aredeer
I have a copy of the March,1980 Model Railroader which has an article " An
easy to build,fully automatic turntable. If you want, I will scan and e-mail it
to you.
Ray
E&M
the article? I can't find my March 1908 copy of MR My real email is below.
Thanks,
Ewen choo...@ns.sympatico.ca
"Aredeer" <are...@aol.com> wrote in message
news:20001226130718...@ng-fn1.aol.com...
Doug Seymour
*perfectly* centered on the bridge. I've purchased a Bowser N-scale turntable.
It's "bridge" consists of a block of wood approx 3/4" wide with a set of soft
metal castings which are inteneded to be attached to the side. The istructions
with it say to simply fasten a piece of flex track/snap track to it, then cover
the ties with scale sumber to make it appear like the real ones. I've tried a
number of times, but ame not able to have the tracks line up so that if I rotate
the turntable 180 degrees, the tracks still line up. Any suggestions?
Incidentally, Bowsers' way of motorizing this was to provide a circle of
plyswood which fastens to the shaft with the fitting supplied, then a geared DC
motor (looks like and old Pitman style) with a rubber wheel on the end of the
shaft. This is hed against the plywood wheel with a spring arrangement.
In general, I was extreemly disapointed with the qualityt of the Bowser unit. I
found it crude (to put things mildly). I would caution anyone else who is
thinking of buying one to take a hard look at it before you plunk down and hard
earned green.
John Purbrick
Brian Smith <smit...@home.com> wrote:
>Happy Holidays!
>
>I am unable to afford the larger turntables that I require to turn my
>Northern, and was wondering if anyone had tried to build their own?
There's some information on how I built a microprocessor-controlled
indexing system on http://www.nyx.net/~jpurbric/ttable.htm
Basically the mechanical system is a strong plywood frame with bearings
top and bottom; the bridge rides on a 1/2 inch shaft through ball bearings.
There is an aluminum platter about the same dia as the turntable which
is mounted to the shaft, and a (very small) geared motor drives this via
a rubber O-ring near the outer edge. The motor's on a hinged arm and gravity
is enough to press the wheel down. It's a good feature that the wheel can
slip if anything stalls the action--more to protect the gearing than to
save anyone's prize loco from destruction!
You can see some pictures on the club's web site at http://web.mit.edu/tmrc
somewhere on the "progress" pages.
I think a good way to build a mechanical system would be a plywood disc on
a "lazy susan" bearing which costs only a few dollars at Home Depot. Then
set up a vertical shaft with some kind of fitting (a large gear bolted to
the disc would do, with a setscrew hub which the shaft goes into). Then drive
it with the gearmotor with a rubber tire.
Gerry Leone
the answer to, too! I remember I had the same problem when I tried to
scratchbuild a turntable eons ago. Seems that if you're off by a 64th of an
inch, you're hozed.
--
- Gerry Leone
http://home.earthlink.net/~gerryleone/trains.htm
"Doug Seymour" <v6...@rac.ca> wrote in message
news:3A48EFCA...@rac.ca...
Trainman
roundhouse area until AFTER the turntable was completely installed ON the
layout. Then all the track was layed "to fit".
Don
--
don.de...@prodigy.net
http://www.geocities.com/don_dellmann
moderator: WisMode...@eGroups.com
Gerry Leone <gerry...@earthlink.net> wrote in message
news:SCe26.23772$RC1.7...@newsread1.prod.itd.earthlink.net...
Doug Seymour
track on the turntable bridge. As Gerry commented, if you're off by a 64th of
an inch, you're hosed. I know that there are folks who have built truntable
that align perfectly both way. I'd like to know how they did it.
Jim Guthrie
Doug,
>Don, that's exactly what I did. The problem is how to _exactly_ center the
>track on the turntable bridge. As Gerry commented, if you're off by a 64th of
>an inch, you're hosed. I know that there are folks who have built truntable
>that align perfectly both way. I'd like to know how they did it.
It's been a few years since I last built a turntable but, IIRC, I
established a centre line on the deck which passes through the exact
centre of the rotational centre of the deck. If you draw what you
think is the centre line then make marks on the pit at each end of the
turntable deck to correspond with the centre line, then spin the
turntable 180 degrees and see if the marks still line up with the
centre line. If not, you have to adjust the position of the centre
line, and re-make the marks on the pit edge until you get them lining
up when the position of the deck is reversed. I had to do it this
way since I was scratchbuilding the track on the deck and on the roads
off the pit and I laid the rails measured from the (eventually)
correct centre line.
An easier way may be to use a straight length of something like snap
track on the turntable deck and clamp this in what you think is the
central position and get two pieces of the same track and clamp them
on the pit walls to align exactly with the rail on the deck, then
spin the turntable and see if they line up at 180 degrees. If they
don't, then move the track on the deck to a new position, re-align
the tracks on the pit wall and try again. It's an empirical method
which can take quite a bit of time to get exactly right, but once
it's correct, fix the track on the deck.
Another thing you can do to help out is file slight tapers on the
inside (running) edges of the rail ends on the pit wall so that the
gauge is widened at the end. This gives you a small amount of play
which allows for slight misalignments of your indexing system. If
you file tapers so that the gauge in H0 is opened up to about 17.5mm,
your locos' wheels should still traverse this wide section with no
problems except for a slight sideways judder if the indexing is
slightly off. If you don't like the idea of filing rails, you can
bend the ends like wing rails on turnouts to achieve the same effect,
but that can look a bit unsightly when compared to the filed taper
method.
Jim.
Trainman
I don't remember how much we fiddled but as I recall it wasn't that much.
OTOH, we were using a piece of heavy inverted aluminum channel as a bridge,
which could be quite a bit more rigid than your wood bridge, so that may
have had something to do with it.
Don
--
don.de...@prodigy.net
http://www.geocities.com/don_dellmann
moderator: WisMode...@eGroups.com
Jim Guthrie <j...@sprockets.co.uk> wrote in message
news:97sl4tgrovvd53ijs...@4ax.com...
Doug Seymour
Jim Guthrie
Doug,
>Thanks very much for your suggestions. Ill try them out.
Be prepared for a right fiddle of a job, unless you're very lucky and
get it right first time. If you can display the end of the deck
pivot shaft, or accurately mark its centre, that would be a good
start, whether you're using the centre line method or the piece of
straight track method, since it gives you a good datum point on which
to base your positioning.
If the end of the pivot is well hidden under the bridge deck, then
your just going to have to take an educated guess as to where to place
the centre line or track.
If you're using the track method, you might find it difficult to
clamp the track to the deck when doing the alignment tests and the
simplest way may be to use a chunk of lead weight on the track to hold
it in position while you do the tests. There should be enough
friction between the track and the deck with a good sized chunk of
lead to hold the track in place. In fact, you're probably better
using two chunks of lead with one at each end of the track. Then you
can make the fine adjustments necessary by lifting the weight at one
end of the track and moving the rail under it - the rail will tend to
pivot round the lead weight at the other end. This will give the
chance for much more predictable adjustment - with one weight, when
you lift it to move the track, you might inadvertently move the whole
piece of track and have to start all over again :-)