Download automatic turntalble - North River Railway

AUTOMATIC TURNTABLE
(PART 1 – ELECTRIC AL)
Presented by BOB VAN CLEEF, MMR
of the North River Railway
• This presentation is NOT complete at this time nor
will it cover the construction of the actual turntable
above table level in more than a general way.
• This optical circuit was first successfully built and
proven over 35 years ago.
• This clinic shows a modern, updated version with less
cost and fewer parts at the expense of slightly more
complex circuitry.
A SCRATCH BUILT TABLE
Scratch building an optically aligned table is not
simple but it does have many advantages.
– Stall tracks do not have to be equally spaced.
– No switches for stall tracks are required.
– No complex mechanical alignment mechanisms that can
wear out are used. Alignment is simple and dependable.
– No precision parts or carpentry is required.
– YES, quite a bit of assembly IS required; This project is NOT
for beginners.
FORWARD
• The roundhouse and turntable is often the
main focus point of a layout yet very few
modelers build their own turntable.
• There are only a few small simple turntables
available on the market today.
• Most commercial tables of any reasonable size
are expensive, hard to find, have few features
and are difficult to use.
THIS CLINIC IS DIVIDED AS FOLLOWS:
1. Theory of operation
2. Electronics
• PIC device
• Support circuitry
• Software
3. Mechanical
• Motor
• Optics
4. Overall Construction
THEORY OF OPERATION
• This is an optically-based positioning system.
• A motor drives the turntable.
• A LED projects a beam of light over a pairs of photo cells for
each track position.
• Circuitry counts the number of cell pairs passed as the table
turns and stops all motion when exactly half way between the
cell pair of the desired track.
• Adjustments are simple and easy.
• Accuracy is reliable and close to about +/- .010”
• Power to the stall tracks is delivered by a special comutator
thus eliminating the need for switches.
A SIMPLE OPTICAL SYSTEM
• This is a simulation of an optical
turntable system.
• A single pair of photo-resisters
represent up to 24 pairs or more of
cells wired in parallel
• The LCD below table level pivots with
the bridge of the turntable.
• Note that no lens or other optical
components are required
HOW IT WORKS
• Light directed to either cell will
cause a signal for that cell to go
from high to low.
• A low signal from either of (2)
cell signals the table is near
alignment and slows the motor.
• A third signal is also generated
from one of the cells that has no
effect until the other two go low.
• Then, but only then, when the
signal changes, the table stops
indexing.
Output of cells and
motor speed as light
source passes.
ELECTRICAL CONNECTIONS
• A slip ring is a method of
making an electrical connection
through a rotating assembly.
• This complex slip ring is made
from a printed circuit board.
• motor brushes on the
underside of a drive wheel
route power to the light source
and various tracks around the
table.
(More on this later)
MORE ON COMMUTATOR DETAILS
THE ELECTRONICS
•
•
•
•
A single PIC device contains most of the circuitry required for this
project.
Special chips are used to control the motor and to display the status of
turntable operation.
A small number of discrete components complete the project.
A USB interface is used to program the PIC only during the
development of the system.
THE PIC MICRO CONTROLER
•
•
•
•
16-bit architecture
16K x 14bit Program Memory
1024 x 8 bit RAM
Clock, timing and all support
circuitry
• Serial Programming I/F
• About 56 other components
all in a single 64-pin package
slightly larger than a
thumbnail for just $4
A TOOLKIT IN A BOX
In addition to the RAM
ROM it contains:
• 6-1/2 ports
• A/D converters
• Timers
• UARTS
• LCD AND LCD DRIVERS
• COMPARATORS
• SEVERAL OTHER
FUNCTIONS
PINS HAVE MULTIPLE USES
• Most pins have
multiple uses
• Device must be
configured to define
pin use
• Configuration can be
changed in midprogram
CONFIGURING THE PIC DEVICE
This project makes use of
the (3) comparators
contained within this
device.
• Note the multiplexed
inputs.
• The polarity of the
output can be inverted
or accessed without the
use of an external pin.
• This leaves the unused
pins free for other uses.
OVERVIEW OF PIC CONNECTIONS
PROGRAMMING THE PIC
• PIC devices are designed to
be programmed without
being removed from their
socket.
• A USB port powers the
programmer as well as the
data to be programmed.
• The programmer supplies
all voltages and signals
required to program the PIC
device.
JUMPERS
• Four jumpers provide direct
access to up to 15 test
routines as well as the
normal “RUN” mode.
• This simplifies testing
• This also allows multiplexing
of multiple tables on one
system.
CONTROL PANEL
• Three buttons control the table.
– CW
– CCW
– RESET
• The 8-character LCD displays
– The number of button presses
– Direction of rotation
– Status
•
•
•
•
Rapid travel
Seeking (slow travel)
Stop (in Position)
Ready
CONTROLER PCB LAYOUT
LCD DISPLAY
• A simple, inexpensive LCD
display is used to show the
turntable status.
• I shows (1) line of (8)
characters.
• Only (8) wires are required
to connect the display
MOTOR CONNECTIONS
Note the extra circuit to turn the
light source on and off.
• A driver uses circuitry
similar to a DCC decoder to
drive the motor
• No decoder is required.
• It can be configured to run
using a wide range of
voltages.
• Logic circuits are electrically
independent of motor
power.
• A simple 2-speed circuit
controls the motor.
PHOTO RESISTOR CONNECTIONS
TURNTABLE CONTROLER
• Very few support
components are
required using a PIC
device.
REVIEW OF MAIN SCHEMATIC
5 and 8 volt POWER SUPPLY
• The turntable runs from a
16v DC wall transformer.
• Two common voltage
regulators provide the
required voltages
A simple power supply
Micro Engineering U2 Programmer
• USB interface for easy use with
virtually all computers
• Generates all required voltages
required for programming.
• Works with entire range of PIC
devices with proper interfaces
• Firmware can be automatically
updated via host computer as
new PIC devices become
available.
CCS “C” Compiler and IDE
• Custom Computer Services
(CCS) offers a complete
range of software for PIC
devices.
• One product offers a full
implementation of the “C”
and other languages at a
very low price.
• It is easy to install.
• All components work well
together.
EVERYTHING YOU NEED
TO GET STARTED
PRINTED CIRCUIT SLIP RING
• This printed circuit board (PCB)
provides connections to the
rotating bridge.
• The Center and first band provide
power to the “light gun”
• The next band simply provides
clearance for power feeds
• The next band provides power to
one of the bridge rails. Note the
split to allow proper reversing.
• The outer band energizes one, but
only one stall track at a time.
RESOURCES
Digikey
http://www.digikey.com/
Source for wide variety of electronic related parts and hardware including
LEDs, Wire, Solder, Copper wire, printed circuit board and headers.
MicroMark
http://www.micromark.com/
Source for small tools and materials useful for modeling.
Custom Computer Services (CCS) http://www.ccsinfo.com
“C” and several other higher level languages for PIC devices
Microchip
http://www.microchip.com
Manufacturer of PIC devices and several programming accessories
Proto-Advantage - http://www.proto-advantage.com
Custom design and assembly of SMT devices and related materials.
This presentation has been brought
to you by the North River Railway
Bob Van Cleef
46 Broadway
Coventry, CT 06238
http://www.northriverrailway.net
THE END
AUTOMATING A TURNTABLE
(PART 2)
Presented by BOB VAN CLEEF, MMR
of the North River Railway
MOTORS
• Vex Robotics carries a line of motors,
gears and metal channels designed
for building robots.
• These are perfect for building a
rugged mechanism the runs at
whatever speed desired.
• Parts include gears, chains, tank
tracks almost any drive desired
including belts.
BRUSHES ON DRIVE DISK
• Brushes for motors
are used to collect
power from the
comutator
• The are attached to
thin metal springs
to allow maximum
movement
PHOTO CELLS ON TABLE BASE
• Photo cells are mounted on
a pylon using a single screw
• Fine positioning can be
accomplished by simply
turning the pylon slightly
until proper alignment is
achieved.
• Simple and crude? Yes, but
very effective and
dependable.
VIEW OF COMUTATOR AND CELLS
UNDERSID VIEW
DRIVE MOTOR
• Any small inexpensive
motor can be used to
drive a turntable
• This system used a
simple rubber shaft to
turn the disk
• The clutch drive was
required to prevent any
binding at slow speeds.
IMPROVED DRIVE SYSTEM
Drive belt made from heatshrink tubing used to turn
drive disk
• A future drive will be a bit
more complex
• The motor will be mounted
solidly and a spring-loaded
pulley will keep a more
reliable tension on the
drive disk.
GENERIC CONSTRUCTION
NOT TO SCALE
A BRIEF HISTORY
Turntables were rare in the first early model railroad layouts. The First crude
table mentioned in the July ‘42 MR used a phonograph table as the base and
was manually aligned. In August of the same year a much more advanced
“automatic” table featured both power to the stall tracks and a mechanical
positioning system. Systems in this era used a split ring rail to power the
bridge track.
Several articles in the MR and other magazines have appeared since then with
many differences in the construction to the bridge and pit portions of a
turntable (see Sept 57, Aug and Sept ‘63 and March ’72 but few advances
were made in the drive mechanism. The exception was a photo-cell system
described in the Nov ’66 MR using a single photo-cell and lens.
In Oct ‘58 Atlas produced a small, inexpensive self indexing table that became
quite popular in both motorized and manual versions. Since then most
commercial tables have been very expensive, not automatically aligned and
required switches to apply power to the stall tracks.
AN “IMPROVED” TABLE
Unsatisfied with what was available at the time, I built a turntable with several novel
features. Because the North River already used a computer controlled block system it
only seemed logical to use a computer to control the turntables too. At the time I
worked with numeric controlled machines with optical positioning systems and found
that with a few modifications the principal worked extremely well. Positioning was
based on a beam of light, not falling on one photo cell, but falling exactly half-way
between pairs of photocells.
It also turned out that by using a printed circuit board under the table eliminated the
need for switches for the stall tracks as well as eliminating the need for pulling power
from a split ring rail to power the bridge track.
This system worked well for over 35 years with only two problems. Controlling the
motor for the final track alignment required the dedicated attention of the computer
at the expense of all other functions of the computer until the alignment was
complete. Also, The rubber drive wheel has dried out and decayed causing unreliable
operation.
A NEW, “IMPROVED” TABLE
The North River Railway has recently been going through a complete renovation to
improve and expand the control system, the turntables included. The new system will
contain turntables with a more detailed superstructure and will operate
independently of the main computer with a dedicated controller of their own.
A modern PIC device greatly simplifies the circuitry involved without interrupting
operation on the rest of the layout while hardware designed for robots will hopefully
provide more reliable operation.
PART LIST
SLIP RINGS PCB TEMPLATE
GENERIC BRIDGE CONTRUCTION
• Very little variations in general construction.
• All had some sort of central pivot, the bridge proper, a deck,
and usually some sort of end support.
• Dimensions varied to size and weight of locomotives
DECK PLAN FOR BRIDGE
• Ties are laid on top of the bridge, some or all of
which extend the entire width of the deck.
• The deck covers pretty much the entire bridge as it
must carry a lot of foot traffic around the
locomotive.
AN ALTERNATE DECK PLAN
BRIDGE SUPPORT
• Use a truck to support the bridge.
• A narrow gauge truck can be used
here with smaller wheels
• Remove wheels from one side of
truck
• Mount truck in usual way so it can
pivot and follow the ring rail
• “Hide” the truck behind the bridge
sides
MORE SIMPLE SUPPORT TRUCKS
Whatever is used to support the
bridge it must …
• Carry the full weight of the
bridge.
• Must roll freely on ring rail.
• Must flex enough to follow
the rail at all times.
• Need not make electrical
contact
AUTOMATING A TURNTABLE
(PART 3 - TECHNICAL)
Presented by BOB VAN CLEEF, MMR
of the North River Railway
SURFACE MOUNT TECHNOLOGY
• This new design will use SMT
chips
• Hand soldering of these chips is
difficult but not impossible.
• It is also possible to flow solder
these parts yourself.
• A third alternative is to use a
vendor to custom mount these
chips on an adapter.
ADAPTER FOR MOTOR CONTROLER
• This adapter is simply a small
circuit board.
• Pads on one side are patterned
to fit the specific IC you use.
• Note the holes along the sides.
• These particular adapter is for
a DIP configuration.
A TYPICAL SMT to DIP ADAPTER
• Proto Advantage is one
source for obtaining such
adapters
• They can also purchase
and assemble an adapter
for a small fee.
• This can be an economical
labor-saving approach that
can save time in the
development of a new
circuit.
A KIT FOR FLOW SOLDERING.
• Kits are also available for
mounting the part on the
adapter.
• This kit contains a sample
adapter and headers and
enough solder paste for
several assemblies.
• It also contains the steel
stencil used for applying the
soldering paste.
SOLDERING STENCIL
• The stencil is placed over
the pads for the IC.
• A squeegee is then used to
spread the paste evenly
over stencil.
• The IC is carefully placed
over the paste
• The whole thing is then
placed in a toaster oven.
MOUNTED COMPONENT
• Sockets for SMT parts are available but are also very
expensive.
• It can be more cost effective to pay a vender to mount the
part for you.
• The cost for ten of these mounted parts is less than a SMT
socket
VOLTAGE REGULATORS
5 and 12 volt Regulators
• These regulators are available in
the same TO-220 package as the
power transistors.
• Note that small capacitors are
placed as close as possible to
the regulators to filter out
voltage spikes that may cause
undependable operation.
• Also, the input voltage must be
at least 5 volts greater than the
specified output
TRANSISTERS
These two complementary
power transistors are
designed to be used in this
type of application
Any number of small signal
transistors can be used.
Beware that several
different pin configurations
exist.