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 Output of cells and motor speed as light source passes. 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.
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)
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 mid- program
CONFIGURING THE PIC 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. This project makes use of the (3) comparators contained within this device.
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
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 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. Note the extra circuit to turn the light source on and off.
5 and 8 volt POWER SUPPLY A simple power supply The turntable runs from a 16v DC wall transformer. Two common voltage regulators provide the required voltages
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/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/http://www.micromark.com/ Source for small tools and materials useful for modeling. Custom Computer Services (CCS) http://www.ccsinfo.com http://www.ccsinfo.com C and several other higher level languages for PIC devices Microchip http://www.microchip.comhttp://www.microchip.com Manufacturer of PIC devices and several programming accessories Proto-Advantage - http://www.proto-advantage.comhttp://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.
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 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. Drive belt made from heat- shrink tubing used to turn drive disk
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.
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.
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 Any number of small signal transistors can be used. Beware that several different pin configurations exist. These two complementary power transistors are designed to be used in this type of application