Turtle Point  Controller


Cost: au$25.00 plus postage
Kits are available



This project controls a set of points with a SERVO.
A SERVO is a motor and gearbox with an output that rotates up to 270 degrees.
By adding an arm (or crank) to the output, we can get linear motion to change a set of points.
It does not operate Peco solenoid points or Tortoise Controllers. It only controls an R/C Servo.

                         TURTLE POINT CONTROLLER 

n Operates points using a SERVO.     
n On-board LEDs indicate "ahead" or "siding"

These features are contained in our simple design and can be built in an evening.  A kit of components is available from Talking Electronics as well as a pre-programmed microcontroller.


Comparison of the TORTOISE™ Slow Motion Switch Machine with BluePoint.
We've had a number of people ask about the price of a TORTOISE™ Slow Motion Switch Machine compared with Blue Points™, so here is a quick comparison. The BluePoint is smaller, cheaper and has a better tag board for connecting the wires.

Size comparison: Tortoise and BluePoint

Comparison of prices for converting from manual to automatic:

  - slow activating Point Motor  $20.00
Blue Point - slow activating Point Motor  $13.00
R/C Servo Point Motor  - free with Turtle Point Controller project.

You will also need
Turtle Point Controller project - $25.00 (comes with ALL components, PCB and miniature R/C servo).

Turtle Point Controller project suits either a LINEAR ACTUATOR or R/C SERVO. Both devices move proportionally to the signal received via the signal line. Both have an IC that receives the signal and produces a pulse to the motor to turn it either clockwise or anticlockwise and compares a signal received from a pot or linear resistor to determine the angular or linear position of the arm.  It does not work with TORTOISE  or Blue Point™ controllers.

There are a number of beautifully-designed LINEAR ACTUATORS on eBay and one design accepts commands identical to R/C SERVOS, but they cost twice as much as a servo.

This Linear Actuator is just a micro motor and pot.
It does not have any proportional-control circuitry
and cannot be used in this project.


This Linear Actuator is available from Waltzmart.com for $11.00 with free shipping. You get 2 Linear Actuators for $11.00

This tiny linear actuator can replace an R/C servo
as it has a chip on the underside that accepts PWM signals
and will operate the points slowly - the same as
a "Tortoise Controller."

A Remote Control SERVO is the cheapest way to control a set of points.
This project operates the servo slowly to get the effect of a TORTOISE CONTROLLER with the advantage of placing the servo next to the track so you  don't have to cut a hole in the layout or any other awkward installation. It is also much cheaper than any other controller.

This is one of the servo's we tested. We call it MEDIUM SIZE. The LARGE servos are too big for this application.



Here is the SMALL SERVO. It uses a micro motor. A Micro Motor is designed "INSIDE-OUT."
The armature is wound on a former and the turns are GLUED TOGETHER with sealer.
The former is then removed and the armature is mounted over a strong magnet that has a North and South pole, with the North on top and South on the bottom. There are 3 sets of windings, just like a 3-pole motor and the ends are terminated at 3 copper plates called a commentator. This commutator can surround the shaft or be located at then end of the winding. Two brushes touch the commutator segments to deliver current to the windings.
A coreless motor can produce twice the torque of a conventional motor because the armature does not have any iron. The iron absorbs magnetic flux and gets hot.
The armature is also further away from the centre of rotation and this produces more torque for the applied current. 
Micro Motors are also known as PAGER MOTORS, where the come with a weight connected to one side of the shaft. When the shaft rotates, the motor vibrates in a mobile phone.
This type of motor can be produced with a very small diameter and a short lenght and this allows a SMALL servo to be produced.

"Cut-Away" view of an expensive servo with metal gears.
The all-plastic versions are much cheaper and have
a very similar compound gearbox to reduce the
motor RPM and increase the torque.

The commutator and brushes can clearly be seen in this photo.
A Micro Motor operates just like a 3-pole motor.
The winding is "skewed" (twisted) to produce
smooth rotational torque.

An "Exploded View" of a brushless motor

The servo in the kit is the MEDIUM SIZE  and comes with a set of HORNS. These are commonly called CRANKS or ARMS or LEVERS and connect to the output shaft with a splined connection (grooved) to prevent the arm slipping on the shaft. Some come with a screw to hold the arm in place.
Make sure you get a SERVO with a bag of horns.

Servo Arms or "Horns"
Single Horn or Arm
Star or Cross
Double Horn or Arm

The secret to making the servo operate slowly is a program in the micro. It creates a "MARK" (the length of time the control-line is HIGH) that tells the servo to advance (rotate) the output shaft a few degrees. The program then creates a Mark to advance the shaft a few more degrees.
This produces a slow, jerky movement, of the output. Each value is outputted a number of times and this creates the slow motion.   You can use an R/C servo or Linear Actuator.  

Connecting a servo to a set of points is very easy by using an arm and a push-rod (pull-rod).
The arm and rod turn the rotary motion of the servo into linear motion and the distance traveled by the rod is the greatest when the output of the servo rotates 180°.
 The distance is called the "THROW" and a number of holes on the arm (also called the "CRANK") selects the throw to suit the distance needed for the points.
The arm and rod is called the "LINKAGE" and this needs to be designed so that the rail sits with a small amount of pressure to keep it in place.

Using a "Star" or "Cross" to produce a linkage to operate the points with the servo near the track:

Using a "STAR"  in the linkage to connect to the rails.
It produces a 90° activation.

The project is designed to produce about 90 degrees of rotation for the servo. This produces enough "throw" to move the rails. 

Here is a photo of the components in a servo from HOW AN R/C SERVO WORKS:

A Block Diagram of the electronics:

Arm positions for PULSE WIDTHS from 500uSecs to 2500uSecs

Most servos will rotate up to 180° and some will rotate to nearly 270°. Our project only needs about 45 degrees rotation to produce a THROW of about 10-12mm when a push-rod is connected to a hole near the axle. The track-points for HO gauge only need 8mm throw and this can be obtained very easily by connecting to a crank on the output of a servo.  

Servos come with different colours on the 3-pin connector:





Turtle Point

Parts List

Cost: au
$25.00 plus postage
Kits are available

1  -  180R
2  -  220R
2  -  22k

1  -  100n SM capacitor
1  -  100u electrolytic

1  -  1N4004 diode
1  -  LM78L05 voltage regulator
1  -  3mm red LED
1  -  3mm green LED
2  -  IR emitter LEDs
2  -  IR receiver transistors

1  -  PIC12F629 chip (with routine)
1  -  8 pin IC socket 
1  -  2m fine screened lead (for testing)
3  -  20cm hookup wire (for testing)
3  -  2-way terminal blocks
1  -  20cm very fine solder 
2  -  Surface Mount PC boards (for train 
         detector pair)
1  -  miniature SERVO
1  -  Turtle Point Controller PCB