André Heijkoop’s equatorial platform


I based my design for my platform mainly on Warren Peter’s design. I want to thank him for getting me started and for his excellent excel spreadsheet in which you can calculate the dimensions of the platform.

The platform I made is for a 14” f6 truss Dobson telescope. With my truss Dobson on my equatorial platform I can track the planets or other objects in the sky for 45 minutes.


Main dimensions 

The main dimensions (in cm and degrees) for my platform are:


Telescope’s Central Gravity



Length of Baseboard



Width of platform






Rotation angle






The materials used:

·        18mm plywood

·        40x90 mm meranti wood

·        30x2 mm aluminum

·        Inline skate wheels ø 72mm, hardness Durometer 82A and ABEC 3 bearings

·        Hurst stepper motor AS3004-001SP2702

·        Unipolar stepper motor driver CK1404 from Carl's Electronics Inc.

·        Ø22mm Nylon stepper motor drive wheel


Sketches of the platform

Main sketch

Dimensions in cm

Click on the picture for a full size version.


Radius North Bearing



Radius South Bearing



Height Baseboard




I used John Reagans idea of the axial south bearing conversion of Warren Peters design. This way you have only one bearing at the center of the South bearing radius (1.97cm above the Baseboard).


Rnb drawing

To avoid making mistakes I made very detailed sketches of the North and South bearing sectors, dimensions in mm.

Click on the picture for a full size version.




Rsb drawing

Click on the picture for a full size version.



The woodwork

The North bearing supports



Constructing the North bearing sector


To make a good radius on the North bearing sector I made a simple wooden tool, I attached it with 2 bolts on the ground plate of the router. I made 2 of these sectors and glued them together to get a sector of 36mm thickness.


Assembly of the North sector


For a perfect bearing surface I used 30x2mm aluminum.


 Assembly of the South sector



South bearing 


I also used an inline skate wheel for the South bearing.



The direct drive

The Hurst stepper motor


I attached an ø22mm nylon wheel on the Hurst AS3004 stepper motor axis.

The nylon wheel drives an inline skate wheel at the north sector; the inline skate wheel drives the platform. With this set up the stepper motor makes an approximately 19 steps per second.

I attached a spring to get a quick release of the drive wheel during Polar alignment. The spring is also useful for a fast rewind.



The inline skate wheel drive 



The little black box I replaced with a bigger blue box with all the electronics in it.



Blue box


The electronics to drive the Hurst stepper motor is mounted in the blue box.

On the foreground you see the Optimate III to charge the 12V 5Ah battery.



10 revolutions linear pot with digital readout


On top of the blue box you can see the end switch, which cuts of the power when the platform is at its end of his travel.

On the front plate of the blue box is a 10 revolutions linear pot with digital readout mounted, next to the linear pot you see the main on/off switch.


Inside the blue box


Inside the blue box you see;

·        on the left the 12V 5Ah gel battery,

·        in the mid a fuse box,

·        on the right the 10 revolutions linear pot,

·        above the linear pot the main switch,

·        at the bottom the unipolar stepper motor driver CK1404,



1)      I replaced the standard logarithmic1M pot of the CK1404 kit with a 47K resistor and a 100K linear pot.
With the logarithmic 1M pot it is very difficult to get the speed right. The 47K resistor gives the hurst motor a basic speed which I can easily fine tune with the 10 revolutions 100K linear pot.

2)      As you can see in the pictures I mounted all the electronics in one blue box, pros and cons:

a)      Pros
No loose controller boxes on long cables.

b)      Cons
Sometimes I have to get out of my observing chair to make small adjustments to the speed.





My pride and joy (finished)

The equatorial platform completed


The complete setup


Handle bars and wheels

Above you see the pictures of my homemade handle bars and wheels for my equatorial platform.
I leave the handle bars almost always attached to the equatorial platform; they are on the north side of the platform so in the field hardly ever in the way.
The wheels are attached in no time. I just lift the south side of the platform and roll them underneath. I let the aluminium U-profile underneath the platform rest on the threaded rod between the wheels, gravity does the rest.



Polar alignment

I made in Visio an instruction for an easy polar alignment. This instruction works for a Telrad or RACI finder. Just watch Polaris shift in your finder and turn or lift your platform according the pictogram.





·        Jan van Gastel; it was his website that get me hooked and started.

·        The eqplatforms group for the advice and taking away my doubts.

·        Warren Peters design and spreadsheet.

·        John Reagen for his axial south bearing conversion of Warren Peters design and spreadsheet

·        Leo van den Heuvel for soldering the stepper motor driver kit.

·        And all others who contributed.




Thanks for reading,


André Heijkoop



51º 44’ 26" N

04º 33’ 23" E