Equatorial Platform Design and Drive

[Dennis G]

I’m seeking information for a proven equatorial platform design, a suitable stepper motor details and stepper driver circuit kit available in Aust on the internet.

A recommended platform design
Stepper motor, size and type
Stepper driver kit

[mswhin63]

Nothing in Australia, although I will be building them in the future maybe the only information is from Yahoo Groups EQ platforms.

[Fleegal]

Hi Dennis, how did u go

[Wavytone]

A NEMA 17 stepper is will give ample torque for this application. Better yet, they are available complete with a 23cm threaded rod and lead screw so the motor can provide a liner drive to push/pull an equatorial platform - see for example

https://www.robotgear.com.au/Product.aspx/Details/4234-Stepper-Motor-with-28cm-Lead-Screw-Bipolar-200-Steps-Rev-42-38mm-2-8V-1-7-A-Phase

The matching driver for this is https://www.robotgear.com.au/Product.aspx/Details/707-DRV8825-Stepper-Motor-Driver-Carrier-High-Current-V2 or https://www.robotgear.com.au/Product.aspx/Details/5671-MP6500-Stepper-Motor-Driver-Carrier-Potentiometer-Current-Control

Assuming you will have a nominal 12-15VDC power supply, use resistors in series with the windings to reduce the current to within the motor specs (600mA per phase), or use the MP6500 configured with resistors to control the motor current.

A simple circuit to drive this can be constructed with a couple of chips (7555 and a stepping motor driver to match the motor) and a handful of passive components from Jaycar - you probably won’t find a kit per-se. A few additional things you will need are:

- a push button to rapidly rewind the lead screw back to the start to reset the platform after it reaches its limit;
- potentiometer to provide a modicum of speed adjustment, say +/- 10%
- limit switches to stop the motor when the platform reaches the end of travel in either direction.

If you can say what effective rotational radius of the platform will be, the required step speed can be calculated. The rotational radius of the platform is a function of the length between the pivot and the lead screw, and your latitude.

[Fleegal]

Hi Dennis
I just built a equatorial platform for my 16"dobsonian. Mine is steel framed, on wheels and runs a windscreen wiper motor driven allthread rod, controlled with a $12 pwm controller. Works magnificently and tracks for about 75 minutes before auto rewinding.

If you are interested I can give you some more information on what I made, it's the best modification I've done to the scope. Good luck

[Fleegal]

Woops, old thread lol