Sky-Watcher NEQ5 + DIY AstroEQ GOTO

If you plan on upgrading your manual German Equatorial Mount with a GOTO system, then hopefully the information contained here will give you some insight.

Should you have any questions feel free to visit Astrobiscuit’s Discord Server and to post your questions there.

I chose AstroEQ (https://www.astroeq.co.uk) as a DIY GOTO upgrade, because

  1. It is easy to build up with already existing hardware vs other DIY GOTOs, which require you to have custom PCBs. In this case, all we need is an Arduino Mega.
  2. The drivers of EQMOD can be used 1:1 without any change.
    This is valid for both Windows and Linux/Astroberry computers.
  3. I don’t have to do any coding. All I need to do is key in all the necessary ratios and the components I used.
Other DIY projects, of which I know of, are:
OnStephttps://github.com/hjd1964/OnStep
rDUINO Scopehttp://www.rduinoscope.tk/
The DIY Arduino Telescope GOTO control projecthttp://astro.neutral.org/arduino/arduino-telescope-control.shtml

Should you know of any more, please reach me (@ Astrokonsti) on Astrobiscuit’s Discord Server.

Shopping List for an upgrade of an NEQ5 to goto with AstroEQ

ca. price per piece
used NEQ5 mount
Arduino Mega or clone: ELEGOO 15 EUR
2xStepper Motor NEMA 17 1.8° (200 Steps per turn), better 0.9° (400 Steps per turn)20 EUR
2xTMC 2209 Stepper Motor Drivers8 EUR
2x16 tooth pulley GT2 size, connected to output shaft of stepper motors5 EUR
2x60 tooth pulley GT2 size, connected to input shaft of RA / DEC axis8 EUR
2x152 mm GT2 timing belt3 EUR
4xNEMA 17 Brackets2.5 EUR
1xAcryllic fresh box for dew protection5 EUR
1xVariable Power Supply Unit, DC 9V-24V, 72W28 EUR
Cables, screws, nuts, bolts, plates30 EUR
Total 176 EUR

Settings for the AstroEQ in the above configuration

Resolution with 200 Steps per turn:

200 steps/turn * 32 microsteps/step * (60 teeth/turn / 16 teeth/turn =) 3.75 * 144 turn/axisturn
= 3456000 microstep/axisturn

1 axisturn = 360°/axisturn & 60 arcmin/axisturn & 60 arcsec/armin
-> 1296000 arcsec/axisturn

3456000 microsteps / 1296000 arcsec = 2.66 microsteps/arcsec

1 microstep = 0.375 arcsec


Firmware Configuration Settings inside AstroEQ (V8.20)

The Configuration Tool for AstroEQ can be downloaded here: https://www.astroeq.co.uk/downloads.php. It isn’t necessary to download the Arduino IDE, since the configuration tool has everything already baked in and walks you through with each step. Just make sure you have the right COM port selected as well as the right board, which is the ASTROEQ ARDUINO MEGA 2560.

ST4 Rate (x Sidereal)0.25
Advanced HC DetectDisableduStep Gear ChangingDisabled
GPIO01 Drive TypePush-Pull
Motor Driver IC Type:DRV8825x *Motor Microstep Level32 uStep *
Right Ascension AxisForward **Declination AxisForward **
Motor Step Angle (°)1.8 ***Motor Step Angle (°) 1.8 ***
Motor Gear Ratio (:1)3.75 ***Motor Gear Ratio (:1) 3.75 ***
Worm Gear Ratio (:1)144 ***Worm Gear Ratio (:1) 144 ***
Goto Rate (x Sidereal)378Goto Rate (x Sidereal) 378

After inputting the settings, hit Update on both RA and DEC axis and click on Done.

* Workaround for using a TMC2209, unsupported by the firmware:

We would like to have the smoothness of a TMC2209, but it’s not listed as a possible driver in the drop down menu. We would also like to use a high microstepping resolution. So after some systematic research, we found in a joint community session, that the DRV8825 and TMC2209 share the same microstepping settings and achieve the same microstepping resolution. Therefore the firmware thinks it’s talking to a DRV8825 and speaks the setting to it, which incidently is understood in the same way by the TMC2209.

Not having this in order means
that either the GOTO functionality will overshoot/not reach it’s target,
and/or
the tracking will be too slow
and/or
the stepper motors will stutter violently that it actually makes the entire Community Rig crawl on the floor.

** Forward/Backward Stepper Motor Polarity Connections

Depending on how you phyiscally connect your motors to the mount and in what order you connect the motor cables to the driver, you will need to see if you have to choose forward or backward individually for each axis.

*** Explanation of how to calculate each setting
Motor Step Angle (°)

Each stepper motor resolves a full tun in a number of steps. In this case, we have 200 steps per full turn. This means we get 200steps/360° = 1.8° per step.

Motor Gear Ratio (:1)
On the right side is the small pulley with 16 teeth, which is driving the 60 teeth pulley via the 154mm timing belt.

The stepper motor output shaft and the worm axel input shaft a connected with a pulley timing belt drive system.

While the pulley and belt drives provide a virtually backlash free movement, it also gives the oppotunity to create a hight resoltion with a ratio created by differently sized pulley.

In this case we have 16 teeth on the output pulley and 60 teeth on the input pulley, which gives us a motor gear ratio of 60teeth/16teeth = 3.75. This means, the resolution get’s multiplied by 3.75 times.

Worm Gear Ratio (:1)

The last power and motion transmission is the worm gear to axis spur gear system.

The worm gear needs to turn 144 times until the axis connected to the spur gear has turned one single revolution.

144 wormturns/1 spurturns
= 144 wormturns/spurturns


Wiring the Arduino Mega and the Steppers

The following image is taken from the tutorial site of AstroEQ. It shows the DRV8825 drivers wiring, which can be used analogue to the TMC2209 drivers. All light green marked connections have been wired.

Wiring diagramme source: https://www.astroeq.co.uk/tutorials.php?link=buildown#building_an_astroeq_with_an_arduino_mega, see Arduino Mega Schematic PDF
An Arduino Mega clone with two TMC2209 drivers and all connections made as marked in the schematic above.