MASTWERKS Rotor with Position Feedback



RotorIntro
Stepper Rotor with controller

Introduction

KI6AWR:

In the Buddipole Users Group, David, KI6AWR presented a simple, yet very efficient rotor with a 12V DC-Motor. It is controlled by a DPDT Reverse Polarity Rocker Switch and a two wire connection between the switch and the rotor. The rotor simply replaces the crank handle at the MASTWERKS tripod hub. There is no position sensing, so the antenna has to be in view, because it is all too easy to keep rotating in the same direction and wind the coax around the mast. (See BUG post #44781, DIY Mastwerks Rotator)

HB9MTN:

I wanted a feedback of the position of my BuddiHEX on top of my MASTWERKS-Mast! The idea came up to use a stepper motor instead of a DC motor and counting the steps forth and back from a given antenna position. Unlike with an electronic compass or a potentiometer there is no absolute antenna position indication.

Calibration of the controller is easy: rotate the Buddihex to north and cycle the power to the controller. Power on resets the software and the LED at N lights up green as an indication. Then the antenna can be rotated 337.5° (360°- 22.5°) on either side in steps of 22.5°.


The Stepper Rotor


CompactRotor


Stepper Case Parts
This Rotor is extremely compact and simple, three 3-D printed parts in addition to the Stepper Motor.


Any NEMA 17 Bipolar Stepper Motor can be used. I had  a 42 x 42 x 36mm  in my junkbox, a dimension that is no longer available. 42 x 42 x 34mm or 42 x 42 x 40mm  with a Holding Torque of about 0.4 N.m. and a resolution of 1.8°/step are fine.
The gear in the MASTWERKS Hub has a reduction of around 55:1. There is no force at the stepper axis when the rotor stops, so the power to the stepper can be switched off between the movements.


HubOpen
Reduction gear about 55:1 in MASTWERKS Hub

The Controller

The controller is set up around a Arduino with Big Easy Driver. 

http://www.schmalzhaus.com/BigEasyDriver
http://schmalzhaus.com/BigEasyDriver/BigEasyDriver_UserManal.pdf  
http://www.schmalzhaus.com/EasyDriver/Examples/EasyDriverExamples.html

With the BigEasyDriver, the stepper motor is only active when a button is pressed, so there is only the power consumption of the Arduino (40mA).


There are two pushbuttons, [CCW] and [CW] and for the azimuth feedback a Neopixel 16 LED ring.


ControllerSchematics

A button press on [CCW] or [CW] makes the rotor move 22.5 degrees either ccw or cw.

I will allow a rotation of 360° minus 22.5°, 15 steps on each side from N. A short press on the [CW] button wil move the Rotor 22.5° clockwise and then stop. The first LED cw from N goes ON. Continuously pressing the [CW] button keeps the Rotor moving  and the LED's indicate the movement in 22.5° steps. After a movement of 270° cw from N over E and S to W, the Rotor is moving out of the "safe sector". It can still be moved further on to N - 1  step, but the LED color turns from blue to bright red.  The last allowed position 22.5°, one LED left and right of N, gives a clear indication in what direction the rotor has to be be moved to get in the safe sector. From here on further cw movement is blocked.
And vice versa.

Have a look at this short video: https://youtu.be/9pHU1JZAdzU


The hardware is extremely simple:

 

On the rotor side
  • 1 NEMA 17 42x42x34 or 42x42x40 Stepper Motor
  • 1 Adapter like the one David is using for his DC-Rotor, modified for the stepper motor

 

On the controller side
  • 1 Arduino NANO or UNO
  • 1 Big Easy Driver
  • 1 NEOPIXEL 16 LED Ring
  • 2 Push Buttons

 

Rotor and controller are connected with a 4 core cable

 

Power supply
  • 12 to15 V DC for the rotor, same as for TRX
  • 5 V DC for the Arduino

 

all available from the PowerMini, but I am using a positive voltage regulator xx7805 1.5A to power the Arduino (Vin) from the 12 V line.

 

Simple pin to pin wiring between the components:
  • 5 wires between Arduino and face plate with LED ring and buttons
  • 6 wires between Arduino and Big Easy Driver
  • 4 wires between Big Easy Driver and rotor
  • 12V to Big Easy Driver
  • 5V to Arduino

 
SimpleWiring
Simple wiring

The wiring is clearly documented in my Arduino Sketch.
For more information about the <Adafruit_NeoPixel.h>  library see: https://github.com/adafruit/Adafruit_NeoPixel


The controller case


Case1
Controller Case


I made a 3-D printed case for my controller, a remix of the (tr)uSDX case.

Case0.
Case, (tr)uSDX style

Case2
Inside viev

Case3
Side view, showing position of the breadboard

Case4.
Bottom view


Unfortunately, all the Neopixle Rings have (slightltly) different dimensions, the same applies to the push buttons and other parts you find in your junk box. So the STL-Files might not fit your parts and you might have to remix the STL's.

Here you can download the STL.Files of the Case

If you are familiar with OpenScad, pse. contact me for the SCAD.Files.


1st Results of Field Test

There is not much to tell. The setup was working as expected. After 2 1/2 hours of operating the stepper rotor did not loose one step!
The resolution of 22.5° is absolutely sufficient.

This video shows the movement of the rotor: https://youtu.be/-c7IjqDggso

The No-Loose-Adapter


N-L-A

N-L-A-2N-L-A-1
The No-Loose-Adapter fills the gap between the hub and the Rotor


The No-Loose-Adapter is a gadget I have been using almost since I got my first MASTWERKS mast five years ago. I did not like the loose feeling of the crank handle so I made a 3D-prited part to fill the gap between the hub and the crank handle. I have my No-Loose-Adapter permanently attached to the hub. It is mandatory for a firm fit of the rotor.

Here you can download the STL-File.




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