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Friday, November 08, 2013

Building your own Antenna Rotator..DIY Antenna Rotator Part 2

Motor

Selecting what type of motor to be used in your diy rotator is also important apart from the mechanical gearing structure. Although your gearing structure may have sufficient torque to rotate the antenna and mast, the motor that is used to turn the input gear/shaft must have enough power/torque in order to translate the capability of the rotator assembly.

Besides the torque, you also may consider the speed (rpm), voltage and also current required by the motor to operate. I have initially thought of using automotive wiper motor or power window motor earlier just like other home made rotator. However, I ditched the idea of using those motor because of their high current requirement. Please do remember that you rotator is away from your shack and the control cable need to be longer. If the motor need a high current, you may have to run a larger gauge of control cables in which not to my liking.

Therefore, I decided to use a small motor # SPG-50-60K that I bought online from Cytron. The motor specifications is DC12V/0.9A/588mN.m/56RPM


With this motor, I don't have to run a heavy gauge control cable from the controller to the rotator.

To couple the motor to the rotator gear structure, you need to select and calculate a required gear ratio to translate the combination so the antenna rotation is not too fast or too slow.. I decided to go for 1 rpm so the antenna will take about 60 seconds to complete a full rotation.

In a commercial rotator such as Yaesu G250/450, the motor used is AC and is has 3 lead so the motor can rotate CW or CCW depending on which lead is used. The motor that I am using has on 2 leads. In order to make it rotate CW or CCW, you have to use either H-bridge or mechanical switching method to reverse the applied voltage at the motor terminal.

I choose mechanical switching method since it's only a low current and I want to use minimum parts count in my controller.

If you choose to use mechanical switch method.. you can refer to the diagram below or read about it here.

The schematic above already had the limit switch included so it will prevent the rotator from overlapping. The limit switch must be install at the output of the rotator assembly, not at the motor output. This is because the output is your concern. You can adjust what is your overlapping allowance too.

Part 3 will be talking about how to know the position of the rotator... to be continued..










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