Automating a Honey Extractor

This is a Honey extractor.  It is used to fling the honey out of the honeycombs you put in there. There is one Knob to set the speed and a three way switch to make it spin left or right op to stop it.

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A typical sequence of operation would be like.:

-Put the honeycombs into the mashine
-set speed to 30%, spin 60 seconds to the left and then stop
-wait untill the mashine has fully stopped.
-set speed to 60%, spin 90 second to the right and then stop.
-wait untill…
…a full sequence goes for about 10 minutes.

Depending on the number and the motivation of the bees, this can be a hole-day-job. A friend of mine is beekeeper and asked me to automate his mashine so it can be programmed and execute the process by itself. He said that he could buy an automatic one, but theese really aren’t cheap. So I did it for a little less:)
This is what the controller-box-inside initially looked liked. The front panel is on the left, there you can see the switch and the potentiometer of the knob, in between is a led indicating operation.

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So, how to automate this two input controls? To me, there were to approaches I had to choose from. The firs one, the electronical one, would have involved a digital potentiometer to replace the analog one, and some transistors to mimic the switch. I didn’t like the idea of breaking into the circuit of an expensive device wich is also connected to main power. I also only had access to the controller box, not the hole mashine so I couldn’t test it while prototyping. This led me to the idea of controlling the device in a pure elekto-mechanical way:

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This is the concept of operation I came up with:
There are two Main modes you can select from by the mode switch (9): “Manual” and “Auto”. In manual mode, the controller behaves like it was before. The Auto mode has two sub modes: “record” and “play” wich can be chosen by the rec/play-switch(8). To record a sequence you select Auto and record and then doing a full sequence manually. By changing the state of either the two switches, the sequence will be saved in the eeprom of the arduino and can be played back any time.

Here is a quick describtion what components I’ve used and how they work together:
The power supply (1) is connected to the main Ac input. This way the main circuit is isolated from my addon circuit and behaves just like both would be connected to a plug board. I don’t recommend to try to get the power from the supply of the hacked device unless you exactly know what youre doing. The output from the power supply goes into a dc-converter (2) and is transformed to 5 volts to power all components. If I’d had a proper five volt adaptor, I’d used this instead). The whole addon is controlled by an Arduino Nano. They’re cheap, small, versatile and easy to use – I just love them. The original potentiometer(4) and a servo motor are mounted on a 3d-printed gearbox are connected via the gears. The ratio of the gears (26 and 18 teeth) correspond to the travel range of the pot (260°) and the servo(180°). The knob on the frontpanel is directly connected to the servo shaft and the bigger gear via a M8 bolt which is supported by a bearing. The servo can be switched on and of by a mosfet(6). If it would be constantly powered on, the knob would be locked by the servo, keeping the postition it is currently set to. To measure the position of the servo when recording a sequence, I have used the output of the potentiometer inside the servo (every servo needs a pot to know were it is). This is connected to an analog input of the arduino. The start/direction-switch is now connected to two digital input pins on the arduino and two relais (10) take it’s original place. Other than transistors, the switching part of a relais is isolated to the control part. Technically they act exactly like switches.

If you attempt to make a similar project, maybe theese design files will be helpful:
https://github.com/fpiesik/automator

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