Pypilot working on my Nicholson 44

[xfactor99]

   //digitalWrite(clutch_pin, LOW);
     analogWrite(clutch_pin, 254);
Could you sailor brothers and sisters share your thoughts on this?

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Hi Kris, 

great to hear that you also kept your "old" Neco and drive it through the Pypilot software from Sean.

I also have been thinking in using PWM for the clutch. But at the end I did not, as I dont understand realy what is necessary.  I also drive the series coil through the clutch and I would have to make here changes as well. I already bought a rectifier diode unit for this porpouse and I might start with this.

I guess you need a 100% PWM for a short time to engage the clutch and then mayby 50% to hold it.  I think one has to consider at this point the state of the battery while sailing so it would be a difference if your battary full is at 14V/28V or low 12v/24V so the PWM should be set high to hold the clutch in any state or change the PWM depending on battery state.

So there are some changes to make to motor.ino (or servo.py ??).

If you make any progress on this please let me know.

Save sailing
Andreas

Hello Andreas!

The old Neco units are indestructible and very dependable pieces of equipment for sure! They are very well engineered for the solutions available then and with a little tinkering can be adapted to the Pypilot. Back then I guess permanent magnets were weaker, so having coils build up the static magnetic field had volume and mass advantages over permanent magnet motors.

I am a bit confused by your description. The drive unit has 4 coils, 3 of which are inside the motor. The main coil that is on the rotor shaft is driven through the armature. The series coil and the shunt coil are in the stator. The clutch coil is inside the gearbox.

The easiest option is to drive the series coil in series with your main coil (armature) as per the original setup. So hook your battery positive to the series coil positive, the series coil negative to the positive battery terminal of your motor controller, the negative battery terminal of the motor controller to the battery negative, and finally the motor terminals of the motor controller to the armature. The shunt coil is a very small coil that is only inside of the motor to generate a small magnetic field to start the motor. (It also modifies the motor characteristics a bit.) The easiest method is to drive this coil together with the clutch coil from the clutch pin of the Arduino through a transistor, like Sean's original plans suggest. I believe that your setup is done this way, we just refer to the coils with different terminology. Can you confirm this?

I do not recommend driving the shunt coil with PWM. The shunt coil takes little power. It is best to switch the shunt coil to full power when even a tiny motor movement is needed. I tried driving it by PWM, but it made the motor very very sluggish.

To save power, I installed a second transistor. The gate is connected to both low side pins through diodes and a resistor. The corresponding low side pin come on just before every motor movement. This is the ideal way in my opinion to drive the shunt. Of course rewriting the code and having a dedicated shunt pin would be a more elegant way of solving the problem, but then I would have to touch up Sean's code every time he updates it.

You are right about "you need a 100% PWM for a short time to engage the clutch and then mayby 50% to hold it". Maybe 25-33% is enough as well. In my opinion the battery voltage drop can be neglected though. Just set the lower PWM value to what is needed in case of lower battery voltage, and that's it. It does not make that big of a change.

I did not find a working solution to the problem:
   //digitalWrite(clutch_pin, LOW);
     analogWrite(clutch_pin, 254);

If ever I get so lucky that someone who gets Sean's code gives me a hand with this, that would be a perfect Christmas gift

Everyone be safe!

Kris

Hi Kris,

you were right I mismach the terminology, it is already some time ago that I was into this.

I guess it is the shunt coil witch I drive through the clutch.

Ther was no Neco electronic left in my drive, just to automotive relays when the Simrad/Robertson AP died ..., the previous owner must have had modyfied the drive before.

Here a basic scrach how it is wired now, except that I´v changed the relay with an SSR-Mosfet later and added end of travel swiches directly to the Pololu dirve.


  Scratch.pdf (Size: 538.33 KB / Downloads: 260)

Save sailing and merry christmas
Andreas