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Potentiometer to control Linear Actuator, auxiliary motor
I am attempting to link 2 different motors (size, hp, make etc) together, so they steer together.
I would typically just tie them together with an auxiliary motor tie bar but in this case that is not easily possible.

The main engine is controlled by pypilot, and is physically moved using an electric hydraulic pump.

So I got to thinking about using a potentiometer on the main motor as a motion/position sensor, linked to a linear actuator (with optical feedback) on the auxilary motor. I want to link them together using an Arduino or esp32...
As I dig into this I am realizing maybe I am over simplifying the project. 
I am pretty sure I will need to know the position of each motor, so feed back is required. But how do I keep them sync'd? It would be impossible for them to move perfectly together as one is much larger than the other, so I am afraid they will get out of sync?
Any ideas how I could achieve this. 
Basically I think need to send instructions to move to a position rather than moving for x seconds in a direction.

Kind Regards
the absolute pilot works on absolution positions requiring a rudder feedback, but i'm not sure this is what you want.

It seems strange that one is much larger than the other. In any case, you could possibly just fix the smaller one to not turn at all, or have a completely separate electric control loop that measures the angle of one and moves the other to this angle. Even then, play or slop in the system will degrade it.

Could you use blocks and pulleys instead of a tie bar?
Thanks Sean

Absolute pilot would not work as I would still need to sync the position of both motors

One motor is much larger 200hp vs 15hp one is my main the other is auxiliary (trolling motor) The main has built in hydraulic assist steering so no easy way to connect to it with a tie bar or really anything, the auxiliary is mounted further back, and they do not align vertically. So a modified single steering cable might work but expensive in parts and still would require custom linkage.
Blocks and pulley will not align and consideration has to be given to tilt and trim.

I have been using the auxiliary under power fixed and using the main to steer, this works well up until the conditions get to windy and wavy.
I have even steered with the auxiliary and left the main fixed and this works too but has the same limitation.
All the research I have done says both engines turning together is by far a superior set up.

The completely separate electric control loop is exactly what I was thinking. And it doesn't have to be exact, but slop is a concern if it degrades over a matter of minutes... over a matter of hours would be okay.

This is the actuator I am considering
it is very accurate as it has an optical position sensor.

The speed and position can be controlled very accurately. I could build linkage with minimizing sloop as a priority.
As an educated guess, how quickly do you think the motors would lose alignment?
Hi Peter,

theese aktuators are also sold with a build in potentiometer as position feedback. IMHO is this better than counting the pulses from the optical feedback. You have to count the pulses and have to know the moving direction of the actuator. With a potentiometer for each motor you just have to use two of the analog inputs of your microcontroller and then just compare them (the one from the main and the one from the aux. motor) and then generate a corresponding control signal.
You have to set a dead band and may be an easy filter for eliminating interferences.

Kind Regards

I didn’t realize the difficulty I was introducing with the optical feedback. Honestly this is the only Ip66 rated actuator with feedback I have found that moves fast enough to be used for steering.
I’ll keep looking
Here is an example of what I would like to do

but instead of a linear potentiometer I would use a rudder feedback sensor like this

Here is a schematic and Arduino sketch for the optical potentiometer, I see now why this is not ideal as the actuator would have to be fully extended or retracted to find the starting position.

I need the starting position to be known without having to find a limit, measuring voltage resistance seems to be the best option.
I can only find IP54 rated actuators with feedback that are fast enough, has anyone used an IP54 rated actuator in the wild?
It is only fresh water, and it would never be submerged, just splashing from waves and rain, but it would be in the elements 24/7.

Thanks for any advice offered

the often used tillerpilots from Raymarine or Simrad like the ST2000 from Raymarine are not more than IP54 or 55. You can´t submerge them without destroying them.

For my new pypilot I bought a linearaktuator from pcnautic. It comes with a better cable entry and better seals then the normal china aktuators. PCNautic does not say anything about the IP-Class but I think it´s also not more than IP54/55. I can´t submerge (and I will not do so  Smile) the actuator without destroying it.

So why not using a cover bag to protect the actuator.
For my old tillerpilot I just use a plastic bag to protect the tillerpilot against rain or salt water spray.

For the new one I try to tailor a cover made of pvc fabric or similar.

Best regards

Well, its not pretty but here is my proof of concept. 
Now I need to figure out how to mount it on the boat and add some start up and shut down rules... maybe an on-off switch.

Can anyone advise me on if I can connect the linear potentiometer to two devices? Say by simply creating a splice, one set of wires could go to my Motor Controller for rudder feed back and the other set would go to the Arduino that is controlling the linear actuator? Is there any danger of degrading the signal, maybe I need to isolate one device from the other?

Or... is it possible to send the data to signalk and have both devices use the data, does tinypilot look to the nmea network or signalk data for installed rudder feedback or is it required this it is attached directly to the motor controller?
it can receive rudder feedback from nmea or signalk (untested) but the motor controller can provide the fastest reaction time to travel limits.

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