Trouble with boat thruster build

@zander 

I understand, I was just trying to make sure @robotBuilder knew about the stationary point as well. He seems to be relating it to the operation of a helicopter and this is an additional complication to that model.

@will Yep, I did mention that also. However it's not part of the arduino based solution, the two are independent and I doubt they will interfere now that I see what will be controlling the rear. The only improvement would be a differential GPS at the front, I think that reduces the error circle from 16 ft to 3 ft, not positive and since mm GPS is many thousands not likely. Could also consider 2 rear thrusters instead of one. Use them push pull for very quick response times.

@will 

No I didn't know about any stationary point I assumed it was about keeping the boat pointing in the same direction when twisted around by whatever. @redaustin88 stated this could be done by someone in the rear physically controlling the speed and direction by hand. How did they decide if some point on the boat was stationary? I doubt they were maintaining any stationary point in 2d space all they could do is maintain a stationary direction with the side thrusters.

As a child I spent a lot of time on a river. To travel from one side to the other we would select two markers in the distance (eg. trees) and and keep them in line by turning into the current.  This kept us on a fixed path although I never knew the exact position on that path. However you could use more distant markers to get a fixed position.  One way to return to the exact same spot in a field.

@robotbuilder Did you not notice he has a MinnKota GPS controlled bow thruster in station keeping mode. Under ideal conditions that means the bow doesn't move, but GPS error may allow some movement.

@robotbuilder 

*channelling Butterfly McQueen* I don't know nothing' about berthing' no boats !

bu apparently the OP has an existing GPS system mounted on the front of the boat that is able to keep the point at a specific GPS location (within about 5m tolerance) and desires to enhance this positioning by adding a motor at the rear of the boat which will only power the rear to the left or right with a goal of setting and maintaining a specific heading regardless of wind, tide, current or government interference.

The discussion has been about the nature of this mystery device and its components and software required.

@zander and I have pretty much bowed out of it now, I'm just answering your questions.

@will Just to clarify. The GPS at the front is in the motor. They come from the store that way. The reason for wanting to limit the swinging is he has a bunch of long poles sticking out in front of the boat and he is fishing close to a brushy shore. If the boat swings, the poles will get damaged when they get caught by the bushes.

@zander 

I know, he said he had 8 14 foot poles off the boat.

@robotbuilder FYI @will The motor on the back to be controlled by the arduino can pull as much as 40A @ 12VDC. he will need a way to control that smoothly from a very slow rpm to max speed and of course be able to reverse the current flow. I am too new to know the name of the device to be controlled, I do know you can't put 40A through an arduino.

@zander 

Google "motor controller for dc motor" or "motor controller for dc motor arduino".

@will Ah, the old H bridge. Gawd my memory is getting bad.

@zander @will
Been very educational for me while googling the subject. My brother in law has a house boat but seems to manage on a windy day or in high side currents to dock and navigate the boat without anything fancy to help. My brother has a sea going sail boat (with motor as well) but hasn't mentioned these problems. The bottom line here is I think @redaustin88 just hoped for a cheap automatic solution using an old 12 volt 40amp motor, which he already has, to replace someone doing it manually. Probably very doable if all he wants it for is to limit the swing when fishing close to a brushy shore.

Hi Redaustin88, hope you are still here, would love to hear how you made out with this, as I want to do almost exactly the same thing.  I'm just trying to find the simplest solution, even if it's not elegant or if I have to buy new parts.  But I also just want to set a heading with a pot, and have a single fixed (but bi-directional) motor/thruster at the back of the boat yawing the stern around an (approximately - based on GPS) stationary bow pivot point (in open calm water) to hold that boat heading relatively constant.  Everything slow, and +/- 10 degree accuracy would be enough.

I've been down a few rabbit holes, but not found any rabbits yet 🙂

These are a few of the rabbit holes:

1. Is it as simple as basing a solution around a model aircraft heading hold gyro to control the trolling motor?  Like this $15 one? heading hold gyro I think this is my best guess at a solution so far, but haven't outlined the additional parts required yet, but I think the bridge electronics would be reasonably simple.

2. Maybe the Blue Robotics parts below can be connected to the above relatively simply, and this would be a solution (albeit replacing the trolling motor).  In my case it is only intended for calm conditions, so the 8lb thrust max is enough.  Maybe the speed controller below could be used to control the trolling motor at low power.

T200 Thruster:

https://bluerobotics.com/store/thrusters/t100-t200-thrusters/t200-thruster-r2-rp/

Basic Speed Controller:

https://bluerobotics.com/store/thrusters/speed-controllers/besc30-r3/

Manual controller:

https://bluerobotics.com/store/comm-control-power/elec-packages/cmdr-r1-rp/

3. It seems like all/most of the autopilot modules include a heading hold mode.  It might be most time efficient to just buy one of these in some simple hardware (eg Pixhawk or adafruit metro mini), and only use the single feature.

eg: Steering Mode in ArduPilot

Once the input returns to neutral, the vehicle will attempt to hold heading, compensating for external influences, ie. “heading hold”.

Some other relevant threads that didn't bear any fruit, people trying to do similar things:

Trying to use a heading hold gyro in a model boat (but I think to control the rudder at speed)

Controlling heading hold using Blue Robotics Thrusters:

Guy that was trying to do a heading hold function on an ROV

Guy that started trying to control a trolling motor with an ardupilot autopilot:

Commercial solution to achieve this function with dual motors (Yamaha Helm Master Ex - Staypoint Mode)

Yamaha’s Helm Master EX system, for instance, offers a number of SetPoint modes. One is StayPoint. On a multi-engine boat, it uses GPS and independent outboard thrust to maintain both the boat’s position and heading to within 10 feet from the point of activation in ideal conditions.

Some good info on trolling motor control here (for a Minnkota powerdrive v1 12v).  He said he tried PWM and couldn't get it to work.

The foot controller is just 3 switches and a potentiometer so I replace that with an arduino controlled set of relays and digital potentiometer. I tested it with an Uno, digital pot, and a protoboard to make sure I could control it this way.

The actual trolling motor has a board in it that interprets this and provides the actual power and control for the motor.

I think somewhere along the way you all scared him off.  I read the first couple of pages and skimmed the rest.  So I could easily have missed something.  He said he just didn't want the front poles to be taken out by trees on the shoreline.  I'm not sure where someone got wrapped around the propeller and thought accuracy was an issue.  A Magnetometer is easily good to within a degree or two.  I'd bet he'd be happy with +/- 10 degrees. 

I'd think all that was needed:

1. ESP8266 - The WiFi wouldn't be needed, but could later add WiFi features if desired.
2. Magnetometer
3. Momentary button
4. Couple of Mosfets - I don't know how to pick these things, but I was thinking running a couple of these in parallel (in each direction) will easily handle his 40 amps at whatever voltage he wants 12V, 24V or 36V.  " https://www.amazon.com/BOJACK-IRF540-Transistors-IRF540N-N-Channel/dp/B082J2Y16 7"
5. I'd even punt the potentiometer. 

Grand total:  about $15

Procedure:

• Simply point the boat in the desired direction and press the button
• The MPU gets the Mag reading, calculates the North
• As the boat swings off that angle PWM the motor in the opposite direction.
• When he wants disable it, press the button again.

Easy-peasy!

VBR,

Inq

@inq As someone who used to own one of those Minkota thrusters, I am unsure what is maintaining the course as the lake I used it on had plenty of magnetic anomalies. I know there were patent claims for gold under the lake, and the area was mined for uranium with tunnels under the lake. The Canadian north area west of the Sudbury basin is loaded with deposits of various metals, likely caused by a large meteorite so I have a problem thinking a magnetometer would follow a straight line. However, I also know conventional GPS also isn't that accurate. Perhaps a combination plus a heavy dose of smoothing? Also would a MPU6050 do the job?