Instead of buying a complete autopilot our plan is to do a DIY autopilot for our sailboat. The reason is to save money and also because it is a bit fun. Both of us has pretty good knowledge about the general theory for autopilots, control theory which we both has read a course in university about. Thomas has also studied, and currently works with electronics design and Petra is a software developer. So, we both have some background knowledge about this stuff. But if you are interested in learning about this stuff and to spend time on it, it should be possible even without education, the internet is full of information!
The idea of a DIY autopilot for our sailboat started when we were looking at finding a good second-hand one. We realized that it would be expensive since all the affordable second hand autopilots were tiller pilots and we need something that is compatible with our wheel steering system. Autopilots made for fix installation, e.g. not tiller mounted where you disconnect the actuator when not in use, tend to be very expensive because some kind of release mechanism or clutch needs to be in the system.
As we realized that the actuator, or drive unit, were going to be the most expensive component in our DIY autopilot we started to design the system from the actuator. Today we have a wire steering with a quadrant on the rudder shaft. The autopilot actuators, or drive units, that we can use in our system are:
- Linear electric actuator
- Rotar electric actuator
- Linear electro-hydraulic actuator
- Hydraulic actuator (if changing to hydraulic steering).
The idea of building our own actuator came up but independent of the actuator design it always got stuck on how to solve the problem with a reliable and low power consuming clutch. Luckily a second hand electro-hydraulic actuator pop up and we bought it.
General idea for our DIY Autopilot
Our autopilot will not be completely DIY, since we will use an open source code for the actual code. This will save a lot of time and we will be able to more easily get extra fancy features, such as waypoints. We may however write a basic back-up code which will simply just maintain a certain course, to have if the other one should fail.
The autopilot will consist of the following hardware and software components:
- Electro-hydraulic actuator
- Rudder angle sensor
- Arduino and H-bridge motor controller
- Raspberry Pi running Pypilot
- Inertial measurement unit and magnetometer.
The arduino will do the following:
- Control a H-brigde that will drive the actuator
- Engage the clutch soleniod of the actuator
- Read the rudder angle sensor
- Read the temperature of the H-bridge
The Raspberry Pi, who will communicate with the arduino over an opto isolated UART, will run Pypilot which is an open source autopilot software. It will also act as our back up navigation system running the chartplotter openCPN and do some other stuff. All of this software is included in OpenPlotter which is like a software package for navigational aid and boat automation.
To be continued….
UPDATE May 18th: It has been some months since we shared this first posts and hope will do a Part 2 soon. We have a lot of other things to prepare on the boat as well but we have made some progress with the DIY autopilot as well. One thing we have done is to take the drive unit apart for some service and also tried to run our setup. Soon we will start to install the autopilot onto the boat and then we will be able to try it out for real.
All future posts we write on this subject will be tagged Autopilot and can thus be found under the tag autopilot. We hope that we will have a part 2 ready soon.