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All one needs to know to get started
#1
Hello! I found my way here while researching ways to save money on autopilots, as I guess many people did. Im looking for a solution where I can hide away my autopilot down below, not having it take up unnecessary space and clutter the deck. 

Im very intrigued by what has been done here, a engineering(all be it very early in my education) student as I am I'm fairly familiar with the raspberry and the potential it brings to the table. Essentially I'm prepared to give the whole combination of Openplotter and Pypilot a go, and build em myself. What I'm not so familiar with are dc motors and mechanical torque needed from the motor the be confident in its reliability when the wind picks up.

i have a First 31.7 sailing boat, and a issue with the design of the boat is that it has very limited space around the steering shaft (English word for that?) meaning its difficult to get good leverage for turning the rudder.

So to get started I'm trying to figure out how powerful of a motor do I need? or rather, how do I calculate how powerful motor I need? I see you guys talking about windscreen wiper motors, but they operate on the tiller arm, that I assume gives them a fair bit of leverage.

Great project all in all, I hope to get this together for next summer as I will try to sail to England Smile
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#2
Basically, it requires a more powerful motor in rougher conditions.

If you had a motor with a variable transmission or different speeds, it could work more efficiently and over a wider range of conditions, but for the most part, this is never used, and a motor is reduced in one or more stages to drive the main rudder with a single ratio.

If you can adjust the offset or add weather helm, you can get away with less travel, otherwise you need to be able to swing the rudder over a wider range and have a longer screw if that is how it is driven. It is also possible and maybe interesting to apply an opposing force using a bungee to cancel weather helm and help the drive motor, allowing a smaller motor to work even with a lot of helm.

A brushless motor would be more efficient and longer lasting, especially if it uses rare earth magnets, but in practice, the power consumption is small compared to what a few small solar panels produce because of gyro sensors. The brushless motors might be able to run more efficiently slowly which is quieter, but brushed motors are much simpler.

There are several ways of gearing a motor down to get more torque and then drive a lead screw. This can then attach to the tiller to move it, look for brushed dc motors that draw 1-2 amps without a load and gear it to move the rudder in and out at 4-8 degrees per second
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