Thanks, Fred, for the information about octapus drive hydraulics -- I was aware enough of them to know that I can't afford one! If I see one for cheap on ebay or in a consignment store I will definitely pick it up! Meanwhile the linear actuator that I am using is pretty good as it's a circulating ball screw type and draws very little current under normal (balanced sail plan) conditions.
On Tue, Jan 21, 2014 at 11:00 AM, Frederick G Street <[email protected]>wrote: > For projects like this, take a serious look at the Octopus hydraulic > linear actuators: > > http://octopusdrives.com/products/octaf1212lam12 > > This model has 12VDC reversing polarity input for the drive (30 amps) and > a 12VDC clutch input with a fairly low current draw. > > And I’ll be curious to see how this project turns out. David — this would > be a great drive for you to use as a below-deck replacement. > > Fred Street -- Minneapolis > S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^( > > On Jan 21, 2014, at 8:57 AM, David Paine <[email protected]> wrote: > > Hi Peter, > > I built a homebrew below deck autopilot for my C&C33 a couple of years ago > using a linear actuator, a mechanical clutch, a H-bridge-like serial power > controller from Pololu, an arduino, a transreflective serial LCD display, > four buttons, and most important of all, a digital compass with serial > communication (NMEA 0183) operating at 10Hz which, along with a sparkfun > gyro (15 degrees/sec) provides heading information. I bout everything from > ebay and probably have $250 and untold hours invested) The programming is > fairly easy with arduino since there is a PID controller library available > (use two, one for the positioning of the actuator, the other for correcting > for the course error (the difference between the intended course and the > present heading. > > I've used my autopilot on many long solo trips including one 80 m mile > offshore run with 20 kn wind directly astern and a large swell off the > quarter (during which I was able to sleep for four hours as the system was > so stable. > > Hints: Forget using GPS (or wind) alone to set the course you need much > faster response time and that is why you need a 10 Hz heading signal. I > thought about using a Kalman filter but soon learned that Kalman filter > math is serious juju and was very glad to have stuck with PID control -- we > only have two degrees of freedom its not like it's a quadracopter! The > worst part of my system as it stands now is the mechanical clutch to engage > and disengage the actuator -- one day I will find a hydraulic actuator > which will allow a solenoid to disengage the actuator. Raymarine actuators > have an electromechanical clutch which is also nice but consumes more > current than I like. Also, try to use components with serial > communications protocols -- these will have on board filtering and make the > whole exercise much easier. > > > Best, > > David > > >> >
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