Rudder calibration not working

[seandepagnier]

Hi Sean, just to say I fixed this last problem and it was because the insulation had melted when I soldered the connector on so the yellow wire was able to touch the black one. No fault at your end! It was a while before I could find time to diagnose and fix that, but since then I have used the pypilot for a 30 hour passage across the bay of biscay with 2m quartering seas and a bit of surfing up to 12 knots (the point of sail the old autopilot really struggled with) and a couple of shorter passages too. It has performed incredibly well and I'm very impressed that without any adjustment of the gains it already outperforms the old Cetrek 619 autopilot by a huge margin. With the Cetrek I had to tweak the settings when conditos changed. The pypilot has handled a range of conditions without any change to settings (which is lucky because I have no idea how to use the gain settings!). The Cetrek was the best autopilot money could buy 20 years ago and was used on commercial vessels not just yachts. The pypilot steers a straighter course and uses a lot less power and less rudder movement to achieve it. The hydraulic pump is running quieter and smoother too.

This is great feedback.

Does the clutch output work now?

Initially the pypilot was moving the rudders way too much - the minimum movement was a quarter of the total rudder travel. Amazingly it still steered pretty well! I was able to use the web interface to reduce the min_rudder setting from 1.0 to 0.1 and that fixed it - since then it has

Are you sure "min_rudder" or was it the servo period or the min_speed?

The min rudder setting if it exists is in the old version and limits the range of travel, not the minimum movement. The minimum movement is based on the minimum speed and period.

moved very smoothly in small steps but still responds quickly. I would suggest that a much smaller default value for that setting would be a good idea.

I'm really impressed with how well the pypilot steers.

I have been controlling it with the IR remote because none of the other interfaces are really functional for me. The web interface is sort of working but the plugin doesn't work properly on mac or android and neither do the python tools. I think the best option for now would be to focus on getting all the features of those other apps included in the web interface. The web interface will work on any device, whereas apps and plugins require multiple versions to be maintained. A fully featured web interface would ensure that all users of the pypilot have at least one working configuration and control interface, regardless of what hardware they use. The opencpn app could potentially even just put the web interface in a frame to reduce duplication of effort developing all these different UI versions?

I am reworking the UI so that the controls are mostly auto populated. This should be a big improvement to the pypilot plugin in opencpn and also mostly avoids duplicating effort, but some duplication is needed since these all use different languages.

We are planning an atlantic crossing in November so we'll be giving the pypilot a really good testing then and maybe I'll have time to do some development on the web interface along the way (though boat maintenance always comes first of course). Let me know if there's something in particular I could be of help with.

Thanks again for all your help getting me up and running.

[syohana]

Hi sean, sorry yes I meant min_speed. Seems wrong that it defaulted to 1.0, works much better at 0.1.

I don't have a clutch, you must be confusing me with someone else on that.

Cheers,
Chris

[seandepagnier]

This specifies the minimum command allowed, so if it is set to 1.0 then the motor can only move at full speed. A value of .1 is very low and means the motor might be stalling more than you realize. Some drives require a minimum speed to move.

This is usually a tradeoff of noise and power consumption. It often uses less power overall at the higher speed, but if you have such a fast moving ram that it already moved 1/4th the full range, then you would need to slow it down and/or reduce servo.period.

Also many lead screws in tillerpilots are very much less efficient below the maximum speed. So using a low period and min_speed=1.0 here gives a lower power consumption. Sometimes I reduced this value to .8 or .6 on a tillerpilot to make it more quiet in light wind since the power consumption is already small.

It might be useful to automatically scale this value depending on the conditions and also depending on the drive unit.

It seems like your hydraulic pump is efficient at low speed? Maybe it is over sized? Can you measure the current it draws at different speeds and compare it to rudder angle? From this compare efficiency at different speeds. I'm planning a calibration routine which can plot this automatically if you have rudder feedback, but it also needs the user to apply "weather helm" using a bungee or weight from pulley to the helm to get results across load.


This "servo.min_speed" will change to "servo.command.min" in future since "servo.speed" now relates to how fast the rudder is moving in degrees per second.