Autopilot rudder position feedback

[KAM]

I'm just about to replace the tiller actuator on my ST4000 with Pcnautic unit. Will wiring in the rudder position transducer make much difference to control accuracy. The old actuator had no rudder position feed back and seemed to work OK. Second question the Pcnautic unit has a much bigger motor. Current draw may be higher. Does anyone have any experience with this combination.

 

[Martin_J]

Double check the current draw for the proposed tiller drive compared to the current one.. The ST4000 might be on it's limits already and it is internal components that can blow if too much current is drawn. (They don't just go slower than expected).

[CA11] Mechanical Linear drive

 

[KAM]

Thanks for the link. Yes I'll measure it. The unit is supposed to be a direct replacement for the Autohelm but the motor looks massive. Maybe there's some added electronics to limit the current draw.

 

[KompetentKrew]

Isn't the ST4000 just the control head? What's the controller? A Smartpilot?

I've read that rudder feedback sensor makes a big difference with the Evolution APUs - I wouldn't be surprised if it helped significantly with the Smartpilot.

I've crossed Biscay with a Smartpilot and a Wuxi Hongba arm steering all the way, force 6 - 7. No rudder feedback, but I'm upgrading to an Evo so I can have that.

And it's steered in stronger winds for me too, when I've been overcanvassed - no need to worry about the power draw of the "big motor". I'm not sure it is actually that much bigger than the Autohelm one - maybe it's just a bulky casting; when you disassemble the Autohelm arm you'll find it's quite a thin tube. Actuators with the potentiometer option are quite a bit bigger than the standard one (see this comparison pic} so there's some wasted space in there.

The potentiometer in the HB-DJ809 is a clone of the Bourns 3590S-2-103L, £3 off AliExpress if you need to replace it, and you will see its size.

 

[KAM]

Thanks Pcnautic. It seems a well made unit. Nice and smooth on the bench tests. I particularly like the limit switches. Looking forward to sea trials.

 

[KAM]

What about peak current?

 

[KAM]

Just measured peak load at 8 Amps 1.4 Amps no load. Peak current on Autohelm ram when stalled is 4 Amps 600ma no load. I'm thinking it will be unwise to use this with the ST4000.

 

[fredrussell]

Apols, mistaken post.

 

[onesea]

Just measured peak load at 8 Amps 1.4 Amps no load. Peak current on Autohelm ram when stalled is 4 Amps 600ma no load. I'm thinking it will be unwise to use this with the ST4000.

We have full PCnautic tillerpilot, with there controller on 30’ boat.

We have never seen more than 0.5 amp current draw I am no expert in these matters. Then we generally sail quite well balanced and have never bench tested.

As for feed back yes then you can set limits before it hits the stops. It can also know where centre is and how much helm is applied. Then I have no experience of how the “ST4000 thinks”

 

[KAM]

Thats surprising. I was measuring the current the ram would draw. It was definatly 1.4 Amps just extending the pushrod on the bench with no load. I couldn't see how it could be less at sea. The meter is correct.

 

[Pcnautic]

The 0.5 is unbelievable low but possible in use with our autopilot because it uses PWM, it only gives full power when necessary, a new unit has first to break in, on our autopilot we fuse it at 5A

 

[Pcnautic]

We fuse it at 5A so the unit will not be overloaded when unintentional blocked, for example on a steel "Lemsteraak" with huge massive rudder he managed to blow a 7.5A fuse and is now using 10A

 

[onesea]

Thats surprising. I was measuring the current the ram would draw. It was definatly 1.4 Amps just extending the pushrod on the bench with no load. I couldn't see how it could be less at sea. The meter is correct.

Maybe it's the fact it's on for such a short period the battery monitor doesn't record the amps used. Either way the current consumption of the plotter is more than the tiller pilot.

 

[GHA]

What about peak current?

I just got my homemade pypilot with the same ram working at sea yesterday, very happy so far! Just now down below running from the buttons on the web control using a IBT-2 motor controller with a clamp meter measured like you about 1.4a running no load. Pushing as hard as I could on the point of stalling it would peak at just over 5A. Using the default gain settings yesterday it would only move in little steps with the speed seeming to ramp up and down so not a hard on/off. Not sure of peak load but average draw might even be under 0.5A. Seems great though, true wind seems good for a downwind course. After such a long time with just an Aries getting the main up & down is suddenly so much easier

 

[KAM]

What course computer are you using. I dedided I didnt want to overload the ST4000 so have knocked up a couple if relays to drive the ram. Dont really need that much thrust. Its a pity to have to do that. I was wondering if there's some way of limiting the current draw instead. It's just a trial at the moment but I'll probably replace them with a sold state device of some sort.

 

[GHA]

What course computer are you using. I dedided I didnt want to overload the ST4000 so have knocked up a couple if relays to drive the ram. Dont really need that much thrust. Its a pity to have to do that. I was wondering if there's some way of limiting the current draw instead. It's just a trial at the moment but I'll probably replace them with a sold state device of some sort.

I have a raspberry pi 4 which runs everything, Pypilot is installed on there along with opencpn. The IMU is a ICM20948. The IBT_2 is only about 15 quid istr. Pypilot might have some current limiting option built in but then you need to get current feedback from the arduino, which is there in the code I think but might need a shunt.
Somewhere online there's a writeup of a guy who put a tinypilot inside a ST4000. Bit cramped