Auto pilot tiller arm position clarifaction

[wiekeith]

Originally Posted by skipmac

If I understand your meaning here, you would use the physical limiters on the quadrant to prevent the drive from pushing the rudder too far port or stbd? If so I don't believe this is recommended. The range of motion of the linear drive and the length of the quadrant should be such that the drive cannot push the system as far as the physical stops. To allow the drive to push until the quadrant hits the limiters could damage the drive or the tiller arm or something in the system.

+1
In the case of Raymarine the initial setup procedure sorts that out. It’s goes something like:
Turn wheel hard to Port – ‘Enter’
Centralise wheel – ‘Enter’
Turn hard to Starboard – ‘Enter’
It then knows how far not to drive to port and starboard, as well as knowing where centre is. I would think other systems would do the same in order to overcome the potential issue of driving against the end-stop limits, which skipmac rightly highlighted.

[Mg451]

Interesting about the stops. I don't have the rm literature I think i saw it there. And it didn't dawn on me what would be going on if one were to yse the stops as limiters

[Mg451]

If raymarines coustomer service wasnt so horrible id ask them About the 90 degree and the rudder stop. But seems they dont have coustomer service just a forum.

[wiekeith]

Originally Posted by Mg451

Interesting about the stops. I don't have the rm literature I think i saw it there. And it didn't dawn on me what would be going on if one were to yse the stops as limiters

Ah, I was assuming you'll be fitting a rudder position sensor. If not, it will have no idea where the end-stops are. In which case, you'll need to ensure the radius/length of the rudder arm is such that the full travel of the actuator is slightly less than the travel required to take it from one end-stop to the other.

Which raises another issue if the arm is not at 90 deg to the actuator at centre position - the distance from centre to port end-stop will be different to the distance from centre to starboard end-stop.

[Frankly]

For normal +- 30 degree rudder travel me thinks you are trying to make a mountain out of a molehill. There is some change in mechanical advantage away from TDC but not a lot.

Most of the energy consumed with a modern rate based AP is used to overcome the polar moment of inertia of the rudder/ wheel system. Inertia is reflected as the square of any gearing ratio which is the reason to drive the wheel shaft and not the rudder shaft if practical.


Frankly

[goboatingnow]

Originally Posted by Mg451

If raymarines coustomer service wasnt so horrible id ask them About the 90 degree and the rudder stop. But seems they dont have coustomer service just a forum.

They discontinued the forum. I’ve always found them very responsive either by phone or email

[goboatingnow]

Originally Posted by wiekeith

Ah, I was assuming you'll be fitting a rudder position sensor. If not, it will have no idea where the end-stops are. In which case, you'll need to ensure the radius/length of the rudder arm is such that the full travel of the actuator is slightly less than the travel required to take it from one end-stop to the other.



Which raises another issue if the arm is not at 90 deg to the actuator at centre position - the distance from centre to port end-stop will be different to the distance from centre to starboard end-stop.

No no , all the linear drive companies will tell you you do not drive the arm into its own end stops. You must hit the external end stops first. Ray marine specifically warn against damaging the arm in that eventually

All the AP have overdrive sensing so they will drive halt if you do hit the external rudder end stops. The problem is they don’t have internal cutoffs abs you can damage the internal end stops.

[goboatingnow]

Originally Posted by wiekeith

+1

In the case of Raymarine the initial setup procedure sorts that out. It’s goes something like:

Turn wheel hard to Port – ‘Enter’

Centralise wheel – ‘Enter’

Turn hard to Starboard – ‘Enter’

It then knows how far not to drive to port and starboard, as well as knowing where centre is. I would think other systems would do the same in order to overcome the potential issue of driving against the end-stop limits, which skipmac rightly highlighted.

Correct under normal calibration the external end stops will be detected and avoided. Equally the drives have over current protection even if you do hit the stops or something jams the rudder.

What you don’t do is ever hit the internal ram end stops.

[Mg451]

I will be using a rudder position sensor. .but the rudder stops...?

[sv_pelagia]

Originally Posted by Mg451

I will be using a rudder position sensor. .but the rudder stops...?

Setup calibration of my autopilot (Comnav P2, 2021) required I turn the wheel end to end in order for it to determine maximum physical limits in each direction. It then sets the autopilot limits to a few degrees less.

In the setup, I can reduce these limits further.

In practice, normal autopilot function doesn't go close to these limits.

[wiekeith]

Originally Posted by goboatingnow

No no , all the linear drive companies will tell you you do not drive the arm into its own end stops. You must hit the external end stops first.

Erm, I think I was agreeing with that?
"In which case, you'll need to ensure the radius/length of the rudder arm is such that the full travel of the actuator is slightly less than the travel required to take it from one end-stop to the other"

[wiekeith]

Originally Posted by wiekeith

Erm, I think I was agreeing with that?
"In which case, you'll need to ensure the radius/length of the rudder arm is such that the full travel of the actuator is slightly less than the travel required to take it from one end-stop to the other"

Ah, just re-read what was actually said - please ignore my comment.

[Mg451]

So...
port -enter ( not to end stop)
Center-enter
Starboard- enter( not to end stop)

Silly question whats the end stops for?

[wiekeith]

Originally Posted by Mg451

So...
port -enter ( not to end stop)
Center-enter
Starboard- enter( not to end stop)

Silly question whats the end stops for?

Ah, sorry, I should have been a bit clearer. When you come to commission your RM autopilot it will prompt you to go through a configuration process to identify when your wheel is centred, when it is turned as far as it can go to port (which I referred to as the end-stop), and when it is turned as far it can go to starboard (which is also what I meant by end-stop).

At each of those three steps it will ask you to push one of the buttons on the control head to ‘enter’ the information and move-on to the next step in the configuration.

Hopefully that’s a bit clearer? If not, let me know and I'll try again, or take a look at the manual as it will probably do a better job of it than I'm doing

[Mg451]

Yes im with you the cou will stop it from hitting the end stops as long as they are set to stop prior..so i assume i dont need the (physical)stops at then?