Any Autopilot Experts?

[Norman_E]

The autopilot on my boat is a Simrad Robertson AP11 with a J3000x controller/Junction box driving an electric pump-hydraulic ram combined unit. The latter was always a bit underpowered and examination following replacement of the upper rudder bearing has shown that it has become stiff to operate and is causing a lot of friction in the steering.

As the J3000x unit will only output a maximum 10 amp current to the drive unit replacement choices are limited unless I replace the entire system, which is a large expense. As far as I can see there are just two wires connecting the junction box to the drive motor, which is reversed by changing polarity. Is it a workable scheme to use the output from the autopilot controller/junction box via diodes to energise one of two relays (depending on direction of current flow) so that a higher powered ram can be used? What I don't know is whether the power output from the j3000x is a simple bi-directional on/off, or something that regulates the amount of current.

 

[prv]

I don't know those specific units, but the Raymarine pilots are a simple on-off supply, and are compatible with at least some third-party drives which implies that this is not unusual. So I would guess that yours is also a simple on/off, not a varying voltage. The relay idea seems reasonable to me.

Pete

 

[lpdsn]

The autopilot on my boat is a Simrad Robertson AP11 with a J3000x controller/Junction box driving an electric pump-hydraulic ram combined unit. The latter was always a bit underpowered and examination following replacement of the upper rudder bearing has shown that it has become stiff to operate and is causing a lot of friction in the steering.

I'm not sure what you're saying is underpowered. Is the electric pump incapable of delivering enough output? Or is it not getting enough power? Thicker wiring and the relays will solve the latter.

Personally, in your shoes I'd be keen to solve the problem of friction in the steering.

I guess it dawned on me that I had to solve the problem of stiffness in my steering when I noticed that some of the lighter-built crew members were taking a bit of a run at it to turn the wheel. ( I exaggerate slightly, but jerking the wheel was hard work for them and not conducive to maintaining a straight course).

 

[prv]

I'm not sure what you're saying is underpowered.
[...]
Personally, in your shoes I'd be keen to solve the problem of friction in the steering.

I think he's saying that the drive unit has excess friction, not the steering, so he has condemned the drive as knackered. Since he's replacing it anyway, he wants to fit a more powerful one, but the pilot computer may not be able to supply enough current for that.

Pete

 

[Norman_E]

The steering was free enough until the autopilot ram was reconnected. It seems to have stiffened up and pushing the ram in and out feels like there is metal to metal contact. It used not to be like that so it looks as if the ram is now faulty. One possibility is that the bypass valve has stuck shut. When I launch the boat in mid month I will be able to see if it still works. The issue with power is that the junction unit can only supply 10 amps maximum, and that is the current drawn by the motor when the ram is providing its maximum thrust. Just fitting a more powerful drive unit would burn out the power supply in the junction unit. I don't know the maximum thrust rating of the ram, but in a swell the unit does have a problem coping unless I have been very good in terms of sail trim to provide a balanced helm. It struggles, and sometimes gives up, going hard upwind if the sea state is other than calm, so a bit more power is desirable. I think that the unit is actually more suitable for a slightly smaller boat and is right at the limit of its capacity.

 

[nimbusgb]

There are lots of reasons relays aren't used in control systems like this. I doubt it will work longer than a month. It would be better to add a solid state extension to the existing drive. Using the existing drive signals you could add an H bridge board and double the capability reliably.

This board https://www.pololu.com/product/2507 looks like it would do it, ( without the Arduino ) 24A drive capability. Your exising drive signals are used to set the drive states on the motor control gpios and the pwm signal is tied logic high.

 

[dial-a-monkey]

I found some Mosfet H-Bridge's (goggling) that can take the 12-14? volts "motor out" from you autopilot as a signal (in) voltage , acting like a relay , the volts out made thing a bit more complicated as it's not the nomal CMOS or TTL signal voltages of 0-5Vdc or +-12 Volts -

I expect the back emf from the constant switching of the pump will fry all but the most hardy control circuity (my windlass has fried some expensive circuit breakers) - So anything with physical contacts like relays won't last long - the Mosfets are supposed to handle the spikes, but I would worry enough to stick some back emf suppressors directly over the motor in addition..

I'm in the process of setting this up as an parallel autopilot system - if any part of my primary fails I can just switch over to the backup.

I didn't find until recently that the Duty could be a factor = how often the drive pump is on over a period of time.

I also found there are a huge variety of electronic linear actuators( instead of the hydraulic system) that might be useful if a electronic clutch could be sourced - and are even more powerfulll than the hydraulic system..BUT again duty might be a problem

https://www.servocity.com/html/1570_lbs__thrust_linear_actuat.html - also made in china - so are a fraction of the cost on Aliexpress or alibaba.

Some ideas to think about? things that I am following..

 

[tjbrace]

Contact Hy Pro for marine linear steering actuators. I think www.hypro.co.uk will find them. I have one of these and they were very helpful when I changed the control system from NKE to Garmin.

 

[Norman_E]

Thanks guys! Some interesting ideas. The Servocity drives look great but seem to have one drawback, in that they might make manual steering impossible as they appear to have no bypass or release mechanism and are advertised to hold position when power is removed. I like the circuit board idea, but need to get something that takes simple bi directional 12 volt power in, and just connects a bigger power supply out. The Polulu board looks very complicated and seems to need USB power at 5 volts.

When I get to the boat I am going to get the controller/junction box which is also the course computer out of its hiding place under a locker floor and check it just in case it is the more powerful j300x, but my memory says it is not.

 

[Len Ingalls]

Least expensive -clean & re-build the existing ram.I believe you may be correct about blocked bypass.Likely just "dirt".
Since you are planning to replace it,take it apart.Seal kits are available.You've nothing to lose IMHO
Cheers/Len

 

[Jeva]

Fitting relays as you suggest is standard practice and has been for many years. Hydraulic A/P's use this method all the time and many large yachts have sailed thousands of miles set up like this. Just make sure that the relays are suitably rated.

 

[danielefua]

Fitting relays as you suggest is standard practice and has been for many years. Hydraulic A/P's use this method all the time and many large yachts have sailed thousands of miles set up like this. Just make sure that the relays are suitably rated.

I agree and indeed I was going to reply to a previous post where the use of relays was discouraged. I have a record of relays in autopilots lasting 20-30 years with continuous usage! The important issue is to fit industrial grade relays and I am ready to give all needed indications.

Apart from that I think that the OP, before doing anything else, needs first to fix the ram.

Daniel

 

[Norman_E]

I agree and indeed I was going to reply to a previous post where the use of relays was discouraged. I have a record of relays in autopilots lasting 20-30 years with continuous usage! The important issue is to fit industrial grade relays and I am ready to give all needed indications.

Apart from that I think that the OP, before doing anything else, needs first to fix the ram.

Daniel

Thank you, I will certainly see if the ram is fixable, because new ones are pretty expensive. In case it has to be replaced I would welcome any pointers to suitable relays, which need to be double pole as both positive and negative need to be switched in, also advice on the type and rating of diodes to use as I am old enough for my experience to be based on germanium diodes, not things like Schottky diodes and Zener diodes.