Changing autopilot from old Benmar to Pypilot, to integrate in Open CPN

[volksbar]

Hello
I would like to connect Pypilot to our existing and aged, still fully functioning Cetic Benmar course setter. This would allow to integrate the existing Benmar motor unit and gear box into Open CPN and Pypilot.

Does anybody have experiences or educated guesses, if that is possible or how to do this?

Pypilot: uses to my knowledge PWM to control the motor.
For motors with brushes and fixed magnets, it is no problem.

But what motor control does Benmar use for motor/gear box? Brushed with fixed magnets or other?

Specs of our Benmar system:

Benmar gear box and motor unit (12V 001-1610):
It drives the rudder both ways by reversing the current. When measuring volts as indicator for the current, it reads between 2 - 12V.

Benmar Control Unit is (L 001-1752; I 12V; M 001-1758)


I have not received an answer from Benmar, and am not sure whether they are still in active and in service.

Any thought or idea on this specific Benmar challenge would be appreciated.

Thxs in advance

Volker

[Frankly]

I don't have any experience about the DIY Autopilot electronics but do have considerable experience with those Benmar drive units (I have 6 if anybody wants to have a really first class AP drive unit). They are such great units I can't resist on ebay if the price is right.

All you need is the drive motor (typically 12V, permanent magnet, brushed), throw the internal circuit card in the trash. Just extend the motor leads to whatever you are going to drive the motor with. I have over the years driven mine with every version of the Raymarine wheelpilot from the 4000 up to now the EV1. I used to design this stuff for the US Navy (underwater vehicles not ships). There is just no way to realistically compete with what RM offers with any home brew stuff IMO, but a lot think otherwise.

The RM units all use some version of pulse width modulation to vary the motor speed. Recent versions just have two speeds (fast, and half fast). As most of the Benmar units are now quite old, I open the drive unit, toss the electronic drive card, remove the motor. open it up and look at the brushes (blow out the carbon dust), put a little oil on the motor bearing shields, and heat it with hot air to get it into the races (have replaced a few bearings if I didn't like the feel). Open up the gear end clean out the old dried grease, relube with some fresh, paint the case, and put it all back together

I did talk to the guy that had the old Benmar stuff up in Idywild long time back. I was looking into getting a spare. He said he would sell me one ($500) but I was not going to live long enough to wear out my current unit (the jury is still out on that but suspect he was right, be 81 in a few months).

Good metal gears, oil lite bearings, and a mechanical (read no parasitic current draw) clutch. Don't get no better than that in this plastic throw away society.

On my IP32 listening to Jimmy Buffett (with the volume turned up a little) uses more electricity than my AP in any reasonable sailing/ trim conditions. You are starting down the right road just keep at it. If you want a spare (you might be younger than me), $300 including domestic shipping.

There is a mechanical slip clutch in the gear assy. I have slipped mine a few times in a badly trimmed real blow, doesn't hurt anything just makes a "what was that noise". Would not try it on anything too big. If I remember the manual says something about 7 amps rating (whatever that means). Recent versions of the RM AP units monitor motor current and send an error message around 10 amps, never managed to trigger that warning.

Old Frankly

[volksbar]

Thanks a lot, Frankly!

This is tremendously helpful information! Also to get an expert opinion on the strength and weaknesses of these Benmar systems.

If I understand you right, the motors you encountered during your dissections of Benmar APs were all 12V, permanent magnet, brushed?

Then it might make sense to keep the existing old Benmar system the way it is, as a back up. Additionally hook up a new AP system to the Benmar motor leads, driving the existing motor with pulse width modulation - as you suggest.

Do you know by chance whether those motors in the benmar system are some standard industry motors?

Then I will try to get spare brushes and possibly even a brushless spare motor that could fit into the existing benmar gear box, with same connections and dimensions .

Merci bien!

Volker

[Frankly]

That motor is somewhat custom in both mounting arrangement and the first gear in the speed reducer train is actually cut into the end of the motor shaft. The units I have examined showed various levels of brush wear but none close to being worn out.

There is a brand new unit for sale on ebay for $500 last time I checked.

I am going to say this one more time and then I will shut up. That Raymarine Evo AP System borders on amazing. When raising my main I put the unit in the vane mode with the wind coming 10 degrees off the stbd bow (my boom rests over on the port end of the traveler track). Tell my crew "keep your damn hands off the wheel" and go fwd to hoist the main. I have watched that main just lay there luffing for as much as 10 minutes. That RM AP would appear to anticipate every move the wind makes even in some pretty gusty conditions. Most normal humans could not pull that off.

Throw that old Benmar electronics in the trash and do include a rudder position sensor. I never designed an automatic depth, heading, roll system that did not have a sensor to measure/ feedback the actual control surface(s) position. Modern computing can estimate a lot of parameters but nothing beats a good real measurement.

Coffee is ready and I must go, Franky

[volksbar]

That's been all very helpful, Franky! Thanks a lot!

So your bottomline is that the mechanical hardware is great, rest is outdated and can be adapted to other systems, including feedback sensors.

Following your hint towards ebay, there was a close-up picture of a motor used by Benmar. Seems they have been built by

RAE DC PRODUCTS GROUP
raemotors.com
4615 Prime Pkwy, McHenry, IL 60050
(815) 385-3500

Regarding those pypilot solutions - from a person who already installed it on his 60ft sailing vessel, crossing the Atlantic, he said he would not go back to another off-the-shelf product.

there would be many more options possibly with the open cpn and pypilot combination.

I will provide a feedback, once we have tested pypilot with the Benmar system

Thanks again

Volker

[donradcliffe]

I agree it should work well. My experience with aging Benmar systems was that all the solder joints in the electronics were going bad, but the drive system was still strong.

[volksbar]

Hi Frankly

I totally understand that the time sailing is at some time much more worth than fiddling with DIY.

Still I am trying to go that route, while blind on many items - as to date I could not source any pdf or hard copy of a Benmar manual (the Benmar person referenced on the web in California has not been responsive)

Frankly, as you suggest a spare power unit on ebay - I got a bit confused now. I don't find such power-unit within our Benmar system.
May I pick your brain once more in this regard?

Attached are image files, that show the parts of our system "below the hood".

Looking at those images,
to my understanding your consult was to hook up any modern AP system to the motor - without any Benmar electronics in between.

Please forgive if this question sounds repetitive, yet without manual, I hope it is possible to double check once more with you and your AP/Benmar experiences:

Does this mean the Control Unit at the left bottom of the first image is obsolete, and it is correct to attach a modern AP system directly to the motor?

And as the recommendation for a spare Benmar Unit references a Power Unit, is there also a Power Unit necessarily in our system (which my lay eyes were just not capable to identify yet?

If I could receive your consult again - would be much appreciated

thanks

Volker

[akopac]

Originally Posted by Frankly

I don't have any experience about the DIY Autopilot electronics but do have considerable experience with those Benmar drive units (I have 6 if anybody wants to have a really first class AP drive unit). They are such great units I can't resist on ebay if the price is right.

All you need is the drive motor (typically 12V, permanent magnet, brushed), throw the internal circuit card in the trash. Just extend the motor leads to whatever you are going to drive the motor with. I have over the years driven mine with every version of the Raymarine wheelpilot from the 4000 up to now the EV1. I used to design this stuff for the US Navy (underwater vehicles not ships). There is just no way to realistically compete with what RM offers with any home brew stuff IMO, but a lot think otherwise.

The RM units all use some version of pulse width modulation to vary the motor speed. Recent versions just have two speeds (fast, and half fast). As most of the Benmar units are now quite old, I open the drive unit, toss the electronic drive card, remove the motor. open it up and look at the brushes (blow out the carbon dust), put a little oil on the motor bearing shields, and heat it with hot air to get it into the races (have replaced a few bearings if I didn't like the feel). Open up the gear end clean out the old dried grease, relube with some fresh, paint the case, and put it all back together

I did talk to the guy that had the old Benmar stuff up in Idywild long time back. I was looking into getting a spare. He said he would sell me one ($500) but I was not going to live long enough to wear out my current unit (the jury is still out on that but suspect he was right, be 81 in a few months).

Good metal gears, oil lite bearings, and a mechanical (read no parasitic current draw) clutch. Don't get no better than that in this plastic throw away society.

On my IP32 listening to Jimmy Buffett (with the volume turned up a little) uses more electricity than my AP in any reasonable sailing/ trim conditions. You are starting down the right road just keep at it. If you want a spare (you might be younger than me), $300 including domestic shipping.

There is a mechanical slip clutch in the gear assy. I have slipped mine a few times in a badly trimmed real blow, doesn't hurt anything just makes a "what was that noise". Would not try it on anything too big. If I remember the manual says something about 7 amps rating (whatever that means). Recent versions of the RM AP units monitor motor current and send an error message around 10 amps, never managed to trigger that warning.

Old Frankly

I can totally attest these drive units are awesome. I currently have one tied to Raymarine EV100. Quit, sips power, and incredibly reliable. I have 2 pi pilot setups that I want to make backup or maybe primary systems for my boat

[Frankly]

"A picture is worth a thousand words". You have an entirely different Benmar drive system (Looks like a hydraulic unit). The Standard Power Unit that I use is a smaller drive with a shaft for a chain and sprocket to drive the steering shaft.

Having said all that, the basic primary mover is still a brushed DC motor. Get the correct voltage and the motor don't care if the current is coming from Ray Marine or a series of flashlight batteries (PWM or plain old DC); even an Arduino with a power output stage should work.

Unplug that plastic connector with wires going to the motor (that is where the 12V, I assume, is going) and run the motor off the battery (include a say 20 amp fuse) and then try to find if there is a clutch control signal (another 12 volts with a 5 amp fuse).

If the rudder turns then, find a large trash can and fill it with everything electrically upstream of those two connections.


One other little side issue that I have observed over the years concerns maximum drive current. Some are bothered by a electronics unit rated at say 20 amps output and an actuator only rated for 10 amps max. Don't matter, feed the motor the correct voltage and the current will be proportional to the mechanical load the motor shaft is experiencing. However note the reverse is not true, 10 amp driver and a 20 amp load is going to have trouble.

Good luck and keep at it, a year from now you will be a lot smarter (and a year older ).


Frankly

[volksbar]

Thanks a lot again for sharing these additional infos -

And I hope to be able to fill the large trash can soon ; )

So I will connect directly to the 2 motor cables, while continuing to look for possible spare parts, fitting the existing system

merci bien!

All your input has been much appreciated!

[VicDoug]

Volkspar
Wondering how you made out adapting your Benmar autopilot drive. Considering the same project.

[hpeer]

Seems like you got your answers, but I will throw this alternative in.

I have an old CPT wheel pilot. The control head placement was an issue so I ditched it for a PyPilot. I bought both the Py controller and associated current controller from Sean.

Inside the CPT all I did was connect the Py to the COT MOTOR. 2 wires. Period.

Si I have the CPT drive motor with the clutch and wheel arrangement all driven by Py. COT is plenty strong for my 44’ cutter and they are readily available used.

I had other issues related to my steel construction, but that is a different matter.

[Donahue]

Does anyone know the max power draw of these old Benmar units? Also, what sort of thrust or force they can generate? Benmar's website is a bit outdated and they list some specs but they look to be for a smaller drive.

My new boat has what I believe is a Cetec Benmar 001-1280 Course Setter 21S. Given the age, I was considering replacing it with a Raymarine Type 2 rotary or a Jefa drive. After reading this thread and some others, however, I'm considering rebuilding and keeping the Benmar; possibly replacing the rest of the system. I just want to make sure it can handle my 36,000 lb full keeler and if I get a new course computer it can supply sufficient amperage.

Thank you.

[donradcliffe]

I drove a boat for 7000 miles that had an old Benmar AP, but it was a 43 ft Grand Banks trawler. My impression was that it never drew more than 10 amps, but that was in protected waters. I kept the old electronics working, but had to resolder most of the circuit board.

your boat will need a 20-30 amp course computer. I suggest you get the computer and try the old drive.

[Donahue]

Thanks, currently the power unit is an older Simrad AC20. I'm going to give that a shot but perhaps upgrade to a modern 9 gryo unit--either a new RM or maybe Pelagic since that is a third of the price.