I need a relay that can change polarity to a DC motor. Input will be either positive or negative

Thread Starter

Vegard

Joined Jul 11, 2017
10
I know there are more elegant solutions, but I like to make it cheap and simple. I have a boat with mechanical steering, that I'd like to be power assisted steering.
The tiller on the rudder has a hydraulic actuator (currently only used by autopilot) that is driven by a hydraulic pump. They hydraulic pump is driven by a DC motor that can be reversed by switching polarity.

My idea was to mount a small DC generator to the steering wheel, that will generate enough current to actuate a relay. In other words, when I turn the steering wheel the DC motor for the hydraulic pump should start in one direction and switch direction when I turn the wheel the other way. It also has to stop when I stop turning the wheel. I need to add that when the hydraulic actuator pushes the tiller, the steering wheel turns as well.

Could this work and if so what hardware and relays could I use?
 

LesJones

Joined Jan 8, 2017
3,899
For your system to work you would need to remove the mechanical link between the wheel an the tiller. If you did not remove the mechanical link the wheel would continue to rotate as it was being driven by the hydraulics which would generate the signal to continue the rotation until it reached the end of its travel. You really need to detect when you applying torque to the wheel. The way you would detect torque would depend on the design of the mechanical linkage between the wheel and the tiller.

Les.
 

Thread Starter

Vegard

Joined Jul 11, 2017
10
For your system to work you would need to remove the mechanical link between the wheel an the tiller. If you did not remove the mechanical link the wheel would continue to rotate as it was being driven by the hydraulics which would generate the signal to continue the rotation until it reached the end of its travel. You really need to detect when you applying torque to the wheel. The way you would detect torque would depend on the design of the mechanical linkage between the wheel and the tiller.

Les.
Yes, you are right. The wheel is connected via a roller chain to a shaft. Is there any way to accomplish this electronically?
 

blocco a spirale

Joined Jun 18, 2008
1,546
I think your best option is to investigate electric power steering kits for cars. New aftermarket units aren't cheap but it may be possible to salvage an electric power steering system from a scrap vehicle, although I don't know how viable this would be.
 

Thread Starter

Vegard

Joined Jul 11, 2017
10
I think your best option is to investigate electric power steering kits for cars. New aftermarket units aren't cheap but it may be possible to salvage an electric power steering system from a scrap vehicle, although I don't know how viable this would be.
Yes, I've thought of that, but unless I could salvage just the torque sensor, It may be too complicated.
 

LesJones

Joined Jan 8, 2017
3,899
If there was a small amount of slack in the chain you could hve a spring loaded roller on each side of the chain. When the wheel was turned one way it would take out the slack from that side of the chain and the movement of the roller aginst the spring tension could operate a micro switch. Each micro switch would drive the pump in the correct direction to assist the movement of the wheel.

Les.
 

Thread Starter

Vegard

Joined Jul 11, 2017
10
If there was a small amount of slack in the chain you could hve a spring loaded roller on each side of the chain. When the wheel was turned one way it would take out the slack from that side of the chain and the movement of the roller aginst the spring tension could operate a micro switch. Each micro switch would drive the pump in the correct direction to assist the movement of the wheel.

Les.
Yes, there's a slack. That's a very good suggestion. Thanks, I will try that. Any suggestion to where I can by the micro switch?
 

profbuxton

Joined Feb 21, 2014
419
If the tiller is actuated by a hydraulic motor with a reversing switch , how do you control the positioning of the tiller with the switch? Do you mean that when the switch is in the off position the actuator stops(is locked) in that position? Simplest way is to just have a switch on your control panel and operate that in the direction you want to go. Don't even have to disconnect the roller chain. If hydraulic fails then you still have your manual steering(if cylinder is unlocked).
Note that a DC generator on the wheel would not work cos you won't generate enough power to operate any relay just by moving the wheel in small steps.. You would have to continually spin the wheel in any direction to get enough volts to operate a relay.
Only other way I see, is to have proper position encoder on wheel and cylinder with suitable electronics to drive cylinder to position set by wheel, after removing chain of course. Then you no longer have manual steering if failure occurs.
 

blocco a spirale

Joined Jun 18, 2008
1,546
Yes, I've thought of that, but unless I could salvage just the torque sensor, It may be too complicated.
I don't think so. The advantage is the torque sensor and motor are integrated into one unit that fits inline with the steering column. My only concern would be whether the electronic control unit can easily be implemented. Any DIY solution is likely to perform poorly and with less reliability in comparison. It all depends on whether or not you consider steering to be a safety critical function.
 

DNA Robotics

Joined Jun 13, 2014
635
I like Les's idea about monitoring the slack that he posted while I was working on this.

I hope I can make this clear.
Steering wheel is mounted on Acme threaded rod.
Sprocket is mounted on Acme nut.
DPDT roller switch rides on face of sprocket wired to swap polarity when not in center neutral (off) position.
When you turn the wheel / threaded rod, the sprocket moves longitudinally on the rod, one way or the other, activating the switch. The switch operates the power steering pump to move the steering mechanism until the sprocket rotates to the center "off" position.
You will need stop nuts on the Acme threaded rod to keep the sprocket from moving past the travel of the switch and you still have complete manual control of the steering.

Boat steering.jpg
 

Thread Starter

Vegard

Joined Jul 11, 2017
10
Thank you guys for very innovative suggestions. I have posted this questions to various people and boating forums and they either told me that it can not be done or told me to buy new steering or a new boat. I will the various suggestions and let you know how it goes. I've definitely learned something today
 

LesJones

Joined Jan 8, 2017
3,899
This is the relay arranement I was thinking of.
Rudder_drive.jpg



Both micro switches have normally open contacts. It would be possible to use the idea with two heavy duty micro switches without the relays. I imagine that the pump takes quite a large current so the high current wiring could be kept short with the relays mounted close to the pump. The micro switch contacts would only have to take the current for the relay coils so almost any type of micro switch would do. As you have not given any information on your location I can't suggest a supplier other than ebay which seems to deal with most countries. I would be interested in the layout of the roller chain drive as I can't think of how it would wotrk unles the chainwheel axis wa vertical, the same as the rudder axis

Edit
I've just noticed that I have missed the link between the normally closed contact of the lower relay and the negative supply rail.

Les.
 

Thread Starter

Vegard

Joined Jul 11, 2017
10
This is the relay arranement I was thinking of.
View attachment 130759



Both micro switches have normally open contacts. It would be possible to use the idea with two heavy duty micro switches without the relays. I imagine that the pump takes quite a large current so the high current wiring could be kept short with the relays mounted close to the pump. The micro switch contacts would only have to take the current for the relay coils so almost any type of micro switch would do. As you have not given any information on your location I can't suggest a supplier other than ebay which seems to deal with most countries. I would be interested in the layout of the roller chain drive as I can't think of how it would wotrk unles the chainwheel axis wa vertical, the same as the rudder axis

Edit
I've just noticed that I have missed the link between the normally closed contact of the lower relay and the negative supply rail.

Les.
The shafts are all horizontal. There are at least 3 chains and 2 shafts before the tiller so the resistance is pretty hard. I don't really know how the last shaft connects to the tiller. The hydraulic actuator will take up some of the slack on the chain from the wheel, but not nearly as much as when I turn the wheel by hand. I really only need the power assist when the wheel is hard to turn (when the weather is bad). I guess tightening the springs would accomplish that

The boat is currently in North Carolina, but I'm on vacation right now and won't be back until late August.
 

LesJones

Joined Jan 8, 2017
3,899
I would put the tension sensors on the first chain in the link from the wheel. I imagine that will be from the wheel axis height to just below the deck level where it drives a shaft that goes towards the stern.

Les.
 

LesJones

Joined Jan 8, 2017
3,899
I imagine the hydraulic drive to be a hydraulic cylinder pushing or pulling on an arm attached to the rudder shaft. If this is the case then it would not be able to drive backwards through a worm reduction gearbox.

Les.
 

Thread Starter

Vegard

Joined Jul 11, 2017
10
It is a hydraulic cylinder attached to the tiller. Yes, I see what you are saying. I guess it has different, more direct connection to the tiller
 

tcmtech

Joined Nov 4, 2013
2,867
Is your steering system loose and easy to turn when not in the water? I'm just asking given that unless this boat of yours is huge moving a rudder in the water should not be much work. The ancient mariners could steer boats 50+ feet long with one person which means either you have a really poorly made or maintained steering system, a huge boat or the arms of a small child.

Can your hydraulic pump handle continuous duty operation? If not you will burn the pump motor out rather quickly in a high usage.

Same with the power source. Can the electrical systems keep up with the pumps electrical demands.

Personally of the few boats I have ever operated steering was quite easy except for one guys boat that used a simple cable system of which he never too care of so all the pulleys on the cables connecting the steering wheel to the back were seized up.

It was hard to steer in or out of the water and and about 1/2 or more of a turn slack on things.
 
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