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Helm ControlsI pondered hydraulic, pneumatic, fly-by-wire using stepper motors, and linier actuators, push-pull cables which are the standard for jet boats, pull-pull cables, and push-pull tubes. I first opted for push-pull tubes similar to those on a Swiss J22 Fighter. The fully mechanical approach had problems related to the
difficulty in producing the components with very close tolerances
that would not be effected by sea water. Also connections to the jet
pump are really designed for cables and not push tubes. Using
tubes only would necessitate steering with a rudder only and not
turning the nozzle on the jet pump. That brought me back to a
fly-by-wire system that I ended up building. Both designs follow as
well as details for the engine throttle control. Push-Pull Tube Controls
With a suggestion from a kit air-plane builder I decided to pursue tork tubes or better know of as push-pull tubes. (1) Thanks to the Swiss J22 Fighter control stick design for the inspiration. The external tube rotates while the internal tube moves front to back. I added bushings with o-ring seals to stop leaks. (2) (3) The internal tube must remain parallel to the outside
tube because of the o-ring seals so the connection from the stick is
not a fixed bolt. Instead a fork on the stick that slips over a pin
on the internal shaft.
The throttle is cable controlled, but I hope to find a cable that is water tight at the sick end. The other end will be exposed in the engine compartment which will be dry. This cable will move the engine throttle as well as a linkage in the engine compartment connecting it to a sliding potentiometer which will in turn control the thruster motor speed when submerged. A simple push button thumb switch will be on the top of the stick that will allow the pilot to reverse the thrusters. Two more switches will sense if the stick is in the left or right turn position, and these in combination with the reverse button on the stick will reverse only the left or right thruster as needed in order make tighter turns. (4) A rudder will rise above the rear deck over the external portion of the Jet drive nozzle. By reversing a thruster, turns while submerged could be made with out a rudder, but a rudder will allow for more gradual turns will allowing both motors to push the boat forward. Front and back motion on the stick will pivot the thrusters and dive planes 180 degrees down and up to control depth. When the stick is moved to its full forward position it will lift the modified clean-out plug on the jet drive, effectively opening a 3 inch hole in the hull in order to flood the hull for diving. After surfacing a bilge pump will be used to pump the water out of the engine's snorkel and once the engine is started the clean-out port will again be opened, this time the water will be sucked from inside the hull by a ventury effect. Hopefully that will be enough. If not, then I will have to fine a way to obstruct the normal intake port. Like wise when the stick in moved to its full rear position, it will cause the jet drives' reverse gate to drop. This arrangement is designed to be as simple as possible, combining the same controls for surface and submerged operation, and almost everything needed being controlled with only one hand. The remaining controls will allow adjustments for the ballast in order to adjust the subs buoyancy and trim, and allow for the legs to be deployed and retraced for setting the sub down on the bottom. There are a few problems with this approach. First, since
the stick in the cockpit is between the passengers, and not between
one persons legs, someone is going to have to move their leg for a
hard turn. Second if the jet pump nozzle were to turn left and
right as it normally does, it would effect the jam the push-pull
tube that controls the reverse gate. So they would have to be
separated by adding a rudder below the jet pump for turns, and the
jet pump nozzle would have to be fix in place, severely limiting the
turn radius. Fly-By-Wire Helm ControlsExperimenting with a Throttle Control
Limitations of push-pull tubes for helm control had me once again thinking about interfacing a joystick with electric motors that drive the helm. I had decided to control the throttle with a 1/4 scale model servo. (1) The controller interface is was using was a $89 OOPic controller board from www.oopic.com is only a 3 inches long yet loaded with features designed with the robot builder in mind. Servos are normally radio controlled, but they can easily be wired to the OOPic. (2) I got used servo for $25 and wired it to the OOPic in short order. Next I connect a small pot; think knob, to the OOPic that controls the servo. All of this is going so well that it was really helping to reincarnated ideas of a complete Fly-By-Wire helm. With a Fly-By-Wire setup, I could sit in the cabin or on the cabin's roof and drive the boat with a simple joy stick. The downside is that without spending lots of bucks, my fly-by-wire system will have relatively slow response, but if I just throttle down the engine, perhaps going slow into the turns is something I can live with. And with a front end shaped like a wedge, going slow into the corners is a good idea. (3) Fly-By-Wire is not new to boats either, many ships use it and Ultra Dynamics at www.ultradynamics.com offers their Ultra Jet fly-by-wire system for smaller craft if you have the budget for it. In order to get the desired reaction time these systems use hydraulics, or more specifically electro-hydraulics which use electronics to control hydraulic pumps and valves. I however don't want to invest in or mess with hydraulics so I am going to try to utilize electric motor control and live with the slow response. If this fails then I'll fall back onto the manual design I already have for the helm. Thinking AloudInspiration comes from the unexpected places when using Google. Searching for joystick helm controls led me to www.martin16.com. They outfit sail boats with automated gear so that they can be sailed by paraplegics and quadriplegics with a joystick or even a mouth piece control. Sailing when you can't swim. Think about that one. I though I was adventurous. I now envision an analog joystick mounted on a 4 x 8 x 2 inch box along with the LCD and a few buttons for things like the flood valve and engine start and kill switch. Inside the box would be the power supply, an OOPic control board, and a mess of wiring. The OOPic's job would be to interface between the joystick and the motors that move the jet pump nozzle, reverse gate as well as the thrusters. Another Experiment(4) The rudder and reverse gate would be controlled by push-pull cables attached to a sprocket that is driven by a windshield wiper motor further reduced by a drive chain to another sprocket. The windshield wiper motors have simple position switches that can be connected to an I/O line on the OOPic and the chain will not allow slipping so the position of the helm and reverse gate will always be know. An on/off switch joystick like the Atari joystick on old arcade games would be workable, but an analog joystick that uses variable resisters or pots would be able to measure had hard the movement is. It would then be possible to control the motors with a variable speed controller, using the 36 volt system. So a small movement would power the motors at slow speed and a hard movement would run them at full speed. Simplifying the Idea and Building It.In an effort to simplify the fly-by-wire controls and reduce the number of points for failure, I am going to move first try a steering and reverse gate control that does not use the OOPic controller card. Just a simple 4 switch, arcade type joystick that controls relays that run motors in either forward or reverse which are connected to push-pull cables which are connected to the jet pump. Limit switches stop the motors so when the limit of the cable is reached. I'd like to use Solid State Relays (SSR) which are much more reliable that electromechanical relays, but most all solid-state relays are Single-Pole Single-Throw, Normally Open (SPST-NO) devices and specialized SSR's are expensive. While playing around with the linier actuators, I have decided that the speed is going to need maximized. Waiting 3 seconds for the reverse gate to drop just seems like too long. So I now plan to power the actuators at their rated 24 volts and possibly 36 volts. That is too much power for reed switches so I'm back to relays. For now I'll just go with simple mechanical Double Pole - Double Throw relays with normally closed push button switches for the limit switches.
(5) To further increase the speed of travel and to allow for the rate of travel to be modified I have designed a box that connect the push-pull cables to the actuators with leaver arms. These actuators have loads of power even at 12 volts so the leaver arms will allow an adjustable amount of power to be converted into speed. (6) The actuators an leavers were enclosed in an ambient box to help prevent water from entering the push-pull cables. (7) The cables connect to the box through PVC Unions, so they can be disconnected and moved if needed. The cable will be epoxied into the outside section of the union and the other side of the union will be epoxied to the box. The same leaver that controls the reverse gate on the jet pump will also control the pitch of the thrusters since the jet pump is only used on the surface and the thrusters only used when submerged. (8) The leavers need to be supported so there is no chance for them to collide with each other and I also need a place to mount the limit switches. Nylon is easy to cut and makes great low friction bearing blocks and guides where there will not be a lot of heat build up. The cheapest and most convenient source are those plastic kitchen cutting boards. I always thought ours was about 2 inches longer that was needed. (9) The limit switches are mounted in the slots where they can easily be adjusted. The switches are "normally closed" so when the button is depressed by the leaver the power to the relay switch will be broken, the relay will open and the actuator motor will stop. As long as the switch is held open the helm will not travel any further in that direction. (10) (11) (12) The relays are assembled into a do-it-yourself relay-block made from 1/4 inch acrylic. The wire connectors were potted with wax before the being potted with a layer epoxy. This will allow the relays to be unplugged and replaced. All of the wires are connected to a screw terminal block that will make connecting power, motor and control cables easier. (13) Only the front face of the box is 3/16 inch, the rest of the box is 1/8 inch and MIG welding 1/8 inch is difficult enough without worrying about pin holes that may be left in the joints, so to make the box pressure tight the inside is coated with 2 part epoxy paint. (14) The completed box mounts one the
inside wall of the hull. Like the other boxes in the hull, this one
will have an ambient air supply line connected to it so that the air
pressure inside of the box will remain the same as water pressure
surrounding the box. The size of the box is kept to a minimum in
hopes that it can be close to naturally buoyant. Engine Throttle Control
Now that I have eliminated using the OOPic control board for the helm's steering it makes since to simplify the servo control for the throttle too and eliminate the OOPic card altogether. (1) So now the engine throttle will be operated by an RC servo that is controlled by a servo tester. (2) The servo tester is a very simple circuit, I'm almost ashamed I paid $20 for it. I removed the button that is not need for my purposes and also de-soldiered the pot which I had hoped was not soldered onto the board when I selected the unit. The trick to de-soldiering is using solder wick, or some stranded copper wire coated with flux to suck-up the solder away from the connection. (3) I then rummaged through my old project box and turned up a nice little AT&T, 2 amp 12 volt to 5 volt DC to DC regulator. It was cheaply potted with plastic that was easily pulled away. (4) I then wired the parts together and potted them together in the box that the servo tester board came in, being sure to test the unit as I went. (5) A simple aluminum bracket replaced the normal throttle cable bracket. It bolts to the air intake and supports the servo that is then connected to the throttle arm with a linkage. There will be a lot of heat on the servo, especially when the engine is shutdown and the fresh air stops flowing in. To protect the servo it will be wrapped with insulation and feed a steady flow of cool air from the ambient air supply line that pressure compensates the engine compartment when submerged. Links
www.seamar.com Teleflex 43BC Push Pull cables for Berkeley Jet
drive. 12 ft for $63.
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