Electric Kontiki motor power supply and PWM questions

Why not run the control circuit from a separate battery?

Donald

Sounds like an interesting project. What is the idea for navigation? The transducer responds to a beacon in the water on the beach? Direction finding with only one ear?

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Donald,

I may well have to but it's something I'm trying to avoid for several reasons. The first is the probable need for an second charger as I don't think I'd be using a 12V battery of any AH to supply the 5V for the PIC and servo and the second is the extra weight. The good thing about these Knotikis is that they are supposed to be a little like submarines in that they should not bob on top of the water but sit low in it so as to push through the oncoming waves.

Thanks for your reply,

Rubicon.

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This isn't a remote control application. Rear prop ones are guided by a rudder that you set after gaguing the offshore current by "eyeometer". Front props are apparently self correcting for as the belly in the towed line gets bigger from side current the Kointiki is turned more into the current. They can have a tiny rudder in front of the prop sometimes.

No doubt you saw SP1 Transducer in the schematic and thought remote control, beacon, but it's actually just a beeper for audio indication of commands via a reed switch or the failure of a startup check.

Funnily enough it's something I've thought about as an old project I've put on hold was using an ultrasonic transmitter to trigger the release and shut it down. Got most things going there. Security and Manchester coded untrasonic signals sent to the receiver at 300bps (or

Sorry but I can't stay online any longer, have to go to work now.

Thanks for the reply,

Regards,

Rubicon.

You can buy them off the shelf in New Zealand.

Please enlighten me - this is something I could use (we don't have/use Kontiki here.

So the idea is to transmit behavior to the robot/torpedo via radio? ala Mars rover?

I have to be missing something basic here. The idea is to carry a fishing line out past the breakers when a kite won't work?

The line goes out and drops, so you can catch bottom feeding fish? OK. Now, with all the money and effort invested in the torpedo how does it get back to shore?

Kontiki was the name of Thor Heyerdahl's raft. He was more or less at the mercy of the currents.

We don't even use kites here . . .

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The big caps at the input to the 5V reg won't help much with the circuit as drawn - they can discharge through the motor. Also, the surge current to charge the caps (depending on how big you make them) can do ugly things to your reed switch. Adding 2 componenst will fix those problems. I'll draw two partial schematics to show the recommended changes:

Existing circuit:

D7 / + --->|---+---o o---+----+-----+---[V/R]--- | Reed | | | | Switch | [CAP] [CAP] }} }}

New Circuit:

D7 / ADD ADD + --->|---+---o o---[33R]---+--->|---+-----+---[V/R]--- | Reed | | | | Switch | [CAP] [CAP] }} }}

The 33 ohm resistor will limit the inrush current to protect the reed switch and the diode will prevent the caps from discharging through the motor, if the motor pulls the supply voltage down momentarily. The circuit will *not* keep the pic running if the motor pulls the voltage down and keeps it down - it is just intended to handle momentary power dips.

Ed

Roger,

That's true but then they're certainly not cheap besides making one to operate in rough marine conditions and learning a little more about electronics at the same time is good.

Regards,

Rubicon.

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No it is not a remote controlled vehicle but as it floats on the water there's no reason it couldn't be. One could install the bits and pieces of a model submarine and using the indicator flagpole as an aerial use Rf to contol it.

Yes that's the idea. I have never used kites but they do have their place if you get a nice wind and are more immune to the offshore current but then setting the weight to hold the line in the water against a vairable wind is tricky. A friend of mine has and will never again. After carefully setting the weight he set it go and one minute the line is in the water the next it's 10m above and no one told him there'd be a flock of seagulls attacking his baited hooks as it went out. Don't think he caught a flying fish that day.

No, most electric Kontikis just go out guided only by a rudder or "self-guided" by the towed line and sit out there once it has timed out and stopped the motor. This has risks as all thing do and the risk is that the main backbone line connecting the Kontiki to shore either breaks or is bitten through. There are sharks everywhere but some areas here have large concentrations of sharks (Birdlings Flat for example) Five-gills, Seven-gills, Greyboy, the odd Mako and more and if a caught and struggling fish gets wound around the backbone line... I'm including a release mechanism just because I can and if I don't want to use it then I'll attach the backbone to a secondary eyebolt fixing at the rear of the unit. If I do want to use it then the backbone is attached to the release mechanism and a second retrieve line to the eyebolt. This way I can get the Kontiki back to shore out of harms way and even set another line out should I want to.

I'm building an electric Kontiki with a mechanical release mechanism because I want to but there's no need to just to get a line out.

We use the name Kontiki for many offshore fishing devices here. It was mainly used to describe small wind driven platforms with a sail that would collapse after a time and drop the weighted line. I know one bloke who with a friend used an old boogie board, broomhandle, bedsheet and a plank as a rudder for a Kontiki. Line was rigged so that when the advanced timing device - a barley sugar sweet dissolved in the seawater the sail dropped and a weight unravelled to the bottom. It worked well and they caught a few fish until they got cocky and set it sail again into even bigger breakers. It got dumped and the boogie board snapped in half. Nowadays there are still sail Kontikis around but usually with twin aluminium pods for stability. I saw a home-made one for sale recently with of all things a petrol powered weed-eater set at an angle into the water between the pods!

The Kontiki-Bag is another offshore wind driven method. It's just a heavy duty brightly coloured cylindrical bag say 0.5m x 1.5m. One end is tightly tied shut, the other end is tied with yes, a barley sugar sweet in the knot so that when it dissolves the bag opens and the air escapes. A strong line from each end of the bag joins the backbone line with the hanging weight on lighter line as are the hooks and all is dragged out into the brine. The reason for the lighter line is so it breaks first should it get snagged and collapsing the bag is to make it easier to pull the line back in when there's an offshore wind to fight against. Additional small weights or floats can be added to the line to give it an angled spread through different layers of the seashore where perhaps different fish dwell. The bag can also get dumped by a breaker and this is were the less tightly tied end also comes into play by popping open first and saving the bag from damage. The good thing about the bag method is that vairable winds that play havoc with a kites altitude don't effect it nearly as much but then offshore current is its pitfall.

There's even a really old device that folds flat when a wave hits it but opens up on the back wash and slowly makes it's way out across a sandy beach bottom.

Goto these sites for more info on electric Kontikis

Regards,

Andrew.

Ed,

Thanks for the advice and the partial schematic. I've already altered mine on the webpage.

I wonder how the commercial units deal with the motor being severely under-powered and still maintain controller stability?

Anyway thanks again.

Regards,

Rubicon.

Well I was thinking about using PWM on the motor to vary the speed via voltage but wasn't sure about its effect upon current, Now I see that I can vary the average current by adjusting the duty cycle. Maybe I can reduce it far enough to not upset the PIC supply?

Any advice on this?

Regards,

Rubicon.

Thanks for taking the time Andrew. This is all very fascinating stuff to me. Most folks around here just use 12-15 foot poles and cast. I've used a kite and it has its problems.

Last big brainstorm was to just sling the weight (with hook and bait attached to a leader) via a huge slingshot. That actually worked quite well providing you have the manpower and a section of beach that's deserted. Surgical tubing (spools of the stuff to make a multi band sling) Soft leather pouch.

Uprights were a pair of 4X6 X12' foot lumber set into the wet sand at the edge of the surf line with post hole diggers (a hassle when the tide changes) or last time a pickup truck with stake pockets in the bed parked parallel to the beach (with a piece of plywood covering the glass on both sides in case things go wrong). Pickup truck is the way to go - 8 foot hardwood spars in one set of pockets and guy wires to the other pockets - no digging necessary. Setup, take down, and moves quickly to follow the schools (providing the team is still reasonably sober and everyone does their job).

Takes four people to haul the bands back about 40 feet to sling 4-8 ounce sinkers into the water, but it will get it out there. It is hard to get four people (drunks) to release the line safely so we added a pull pin trigger to keep our fingers safe. The latest refinement is to add a auger in the dunes so we can stand back in case the hook comes out of the pouch. A fifth guy holds the spinning rod and follows the line with it.

Its all very athletic and once in awhile we catch a fish. More fun than an effective fishing technique. We can put two lines out without moving the truck if we don't use the auger

One of my cohorts wants to build a trebuchet and sling big rocks out with lines attached - no ones taking him too seriously but he bought a trailer to build one on. No ammo on the beaches or even nearby so he'd have to haul the rocks too.

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It is already PWM, per the schematic.

Nope - that is not the issue. First, when you control the speed of the motor, PWM is the way to go to save battery power. Your circuit is PWM. But PWM doesn't prevent upseting the PIC. In fact, it can do the opposite. What you want is a solid supply to the PIC, free of the electrical noise that PWM will cause. The diode isolation with the big cap after the diode, and the small caps in parallel with the big cap and the output are there to do that.

I took another look at your schematic. The diode marked D1 is not necessary, and will vaporize when you run the thing, in any event. It is rated at only 1 amp, and the motor is rated at

Ed

Certainly. The difficulty, I suspect, is getting these things off the beach in rough conditions. Once off there should not be too much of a problem. The electronics should not be too complicated if you use a simple timer to stop the motor. A single 555 will not give you a long enough time period but there are a range of count down and count up chips which will do the job. If the timing circuit includes a 555 to provide the input to the counter the 555 can vary the frequency of the input to the counter thus providing a means of varying the running time. One potentiometer should be enough to control the 555 within the limits you need. That can be accessible within the waterproof battery case. The timer interfaces with a transistor(s) which will pass enough current to operate an ordinary motor vehicle headlight relay. The relay switches the motor off. As the motor uses 12 volts you can use two or three motor cycle batteries in parallel.

Roger,

That's a good and much easier way of doing it but at the moment I'm learning to use PIC microcontrollers and as they have built-in timers, voltage comparators, pulse-width modulation modules and such I wish to use one of these. The PIC can be set for the time you want, give audio beeps to confirm the settings, control the speed of the motor, control a strobe, check the battery, check for leaks, set off the release mechanism and shutdown the whole thing afterwards. The only thing I'm really having a major problem with is having it use the same power supply as the motor.

Thanks for the good advice for I may yet throw a wobbly and return to the KISS (Keep it simple stupid) principle,

Regards,

Rubicon.

use a pic that runs off 3V instead of 5V ?

Ed,

Thankyou for your comments and advice on the circuit.

I am the first to admit that "A little knowledge is a dangerous thing." and I thank you for saving me from the "Magic Smoke" of a vaporised diode!

Yes I know it's already PWM as I intentionally (as best as I could) made it that way but more as "In-case I need it" rather than "I will need it".

I had hoped that PWM would reduce the current enough but perhaps now I need a separate supply for the PIC and a dedicated motor controller circuit to limit the current to the motor. More searching and reading and asking required.

Regards,

Rubicon.

With PWM, you turn the motor on/off very rapidly, and use duty cycle to control the speed. It is really the only way to go for this project. Since it is the only way to go, we really can't talk about saving power or reducing average current, as that implies a comparison to something else.

The concern is not exhausting the batteries to the point that the microprocessor (mp) won't run. The motor needs hundreds of times the current that the mp needs. When the batteries drop low enough that they can't run the motor, they still would be able to run the mp.

Therefore, exhausting the batteries is of no concern when looking at keeping the mp running. What is of concern is the temporary voltage drop created when you first turn on a motor that is not moving. You get a very large surge current, far in excess of the motor's steady state draw. That causes the voltage to drop briefly, until the motor gets going.

Your LDO voltage regulator needs at least 5.6 volts in to provide 5 volts out. If you use a 7805, you need at least 7.5 volts in. So the idea is to keep at least

Your LDO regulator is capable of 100 mA, so we must assume you are keeping the mp from drawing more than that. Using 100 ma as worst case, and figuring your capacitors at 80% of their value, they will keep the regulator satisfied for ~ 300 mS with the 7805 regulator, and longer with the LDO LM2931.

Whether 300 mS is sufficient I can't say. I don't know how long it will take the motor to get up to speed, nor how low it will drag the voltage at startup. Among other things, the duration of the start up time (getting the motor up to speed) will depend on the load on the propeller and the condition of the batteries. Weak batteries will have a higher internal resistance, and therefore a greater voltage drop.

A separate battery for the mp avoids the problem, but may not be the best solution. It could be that a separate battery is not needed - the existing circuit may do the job nicely. Do you have any specs on the motor operation at startup?

Ed

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Sounds fun but a dangerous way to fish! A year ago when I first broached the Kontiki thing I think someone suggested the butane powered spud/melon gun to launch the line out. Compressed air would work too but if butane or another flamable gas was used then I would expect that a stainless steel (flame-proof) leader connected to the projectile followed by a length of heavy line to take the shock of the launch followed by the backbone would be required. That, a long ignition switch wire and a well placed dune to hide behind wouldn't go astray either.

Regards,

Rubicon.