Electric Kontiki motor power supply and PWM questions

[Rubicon]

Hello,

I'm finally getting around to building an electric fishing Kontiki and
have some questions about how to do so. First off an electric Kontiki
is basically a timed torpedo with a prop either at the rear or more
recently at under the front to take a line out past the breakers into
deeper water where hopefully more and bigger fish lurk.

I have a schematic I've drawn up at
http://www.geocities.com/talionis.geo/Temp/temp.html.

The trolling motor is a Mercury 12VDC/30Amp, 30lb thrust type. I have
no other specs on it and the suppler couldn't provide any either.
Other commercial Kontikis use the same motor, one brand with two
12V/7.2Ah SLA batteries and the other with two 12V/12Ah SLA batteries.
I'm intending to use three 12V/7.2Ah batteries but my concern is that
the motor will draw so much under load that the PIC will reset itself
or just turn off the power supply relay. I do intend to disable
Brown-out Reset on the PIC and have a huge cap on the PIC power supply
to try and combat this. The motor is also connected to the PWM port of
the PIC and using the power mosfet I can PWM the motor rather that
just turning in on via a relay. This way I could possibly program it
to go-hard to get through the breakers then slow down. Also I read
something about using a zener diode across a mosfet and not just D5
but I'm not sure about what value zener to use.

Basically I have a reed power switch to provide power to the PIC that
in turn does some startup checks (battery level, leakage) then if OK
switches on the power supply relay and checks the light level for the
weak strobe.
The time is set at a default of 0mins and the Timeset reed switch sets
the time in 5min increments to a max of 25mins then back to zero.
The Motor Start reed switch starts the motor but if the Timeset switch
is activated while the motor is going then it stops the motor and
adjusts the time.
During operation the PIC runs battery level, leakage, light-level
checks and once the set time is reached it stops the motor, activates
the servo release mechanism to drop the line and shuts down by turning
off the power supply relay. Naturally to use the release mechanism I
have to have a second line to the Kontiki but there will be an
alternate mounting point for single line use.
If it's turned on and then needs to be turned off then setting the
time to 0mins and trying to start the motor will shut it down. That or
some other combination or maybe a timeout. Haven't decided yet.

I hope I've provided enough information, sorry if I haven't.

Any and all advice is greatly appreciated


Regards,

Rubicon.

 

[Donald Kinney]

I'm intending to use three 12V/7.2Ah batteries but my concern is that

the motor will draw so much under load that the PIC will reset itself
or just turn off the power supply relay. I do intend to disable
Brown-out Reset on the PIC and have a huge cap on the PIC power supply
to try and combat this.
Rubicon.

Why not run the control circuit from a separate battery?

Donald

 

[default]

On Mon, 18 Dec 2006 11:22:34 GMT, (Rubicon) wrote:

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?

 

[Rubicon]

Why not run the control circuit from a separate battery?

Donald

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.

 

[Rubicon]

On Mon, 18 Dec 2006 11:22:34 GMT, (Rubicon) wrote:

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?

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
600bps and even 1200bps) but multipath signals and the fact that I
don't know how to get an automatic gain stage working in the receiver
were the breaking point. Unless you were at just the right distance it
couldn't detect the serial non-FSK signals. Getting a clear signal
through the breakers and signals bouncing off the beach would be a big
problem I expect.

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

Thanks for the reply,

Regards,

Rubicon.

 

[Roger Dewhurst]

Hello,

I'm finally getting around to building an electric fishing Kontiki and
have some questions about how to do so. First off an electric Kontiki
is basically a timed torpedo with a prop either at the rear or more
recently at under the front to take a line out past the breakers into
deeper water where hopefully more and bigger fish lurk.

You can buy them off the shelf in New Zealand.

R

 

[default]

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
600bps and even 1200bps) but multipath signals and the fact that I
don't know how to get an automatic gain stage working in the receiver
were the breaking point. Unless you were at just the right distance it
couldn't detect the serial non-FSK signals. Getting a clear signal
through the breakers and signals bouncing off the beach would be a big
problem I expect.

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

Thanks for the reply,

Regards,

Rubicon.

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 . . .

 

[ehsjr]

Hello,

I'm finally getting around to building an electric fishing Kontiki and
have some questions about how to do so. First off an electric Kontiki
is basically a timed torpedo with a prop either at the rear or more
recently at under the front to take a line out past the breakers into
deeper water where hopefully more and bigger fish lurk.

I have a schematic I've drawn up at
http://www.geocities.com/talionis.geo/Temp/temp.html.

The trolling motor is a Mercury 12VDC/30Amp, 30lb thrust type. I have
no other specs on it and the suppler couldn't provide any either.
Other commercial Kontikis use the same motor, one brand with two
12V/7.2Ah SLA batteries and the other with two 12V/12Ah SLA batteries.
I'm intending to use three 12V/7.2Ah batteries but my concern is that
the motor will draw so much under load that the PIC will reset itself
or just turn off the power supply relay. I do intend to disable
Brown-out Reset on the PIC and have a huge cap on the PIC power supply
to try and combat this. The motor is also connected to the PWM port of
the PIC and using the power mosfet I can PWM the motor rather that
just turning in on via a relay. This way I could possibly program it
to go-hard to get through the breakers then slow down. Also I read
something about using a zener diode across a mosfet and not just D5
but I'm not sure about what value zener to use.

Basically I have a reed power switch to provide power to the PIC that
in turn does some startup checks (battery level, leakage) then if OK
switches on the power supply relay and checks the light level for the
weak strobe.
The time is set at a default of 0mins and the Timeset reed switch sets
the time in 5min increments to a max of 25mins then back to zero.
The Motor Start reed switch starts the motor but if the Timeset switch
is activated while the motor is going then it stops the motor and
adjusts the time.
During operation the PIC runs battery level, leakage, light-level
checks and once the set time is reached it stops the motor, activates
the servo release mechanism to drop the line and shuts down by turning
off the power supply relay. Naturally to use the release mechanism I
have to have a second line to the Kontiki but there will be an
alternate mounting point for single line use.
If it's turned on and then needs to be turned off then setting the
time to 0mins and trying to start the motor will shut it down. That or
some other combination or maybe a timeout. Haven't decided yet.

I hope I've provided enough information, sorry if I haven't.

Any and all advice is greatly appreciated


Regards,

Rubicon.

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

 

[Rubicon]

You can buy them off the shelf in New Zealand.

R

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.

 

[Rubicon]

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 . . .

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
http://www.seahorse.net.nz/
http://www.fishingkites.co.nz/electrickontiki/electric_kontiki-PT400.html

Regards,

Andrew.

 

[Rubicon]

Hello,

I'm finally getting around to building an electric fishing Kontiki and
have some questions about how to do so. First off an electric Kontiki
is basically a timed torpedo with a prop either at the rear or more
recently at under the front to take a line out past the breakers into
deeper water where hopefully more and bigger fish lurk.

I have a schematic I've drawn up at
http://www.geocities.com/talionis.geo/Temp/temp.html.

The trolling motor is a Mercury 12VDC/30Amp, 30lb thrust type. I have
no other specs on it and the suppler couldn't provide any either.
Other commercial Kontikis use the same motor, one brand with two
12V/7.2Ah SLA batteries and the other with two 12V/12Ah SLA batteries.
I'm intending to use three 12V/7.2Ah batteries but my concern is that
the motor will draw so much under load that the PIC will reset itself
or just turn off the power supply relay. I do intend to disable
Brown-out Reset on the PIC and have a huge cap on the PIC power supply
to try and combat this. The motor is also connected to the PWM port of
the PIC and using the power mosfet I can PWM the motor rather that
just turning in on via a relay. This way I could possibly program it
to go-hard to get through the breakers then slow down. Also I read
something about using a zener diode across a mosfet and not just D5
but I'm not sure about what value zener to use.

Basically I have a reed power switch to provide power to the PIC that
in turn does some startup checks (battery level, leakage) then if OK
switches on the power supply relay and checks the light level for the
weak strobe.
The time is set at a default of 0mins and the Timeset reed switch sets
the time in 5min increments to a max of 25mins then back to zero.
The Motor Start reed switch starts the motor but if the Timeset switch
is activated while the motor is going then it stops the motor and
adjusts the time.
During operation the PIC runs battery level, leakage, light-level
checks and once the set time is reached it stops the motor, activates
the servo release mechanism to drop the line and shuts down by turning
off the power supply relay. Naturally to use the release mechanism I
have to have a second line to the Kontiki but there will be an
alternate mounting point for single line use.
If it's turned on and then needs to be turned off then setting the
time to 0mins and trying to start the motor will shut it down. That or
some other combination or maybe a timeout. Haven't decided yet.

I hope I've provided enough information, sorry if I haven't.

Any and all advice is greatly appreciated


Regards,

Rubicon.

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

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.

 

[Rubicon]

Hello,

I'm finally getting around to building an electric fishing Kontiki and
have some questions about how to do so. First off an electric Kontiki
is basically a timed torpedo with a prop either at the rear or more
recently at under the front to take a line out past the breakers into
deeper water where hopefully more and bigger fish lurk.

I have a schematic I've drawn up at
http://www.geocities.com/talionis.geo/Temp/temp.html.

The trolling motor is a Mercury 12VDC/30Amp, 30lb thrust type. I have
no other specs on it and the suppler couldn't provide any either.
Other commercial Kontikis use the same motor, one brand with two
12V/7.2Ah SLA batteries and the other with two 12V/12Ah SLA batteries.
I'm intending to use three 12V/7.2Ah batteries but my concern is that
the motor will draw so much under load that the PIC will reset itself
or just turn off the power supply relay. I do intend to disable
Brown-out Reset on the PIC and have a huge cap on the PIC power supply
to try and combat this. The motor is also connected to the PWM port of
the PIC and using the power mosfet I can PWM the motor rather that
just turning in on via a relay. This way I could possibly program it
to go-hard to get through the breakers then slow down. Also I read
something about using a zener diode across a mosfet and not just D5
but I'm not sure about what value zener to use.

Basically I have a reed power switch to provide power to the PIC that
in turn does some startup checks (battery level, leakage) then if OK
switches on the power supply relay and checks the light level for the
weak strobe.
The time is set at a default of 0mins and the Timeset reed switch sets
the time in 5min increments to a max of 25mins then back to zero.
The Motor Start reed switch starts the motor but if the Timeset switch
is activated while the motor is going then it stops the motor and
adjusts the time.
During operation the PIC runs battery level, leakage, light-level
checks and once the set time is reached it stops the motor, activates
the servo release mechanism to drop the line and shuts down by turning
off the power supply relay. Naturally to use the release mechanism I
have to have a second line to the Kontiki but there will be an
alternate mounting point for single line use.
If it's turned on and then needs to be turned off then setting the
time to 0mins and trying to start the motor will shut it down. That or
some other combination or maybe a timeout. Haven't decided yet.

I hope I've provided enough information, sorry if I haven't.

Any and all advice is greatly appreciated


Regards,

Rubicon.

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

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?


http://homepages.paradise.net.nz/bhabbott/esc_theory.html
To improve efficiency and reduce controller heating, we need to use a
switching controller. Instead of simply limiting current continuously,
the switching controller sends short pulses of full power to the
motor. If the pulse rate is high enough, the motor's inertia will
cause it to respond to the average current. To vary average current we
can adjust the duty cycle (ratio of ON to OFF).

Any advice on this?


Regards,

Rubicon.

 

[default]

On Tue, 19 Dec 2006 09:18:07 GMT, (Rubicon) wrote:

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.

 

[ehsjr]

Rubicon wrote:

Well I was thinking about using PWM on the motor

It is already PWM, per the schematic.

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?

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
30 amps. The 25 amp fuse serves no useful purpose,
as drawn. It needs to connect to the battery before
any other component in the circuit, and has to be
rated to handle the 30 amp motor load. Relay RLV1
needs to have contacts rated for the motor, too.
The IRF540N is rated 33 amps maximum, at room
temperature. 33 amps is too small. If you go to 100%
duty cycle (full speed) it will heat up and die.
You can put two of them in parallel for a better
safety margin, and keep them cooler with a heat sink.

Ed

 

[Roger Dewhurst]

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.

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.

r

 

[Rubicon]

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.

r

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.

 

[jasen]

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?

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

 

[Rubicon]

Rubicon wrote:



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
30 amps. The 25 amp fuse serves no useful purpose,
as drawn. It needs to connect to the battery before
any other component in the circuit, and has to be
rated to handle the 30 amp motor load. Relay RLV1
needs to have contacts rated for the motor, too.
The IRF540N is rated 33 amps maximum, at room
temperature. 33 amps is too small. If you go to 100%
duty cycle (full speed) it will heat up and die.
You can put two of them in parallel for a better
safety margin, and keep them cooler with a heat sink.

Ed

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.

 

[ehsjr]

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
7.5 volts available to the mp when the voltage from
the batteries drops due to the surge when the motor
is first turned on. The job of the capacitors at the
input of the regulator is to do that.

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

 

[Rubicon]

On Tue, 19 Dec 2006 09:18:07 GMT, (Rubicon) wrote:

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.

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.