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Old Jun 19, 2012, 12:54 PM
DO OR DO NOT--THERE IS NO TRY
United States, AZ, Prescott Valley
Joined Mar 2006
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Independent twin elect.motor control for PT Boat Project

Hi All,
Here's the deal...........I'm building the 48 inch PT596 from "Frank's" Mesquito Boats in CA. The glass hull is magnificant, by the way. My question is about electronics, however.

I've got 2 12Volt motors @ 7 turns/20 amps ( I really don't know what this means) and I want to be able to have independent motor control for each of the two motors/ props. I THINK I need 2 esc's, but I'm not sure about the configuration/wiring between the 12V battery power source, the esc's, motors and what transmitter/receiver I need. I've got a 6 channel radio receiver and transmitter that I'd like to use if possible. It's the usual aircraft type that frustrate us all because the VERY few designs for boats are SO $$$$$$$$$$

Can anyone help with communication that an electronics novice had understand?

I'm an accomplished model builder, but I'm electronically challanged.

Thanks, John De Broske
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Old Jun 19, 2012, 01:04 PM
Semper Fi
GreenAmphibian's Avatar
Northern Triaid North Carolina
Joined Jun 2008
994 Posts
Unless your radio is a 2.4 type or a ground vehicle one you can not legally use it on a boat. There are a couple of ways to do what you want. Two ESC's will do it. Just hook up the battery to the inputs through a Y harness. Make sure you also use a breaker or fuse too. Hook up two channels from the rx. to the ESC's using v tail mixing on the radio. That should allow you to have independent control as well as operate both in unison. You can use another channel for your rudder.
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Old Jun 19, 2012, 01:13 PM
Registered User
United States, CA, Hayward
Joined Feb 2006
877 Posts
Or hook up the throttle to one and the elevator to the other. Bus bar to split the main power works for me. But the bottom line is that a PT is so narrow it gives you very little advantage.
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Old Jun 19, 2012, 01:29 PM
Veni, Vidi, Feci
patmat2350's Avatar
Motor City
Joined Dec 2004
12,300 Posts
Quote:
Originally Posted by CaptLee View Post
...But the bottom line is that a PT is so narrow it gives you very little advantage.
Sorry, but I beg to differ! I have independent motor control on my 4 ft PT, and it's fantastic for low speed maneuvering, I can even spin the boat almost on its own center.

However, I don't have an easy solution: I programmed my own microcontroller to do the job with a 2 channel radio, which makes operation very easy... but one needs to know one's electrons and coding for this. I discuss it a bit at:
http://matthewsmodelmarine.wordpress...e-expendables/
(see the "Motivating" section):
  • Forward: The motors pull a fair amount of current even under light load. To conserve power, only the center motor runs at part throttle ahead. At about 50% throttle, the two outboard motors gradually kick in until all three reach 100% at full throttle. The transition is seamless.
  • Reverse: To avoid swamping, only the center motor is active in reverse, and is limited to 50% throttle.
  • Turn-in-place: With no throttle, turning the helm counter-rotates and progressively increases the speed of the outboard motors; port helm spins the bow to the left, starboard helm spins to the right.

For low speed work, like a maneuvering competition, I'll goose it forward a bit, go to zero throttle and steer a bit, which kicks in the wing motors' counter-rotation... that spins the boat around, almost as fun as driving a forklift!


p.s.: There are some commercial mixer devices out there, such as the one from Action... tried it, was completely unsatisfied with how it worked for me. I also suspect that mixing on modern radios may let you achieve some of these goals, but I don't see how you can get exactly what I have with my on-board micro.
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Last edited by patmat2350; Jun 19, 2012 at 01:35 PM.
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Old Jun 20, 2012, 12:06 AM
Registered User
Waukesha, WI
Joined Dec 2006
256 Posts
mixer help

Pat
Saw your pt page-impressive model work!!!!!!!!!!!!
Can you post some further help for us old school electronic hackers. I never learned about microprocessors/programming.
Do you have plans for your pt controller mixer. tips on code/programming?
Do you just program pulse rates to three electronic speed controls?
Looking to do something similar for my Berlin.
Thanks,
Jim
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Old Jun 20, 2012, 03:34 AM
WooHoo!
woodybob's Avatar
Lake Balboa, CA
Joined Jun 2007
5,064 Posts
There are a bunch of configurations over in the Electrical Discussion thread. Perhaps one of these may be just the ticket.
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Old Jun 20, 2012, 07:26 AM
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JOHN SCALE BOAT's Avatar
United States, PA, Slatington
Joined Feb 2007
400 Posts
I would recommond looking at the Sabertooth ESC. I run the smaller one in my towboat. In mixed mode the throttle stick on the transmitter with throttle both motors at the same rate then when you move the "rudder stick" it will reduce and one motor speed all the to full the other direction. Then use the alerion stick for rudder control. I have had this ESC for over two years now and has worked like it should with no issues.

http://www.robotmarketplace.com/prod...ER2X25-RC.html
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Old Jun 20, 2012, 04:41 PM
Webmaster, MMCNE
Acton, MA USA
Joined Feb 2000
582 Posts
Take a look at the P94 dual ESC from Action Electornics. It is a single unit that can give fully independent control for two motors, or it can be configured to coordinate them. There is also a diagram available for using a third motor, as in a PT.
http://www.action-electronics.co.uk/pdfs/P94.pdf
I just ordered one for my twin screw 1/16 scale Landing Craft, hope to have it in a few days. (I have one of their smaller units- it is great.)

Dave at Action is terrific-- he answers emails personally, and will help you pick the right product for your particular battery/motor combo and needs.

They aren't the cheapest- but they are designed by a scale boater for use in scale boats. And if you're in the USA, you don't have to pay VAT- so that's a 20% discount off the published price. (Of course the pound is about $1.60 now, so that drives the price back up...)
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Old Jun 20, 2012, 04:48 PM
Did you check the FAQ already?
SoloProFan's Avatar
The Netherlands
Joined Jul 2010
12,044 Posts
One thing to observe, didn't see it mentioned here yet, when the ESC have BEC system, you should remove the red wire on one of the receiver plugs, to avoid both ESC "competing" to supply the required voltage to the receiver.
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Old Jun 20, 2012, 07:30 PM
Veni, Vidi, Feci
patmat2350's Avatar
Motor City
Joined Dec 2004
12,300 Posts
Quote:
Originally Posted by jshander View Post
...Can you post some further help for us old school electronic hackers. I never learned about microprocessors/programming.
Do you have plans for your pt controller mixer. tips on code/programming?
Do you just program pulse rates to three electronic speed controls?
Looking to do something similar for my Berlin.
Thanks,
Jim
*sigh*
No, not really... books have been written on the subject, and I'm in no position to write another one here. And the little programming I know I've picked up over YEARS, in hobby and professional work.
But anyone truly interested in learning can do it too. Look up Parallax's Basic Stamps, and the open-source Arduinos from a number of supppliers. Try one of the available projects (little robot things)... it's like starting with a kit for a first time model builder.

Essentially, the micro (which you program) reads the Rx output, which is just a train of varying length pulses. Your program decides what to do based on these pulses (which correspond to Tx controls positions). And "what to do" is to send other pulse trains out to whatever is connected to the micro... ESCs, servos, whatever.

If you're the type who laughs at proper grammar and punctuation (like you don't know the difference between Violators and Violator's), then don't bother, as programming is very unforgiving to the grammatically challenged.
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Old Jun 20, 2012, 10:13 PM
Registered User
Ladysmith Vancouver Island
Joined Feb 2008
577 Posts
I've got twin esc's in my 40inch PT

and they do work very well for manouvering independantly

I'm running 4 battery packs to a bus bar (esentially making 1 big battery)... the whole bar feeds both ESC's (so power draws from all packs at once no matter which esc is running or how hard) ... then each ESC ofcourse has it's own motor.

on my 2.4 futaba 6EX I have 1 ESC on my left stick up/down (main throttle) ... and master that channel and slave my left stick left/right channel for the other ESC for now

next I'll be playing with Vtail and/or elevon mixing with dual rate for high speed running and harbour manouvering ...

that'll be ... master on left up/down (throttle) nothing connected to that channel, and slaved to right up/down ESC#1 (elevators on a plane) .. rudder on right left/right (ailerons on plane) ...
then ESC#2 on left right/left (rudder on plane) with aileron as master and rudder slaved
turn on elevon/Vtail mixing %'s on each side of the dual rate.

if you didn't understand that, it's alright I know my explination kinda sucked...

basicallly.. throttle forward both go forward ... add left rudder and it'll cut throttle to the left motor to let the inside of the turn dig in more and forced more by the outside motor... same for a right turn... the degree of inside motor cut out is set by the % in the elevon/Vtail rate you set ... if you set over 50% and go hard enough over it'll actually send the inside motor into reverse too.

basically.. when I hit the throttle the master/slave will operate the 'elevator' channel of the
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Old Jun 24, 2012, 03:50 PM
DO OR DO NOT--THERE IS NO TRY
United States, AZ, Prescott Valley
Joined Mar 2006
152 Posts
Thanks

I just want to say THANKS for all of the help............this is such a great site.

Your help has been invaluable as has that of the esc manufacturer AstroFlight. They spent time and patience with me. GREAT!!!

AZCAPTAIN
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