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Old Jul 16, 2012, 09:10 AM
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S.O.S. from PT-109

As someone who doesn't know a dogbone from a hex nut when it comes to R/C boating, I need some helpful advice. About 25 years ago, I bought the Lindberg 1.32 model of PT-109, and rigged it for radio control. Of course, back then, the technology was primitive. No speed controls, etc. It was on & off, and if delux, you could also do reverse. That was it. With two pounds of D cell batteries powering a thimble-sized motor, turning twin props through a PLASTIC gearbox, it was barely able to move through the water. It went on a shelf and stayed there for decades.

Recently, I discovered the technology has advanced and r/c boats can really rock and roll now. SO I decided to upgrade....got a new motor, got rechargable batteries, got a speed control...the works. Only to find, at high rpm's, the gearbox would explode and the gearshafts (also plastic) would snap like twigs.

After a year of trying to fix it so it would keep up...I finally had enough and sent the whole damn gear set-up to hell where it belongs. Now, I'm trying twin motors with a direct drive set-up and steel couplers.

I thought twin CAR motors would give me the torque I needed, only to find they sucked the battery dry in no time...and managed to totally cook a brand new 30 amp ESC in the process.

So here's what I intend to try next, and really want ANYONE to let me know if I'm asking for more trouble and wasting even more money...my new set-up will be twin Aquacraft 6.V 550 motors, direct drive with steel couplings to twin counter-rotating 3-bladed brass props, channeled through a Viper 40 amp ESC, powered by a Ni-MH 7.2 volt, 2100 mAh rechargable battery.

CAN ANYONE TELL ME......will it work and allow a 1/32 scale PT boat to replicate 40 knots at scale?
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Old Jul 16, 2012, 10:00 AM
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Wisconsin
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Welcome! Your question is a good one. There are lots of PT builds in the Scale Boat forum, so check (search) around in there. I have a couple of Lindy PT's, and I am a fan of a single motor, prop and rudder. Now before everybody blasts me for that sacriledge, I agree that doing a triple would be waaaay cool. Twin motors fits in between somewhere.
The trick with a PT is to keep it light. Twin 05 can motors (car motors) is they are not very light. And like you said, they go through the batteries pretty fast. Twin brushless motors with direct drive would be easy to do since you have the shafts already. I don't know what the motor specs would be, but I'm sure someone will suggest something.
My PT-196 has a single geared speed 400 with a gear drive and a standard Dumas shaft/tube assembly.

Dave

PT-196 short video. (1 min 20 sec)
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Last edited by boater_dave; Jul 16, 2012 at 12:26 PM. Reason: spelling
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Old Jul 16, 2012, 12:54 PM
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PT-109 to PT-196

Thanks, Dave....appreciate the feedback. The setup as described in my question has already been suggested (by someone who seems to know), and I really want to stay away from brushless if possible.

What I'm hoping to learn is whether the setup as described SHOULD work...or is there some technical reason why it won't that I just don't realize due to my massive ignorance on the topic.

I plan to order the motors and ESC tomorrow (will cost just over $100)...so if I'm making a mistake with this setup, I'm hoping someone will shoot me a head's up before I place the online order.

Thanks again, Dave. Mosquito boaters rule!
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Old Jul 16, 2012, 01:24 PM
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If there is a reason why most set ups fail, it is because the propellers are
too large. The motors get loaded up, and then draw high amperage to compensate.
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Old Jul 16, 2012, 02:21 PM
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Are you saying twin Dumas tri-blade counter-rotating brass propellers (with the same size diameter and same pitch as the original 2-blade plastic propellers) are too large for twin 6.v Aquacraft 550 motors to handle easily?
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Old Jul 16, 2012, 02:51 PM
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Sneek, Netherlands.
Joined May 2004
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Hi SeaJay,

I suggest you do some more reading on the set-up of this boat in the scale section.
You'll find that boaterdave is right and keeping things light is the key.

Your twin motorset-up will be on the edge of what the hull can carry without sinking in too deep, spoiling the appearence of the boat.

Regards, Jan.
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Old Jul 16, 2012, 03:02 PM
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I couldn't find the motor/prop specs on the Aquacraft web page, but that seems like a lot of money, and weight, for a Lindy PT. Generic 550 can motors usually go for $10-$15. And as long as you are staying with brushed, a car esc like a Traxxas XL-1 or similar would be fine. E-Bay has 'em cheap, like $20-$40 if you are patient.
Props are the other side of the story, as Umi was saying. The three blade racing props on the Aquacraft page look like they will draw large amps, especially driven directly with a 550 can motor. And you have two of them. 20 to 40 amps (total) is not out of sight, so your 2100mah pack will last only a few minutes.
My vote would be against the setup you suggested. I think there are better choices, even keeping the twin drive.
As a comparison, my PT at one point had a single hot stock rc car motor. I had a very small two blade prop and I was still in the 20 amp range. The boat ran very fast for five or six minutes, and when it came back in you could not touch the motor (too hot) and it was not uncommon to melt the shrink wrap off the battery pack. Fun, but silly. Now my boat goes a bit faster than scale, and with a 3000 nimh pack I can patrol for 30 minutes of mixed (mostly fast) driving. I am looking at 5000mah lipos to take even more weight out and add to the run time.

Dave
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Old Jul 16, 2012, 04:54 PM
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Well...my QUESTION was whether or not the setup will WORK...and in the avalanche of helpful advice received, nobody has yet offered a simple "Yes, it will" or "No, it won't".

Therefore, since nobody has said it WON'T WORK, I'll go ahead and assume that it WILL.

This is the same situation I find when asking for help among fellow boaters at the lake....I ask a simple "yes or no" question, and I get buried in advice, suggestions, recommendations and tips....often contradictary...without getting the simple answer I sought.

Appreciate the effort, though. Thanks guys.

Here's a suggestion of my own....who is admittedly a raw, green, rookie newbie at this stuff and will never know as much as the rest of you. When someone like me comes along and asks a simple question...we're looking for an answer, not a lecture, or a seminar or a full course of educational study. We already know how knowledgable you are, which is why we're asking the question...so please, focus less on displaying the depth of your expertise, and a bit more on providing the specific ANSWER to the QUESTION asked.

But like I said....I sincerely appreciate the effort anyway, and offer my thanks.
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Old Jul 16, 2012, 05:43 PM
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Simple answer is nobody can give a yes or no because of the variables involved. Unless somebody else has tried the exact same setup there is no way to say yea or nay definitively. You get to be the test dummy on this one and maybe help the next guy in line. That's pretty much how it works.

I have no doubt this setup will move the boat. Whether or not it meets your expectations is an entirely different issue. Ask yourself if your perception of 1/32 scale 40kts is correct. The vast majority of the time boats are run way faster than scale speed. Also speed will always kill run time. The faster you suck amps the quicker the pack dies. I question your expectations due to the "simple" fact you posed a question which is unanswerable as put, then took umbrage at being "lectured".

What was being offered were proven setups from experienced modelers that would make this brick run adequately and where you could avoid being a guinea pig.
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Old Jul 16, 2012, 07:04 PM
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Thanks, Willem.....as I declared right up front, I don't know SQUAT about R/C stuff...so I had no way of knowing the question couldn't be answered yes or no...I'm not even sure what the hell variables are, much less how they would influence anything in the setup.

I was only asking if it would work. First, you say the question can't be answered yes or no, then you say you have "no doubt" it WILL, but perhaps not up to my expectations. No wonder I'm so friggin' confused.

My expectations regarding what constitutes a realistic "scale speed" for the boat is based on what another boat was doing, driven by a former Soviet naval officer who is absolutely anal about authenticity. He showed me what 40kts should look like for a 1/32 scale PT. And it's something I've been able to achieve using only half throttle on my previous setup...which I'm changing due to heating issues in the ESC only....which I was told had been caused by using car motors with a 15 amp controller. That's why I'm switching to marine motors and a 40 amp controller.

I disagree that I took umbrage at being lectured, and apologize if I gave that impression. I was only frustrated at not being able to get a straight answer to what seemed, at least to a raw beginner like me, a straight question. Hell, even boater Dave said it was a good question.

If I had asked for suggestions, then alternative options for "proven" setups would've been welcomed. However, I was only trying to find out if the setup ALREADY SUGGESTED would, in fact, WORK.

To put it another way....if someone asks what time it is, it's NOT because they're interested in learning how to build a clock.

However, I sincerely do appreciate your taking the time and making the effort to reply and to be as helpful as possible under the circumstances. And I shall be proud to return the courtesy if and whenever I may.
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Old Jul 16, 2012, 09:30 PM
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As was mentioned, there are too many variables.
You can't "DO" what someone else has done, because you don't have the same parts.
That can be motor, windings, battery, speed control, propeller shafts, propellers.
It's just not a monkey see, monkey do kind of thing.
Your battery, esc, and motor might work great together, but that pesky propeller can be maddening.
What diameter, number of blades, and then what pitch.
Will the motor turn that propeller, yes, but at what "cost".

Ninety percent of the time many of us can't tell you the pitch of our propellers.
But it work good...

Model boat racers could dial that in a bit more for you, but even though I am
no beginner, when someone starts talking torque, joules, and watts, I'll often only
be hearing a dial tone...
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Old Jul 17, 2012, 05:30 AM
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Sneek, Netherlands.
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Hi SeaJay,

I understand your frustration about not getting a straight answer...
If you would be so kind to provide links to the components you want to use, it's somewhat easier to give an opinion on if this should work, yes or no.

Knowing my fellow formmembers, they have been searching for the components you mentioned and didn't find them (right away, or at all).

If you want to know about specific items, provide a link.

Regards, Jan.
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Old Jul 17, 2012, 12:54 PM
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Powering up a lindberg PT

I went to Mack products and got 2 3150 motors, and then from Dumas got the drive system in 1/8 drive shaft for a Dumas 44 foot coast guard boat and the correct dog bones. I used the dumas props that were about the right size and currently it has a single electronic speed controller for I think 12 turn motors and has a slight wine at low running, a good one that I saw was the Traxxas EVx2 tower number KG6225 -115.98 I run a single 9.6 volt c-size battery back velecroed between the shafts. - With this set up the boat "on step" looks like the real thing about half way out of the water - I also modified the boat to look like a PT, including making the bow stright like an Elco 80.

You can do the boat on the cheap if you have allot of experiance, or you can go to quality providers like Mack and Tower who not only can set you up with the motors but a full drive train and universals and then look for a good electronic controller -

I build my PT in 1994 and she still runs good and looks good, my only plans is to do twin speed controllers Y controlled to the 9.6 pack and use a twin throttle modified 4 channel so the motor controls can be handeled like a real twin. for this I will proably use 2-15 amp vipers - I am in the process of doing my Southampton tug right now.

The attached picture is a quick shot I took in 2009.
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Old Jul 17, 2012, 03:31 PM
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Hi Jan.....the motors and couplings are coming from Tower Hobbies and the ESC is coming from Harbor Models. Both have online sites. The motor (550) is by AquaCraft and is intended for the AquaCraft "Bristol Bay" boat, which runs a tri-blade prop like the Dumas' ones I'm using...same diameter and pitch. So I figure TWO of 'em should move the PT pretty well. The ESC is a Viper 40 amp....which ought to handle the power demand from the twin motors spinning twin tri-blades without burning up.
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Last edited by SeaJay; Jul 17, 2012 at 03:48 PM.
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Old Jul 17, 2012, 07:07 PM
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bgnome's Avatar
Richmond Virginia
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straight answer based on the comments...

YES, it will work
NO, you probably shouldn't do it that way.

the whys have been explained.
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