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Old Mar 07, 2012, 01:52 AM
Keep a Steady Strain....
capntroy's Avatar
Orange County, CA
Joined Nov 2007
1,220 Posts
As has been mentioned, a vessel that will spend a good portion of it's time "twisting" to port or starboard, such as a harbor tug or warship, will benefit from outboard-turning wheels (TTO), while a vessel such as an offshore supply boat or towboat that will spend a good portion of the time "walking sideways" will benefit from inboard turning wheels (TTI). The prop rotation aids the maneuver in both of these situations.

The best compromise is to install inboard-turning wheels (TTI) because you have the ability to "walk" or "crab" very efficiently and you can overcome any shortfalls during "twisting" maneuvers by adding a little throttle, not so if attempting to "walk" a boat sideways with outboard-turning wheels (TTO), you'll almost never be able to crab the boat sideways without backing and filling or see-sawing the throttles back and forth, making for a very ugly maneuver.
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Old Mar 07, 2012, 12:58 PM
We shall serve the Lord
kingsflyer's Avatar
United States, TX, Kingsland
Joined Sep 2005
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With the advent of computer radios, it is now very easy to program throttle differential. Throttle differential is the ability to slow down one motor by mixing the throttle channel with the rudder channel. A turn to port slows down the port motor and speeds up the starboard motor. A turn to starboard slows down the starboard motor and speeds up the port motor. I have used this system on a number of twin engined airplanes with great success. I usually set this up as a switch enabled function so that I can choose to use function, or turn it off and have the motors run in sync with each other.

Here's the issue, would TTO work better with differential throttle when under way, or would TTI?

McD
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Old Mar 07, 2012, 04:54 PM
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Portland Oregon
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HELLO ALL some of you know me some of you dont. All of the advice I have read that your giving is all good. I do agree with all of you .

BUT ?? ONE thing all though the theards I have read is no body have said anything on the prop it self. IF it is a right hand or left hand turn prop.

Belive it or not I learn that one many years ago along with some fustration;-)
. IT all depends on how the prop is cut and whitch why the cutting edge is going that tells you what prop you have and witch way it is suppose to run..
ONE other thing I learn though my years if you hit full speed on your prop when testing on your work bench or out side is when your at full speed or partley and you feel wind blowing toward ya that tells you the your prop is turn to push the water not pulling it . Then your boat or ship will run forward not back wards. It all depends on witch way your prop is turning pushing or pulling . No matter what props your useing for what set if it not runing the right way your infor many problems . Allways a good idea to test bech befor you go out to the pond . OK I am talking model boating .

That is how I use to figure out witch way my prop is turning. If I did not feel air blowing towards me i know I had the motors wired wrong .
I learn the ways of props the hard way and i had done many set ups.. IF you dont have the right prop going the way it is cut you do have problems . I had my share of learing when it came to props. for sure. I dont know everything when it comes to props but I learn enough to make sure witch way my ship was going to go when I put it in the pond.

I can tell you a story it was late this one evening I was getting tired and I wanted to run this cutter I was building the next day. First off I made my own mistakes. first off I put a right hand prop on the left side and the right on left I did not check it in the moring it was a meet. When I put it in the pond it just sat there and churn up the water. I knew right off what I did wrong . Took it back to my docking aria change over the props to whear they were suppose to be and it ran like a rockit and it was go fast. I usely did not deal with go fast but this was a PT boat. THEN one other time I wired a pair of motors the wrong way and use the right props still had problems. So I learn alot about props and wireing up motors from the school of hard knots. But that was in my early years . I have help others with props problems in the pass and first thing I tech them is how to read prop. It is not hard if you can tell the difference on witch side is your cutting edge that will tell you witch way the prop is suppose to run. FOR THE cutting edge of a prop will be going toward the back not the front .

SO just remember to read your prop and listen to what the others are saying. O Ya dont do any of it if your tired or in a hurry.;-)) I built for about 20 years now no longer doing it had to back off but I still maintane my personal ships and will help others.
I hope some of what I said will help some.
Don the Portland Rustbucket.
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Old Mar 07, 2012, 05:21 PM
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United States, CA, Hayward
Joined Feb 2006
896 Posts
Towing 101 Got a Frasier River log Tug model 16" long, 2 " Robbe nozzle, prop Shop prop, way overpowered and it requires 5 degrees of rudder to run straight at full chat. So it proves that nozzles will propwalk just not as badly. Slow her down and she is a dream to manuever and will handle a 250# barge with authority.
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Old Mar 07, 2012, 06:23 PM
Keep a Steady Strain....
capntroy's Avatar
Orange County, CA
Joined Nov 2007
1,220 Posts
Quote:
Originally Posted by kingsflyer View Post
With the advent of computer radios, it is now very easy to program throttle differential. Throttle differential is the ability to slow down one motor by mixing the throttle channel with the rudder channel. A turn to port slows down the port motor and speeds up the starboard motor. A turn to starboard slows down the starboard motor and speeds up the port motor. I have used this system on a number of twin engined airplanes with great success. I usually set this up as a switch enabled function so that I can choose to use function, or turn it off and have the motors run in sync with each other.

Here's the issue, would TTO work better with differential throttle when under way, or would TTI?

McD
If you're always planning on making turns by slowing your inboard wheel, then outboard turning (TTO) wheels would be better, but the loss of maneuverability (flanking & walking) that you'd experience isn't worth the trade-off.

Now if your boat is some sort of mahogany runabout or warship with little props and little rudders that are close to each other, then you aren't going to be doing much walking anyways, so go with the TTO then...
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Old Mar 08, 2012, 10:28 AM
jayman
Joined May 2007
309 Posts
With a model, it is easy to try out different combinations. Just swap out the props and some wires and go from TTO to TTI and see what happens.

jay
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Old Mar 08, 2012, 02:03 PM
We shall serve the Lord
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United States, TX, Kingsland
Joined Sep 2005
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Since my Crockett still has brushed motors, and each motor is marked with a red dot for the positive connection, will there be a problem with the brushes if I reverse the motor rotation?

McD
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Old Mar 08, 2012, 02:21 PM
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United States, CA, Hayward
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Kingsflyer Never had a problem with that setup in 30 years, figure it is because we are not asking for 120% like the go-fastee folks so the motor is under much less stress. Tend to seek out zero timed motors so forward reverse is similar.
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Old Mar 09, 2012, 12:52 AM
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United States, CA, Orange County
Joined Aug 2011
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Info on Props

Guys, for those of you that don't know, when you read a comment from capntroy, READ it as from: Captan Troy ______, as that IS, what he does for a living. CB
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Old Mar 09, 2012, 08:37 AM
We shall serve the Lord
kingsflyer's Avatar
United States, TX, Kingsland
Joined Sep 2005
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Thanks so much for all your assistance. I have learned more in just a few short days here on RCGroups than I could possibly have learned from the school of hard knocks. It's great to be part of such a great community of dedicated modelers.
McD
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Old Mar 09, 2012, 09:51 AM
Veni, Vidi, Feci
patmat2350's Avatar
Motor City
Joined Dec 2004
12,573 Posts
One more lesson:

In a model, all this makes for less than a hill of beans... you will have to look long and hard to detect any difference at all, when just bopping around the pond.

Through modeling, I like to learn about prototypical operation and theory... and I try to replicate 1:1 details accurately in my models... but as far as performance goes on the pond with scale models, fuhgettaboutitt!

The reasons?
- The small scale of our operating theaters... straight line stability and long distance fuel consumption are of no account on the boat pond;
- The non-scaling of water properties (thank you, Messrs. Froude and Reynolds): It is easy to way-over power a scale model, even with a scale prop. Those little marginal gains that are so important in 1:1 operation- again, they just don't figure on the boat pond.

By paying attention to these details, can you do a bit better in a scale model handling or towing contest? Maybe... but a whole lot more edge can be gained by just learning how to finesse the controls on your radio- no mean feat!

Best advice: Learn all you can, and have fun along the way.
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Old Mar 09, 2012, 10:05 AM
Old wreck in Milwaukee
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United States, WI, West Allis
Joined May 2007
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kingsflyer if you want to be accurate then you need to find out how the Navy had them on the Ashevilles. It is a detail that is sometimes overlooked in scale judging (ask boater_dave about the WMM contest sometime), so whatever you do is fine.

With mine I spent most of the time just slow cruising on the trim tabs, or flat out racing around the pond. The model is agile and a bit twitchy due to a high superstructure and no draft, so fine maneuvering, especially in any breeze is problematic. What Pat said in the above post holds even more so with a touchy model.
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Old Mar 09, 2012, 09:22 PM
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R/C Tug competition, is the main place where this really makes does make a difference. That is what Troy and I compeat in most, but Pat is right, if you can't drive, it really doesn't matter. CaptCB
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Old Mar 09, 2012, 11:38 PM
We shall serve the Lord
kingsflyer's Avatar
United States, TX, Kingsland
Joined Sep 2005
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Thanks again guys. Even as a kid, I always wanted to know what made things work the way they did, and how to make them better. As a retired Electrical Engineer, I still what to know the science behind the process. Sometimes I'm the only one that notices when one of my twin-engined planes performs a perfect taxi and takeoff in a strong crosswind because I programmed and used differential throttle correctly. I hope I will eventually be able to operate my boats with the same precision.
McD
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Old Mar 10, 2012, 12:19 AM
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Ladysmith Vancouver Island
Joined Feb 2008
577 Posts
I'm actually really interested in this as I'm working on a few twin screw boats and wonder which ways to set my props (all counter rotating)

2 are RTR's that I'm modding/bashing .. a southhampton Tug .. spinning around on the spot, crabbing are it's main goals for rescue, competition and play .. twin ESC's mixed on the radio

the other is a proboat PT (yes I'm aware that proper to scale all the screw turned the same way) which also runs twin esc's mixed on the radio, but i've also programmed dual rates into it ... its a big model for the smaller area I mostly run it (basically a dock created harbor)

the others on deck are a traxxas villian EX .. and a 56inch long scratch recreation of the FHE400 BRAS D'OR
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