Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Tutorials & "How Tos" ... => Topic started by: GG on February 18, 2020, 03:10:37 pm

Title: Vectored Thrust
Post by: GG on February 18, 2020, 03:10:37 pm
Be careful of what you say....
I mentioned the term "Vectored Thrust" in my posting about checking the bottom of a model boats hull for damage and now someone asks what it refers to, so here goes.  For those wanting to read the full details, these and a model built to test it (which is now my "go-to" second recovery model when setting out on a sailing session) were published in the January and February 2011 issues of the magazine Model Boats.

After seeing many commercial items that could offer a model boat great maneuverability, but at equally great cost, I thought it worth trying to see if something a little more economical could be made in my workshop.  I wasn't aiming for the extreme performance of a commercial unit but something that would beat the conventional rudder or possibly steerable nozzle, hopefully another case of my 80/20 approach (80% of the performance for 20% of the cost/effort)  Lots of ideas were investigated which were covered in the first part (Jan), but for one reason or another none appealed.  One thing I wanted to avoid was a submerged motor in a steerable pod, experience having taught me that it is near impossible to avoid a wet and rusty motor with simple (cheap again) methods. Luckily, I tend to let problems float around in my subconscious and a potential solution can sometimes pop out of the "nowhere".

In this case it was to use a simple pulley and gear drive down to the propeller shaft which was firmly embedded in a steerable rudder blade.  The rudder was secured to a brass tube which entered the hull through a conventional fixed tube.  The rudder tube being steered by a simple double servo/tiller arm linkage.  The drive shaft for the propeller passed down the rudder tube, across a hole cut in the rudder and into a lower bearing.

The vertical drive shaft and prop shafts were connected with crown and pinion gears which I had to hand but other types could be used.  This combination of pulleys and gears gave a total speed reduction of around 3:1 and allowed a standard RE 540 motor to comfortably drive a three bladed propeller and to economically produce more than enough thrust.  The assembly can turn though 40/50 degrees either way and results in immediate response both ahead and astern.  Hopefully the attached diagram and pictures will illustrate this.

One of my aims was to achieve a simple to build (just involved cutting some brass tubes and steel rods to length) and reliable system.  The reliability has been shown by the fact that until I gave it it's first service recently, when the hull bottom damage was noted, it had worked for a decade without any attention other than a light spray with one of water displacing and lubricating oils after sailing runs.

For anyone worried about the exposed gears in the hole through the rudder and I was at first, they have never given me any problems.  They are brass and probably ex-Meccano and seem to chew their way through any thing in the lake that gets in their way!

Like most simple and successful ideas, the hard part was thinking how to do it.  Somewhere in my files there's a scheme for a double ended model using two of these units for some interesting on the water maneuvers....!

Title: Re: Vectored Thrust
Post by: Tug Fanatic on February 19, 2020, 11:36:28 am
I remember liking this idea in 2011 and I am very interested to learn that it has stood the great test of time. Looking at it now it would not be difficult (nor expensive at Chinese prices) to use a timing belt on the servo (or a stepper motor) with different sized pulleys  so that 180 degree control was possible. With 2 of those on the model anything becomes possible. This would be a fairly standard Rotor Tug module which I prefer to a double ended model. Some full sized tugs use 3 modules partly to eliminate the units being inline but that might be overkill in a very stand off scale model! ( (
Title: Re: Vectored Thrust
Post by: GG on February 19, 2020, 12:15:07 pm
Tug Fanatic,
              Yes, using pulleys or gears to connect the servo to the rudder tube would be the next step and allow 180, or more, degrees of movement. I don't know if anyone else tried to develop it along these lines.  To be honest, I find it very rewarding when people do but hope they credit the source of their ideas.  In fact I later discovered that Philip Connolly had reported his experiences with a similar device a few decades before!
But, the aim was to keep it as simple as possible for a first attempt and to be honest, I was more than satisfied with the result.
If you try then please let us all hear about it.
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