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2008/12/01

Pat's Hacks, servo motor conversions

Thank Pat Matthews for sharing the following post on servo hacks!

Servos are wonderful little devices! Not only do they provide an inexpensive way to activate mechanical linkages through radio control, but they can be hacked to provide inexpensive drive units for small boats and cars with their self-contained motors and electronic speed controls (ESC's), and they can serve as part of a simple on/off power control switch.



Basic servos can be found for less than $10

A servo is a little gear-motor, ESC, and a position sensing device in one package. Rip the guts out of the case, and you'll have:
a) A lead from the Rx… it carries +5 volts, ground, and a signal wire.
b) A circuit board.
c) A small 5v motor, which may be soldered directly to the circuit board.
d) A pile of gears connecting the motor to the servo output. Bin these.
e) A potentiometer (pot, or variable resistor) connected to the circuit board with 3 leads, and mechanically connected to the servo output.


Step 1: A few screws loose, and things start to open up.

Step 2: Pressing on the two shafts popped the board out of the case. Don't pry directly on the board.

Step 3: Using desoldering braid to wick off the solder, makes it easier to pull off the motor.
Loose parts.

Hack 1: Going Pot Free

First trick in hacking a servo: Disconnect the pot from the servo output. Normally, as the pot moves with the servo output, it produces a varying voltage which is read by the circuit board, telling the servo that the output has moved to the desired position (or not). See Schematic 1. When you disconnect this little knob from the gear train and the servo output, leaving it in it's centered position, and then command servo movement at the radio, the circuit board never detects any movement, and thus keeps telling the motor to run.
So now center the stick, servo is happy, goes nowhere; forward stick, and the motor kicks in and just keeps buzzing; reverse stick, ditto the other way. You'll want to put a drop of glue on the pot to keep it from drifting.

Hack 1a: If the Pot itself doesn't suit you, you can replace it with a pair of 2.2k ohm resistors- both tied to the center tap's lead, opposite ends of the resistors to the pot's "outer" leads.




Another nice feature- most servos have a soft start, which means that a little bit of stick will give part throttle… other than that, it's pretty much off/on.



Hack 2: Motor Swapping

Next hack: The little motors that comes with servos may not suit you… they have tiny little short shafts. Any small 6v toy motor will do instead, as long as you don't load it heavily- the servo's ESC isn't designed to deliver much current! If the motor is connected to the circuit board with wires, no problem to swap them. If the motor is soldered directly to the board, you'll need to work a little more carefully. You can get "solder braid" from Radio Shack- braided copper wire that you heat with a soldering iron while pressing onto the board's soldered joint. The braid sucks up the solder, and you can pull the motor loose much more easily.


If you decide to keep the servo motor, no problem. You can leave the motor on the board- that's what I did on my plastic landing craft. And you can get tiny little plastic u-joints to press onto various miniature shaft sizes, metric and English, from Northwest Shortlines- catalog page at http://www.nwsl.com/Catalog/cat-UJoint.pdf







Servo motor still attached to board. Motor can is pressed into plastic structure. Twin drive in landing craft.
Servo motor set in Revell Trawler Close-up of NWSL U-Joint on servo motor's 1.5mm shaft. "Horn" is sized for 1/16" prop shaft, which is only slightly larger than 1.5mm.



Pat'web site http://www.geocities.com/patsmodels/servo/

2008/11/13

The Star 45 R/C Model Sail Boat

The Star 45 R/C Model Sail Boat - Builders Journal
The Star 45 R/C Model Sail Boat - Builders Journal

Construction photographs, articles about the Star 45. -- Join the AMYA STAR45 Class discussion group http://groups.yahoo.com/group/Star45/ -- Read about How To Build A Wooden Star45 R/C Sailing Model! Browse http://woodstar45.blogspot.com/ Based on the International Star Boat this semi-scale Star45 can be scratch built by novice or seasoned skipper. Easily radio controlled and large enough to see out on the water this is a classic model model built by hobbyists for over thirty years!

2008/10/16

Thinning Epoxy

Thinning West System Epoxy by Brian Knight
http://www.seqair.com/skunkworks/Glues/WestSystem/Thinning/Thinning.html

"This article appeared in the Fall 1999 issue of Epoxyworks, published by Gougeon Brothers, manufacturers of the West System epoxies." Brian Knight thanks Gougeon for permission to publish this in the December 1999 Falco Builders Letter. "

Here are key excerpts for your review and discussion:

"With wood, the best method of thinning epoxy with heat is to warm the wood and have the resin and hardener at room temperature. Mix the components and apply the mixture to the warm wood surface. Remove the heat source just before the epoxy is applied. When the epoxy mixture comes in contact with the warm wood, it gets warm and its viscosity becomes lower. As the temperature of the wood falls, the thin epoxy is drawn in deeply before it begins to gel. By heating the substrate instead of the components, you get the best of both worlds-low viscosity epoxy on the work surface and longer working time in the mixing pot."

Thinning epoxy with solvent
Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected. Below are some of the effects adding solvent has on West System epoxy. While there are a large number of chemicals available to thin epoxy, we selected acetone, lacquer thinner and denatured alcohol for this discussion because they are commonly available and do a good job of reducing viscosity. Additionally, these solvents evaporate quickly and are less likely to be trapped in the cured epoxy-an important characteristic. For a variety of reasons, fast evaporating lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol.

2008/10/15

So you want to build a sailing model

Find plans for a sailing model, buy or find on-line.

Join a model boat forum for advice.

Buy or borrow books on boat building.

Decide on type of planking and wood to be used to build the model.

Set aside a work space for building.

Review the bill of materials need to build the model and buy the materials.

Order deck and mast fittings.

Order mast (if you are buying the mast) and order sails (or sail material).

Choose the radio system, buy a sail control unit, Order keel bulb or get advice and discuss issues of building your own.

While the hull is under construction build:

Keel fin and ballast bulb

Rudder assembly

Make or assemble spars ( mast and booms)

Build cradle to hold boat under construction and when finished.

Test Radio System and sail control unit

After hull is planked:

Install keel trunk or make provisions for mounting keel.

Install radio and sail control unit, Then remove while construction continues.

Construct deck and hatches

Install/mount deck fittings

Test access to radio and sail control inside the hull.

Provide a exit guide for radio antenna so it can be attached to mast or stays.

Install power switch for turning off batteries

Test mount keel

Paint hull, rudder and keel

Assemble hull, rudder and keel

Set up mast and boom.

Install radio controls.

Check running rigging.

Attach Sails

dry sail model

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Sail
Display
Storage

Hull Templates - bulkheads for building model sailboat, S45














The grid shown is set to 1/4 inch squares. So if you print the templates you can check the size by making sure the grid yields a 1/4 square.

Modelers will use different building materials for the model.These are JPG drawing and print outs may require adjustments to get the widths to correct sizing. For a Star45 AMYA class you need to make adjustments to allow for planking thickness. The rules establish the maximum allowable beam dimension and hull length.

Most browsers will allow you to right click and open the jpg files. You can then save them to your machine.

This set of templates are based on drawing from John Fisher back around August 2006. John may have new and updated drawings available. Check with http://groups.yahoo.com/search?query=star45 membership required.

If you want to scale to use for different model you can change the print out to give you a different grid size.

I want to thank J. Herrmann, www.graphicLanguageOnline.com, for his assistance in converting pdf's to jpg drawing, adding color to the templates and adding the grid to the final images.Rudder templates for a Star45 Class sailing model.The grid shown is set for 1/4 inch squares. So if you print the templates you can check the size by making sure the grid yields a 1/4 inch square.

This set of templates are based on drawing from John Fisher. John may have new and updated drawings available. Check with http://groups.yahoo.com/search?query=star45 membership required.

I want to thank J. Herrmann, www.graphicLanguageOnline.com, for his assistance in converting pdf's to jpg drawing, adding color to the templates and adding the grid to the final images.



These are half shadow that ar eplaced between the templates to add strength to the hull.

Keel Templates for S45 model sail boat





Building templates for S45 Keel fin.
Originals drawings are based on 1/16 ply.

Modeler may want to use different building materials for the fin.
Final keel fin will be shaped the builder. Also these are JPG drawing and print outs may require adjustments to get the templates to correct sizing.

The grid shown is set for 1/4 inch squares. So if you print the templates you can check the size by making sure the grid is a 1/4 square. If you want to scale the keel fins for another model you can change the print out to give you a different grid size.

This set of templates are based on bolt mounting. The grid makes it easy to add to the template to have the keel extend into the hull or extend into the keel bulb. Modeler's choice.

Most browsers will allow you to right click and open the jpg images. You can then save them to your machine.

This set of templates are based on drawing from John Fisher 2006. John may have new and updated drawings available. Check with http://groups.yahoo.com/search?query=star45 membership required.

I want to thank J. Herrmann, www.graphicLanguageOnline.com, for his assistance in converting pdf's to jpg drawing, adding color to the templates and adding the grid to the final images.

Rudder templates for a Star45 Class sailing model




Rudder templates for a Star45 Class sailing model.The grid shown is set for 1/4 inch squares. So if you print the templates you can check the size by making sure the grid yields a 1/4 inch square.

This set of templates are based on drawing from John Fisher. John may have new and updated drawings available. Check with http://groups.yahoo.com/search?query=star45 membership required.

I want to thank J. Herrmann, www.graphicLanguageOnline.com, for his assistance in converting pdf's to jpg drawing, adding color to the templates and adding the grid to the final images.

Model Sailboat Plans on line





Most browsers will allow you to right click and open the jpg images. You can then save them to your machine.

This set of plans are based on drawing from John Fisher 2006. John may have new and updated drawings available. Check with http://groups.yahoo.com/search?query=star45 membership required.

I want to thank J. Herrmann, www.graphicLanguageOnline.com, for his assistance in converting pdf's to jpg drawing, adding color to the templates and adding the grid to the final images

You can print these drawing to many different sizes.They are not necessarily to scale.

HULL defintion of:

Dave Mainwaring's definitions

HULL defintion of:
The outer shell, including frames, ribs, interior bulkheads, exclusive of masts, rigging, deck and equipment.



"bare hull" defintion of:
A model boat's outer shell, EXCLUDING, ribs, interior bulkheads, exclusive of masts, rigging, deck and equipment. Example. A fiberglass hull as pulled from a mold.

--

A wooden hull:
one constructed of wood (including plywood).



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A glass hull:
one constructed of reinforced plastic (cloth impregnated with resin). Nominally referred to as a fiberglass hull.

--
A composite hull:
a hull constructed of wood and covered with reinforced plastic (cloth impregnated with resin).
OR:
a hull constructed using a laminate (sandwich) consisting of reinforced plastic (cloth impregnated with resin) on two sides of a core . Core materials may be foam or wood.

Inside a R/C sailing model hull

John Fisher photographer and builder!
Radio Board stringers between bulkheads
(Note the method of keel support using these stringers)
radiobd_1sml.2.jpg


Radio Board
radiobd_2sml.1.jpg


Rudder Servo
servo_sml.2.jpg


Mast support (inside hull)





internal mast support

S45 sail boat Rigging Bill of Material from John Fisher

To:Star45@yahoogroups.com
From: 'J Fisher'jfisher@wildblue.net
Sender: Star45@yahoogroups.com
Date: Wed, 3 Jan 2007 21:02:38 -0700 (Mountain Standard Time)
Subject: Re: [Star45] Deck rigging and such

Here is the list on the star 45 yahoo groups for rigging. I am using the following for my next couple of builds:
GBMY item #, description, qty, purpose
019, 3/8' alloy tube, 1, Jib boom
034, Hales single block, 2, main and jib sheets
146, tapered drain plug, 1, plug in transom
182, Z sheet hook, 2, sheet ends/boom attachment
202, large bowsie, 1, back stay/forestay with 80 lb Dacron, order small ones if using spektra
206, O-rings, 1, hold the Z hooks to the boom.
254, double block, 2, main sheet and jib sheet adjuster
255, sheet exit, 1, turning block for main sheet from under deck to above deck.
269, eye plate, 1, mounting for jib block.
272, 180 deg sheet lead, 1, turn around for jib tweaker
280, sheet hook, 1, hooks for backstay and fore stay.
282, tang, 1, attach lowers to mast.
907, rigging screw, 4 hooks, 2 packs, upper and lowers to the deck.

I also build my own chain plates, so I don't order them from GBMY. Don does carry them if you need them. I also like the Ludwig mast better than the bantock mast, so I ordered 8 foot masts cut to 69' from Larry Ludwig, the other 28' or so is the main boom. Last time I made all my own boom vang, mast fitting. This time I ordered them from Larry. You can use the bantock mast, boom, and fittings from GBMY as well. They are good stuff and I have them on my IOM.

The back stay crane is made from 1/16 (.063') aluminum that I bought at the local hobby shop.

John Fisher

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photo's courtesy of "Larry Ludwig" at www.LudwigRCYachts.com, Ludwig Mfg.

Jib Tweakers

Jib tweaker with swing arm sail control unit:

Adding a servo to the end of the jib sheet allows the jib to be "tweaked" by changing the effective length of the sheet while under sail. The challenge is to set the servo to mid point when setting the model up prior to sailing.

Tweaker with drum type sail control unit.


___________________________________

A jib twicher is a rig that pulls the jib boom to port or to starboard when sailing down wind.



These to devices are often confused with each other :)