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Posted by 1Ironhorse | Feb 20, 2018 @ 12:30 PM | 1,137 Views
Greetings my friends. I’m going to take a short deviation from the electrical system and go over the propulsion system that I introduced in Electrical Systems, Part 1 and expanded in Part 2 and 2A.

By propulsion system, I mean the propeller, shaft, and interconnect mechanism between the electric motor and propeller shaft. Because the propeller I have chosen (Raboesch 157-14) has a limitation of 5,800 rpm, I knew that I would not be able to do a direct hook-up, but would need some gear reduction to convert motor rpm into propeller rpm. To use a gear-to-gear reduction system requires high tolerances and is potentially noisy since I would have to use spur gears (straight teeth – only one tooth engaged at a time) rather than quieter hypoid gears (2 or more teeth engaged at a time). I found www.SDP-SI.com which has belt drive components (as well as other types of drive components).

I used HTD profile belts and pulleys for the testing I did with a gear ratio of 2.27:1, which actually oversped the propeller by about 122% at 31 volts (limit of the power supply). I did some additional design review as I was getting ready to order the pulleys and belts including reading technical data provided by SDP-SI, (I won’t reproduce it here, you can go on line and look under Technical Resources). I chose to change the belt profile to the 3mm GX2 because if can handle to horsepower and it is a thinner profile. This allows for smaller drive pulley (on the motor) and a...Continue Reading
Posted by 1Ironhorse | Feb 18, 2018 @ 01:47 AM | 1,159 Views
Greeting my friends. Just wanted to update you with information that I received the two 639521-00SV motors that I have been waitin on because they were on back order. These will be the wing shaft motors, while the original 639521-00 motor I purchased so long ago (2007) will be the keel shaft motor.

OK, thats all for now. Until next time..."Keep it simple, make it FUN!"
Posted by 1Ironhorse | Feb 15, 2018 @ 01:53 PM | 4,037 Views
Alright my friends I tried to locate the videos I shot of my motor test using the water tunnel I devised (similar to a wind tunnel) but was unable to find them. I didn’t realize that it was over 10 years ago I did those tests. I did find some still shots of the set up. So, see the attached photos.

The orange section of 4” PVC pipe has the motor/propeller set-up installed, all other pipe (white) is simply 4” PVC pipe. I took ½” plywood cut to the shape of the motor/propeller section of the keel, I used a router to cut a half round 3/8” slot in each side, inserted the 3/8” brass tube to support the sleeve bearings for the propeller shaft and glued the two ½” plywood pieces together, and painted all surfaces to seal them against water intrusion. I cut a 1” slot into the section of 4” PVC pipe I would later paint orange that would accept the motor/propeller mount assembly.

This set up worked fairly well, the only change I would make is to use a larger reservoir (I used a 20 gallon storage tote) and make the water inlet deeper below the water surface. During the testing, I had the water lever only about ½” above the inlet, and at higher power settings, a whirlpool would form and air would be pulled into the propeller. By raising the water level in the 20-gallon tote I was able to keep the propeller completely submerged. But I had to keep a hose running into the tote because the tunnel’s return pipe was situated such that water splashed out of the tub at high...Continue Reading
Posted by 1Ironhorse | Feb 13, 2018 @ 05:26 PM | 1,363 Views
You might be asking, “Why all the chit-chat? Get to the good stuff, BUILD SOMETHING!” Ah, patience my friends. “Big Boats Take Big Bucks!” Just this week I ordered the 4 sheets of 1/16” x 4' x 4' plywood needed by the laser cutter to make all the hull parts. In about 3 weeks I should have wood parts in hand and can start to assemble the hull. In the meantime, I’ve already got most of the electrical system components and have done some of the assembly of the electrical system. I’ve already gotten the laser cut parts for the three battery trays and have assembled them to start the actual layout of electrical components on them.

This time I will expand on the propulsion system as a whole. The propellers were chosen mostly by matching scale size as close as possible. I chose the Raboesch 157-14 (2.4" Dia., Left, 61.5mm pitch, 3/16" Shaft #10-32 Thread).

I purchased a 639521-00 DeWalt motor and used it to do some preliminary testing with a 157-14 Raboesch Propeller and drive train. I designed a belt drive propulsion system and set up a water tunnel (20 gallon storage tub with 4” PVC pipe fittings and a loop of 4” PVC pipe for the tunnel) to test the power consumption of the motor/propeller assembly. Initial design limitations dictated a gear ratio of 3.23:1 (See below), however space considerations limit the gear ratio (diameter of pulleys) to 2.27:1. See the “Motor/Propeller Test Apparatus” picture from my Electrical System Part 1 post.

Propulsion...Continue Reading
Posted by 1Ironhorse | Feb 10, 2018 @ 03:23 AM | 1,961 Views
OK, last time I determined that the weight of the scale boat should be 68.625 lbs. Using the axiom “to have your scale aircraft perform like the full scale aircraft, use the same power-to-weight ratio” to determine the power required for my boat;
4,500 HP/122,000 lbs = 0.037 HP/lb
Horse Power = .037 hp/lb * 68.625 lb = 2.54 hp
Each motor then should output .85 hp

This is the first parameter I need to find a solution for. It took me a while to find a DC brushed motor that would meet my requirements, minimum of .85 hp, low weight and small size. Not an easy task. Trying to design around a 12 volt system was nearly impossible. To get the power needed, I had to start looking at higher voltage motors. I finally found a DeWalt 36V hammer drill that is rated at 1 horsepower output at the chuck. I figured that the losses in the gear reduction transmission would factor into a motor that would output about 1 ¼ HP. I found the part number of the motor and purchased one from my local DeWalt repair shop.

Now, this is my area of expertise, DC Electrical Power Distribution Systems.

So, the 36V motor sets the first parameter I need to design around. My initial design used 12S1P Li-Ion batteries for the main propulsion motors. The Li-Ion cells I chose have a nominal voltage of 3.3V with a max of 3.775V and min of 2.5V....Continue Reading
Posted by 1Ironhorse | Feb 07, 2018 @ 02:06 PM | 2,294 Views

Some additional features for my model that I did not mention in the first blog post include:

2. Power is all electric;
3. Three 1 HP electric 36V DC brushed motors that I derate to 0.85 HP; (Note 3)
1 horse power = 746 Watts, Watts = Volts * Amps
Test data on the motors yields 864 Watts @ 36 Volts (24 amps)
Limiting the input voltage to 30 Volts (21 amps) = 630 watts or 85% of 746 watts
4. The outboard (wing) propeller shafts located 53” (scale) outboard of the centerline of the boat; (Note 4)
5. Engine Sound System;
6. Exhaust Smoke System;
7. Operational underwater exhaust system;
8. Automatic electric bilge pump;
9. External hull features: Auto Bilge suction scoops, zinc galvanic plates, propeller & rudder fairing plates, Generator engine saltwater intake and exit scoops, and Outlet Scoops;
10. Navigation light that are dimmable;
11. SO-3 Radar Dish that rotates;
12. All removable access superstructure held in place with magnets. No screws to remove;
13. Master power switch and charging jacks hidden in ammo ready lockers on deck;
14. Forward and Aft 50cal BMG turrets pan & elevate remotely;
15. Operational search light, pans & elevates;
16. 27mm, 37mm & 40mm Cannons pan & elevate;
17. Rocket launchers rotate out & elevate;
18. Operational Mk 13 torpedoes & launchers;


Taking a page from the...Continue Reading
Posted by 1Ironhorse | Jan 28, 2018 @ 10:47 PM | 1,273 Views
As an Engineer, I am probably going way overboard (pun intended) with my design and documentation. However, this is part of my paying job, so it is second nature to me to do so.

Therefore, let us begin:


This report is to document the design and construction of a 1:12 scale model of the US NAVY Torpedo Patrol Boat PT-615. Since no commercially available parts are available for a model of this scale and design, I have engineered and produced all of the boat specific parts and components. Some components such as electric motors, batteries, lights, bearings, couplers, and hardware are purchased parts.


The design concept of this model was to create a 1:12 scale remotely controlled, accurately detailed model of a US NAVY 1945 PT103 series ELCO (Note 1) 80 Ft. Torpedo Patrol Boat. PT-615 was chosen as the prototype . Although PT-615 was not deployed during WWII, it was completed and put into active duty before the end of the war. It represents the last configuration of the ELCO 80’ PT-boat design. Note that the last boat completed by ELCO was PT-624 as the war had ended and the contract for PT’s from ELCO was cancelled.

As designed, the PT103 Series 80’ boats were equipped with Packard Marine engines of increasing horsepower, the first boats having engines with 1200 hp rating and the later boats 1500 hp each. The majority of the boats were equipped with the center engine having direct drive, and the two wing...Continue Reading