For my second Battlestations ship I decided to build the French Henri IV pre-dreadnought. It has already been on the water and battled, but I thought I would detail the building from the start, since it is an unusual ship. In July I wasn't even close to having a Battlestations ship ready. The problem was that I had lost motivation to work on my Tashkent, originally framed up by Phil, when I could not figure out how to arm it. I learned that Phil was interested in getting the Tashkent back, which got me to thinking about what I would build if I was to start from scratch. I would like to build a Kersage, but I didn't have time to start from nothing and still make our September battle. Then the Henri came to mind - I already had a 144 scale design, so modifying it for Battlestations would be quick. I spent three evenings modifying the design and then emailed it off to be laser cut. Normally, I would cut the parts for a one-off project like this at home on my CNC mill, but I decided to splurge this time. It took another week and a half before I got the call that the kit was ready. I picked up the kit at 4 PM on a Friday. Then I controlled my building urges and took the Admiral out to dinner. Priorities are important you know. After dinner the hull was put together in about an hour. Then I watched the opening ceremonies for the Olympics with the family. Priorities again. Then I went back down to the shop and put the superstructure together. All that progress made and I was still in bed by midnight. I love laser cutting!
Yes, I did have the superstructure laser cut. Generating those patterns was what took most of the CAD time. I did not take the time to design joints for the pieces, so it was assembled free hand. I also had saddles for the tank and batteries cut into the ribs.
The rudders and props are arranged in an unusual configuration, with the rudders actually between the center and outside props. The picture also shows the sheeting frames for the 3/32 sheeting, which worked reasonably well for my first attempt. The build schedule is in the background - it was necessary to keep me on track to make the battle. The outer shafts have 1.5" props with 750 Kv brushless motors, while the center shaft has a 1.75" prop and is driven by an Astro 01 geared with a Kv of approximately 650. An unusual prop and rudder arrangement calls for an unusual drive set up: the motors are all run by non-reversing airplane ESCs, the center shaft provides only reverse while the outer shafts provide only forward. Setting it up in this manner gives some prop wash over the rudders both in forward and reverse. The setup worked well on the pond, providing a turn radius in the 15' range. I used plastic chain and sprockets from Servo City for the rudders. I was originally going to use just one rudder servo and had only put two servo mounts so that I could choose which side would work best. But having not used the chain and sprocket before, I decided to use two servos for redundancy. Having separate ESCs on all the motors also gave me an opportunity to experiment with differential thrust for steering. In discussions with some of the local battlers, we felt that differential thrust might be necessary to turn some of the big ships in a reasonable distance. What we lacked was any data on how well it worked and if it was necessary. So I programmed my radio to slow down the inside prop in a turn - remember that I have one-way ESCs so I could not reverse the shaft, only slow it down. The differential mixing was set up on a switch, so I could turn it on and off at the transmitter. To accomplish the mixing I used three channels, 2 throttle curves, one multi-point mix, and two linear mixes. It took a bit of work and I learned a lot about radio programing in the process. Turning the differential thrust on does make a significant difference in the turning radius, changing it from about 15' to 10'. I didn't use the differential thrust during the battle, and I still out-turned the Gustav V. I also tried to get even more fancy, mixing in opposite thrust at full throttle to create extra drag. So at full forward speed on the outer shafts, the center shaft revolved in reverse at about 10% to create more drag. This ended up having the opposite effect of what was intended, actually making acceleration from a dead stop slower. So I removed that programing.
Good data to have! I wonder how much difference differential steering would make on a Baltimore. I know the real ships use it...
Here's the motor info: http://www.cermark.com/products/NEO...A-750.html - I think these are well suited for many of our direct drive systems. In the Henri I had to dial the ESC down to 42.5% to make speed - 44 seconds - so they have plenty of head room for faster ships. http://www.radicalrc.com/category/A...shless-112 - scroll down to the Astro Flight 801G Geared Drive System. An excellent motor, but if I didn't already own one I would not have spent the money just to power a ship. The mounts are machined to attached directly to the brass tube that forms the stuffing tubes. The drive shaft is connected to the motor with a solid connector (no u-joint). The only bearing in the stuffing tube is the one right by the prop, so the motor bearings support the end of the shaft inside the ship. I'll take a close up picture of the mount when I get home. I'll also post amp draws, watts, and RPMs from my tests of various props with these motors.
The picture shows the prototype motor mount with a drive shaft next to the final mounts. The mount is attached to the motor with two screws and is about 3/4" long. The mount slips over the stuffing tube and then is held in place by the screw on the side. The shaft connector is soldered to the shaft on one side and the other has a 4-40 set screw to attach to the motor shaft. The hole in the mount allows you to reach the set screw. At speed, the NEOs are turning a 3 blade 1.5" 25 pitch prop at 2900 RPM and pulling 0.4 amps / 2.8 watts each. That's at 42.5% throttle. At 100% throttle and the same props the motors draw 1.4 amps / 9 watts and turn at 5000 RPM. The Astro drives a 3 blade 1.75" 25 pitch prop using 1.1 amps / 7 watts. That's at 48% throttle. At 100% and the same prop, it draws 2.5 amps / 16 watts. I don't have RPM figures because it's an inrunner.
Right, I machined them myself. Most of it is turned on the lathe, while the slot and screw hole is done on the mill.
To keep the wires from 4 ESCs and 9 channels organized, I made a board to hold all the components. Each one is held on with a Velcro strap to make reconfiguration or replacement easy. In fact, the ESC for the center prop is actually under the board, since I found it was in the way of the stern gun rotate servo when on top. A power distribution board allows me to plug each ESC in separately, again making replacement easy. The pump is mounted just forward of the board. I had some issues with the pump that contributed to my sink. I had mounted a brushless motor with an 890 Kv on the pump and had planned to calibrate the flow and change motors if the first choice was unsuitable. Because I wasn't sure if the motor would work, I didn't grind a flat on the shaft for the set screw. I never did get around to calibrating the flow before the battle so I forgot about the shaft. Sure enough, that shortcut caused me problems. When I tore the pump down after the sink the rotor was not entirely loose, but I was able to turn it by hand. Tests in the hot tub showed that the pump with a tight rotor was easily able to keep up with, and even get ahead of, the damage I had taken. Another lesson learned. The good news is that the pump motor works great, pumping my allowed 3/4gal per minute with about 0.4 amps. Full speed on the motor gives me 1.25 gal per minute using 0.7 amps. Interestingly enough, amp draw at full throttle goes up to 1.5 amps when the motor is submerged and that outrunner portion is churning the water. I'm considering a motor shroud just to make sure the churning doesn't add air into the pump intake.
