I'm starting this thread to share ideas about how to equip our PDNs. Since they are smaller, slower, and lighter armed than the typical battleship we use, they might benefit from equipment that is smaller or lighter. I'll share what I'm working on, and hopefully others will contribute. Types of equipment to consider: Speed controls, either ESC or switches Rudder servos and hookups Valves and valve actuators CO2 tanks Batteries Pumps Gun magazines
The first thing I would like to discuss is the ESC. In general, I expect most of the PDNs to use brushed motors, because there is simply no need for the power or even efficiency of a brushless setup. This creates a problem. There are great brushed controllers out there, like the Mtronics Viper at $50, but it has been hard to find a cheap ESC that would work. Until now... I've just got done testing the Hobbyking X-Car 45A brushed ESC http://www.hobbyking.com/hobbyking/...duct=43377 which is available from the USA warehouse for about $11. One of the great things about this controller is its simplicity. You can only change two things, the battery cutoff and the reverse type. And no beeps or flashing lights, you use a simple pushbutton switch for the selection. The first programmable item is for the battery cutoff. From the factory it is set to cutoff when the battery reaches 5.6 volts. This cutoff would actually work pretty well if you are using LiPo, Life, or NiMH batteries. For SLAs I recommend that you disable it. The second programmable item is the reverse type. The instructions refer to the options as "practice" and "climbing" modes. Practice gives you full forward and reverse, but you need to stay in neutral for about a second before it will change direction. Climbing is was we need, it gives you full forward and reverse with instant transition. To change the cutoff you hold the button down while turning on the ESC. To change the mode you turn the ESC on and then hold down the button. Very simple. Testing of the ESC on the bench has been very positive. It has a somewhat wide dead band around neutral, but not too bad, estimated at about +-5%. It has pretty good resolution on the throttle curve. It was quite useable down to about 30% ATV on the transmitter, still having good control of the throttle at this point. At about 20% ATV, you started losing throttle definition and it was more like on/off. This performance is much better than the cheap controllers I have tried before. Here's the unit. It is a two board system, which makes it a little harder to waterproof. I created a mold to cast polyurethane around the ESC to waterproof it. As you can see, I have replaced the 14 gauge wire with some 18 gauge wire. I find the larger wire to be very stiff which makes it harder to put the ESC where you want it. Since I'm not going to use anywhere near 45 amps in my ship, the smaller wire works fine. Of course replacing the wires is optional. Given that the mold is open on the top, you can even add the heatsink back on the ESC when you cast the protective case. Here's one I left with the original wires and added the heatsink, just in case I have an application in the future that draws a few more amps.
You all need to start looking outside the box on these power components. There's more out there than what Hobbyking sells. For example, the Wasp controller from Robotpower.com. 10A continuous, 30A surge, 6.5V to 28V, instant 100% forward and reverse, thermal cutout, no battery cutoff, the onboard BEC can be disabled, and no fiddly programming required. Price $35. I'm running this in my Mogador waterproofed with a couple coats of E-6000. http://robotpower.com/products/wasp_info.html
Forgot to add. The Wasp (and most robot grade controllers) does not self-calibrate everytime its powered up like many hobby grade ESC's. Important point with this is that servo end point adjustments dont' have to be redone every power up (handy if your using that for speed limiting).
Thanks for sharing that controller, it's certainly a better choice for a small ship like a destroyer. At $35 it's really not cheaper than a Viper, since I can get a Viper 10 without waterproofing for $29. I'm still looking for an inexpensive, small, controller for my small convoy ships. Inexpensive is important because I have several ships that I want to outfit. In the $30-$40 range there is a decent selection, I'm looking for less than $20. Pololu has several motor carrier boards for about $5 that have the right amperage (about 2 amps), but none of them have an RC interface.
A cheap convoy boat ESC? Here you go, the VEX motor controller for $9. Keep it under 8.5V and 3A stall. Looks like it'd be easy to waterproof also. The only issue is that you have to change the gender on the Rx connector (stupid VEX proprietary crap). The way I'd wire this is to run the red and black on the Rx lead directly to a 7.2V supply. The white goes directly to the Rx which would be on a seperate 5V supply. Wired this way you might even be able to pump 12V through it. http://www.robotmarketplace.com/products/VEX-276-2193.html
I used the original VEX motor board as an ESC in a torpedoboat. Worked pretty good, but it was only good for 1A and the boat needed 1.5A, so it kept on overheating. Looks like the newer one has a higher current limit.
Next I would like to talk about the rudder servo and linkage. The stern of most PDNs is pretty narrow, as well as shallow. If we were to use a standard sized servo, the servo would probably have to be so far forward that it would interfere with the stern gun. My favorite rudder servo is the Hitec HS-82 MG. This is a mini servo which has metal gears and as much torque as a standard servo. It costs about $20. I have been using this servo for 4 years in my cruiser and it has been very reliable. If you have one of my PDN kits, this is the servo that the servo tray is designed to use. To waterproof the servo, I first disassemble it. I coat the control board on both sides with liquid electrical tape as well as the motor and potentiometer connections. I also add some waterproof grease to the gears, since I have had them seize on me. Don't fill the case with grease, just add a generous glob to each side of the gears. I re-assemble the servo before the liquid tape has time to dry. If you wait for it to dry, you may have trouble squeezing the parts back in the case. A standard rudder linkage may work, but due the narrowness of the PDN stern, there are some alternate methods. To hook up the servo to the rudder, my favorite method is to use plastic chain. This 0.1227" chain is available from Servo City, along with plain bore sprockets and servo sprockets. One of the nice things about the HS-82 MG is that the spline is the same as on the standard Hitec servos, therefore all servo sprockets designed for standard Hitec servos fit it. The downside of the chain drive is the cost, which will run about $15 for the set. Another way to hook up the rudder is through a pull-pull system. I first developed this method for my Golo kit and I have included the two pulleys in my PDN kits. It works by using some fishing line to connect the rudder pulley to a pulley on the servo. While cheap and reliable when setup properly, it can be tedious to get hooked up and tensioned. If you are interested more in how it works, download my Golo instructions. One additional note of caution: The parts with kits are designed with a 2:1 throw increase so that you can easily achieve 90 degree rudder swing in both directions. Because of this, you need to have a radio with end point adjustment or you will most likely over rotate the rudder.
Kinda thinking out of the box, I ended up putting the Verite's standard sized rudder servo offset to the side of the ship and slightly forward of the motor. The servo sits high enough to avoid anything sitting on the bottom of the stern and offset to run along the side of the ship out of the way of anything in the middle of the stern (to include twin cannons). There is enough room in the stern itself for a short arm on the rudder post that matches the short servo arm.
Syncromesh cabling from SDP/SI would be fun to play with in rudder applications. The pulleys are a little costly but the cable is cheap. http://sdp-si.com/web/html/newprdbelts6.htm
A few thoughts. First, liquid electrical tape has been known to slowly separate over time on a very small level, allowing tiny amounts of moisture to enter on sinking and then trapping it inside the circuit. Skotchkote (where still available) does not, so that would be a preferable treatment for servo waterproofing. I also drill a few strategically-placed holes in my servo casings, to allow water to wash in and out freely. The treatment works quite well, as other Georgia-based battlers can attest. My destroyer has been sunk at least 3 times each month for the past 3 years, and it still drives back to shore under its own power with just the tip of its bow poking above the water. The servo city plastic sprocket and chain works great for rudders as long as it doesn't get shot. I've seen it separate (with loss of steering) when the rudder gets shot, when the chain gets shot, and when you back up too hard onto shore/rocks/other boats/etc. That pull/pull mechanism looks amazing. I'd love to try it at some point.
Liquid electrical tape is OK as a temporary solution b but the above post is correct. I used to use it on my electronics until I noticed it would separate from some surfaces and let in water.
I also have had the liquid tape separate in the past. The separation I observed was at the edge of the coating. So now I make sure that I coat both sides of the card and make sure that there are no edges to lift up. So far I have not had additional failures. The advantage of the liquid tape for this case is that it doesn't bond to the board. Because of this, if I want to remove the coating to reprogram the switch board I can. Perhaps I should put a dab of liquid tape just on the program contacts and then cover the whole board with Scotchkote. I should be able to cut through the Scotchkote and remove the liquid tape to get to the contacts. I've contemplated drilling holes in the servo to let the water out. I suspect that my one instance of frozen gears was because the water was unable to drain out of the gear area. I just hate the thought of making a hole that guarantees that water can get in to the servo.
Very nice thread. As I am in the middle of building a couple/few of the little battleships myself, I will enjoy following this. But I am not sure that I will have much to add, as most of my technology is still from the last century.. Haha. Well done. Mikey
Very well-said Darren. However in my case. Not only do folks that see my internals wonder how old it is. They also wonder if it still works at all. And if so... Why? One of the battlers at the clash of the titans event last season looked into the Alsace and after a moment of silence simply said.. Interesting! To be honest. I felt warm and fuzzy inside. Mikey
I bought two motors from the Electronic Goldmine that I thought would work for PDNs. I finally got around to testing them this weekend. The first motor is an RS280: http://www.goldmine-elec-products.c...ber=G19724 Overall I was not impressed by this motor. It would work fine with a 3/4" prop, but draws way too much to run a 1" prop. I also would only run 6.0 or 6.6 volt batteries. Here's the test results: Motor: G19724 Kv: 1860 I0: 0.17A Prop Voltage Amps Watts RPM Est Thrust 3/4" x 25 pitch 3 blade 6.00 1.1 6.60 8600 3.0 6.60 1.3 8.58 9200 3.8 7.20 1.4 10.08 10000 4.2 7.40 1.5 11.10 9800 4.01" x 25 pitch 4 blade 6.00 2 12.00 6400 8.2 6.60 2.2 14.52 6900 8.8 7.20 2.4 17.28 7100 8.9 7.40 2.5 18.50 7300 9.0The second motor is similar in size, but with flat sides: http://www.goldmine-elec-products.c...ber=G18235 This motor is actually quite nice. It has low current draw and can easily handle a 1" prop. Thrust on a 3/4" prop is low because the RPM is low. Still, I think I might try two of these on my Golo. The Golo is so small that 2 oz of thrust is probably enough. Two of these with 1" props will give about 8 oz of thrust, and at about 1/3 the current that is required by the other motor to get 8 oz of thrust. Here's the test results: Motor: G18235 KV: 1000 I0: 0.07A Prop Voltage Amps Watts RPM Est Thrust 3/4" x 25 pitch 3 blade 6.00 0.31 1.86 4800 0.9 6.60 0.35 2.31 5300 1.1 7.20 0.38 2.74 5900 1.5 7.40 0.38 2.81 6200 1.61" x 25 pitch 4 blade 6.00 0.5 3.00 4100 2.5 6.60 0.59 3.89 4500 3.2 7.20 0.63 4.54 4900 3.9 7.40 0.65 4.81 5100 4.1These tests gives a pretty good starting point, next I plan to get them into a PDN and see how they work on the water.
