There is a large variety of connectors to choose from but my favorite, for applications under 10 amps, is the Micro-Deans. Unlike the standard Deans, these are compact and easy to separate. They are still gold plated, for good corrosion resistance in ships. They come in either polarized, for the battery side, or non-polarized, for the motor side. Both types are also available in both black and red, if you want to do some color coding. There is even a three prong version for your brushless motors, which you can disconnect, rotate 180 degrees, and reconnect to reverse the motor. Best of all, these run me $2 a pair at my LHS.
Oh neat I haven't seen the non-polarized 3 prong plugs. I hope they dont get rid of the polarized 3 prong version, those are great for radio connections. The two prong connectors work great for solenoids and firing board connections. All these connectors are about $1.50 on towerhobbies(you can find them cheaper with a little digging) which is great when you're buying them in bulk. Deans seems to have some sort of production issue with some of these smaller connectors which is the downside to using them that I've experienced. Occasionally they become really hard to find for a few months.(2-prong styles are less prone to this than the 3 prong) I guess they don't do a great job pre-planning their production runs to maintain stock levels. Still worth using.
Drive shafts and stuffing tubes for these PDNs can be made inexpensively. Materials needed are 3/16” OD brass tubing, 5/32” OD brass tubing, 1/16” music wire, 1/8” x 1/16” stainless steel tubing, and some loctite high strength retaining compound. The stainless steel tubing I get from my local ACE Hardware. It’s a little expensive at $4.50 per foot, but that’s enough to do 12 shafts. I start by making up the stuffing tubes. Cut the 3/16” tube to the length needed for the stuffing tube in your ship. Then cut a 1/2” long piece of the 5/32” brass tubing. Make sure to clean up the cut ends so that prop shaft fits inside easily. glue the short piece of 5/32 tubing into the end of the stuffing tube using the retaining compound. This short piece of tube acts as a bearing and can be drilled out and replaced if it gets too worn. If you are not interested in the ability to replace the bearing, the stuffing tube can be made with straight 5/32” tubing instead. You might be tempted to solder the two brass tubes together instead of gluing them. If you like to solder, go ahead. However, the glue is extremely strong and easier to use. Next, cut some 1” pieces off the 1/8”x1/16” SS tube. Clean up the ends so that the 1/16” music wire fits through the center. This can be the most frustrating step, since the music wire is generally a little oversize and the smallest bur will prevent you from sliding the two pieces together. Make a flat on one side, about 1/2” long, for the prop setscrew. Cut the 1/16” music wire to the length needed for your prop shafts. Now glue the SS tube onto the end of the music wire with the retaining compound. On this step I don’t recommend solder, because you need the right flux, silver bearing solder, and perfect technique if you don’t want a failure. The fast electric crowd has successfully tested the retaining compound to torque values far above what combat ships will ever see. Glue the stuffing tubes into your ship. Install the drive shaft into the stuffing tube, leaving about 1/2” out for the prop. Put a short piece of Nyrod into the other end of the stuffing tube to center the drive shaft at that end. Put a little bit of oil on the shaft right where it comes out of the stuffing tube in the ship. Then shrink a piece of heat shrink tubing around the stuffing tube and shaft. The heat shrink tubing will close down over the 1/16” wire drive, sealing it to prevent water from coming through the tube, but still allowing the shaft to turn without binding. When I first saw this technique I had my doubts, but it really works well. Use a piece of 1/16” ID Clippard tubing to attach the drive shaft to your motor. The tubing is plenty strong for PDNs and eliminates the expense of dog bones.
I came up with a variation on Steve's suggestion of synchromesh cabling. It uses ball chain (3' for less than $2) and some printed pulleys. My spring connector is a little long and I want to design a smaller pulley for the rudder shaft, but it did work. For those that want to try it, the files are here http://www.thingiverse.com/thing:317721
It holds its registration very well, is smooth and has no slop. You can get it to slip if you put enough force on it. It does take a lot of force, so you would expect it to slip when you hit a rock, but not during normal operation. I'll put a extra strong servo on it this weekend and see if the servo torque alone can make it slip. Even when it slips it stays on the sprockets and re-engages, so you would retain some rudder control. I am planning on making the holes a little deeper and that might make it harder to slip. As a proof of concept part I'm very pleased with its performance.
Update on the HK speed control: It has excellent reverse battery protection. Mine still works after hooking up the battery backwards, although I just barely got the flames blown out before they reached the board. Some days I wonder if I'm ever going to learn from my mistakes :blush:
This last weekend I was able to conduct tests on some of the motor/prop combinations I've recommended. The Golo was re-motored with two of the G18235 motors, driving 3/4" 25 pitch props. At full throttle the ship was making 36 seconds, slightly slow for fast gun, but perfect for Treaty. I dialed down the ESC to about 90% to get the required 40 second speed. These motors should still work good for a fast gun setup, you would just need to change the 6.6 volt battery out for a 7.2 volt battery. I also tested my Potemkin with the same motors and 2 cell LiFe battery, but with 1" 25 pitch 3 blade props. I was initially disappointed with the speed, since I only measured 41 seconds. Then I discovered that I was missing a prop. So 41 seconds on one motor and prop may not be bad, I'll have to check it out again when I get it repaired. The reason that I lost the prop was that it pulled out from the tubing I was using as a u-joint. I've been spoiled by my Golo which allows me to use about a 1" piece of tubing to connect the prop shaft. With that much tubing, the shaft is held securely and I don't have to worry about losing a prop. However, in the Potemkin I was limited by space and the tubing was less than 1/2". The fix is very easy, I just added a 1/8" wheel collar to secure the tubing to the shaft.
I got more testing in on the Potemkin this weekend, so here's a motor/prop update: With 1" 4 blade 25 pitch props, the Potemkin made speed at about 92% throttle. Amps were 0.8 total (0.4 for each motor) for a total of 5.3 watts. With 1.25" 3 blade 25 pitch props, the Potemkin made speed at about 60% throttle. Amps were 0.5 total for a total of 3.3 watts. Starts/stops may have been slightly better, turning seemed to be about the same as the other props. Based on these results, I would go with the 1.25" props just for the lower amp draw. With the 2000 mAhr battery I have in the ship, it could stay at full throttle for about 4 hours
