Just ordered a Mogador kit from BC. Was wondering what propulsion setups have been used in the past in a DD? I'm building it for IRC/Treaty. Looking for pros and cons on single/dual motors, gear reductions, comment on prop sizes etc. Also, what amp hour capacity is recomended? I'm leaning towards A123 LifePo 2.3AH 3.3v cells. Steve Tyng
Hi Steve, I'm on the RC Tanks list as well (Clark in Georgia); I'm much better at doing boats than I am at finishing tanks Welcome to the RCNC forums! For a DD, I'd go with a single speed 380 motor driving a pair of 1" (or 3/4") props via a gearbox. This will also allow you to run a 380-size motor on your pump. Gear reduction I used on my DDs is around 2.5 to 1, although with the Speed 380 motor you may need to go to 3 to one. Battery-wise, you're allowed to swap every sortie (vice every battle with bigger ships) and I can't imagine you'd use more than 2000 mAH at 7.2 volts. The battery you're looking at should be plenty good. If you want to go with brushless motors, let me know, I can recommend a couple of good choices. You may also wish to bookmark the Marine Nationale historical service page for Mogador; The French Navy posted the shipyard blueprints for nearly every ship that they've used from the late 1800's up thru the 1960's (and a few newer than that). Nothing like the real thing to guide your build! www.servicehistorique.sga.defense.g...anbato.php
Tug/Clark I was leaning towards two smaller direct drive motors (and controllers) for redundancy. Hadn't thought how that would limit my pump motor size in IRC (though not an issue in Treaty). Was looking at these, 4K rpm at 12volt: http://www.allelectronics.com/make-a-store/item/DCM-300/12-VDC-IRON-CORE-MOTOR/1.html Controllers would be the Scorpion Mini from Robotpower.com: http://robotpower.com/products/scorpion_mini_info.html What brushless motors are you recommending. I was originally thinking of going all brushless but started thinking brushed as it be easer to implement. Could go brushless on the pump to keep the motor size small (unidirectional brushless controllers are dirt cheap also). Steve
Having tested 3 different sizes of 380/400 brushless motors, the best of them (for pumping purposes) was: http://www.hobbyking.com/hobbyking/...oduct=5223 I'm running those pumps with 30A brushless aircraft ESCs from Hobbyking.com, which I have epoxy-potted to waterproof them. Those are not the cheapest 380 size brushless motors, but they're really good.Between the motor and ESC I think I spent $25-30 bucks or so. I'm using an identical motor for drive in my cruiser, with a car ESC. Note of warning: The Scorpion mini ESC will not be able to handle the current demands of the DD drive motors, 2.5A is not nearly enough and they will smoke... I think using an H-bridge wouldn't be legal under most rulesets anyhow, they won't allow slowing the inside motor in a turn. Either a straight-up car ESC is fine, or a MAG throttle. If you want a smaller motor for your DD I can look at the parts numbers of the other ones I've ordered (which are smaller and cheaper). If you look in the Builds section of these forums, there is an ongoing thread 'The Cheapest Point of Entry' in which I have discussed motors and such and have links to ones I bought. If you've never built a boat before, it's worth a read in general, along with the stickied Bearn build by Mike Mangus (on tank list with the Spartan supply vehicle). There are also a few destroyer builds in the Build section although Moggie is a big DD, almost a CL, so space and weight aren't quite so critical.
Take a look at these: http://www.halted.com/ccp21544-precision-swiss-dc-motor-maxon-a-max-6-vdc-80ma-8-a-max-series-21283.htm ultra-high-efficiency, high-torque Maxon motors. I'm currently running two of these direct-drive in my Z-boat, and it really boogies. I would like to switch out for a two-shaft gearbox if I can find one suitable, because these particular motors have a lot of torque. My brother Gascan will be using a pair of them in his HMS Invincible project, once he gets off his lazy butt and starts working on it.... For speed controller, consider the Mtroniks Micro-Viper 10, available from Strike Models. Much higher amp rating than the ESC you discovered, plus it's by the single most-proven brand of factory-waterproof ESCs on the market. I don't use anything else.
Carl, the gearboxes aren't too hard to make, and you have much better access than I to a CNC mill After the CPOE class is over, I'll sneak in a quick howto on bulletproof gearboxes. I'd send you one of mine, but the holes are drilled for the 550-size motor. Of course, Steve, you could run your Moggy on a 550-size motor
I think people have a tendancy to over estimate the amp draw on their drive motors. I've been spinning the 20 pound turret on my 1:6 scale combat tank without issue for six years now using the Scorpion-Mini (attached to an appropriate heatsink). The mini has a max surg of 6A and is current limiting. Not sure if the typical budget car or boat ESC has the current limiting feature. If I recall, the old-school MAG switches are built using small snap-switches which don't have that much in an amp rating. I'll pick a controller once I settle on a motor and do some stall amp measurements. Regarding using an H-bridge, a reversing car ESC is an h-bridge, for that matter so is the MAG switch. Having two seperate drive motors and controllers does open the posiibility of drive mixing in a turn. Of course, this would be unethical and I would never consider doing such a thing! ;-) Steve Tyng
Apparently a bunch of Fast Gunners melted their ESCs when Mtroniks released the first truly waterproof ESC. Their drive motors continuous draw was within ratings, but startup draw was much higher. Keep in mind that this was battleships with 550's and bigger, though. Mtroniks has since introduced current-limiting, heat protection, and other protection features. Now if only they'd figure out how to protect against accidental receiver battery plug-ins.... I would be interested in learning about gearboxes. Especially a design that I can order laser-cut from Polulu, like I did with the Mikasa's cannons, and set the shaft spacing to exactly match what's already in my Z-boat.
Trust me Steve, you will pull more than that ESC will handle. I could be wrong, but I doubt it. Our use profile is different than a lot of others and the motors tend to do a LOT of back and forth and hence tend to spend a lot of time in the 'starting surge' time. But go with what you like you do have a lot of RC experience to draw on I will happily eat crow at the end of Moggie's first battle.
I'm sure there is a way to laser cut a gearbox but I will say the last time I tried to build one from flat plastic, it was far too flexible to be usable. Went back to aluminum for something both lighter and smaller than what the flat laser cut plate gearbox would have had to be.
I've been machining mine by hand (as opposed to CNC) from 3/4" x 1.25" aluminum box section. Pretty sure it's 1/8" wall but I'm at the in-laws and can't go look But I've been abusing my drill press to do it and I'm pretty sure I need to get new bearings at some point as a result Someday I'll get a mill! (anyone wanting to help can buy a Baden or Iowa hull that are sitting in the shop lol) (Brandon has already helped by commissioning me to build his Gangut hull, so I will someday buy the 'Brandon Memorial Mill' for the classroom of Model Warship U.)
The gearbox could be built in. Such is the direction I went when I started a Mogador build. The stuffing tubes were set into the hull with the correct amount of space between them for a gear on each shaft to mesh with a gear on the other shaft. Once the stuffing tubes are anchored into the hull, the gear mesh between the two shafts does not change. The motor was mounted so that it's gear meshed with one of the prop shaft gears. The motor drives one prop shaft and the power is transferred between the driven shaft to the second shaft. The upside is a simple gearbox. The downside is the gear ratio cannot be changed. I'm not worried about that ... an ESC and proper selection of motor and voltage will get me into the correct speed range.
Mike, that method is what I did on DD Othar; the motor drove one shaft via stepdown gearing, and the bull gear of that shaft drove the bull gear of the other, in the opposite direction. Weight-saver, aye!
I think that I will also build the gearbox into the boat as Mike described. I've ordered a couple of 2830 750kV outrunners (one for propulsion, one for the pump). I'm going to mount the outrunner directly to one of the prop shafts for a direct drive setup. Has anybody looked at these props? http://www.proboatmodels.com/Products/Default.aspx?ProdID=PRB3356 Their for the Pro Boats Arliegh Burke Destroyer model. I can't find and size info for them. They look nice and the price is right. Steve Tyng
They certainly look good and are a good price, but I'd do some google-fu and figure out what size they are. More than an inch would be too much. What size shaft do the motors have?
I've already spent some time looking for the specs on these props. Not much beyond a part# and Pro Boats so-far is unresponsive to my queries. I'll probably order a pair just to look at them. The motor has a 1/8" shaft: http://www.rctimer.com/index.php?gOo=goods_details.dwt&goodsid=123&productname= The low kV and the 13v I plan to run at should make for a nice efficient system. Steve
I agree; my brushless drive motors tend to be low kV unless I just have to have gearing to get good driveline angles, and even then they're pretty low. Pumps can run faster without penalty performancewise. Some of the high-speed pumps in use top 16k rpm without too much cavitation, and at least person with the skills has looked at impeller designs for >20k rpm. I'm not that awesome But there are some amazingly talented people running boats these days I like how you're going to do the drive, it's definately the way to go in lightweight boats. The DD Othar Tryggvassen had to come in at like 2.48 pounds and THAT was an educational build. I may bring it to an IRCWCC event along the East Coast sometime next year.
For those who have built DD's. How much AH capacity did you put into them? Right now I'm looking at 6.6v 2.3AH or 4.6AH.
I was thinking somewhere around 2 - 3 ah due to the smaller motors (lower amp draw) and being able to change/charge the battery between sorties. But I am curious what others have used so far.
