Well i have a choice in front of me & I would love some input. The New Jersey has 4 shafts, the "wing" shafts are powered & geared independently for big gun & will (probably) be drag disks for MWC. The center shafts will be powered & will have a transmission. The question is do I use 1 motor or 2? I am using ESCs; my ESC is rated for two motors, it is also water cooled. Center ESC Ratings: 50 amp continuous 120 amp surge, 5 seconds I could easily install 2 motors and create two transmissions, using the same transmission design as the wings... OR I could use 1 motor & create a geartrain so to power both props from the same motor. Using a gear train: reduces current draw. Increases complexity, I have to design a new gearbox Increases complexity, I have to use a geartrain. Which means the two drive gears have to be drilled perfectly so not to bind. Using two motors: Increases available torque/shaft Increases current draw Increases heat & load on the ESC Reduces Complexity, as I can "adjust" the motor's spur gear easily by moving the motor. Reduces complexity, as I can use the same design Reduces complexity, as there is a 2" separation between the center shafts & a ~3/4" distance between drive gear shafts.
RE: Current Draw > gear train? Well, on my Wisconsin (MWC Fast gun) I ran with 600s on the inner shafts and 2" drag disks on the outer props. Center props had 2" high pitch swampy props (I forget what the actual pitch is on them). Probably the second hottest that I've ever run those motors too (I burned up several trying to run my Bismarck's center shaft before I switched to a 700 series watercooled motor on it). Don't underestimate the torque it will take to move that ship at 24 seconds with drag disks (and you want the drag disks, they made a large difference in the beast's turning ability). If I ever revisit Wisconsin's drive (and can find more of the 700s) I will likely move her to the larger motors just so that I don't have to have fully loaded 600s trying to push her around.
RE: Current Draw > gear train? So you recommend twin motors because "you can never have enough torque"? Sounds like a viable argument. Any one else?
RE: Current Draw > gear train? I'd go with 2 motors as well, for anything that isn't tiny & can't fit 2 motors in. Driving the inner shafts only will help your steering. JM
RE: Current Draw > gear train? Justin, I disagree with your pro/con list that two motors increase the current draw and increase the heat & load on the ESC. It takes the same number of watts to move the ship at speed regardless of quantity of motors. Any theoretical extra power to operate a second motor is insignificant compared to the total power. It will take about 60W to move your NJ. A single 550 size motor will be mighty hot doing that. I suggest two drive motors.
RE: Current Draw > gear train? The biggest advantage that you MIGHT get with two motors is that instead of heavily loading one motor outside it's peak efficiency region, you can pick two that will run in their peak efficiency region... that would, in the end, reduce current draw if done right (that and it simplifies gearboxes, etc.)
RE: Current Draw > gear train? Even two 550s pushing an Iowa will get too hot for my comfort unless you watercool them (mine were usually too hot to touch after a sortie even with heat sinks added). Mark has a very good point about the power requirements remaining the same no matter the motor arrangement. The two variables that you get to play around with on propulsion are motor size and prop design/size. You can't really change your hull shape or displacement (well, you can play with the full load displacement a bit, but not all that much). Smaller props will make the two 550s happier but your acceleration/stopping will suffer. The original ship designers had to deal with turbine power output limitations and the size limits of the bronze casting technologies of the era. We on the otherhand have pratically unlimited (depending on how much your wallet screams power and prop size choices.
RE: Current Draw > gear train? At the fast guns battle this weekend, we had a Yamato and an Iowa both using twin 550's and they had radio problems but no propulsion difficulties... Even when the Yammer got chased down and sunk by everyone. After my lil Invincible had been I took a zillion hits and only sunk after I got rammed rather thoroughly by a North Carolina. Good weekend, thought I'd share But the Iowa and Yammer could run all day, no motor cooling, at fast gun speeds. The Yammer (which I looked at quite a bit) was driving a pair of 2 1/4" three-blade props at I think a 25 degree angle on the blade. Very cool ship, I believe the radio difficulties were due to a receiver problem (they were powered off the mains, some thought it was a factor, some didn't)
RE: Current Draw > gear train? 25 degree angle on the props might be the difference. My Wisky runs 2" 38 degree props and the motors (they haven't given any performance troubles yet) do get very hot. Makes for an impressive prop wash though
RE: Current Draw > gear train? Thank you for all your feedback.. I have decided to go with your suggestion and run two motors & two transmissions. Actually, I have more than decided; both are built & installed into the ship as of yesterday. I will also be running water cooling if for no other reason than for the ESCs -- Which I think will need it. That sounds like my Fast Gun props! Were they those cast "bronze / bronze-ish" ones? For quite a while I did not agree with your comments, Mark & renner... I was stuck on: like in automotive, vehicle speed is directly related to torque. The more torque you apply to the wheels, the more acceleration. Marine is different as it cannot rely on torque because of slip. In automotive, a vehicle demanded to accelerate as quickly as possible is limited by the amount of torque it can apply to the road. Therefore, there is never an upper limit to how fast a vehicle can accelerate; all you need is more power. With that, my statement is correct... Two motors increase the capacity for torque & therefore (could) demand more current. In marine, a vehicle demanded to accelerate as quickly as possible is limited to: 1.) The "bite" of the props, size/pitch/#blades... The maximum amount of water a prop can push @ given RPM. 2.) The max RPM of the motor (that can be sustained at given water resistance) ---That being said--- What makes things interesting is when a prop is mucked up... It can demand its maximum amount of current, with two motors... I will have much more torque capacity & therefore could demand more current... However this is a not something to worry about because it is better to draw more current than to be stuck in the mud.
RE: Current Draw > gear train? Good idea to have a safety margin. Its better to work less efficiently than to not work at all. Hehe... I once got mossed so bad that the prop was a spinning blob of moss, with no surface to push water with. After that, another club member brought a couple garden rakes to clear the moss before battles.
RE: Current Draw > gear train? I am definately in agreement on the watercooling the ESCs! Good thinking
RE: Current Draw > gear train? The Iowa had 550, the Yamato had the sweet 700 series motors that we found. They are using less than 1/2 the amps, and out starting and stopping the 550's with ease. Yes it was receiver power issues with the new spectrum radio's, since we are powering the receiver off the main battery, when the serge current from reversing hit the receiver, with the resulting voltage drop, the receiver was losing sinc with the transmitter. Spectrum makes a cap with a plug on it that plugs into the receiver that solved the problem. We are replacing the motors in the Iowa as we speak, the 700 are just sightly getting warm, pushing that 59 pound Yamato around, with torn of power to spare.
