Realistically, not that much, although the stall current on the brusless motors I have used is not known. I have always tried for overkill. the other thing to be aware of is the BEC in the esc's can be burned out easily,especially at higher voltages, I did that on my mamba esc. I hadn't seen the mtroniks one, you will want to verify that it does have reverse.
The M tronics esc has reverse, there is a 15 and a 30 Amp version. OK I looked at the e flite 450, which is a outrunner, and is supposed to be capable of 18 A burst current. (890 Kv) If you pared that with the m tronics Hydra 15 or 30 ($60-$75), wouldn't your power system need only 15 Amp-hours to run for an hour, rather than a brushed system's 40? (assuming constant running at maximum speed)
unfortunatly, it is not that simple. Running at max speed does not necessarily mean running at max current (not that you would want to run near the max for very long anyway, due to heat concerns for both the esc and the motor). You would need less batteries to run for an hour than brushed, but particularly in larger ships, you need the weight anyways, so you might as well put the batteries in. You also need to remember that there are inefficiencies in the ESC, in the battery, etc.. and you also have to consider the voltage you are running at, as 15A at 6v is a lot less power than 15A at 12V (in fact it is 50%). In reality, I would expect a proper system with a proper motor choice to pull in the 2-8A range for any ship, and I would over-rate the esc to deal with any stalls. the hard part is motor choice, as not enough folks have tried various motors and combination. Please try, if you are up to it, and let us know the results so we can learn what combinations work.
Your right, I forgot about voltage... I'd like to try, but I'm not sure I know enough about electricity to pull it off first try. The only reason I would go brushless on a bigger ship (like my ID) would be to try to save money and have less battery packs dangling around in the hull.
You won't save money. you may save hassle as you won't have motor brushes risking corrosion (but you do have bearings). for the tirpitz and the karlsruhe one of the big benefits was the space it saved right underneath the aft turret, which helped with cannon mounting, etc. another thing to remember is that these motors, if chosen properly, have very high torque when running... and are good candidates for almost 1:1 gearing (in fact on the tirpitz the motor was geared up) some weekend if you want to chat on the phone about it, I would be happy to do a brain dump of what i know. If you are space/weight constrained, it will help a bit with batteries...
I'm seriously considering going to brushless, I do want to save weight on batteries, and the extra space could be put to use... How do you choose a motor? I just looked at the Kv rating and the current draw. Would a 450 size motor have enough power to use on a small battleship like ID?
definately. unfortunatly, all there is to go off of, really, is kv, although I also try to make certain that the max watts are high enough (consider that we really don't pull much for our motors, as even the brushed ones, genearlly pull under 10A at 6V (60W) when normally working.. Chances are, that any motor you get with a small enough kv will be more than overkill in the current department . the motor listed (the speed 480) ran the tirpitz just fine on 6V, and she was not small. (hell, she could almost plane on 12V)
So, if I'm understanding this correctly, the lower the Kv, the lower the rpm per given voltage. But does the motor develop more torque than a motor with a higher Kv rating of the same size? (would a ~900Kv speed 450 hav more torque than a ~1200 450?) Another problem I see is the MWC rules require the pump to be not physically larger than my drive motor!
generally, the lower KV costs you a bit of top power (although generally, there is sufficient overkill) but at the same power output as a higher kv variant, the torque is higher (has to be, power is product of torque and angular speed). I tended towards lower kv in the hope of quazi-direct drive, but any will work if geared properly.
If I used a brushless 450 as a drive motor, does the pump rule mean I would need a similar brushless motor for a pump and an ESC for it? Would the motor be compatible with Battler's Connection pump?
I do not know how the MWC applies their pump rule, but the IRCWCC seems to have gotten rid of that rule at some point. It may be worth asking the elected folks in the MWC how they would apply the rule to brushless motors. The motor will almost certainly not be compatable with a BC pump, as the screw mounting and shaft sizes will be different. The other thing to note is that there is no one I know of who has found a suitable brushless motor for pumps (although I am working on it). The IRCWCC rule that does not appear to exist -Greg
Yes, we have to have a pump motor smaller than the drive motors. I already have the brushed drive motors, anyway. I think it would be a good idea to find a way to use a brushless motor in a pump, since they take almost as much power as the drive system. Couldn't you just rig up some sort of shaft extension and motor mount? The extra torque would probably be useful...
You should be able to make a custom shaft and mounting bracket (or drill new mounting holes to match your motor). If you can figure out the current draw, voltage drop and rpm of a good working pump with a brushed motor, we could then make a good stab at a good brushless equivalent..
These could be useful: http://store.polkshobby.com/scripts/cgiip.exe/WService=takestock/itemdet.html?itemnum=PLKDYNAX1806&conum=002 and http://store.polkshobby.com/scripts/cgiip.exe/WService=takestock/itemdet.html?itemnum=PLKDYNESC18A&conum=002 They are cheep, and the motor looks like it would be easy to mount to some sort of homemade pump-bracket thing (not sure if it is inruning or outruning, though)
I have no idea if those motors would work.. without a good baseline for what the full sized pumps do, we are shooting blind, and while we may get lucky.... -Greg
I haven't even gotten my pump yet, so I can't help much there. How do you measure the current draw? My multimeter only goes to 10 A. That sure would draw less than the Titan 12 t I was planning on using!
you can get a clamp on current meter from home depot. The hard part is that we need some kind of idea of the rpm of the pump motor...
I know they make laser tachometers for model planes, I wonder if it would be possible to rig up one of those.
