Has there been anything new on the brushless front? As I have started looking into converting to brushless there are a couple of issues that I have run up against. · Bolt pattern. All of my ships have been built with gear boxes that fit a 550 can brushed motor. I am not finding a lot of options that fit this. M3 screws spaced 25mm apart. My questions to those of you who are running gearboxes on brushed motors are: · Are you building custom gearboxes for each motor you install? If not what are you using? · All of the motors listed at the beginning of this article have a can size diameter of 42mm. I do not see the “bolt pattern” for these. Do they bolt up to our standard gear boxes? Most of the brushless motors are set up for 2-3s, 3-4s or 5-6s These numbers represent cells of 3.2V batteries. More motors are available at the higher “s” range. What are most of you running at with the brushless motors. Are you running at higher voltage than the old standard of 6v? I have found a nice standard size motor that comes in a wide range of kv values (450 series Helicopter) but they are smaller, 380 can size (3M screws 16mm apart). For a brushed motor the size of the can made a difference for torque. I assume it is the same for brushless??? Are the smaller cans adequate for bilge pumps?
Look at the SMS Nassau, and her pump and drive is a 2100 KV. turnigy running 3 cells of LiPoFe. Small bolt pattern of 3/4" (16 mm) and 3 mm shaft. output of pump is 2.3 GPM 3 cells and 3 GPM on 4 cells.
Usually you can find the bolt pattern in specs. For 28mm outrunners, the bolt pattern is usually 16mm and 19mm. Once you get to 35mm outrunners, the 25mm bolt pattern becomes pretty common. Example: I don't use gearboxes, I don't like them. They are noisy and an additional failure point. The outrunners have plenty of torque and are available in plenty of Kv ratings to match your prop and battery voltage without gearing. The battery "s" ratings are pretty useless for ships, they apply more to airplanes where more amps are drawn. And unless it specifically calls out LiFe batteries, each "s" is generally equal to the 3.7 volts of a LiPo battery. Kv is a much better number to use when buying motors. I run a 2S LiFe battery in my ship, so only 6.6 volts. For example, my 25 second Hawaii has 750 Kv motors and 6.6 volts, so the maximum RPM is less than 5000 RPM. If you want to run a higher voltage pick a lower Kv motor. I recommend that you keep the total RPM less than 8000 to avoid excessive amperage draw. So if you want to run a 2S Life battery at 6.6 volts, pick a motor of 1200 Kv or less. 1200 x 6.6 = 7920. The same motor would still work with a 6V lead acid: 1200 x 6 = 7200. If you want to run a 4S LiPo battery at 14.8 volts, then pick a motor with a Kv of 540 or less. 14.8 x 540 = 7992. If you have a brushed setup that you like, measure the RPM at full throttle and use that to determine what you need for the brushless setup. Just remember to add about 25% to the RPM because the numbers above are maximum theoretical values and are never reached in real life. Example: current setup turns 3800 RPM and you want to use a 6v lead acid cell. First find the maximum RPM: 3800 * 1.25 = 4750 RPM. 4750 RPM / 6 volts = 792 Kv. Round up to 800 Kv and start looking there for your motor.
If I wanted to match Carl’s setup for a pump. “3 cells of LiPoFe” , 2100 KV motor. 9.6 x 2100 = 201600 201600 / 6.4 = 31500kv motor This is the closest that I could find: http://www.hobbyking.com/hobbyking/...26_3000_70mm_EDF_Outrunner_US_Warehouse_.html 6.4v x 3000kv = 19200 The motor is designed to run at 14.8v (4s). I don’t need to worry that I am only running 6.2v (2s)? I can ignore this?
Re back to my 81 amp pump as my first brushless pump system attempt. I failed to take in account that the higher torque brushless motors under load tend to not drop much in rpm and instead draws a lot more amps. Luckily, there is a guys that have pretty much perfected the brushless pump (Carl and Kessler) to benchmark from.
There's an extra zero in that number, it should calculate out to 3150 Kv instead of 31500. This motor looks like a bolt-in replacement for a 550: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=27865 The water cooled one is also intriguing: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=25091 Run a strong ESC and keep it at low speed until you really need the pump.
Have you run an inrunner? They have no vent holes (water drainage holes). They don't "look" like the right product for our application. Everything else about it looks very promising. Please tell me I'm all "wet" on the inrunner opinion. Keith
The coil that powers the thing is on the case (you can't drill through the case to vent), the armature has the magnets attached to the shaft (if it fouls it stops). The outrunners have the ability to drain freely, inrunners are sealed and don't drain well. When I designed my pump I included a oil seal in the case that keeps the water in the case and not spraying up through the top of the pump. This helps keep the pump primed as well because little air will pull through the shaft seal. All in all this will work but amps will be high and life will be short.
