I am interrested in trying a brushed motor setup for a battlestions ship, I need three motors, that can propel a ship in excess of 150lbs at 35 seconds without frying. In my New Jersy I run two direct drive 973 Johnsons, and have a geared set of long can 550s as backup on the outboard shafts. I know that Kershaw designs makes a HO 700 bushe motor, but have no clue how the whole brushless thing works, I know that three 970s would work, but I have heard that brushless is the way to go, if you want really powerful motors
For brushless motors, I generally size the motor based the needed watts and then pick the winding based on what RPM is needed. A second way of looking at it is in terms of efficiency. I use a value of 50% efficiency for a generic can motor and 70% for a generic brushless motor. The efficency does of course vary with the loading and quality of the motor but I find these to be good ballpark figures. So pick at brushless motor that puts out .5/.7 or 71% of the can motors you are using. A 100 watt can motor can be replaced with a 71 watt brushless motor. So how many amps are the current motors drawing? What size props are you using? Have you considered using 24 volts instead of 12? I'm not sure about the availability of controllers, but it would be one way to get more power to the props while keeping the amp draw down.
I've done a lot of testing and figuring on brushless since last year and have been running brushless in all of my ships since June 2010. Some things to come out of all that is: - (fastgun) ships like 4000 - 6000 rpm at the props to make 28 - 22 seconds of speed. May need to adjust a little lower for slower speeds. - For large ships, pick a motor with a can diameter larger than 35mm. For the New Jersey, look large ... probably around 50mm+. - Decide on your propulsion voltage. Most large 35mm or larger motors like higher voltages, i.e. 11 volts or more. - Figure out how much Kv (rpm per volt) your ship will need to make 4000 - 6000 rpm at the props using your selected voltage. For example, using 12 volt power and a 2 to 1 gearbox, a ship would need a motor with around 1000Kv ... 6000 (expected prop rpm) * 2 (gearbox ratio) = 12,000 motor rpm, divide by 12 (voltage) = 1000Kv motor. - Outrunner brushless motors tend to have lower Kv and more torque than Inrunner type brushless motors. Outrunner motors work nice for direct drive applications, Inrunner motors are well suited for geared applications (most of the time. Some examples of ships with brushless include: - HMS Erin uses a 36mm diameter inrunner motor that has 2600Kv mounted to a 3:1 gearbox operating on 6.6 volts. This combo gives too much prop rpm and requires the throttle EPA reduced to 44%. A 1800Kv version of the same motor would work much better. - FN Verite uses the same 36mm diameter inrunner motor as the Erin except as direct drive on 6.6 volts. This is far too much rpm for a 28 second ship and requires the throttle EPA reduced to around 25%. Again, the 1800Kv motor would be a better fit and even then it will need dialed back. - FN Richelieu uses 36mm, 1300Kv outrunner motors running direct drive on 6.6 volts. This was pretty close to the mark, pushing the Richelieu at 28 seconds with 44% throttle. Fast gun 24 second speed should be around 60%'ish throttle For the New Jersey, perhaps one of the 50mm outrunner motors on direct drive will get it moving at the right speed. This one (www.hobbyking.com/hobbyking/store/uh_viewItem.asp) looks like a good possibility. Although it is rated for 4S voltage and higher, it will run on 12 volts. It will handle 1200 watts with no problem. Some sort of adaptor will be required to connect the 8mm shaft to the prop shaft. I plan on using these motors in the 1/96 Bretagne.
You can't. Since motor timing is controlled by the ESC, each motor requires its own ESC. I've successfully run two ESCs off one channel using a "Y" harness. I've also run an ESC per channel and electronically mix the channels in the transmitter.
Thanks for all the feedback, I will more than likely stick with the 970s in the Jersy for now, but there is another very large battleship being contemplated
1200W? I never imagined almost 2hp to run one of these ships. Two of these motors have more potential power than my combat tank. On another tack, I purchased a couple of tiny 19mm low KVM outrunners that I never used for my Mogador. I was just thinking it might be a cool experiment to build a prop around them to see how that might work. Something like a mini azimuth pod. Steve
Heh. If anyone hasn't noticed the trend, I tend to go a little overkill when it comes to motors. The New Jersey would never hit 1200 watts on one motor, much less two motors used for propulsion (12v x 100 amp draw = 1200 watts x two motors). But it is nice to have just in case something unthinkable happens. The idea with the large size motor is big torque. That New Jersey is a heavy 100+ pound ship ... it'll need the torque to accelerate and stop half decently. Some of the large three shaft 1/144 ships might do well with the 50mm motor powering the middle shaft. Again, big torque for those large props. The Richelieu running two 36mm outrunners has very good starting and stopping. The torque also keeps the props turning at speed to helps keep ship speed up in turns.
The new vessel which will be powered by the brushless motors, is an H-39 class battleship, in Battlestations format, I agree with Mr Mangus, in that more is better in regards to torque, and can attest to the acceleration/deceleration of his Richelieu. Running three motors, I would need three ESCs i take it?
I guess my next question, is how would I connect the three speed controls to one channel? Is it simply make a Y harness that has three connectors going into a common connector for the Throttle channel? or?
Yup, one per motor. We've been running Hobby King 100 amp car ESCs (www.hobbyking.com/hobbyking/store/uh_viewItem.asp) with the fans removed and electronics potted in resin. They are only $35 each and work well, though sometimes they have a problem with voltage spikes from high powered pump motors if run on the same battery as the pump. Mtroniks also has a quality marine brushless ESC for around $75'ish each I think. There are other waterproof brushless ESCS out there, but most either do not have reverse or has some sort of delay before going into reverse. I tried battling with one ESC that required the throttle to be in neutral for 1 second before it would go into reverse. 1 second may not sound long, but in fast gun direction changes need to be instant to prevent ramming someone else ... and I rammed a lot of people even when remembering to pause in neutral. Heh.
Yup. You could try that. I haven't tried it with three ESCs, but have sucessfully run two ESCs off a Y harness. Currently, the Richelieu runs on a Y harness. It is also possible to use any extra channels on the transmitter and mix the channels to the throttle. The Erin when it was dual motored used this method.
Nice, some of these questions may have been answered in prior threads, so i appreciate you answering them
Actually, I don't think anyone has asked a brushless question on these forums until now. There has been discussion on the MWCI email lists, plus a forthcoming article for MWCI's TF144 newsletter.
Mike, Since it's impossible to find bushed brushless motors anymore. Was wondering what you do to maintain the ball bearings in your motors? Steve
Good question Steve. The short answer is WD-40,machine oil, and dilligent preventive maintenance. There is some additional maintenance with brushless motors ... but only for a person that does not maintain thier brushed motors well. It doesn't matter if the motor is brushed or brushless, it should still be oiled at least every evening after a day's battling to prevent any corrosion and help lubricate the bearings (bushing or ball). If the captain is the type to toss the ship onto a shelf after a battle without doing any maintenance to it, then brushless systems is not for them. All the motors should be taken out of the ship, cleaned, and reoiled before the ship is put into storage. I recommend this no later than a week after a battle. I personally do this within a couple days after a battle weekend after having a set of gearbox gears corrode so bad the week after a battle that the gears and shafts would not turn. Of course, that was from a week long Nats at Conron NY which seemed to have very powerful corrosive effects on metal. heh. Every evening after a day's battle, I spray WD-40 into the bearings to help displace any water that in them. Within a couple days after a battle weekend, the motors are taken out of the ship, spray cleaned with WD-40 and a motor cleaner, then oiled with machine oil. Only them does the ship get put on the shelf. This maintenance process was learned the hard way after loosing bearings in the first couple brushless motors I used in ships. Since going to it, not a single bearing has failed in brushless or brushed motors. There is another product out there that is supposedly better than WD-40 and does the same job without the propane ... LSP-1 or LS-1 or something like that. Maybe someone using the stuff will chime in about it. If there is anything from this post to be learned, it is do not skimp on preventive maintenance or it will come back to sink you.
Mike, I've been meaning to ask you since Treaty Conference, what specific motors do you use in Richelieu?
Hi. The Richelieu is using two Turnigy 500 H3126 outrunners (www.hobbyking.com/hobbyking/store/uh_viewItem.asp) Each motor turns 1300kv (rpm per volt) which is almost perfect for direct drive on 6.6 volts. At the Treaty Conference, the Richelieu was dialed down to around 44% throttle to make 28 seconds. What was really nice about the motors was the sheer torque they have. The Richey has never accelerated as well as it did at TreatyCon (first time with brushless power in the ship). In fact, before the start of a sortie one motor torqued itself off the aluminum motor mount! The extra torque really helped with turning also since the prop rpm barely dropped in a turn. I can hardly wait to see what it'll do at MWC's 24 second speed. Heh.
