So not sure how much you know about brushless, so I'll spiel here for you and any other who finds this later on: Brushless motor KV ratings are RPM x Volts. You are supplying 11.1v, so if you use a 1000kv motor you'll be at 11,100rpm if you are direct drive to the prop. For example, my 28 sec dual shaft Courbet has two 1000kv outrunners going into 1.5:1 gearboxes at 11.1v. 11,100 rpm / 1.5 = 7,400 shaft RPM. In order to make 28 second speed, I have my radio endpoint at 9%. This is using a 1.5" 3 blade prop. There are a lot of ways to size your combination using the 3 variables at play. Motor KV, Gear ratio, and prop. Props obviously have two major speed contributing factors, other than size. For size, I'm assuming you have the prop matched to what you can physically fit and matched to your rudder area. These two factors are Blade count and pitch. Pitch is measured on 1:1 boats as a unit of distance, so a 12" pitch prop would move the prop 12" forward through a solid surface for every 1 rotation. Think like a screw driving into wood. Some vendors measure their props for us in degrees though, like 25 vs 40. The big thing to remember is the flatter the blades the less the pitch the less the boat will move forward per RPM but she should have more torque. Blade count will matter, generally more blades are slightly smaller individually than fewer blades on the same prop but they cover more surface area letting the prop get more bite into the water. All things being equal, a 4 blade prop would require slightly less pitch than a 3 blade prop to keep the motor at the same RPM. More blade, more surface area. Generally. Not always. For something like a Baden, a 28 second boat, I would recommend something in the 36mm can 1000~kv range considering all the above. You have a single prop so it's going to need to do all the work, so expect to see a higher shaft RPM than what I mentioned above in order to make speed. Also, don't get caught up just focusing on the KV range. The motor can diameter and length also play a big role in the motor's total power output. Think of it as Voltage = RPM, Amperage = Torque. The larger the motor can the more magnets you can fit, slowing down the motor and generating more torque. Most of the Propdrive brand motors a lot of us use are on backorder, but you can get this guy on Hobbyking in-stock in the US warehouse. I'd probably run him if it was me, with a 60+ A ESC. Also remember, guys have been driving our boats at acceptable speeds and accelerations using whatever random 380-540-550 can brushed motors they can find out of whatever they have lying around. Sooner or later it doesn't matter, so I personally wouldn't spend beaucoup bucks trying to get ubermotors. https://hobbyking.com/en_us/turnigy-3648-brushless-motor-1450kv.html A little more KV, but that's why you have radio endpoints. Disclaimer: I'm some guy from the internet, someone else may come back and say I'm completely wrong and they may be some brushless motor engineering and hey, listen to them. This is what I've learned works based on our application and the advice I've given others.
yea, i know the KV and can sizing and all that, from racing, but wasn't sure how that translated to what would work for a boat, with the gearing. and that i'd want the lowest pitch i can find that's not 0 i'm going to build it brushed with the thought of going brushless later, want to get in on the water, and have the brushed stuff. I'm not sure what prop I have on it now, should probably figure that out, but I can always get another one if need be. How about a 3650 can, 1250Kv motor. not sure what gear ratio i'd run though.
That motor would work well. Most 36 can brushless will bolt up to a 550 brushed mount. So whatever gear ratio you are using brushed, leave in, and try it brushless.
For boats you want the lowest Kv you can find in the right can size. 750 or 800 would be better, sometimes those models are available. With a big prop the rpm will be low to make speed. 2” prop recommended. Also should use 32 pitch gears, 3/16ish shaft. Brushless would eat 48p or 1/8 shaft
Wouldnt that take me into 40+mm or outrunner territory? I suppose I can always refit for those later. Not sure what shaft I have now, I'd guess 1/8. and with 48p, but I have a collection of 32s, just gotta go get them. But I might go mod1 and 5mm, if I can find a shaft amd prop, that would be best
I have 42mm 650kv motors in my Jean Bart driving 55mm 5 bladed kort nozzle props with 2:1 gear reduction and I'm at about 30% to make speed. Then again, there are battlers out there who are direct driving boats using 1000kv brushless motors and they are just fine, they just set the endpoints appropriately. Your mileage will vary. The 1250kv motor you mentioned would work, yes. You'd probably be at about 20% forward throttle on your radio endpoints, if that, with a 2.5:1 gear reduction. Ideally, you'd want the lowest KV you can find in the correct can diameter. In a 35mm can, I've seen as low as 750-800kv. That would be the one you want. The one I suggested above was in light of current real-world stock at Hobbyking.
I don’t build for failure, sorry. I have data that shows the setups I use work, you are correct that I don’t have data that lesser setups will fail. Thanks for noticing. The reasons I use a larger shaft on the 20+ pound boats has more to do with integrity of the gear to shaft and prop to shaft joints than a shaft shear. The additional meat in those areas is nice considering the flat spot and set screw diameter that can be used. I only recommend things I run and have tested through many battles, it is certainly possible that lesser setups would also work, but I choose to spend time/money on the known good. I’d also add that I possibly witnessed plastic twisting deformation on a 3/16 shaft a couple times in seydlitz with the single motor dual drive gearbox I used for interwoven props. There was relative rotation between the gear and the prop a couple times resulting in a binding failure. Both the gear to shaft and shaft to prop connections were solid, and the gear engagement was constrained by aluminum. This was with a 35mm 1000kv propdrive outrunner, 1.6” props. I gave the system 3 strikes then did a chop and swap, but process of elimination led to shaft twist being one other the only remaining suspects. Never ran the calcs to verify the feasibility because I have better things to do. Potentially Going plastic on 3/16 makes me not recommend 1/8
Dude, no need to be defensive about it. Nobody is criticizing you or anything, just curious. I don't think anyone builds for failure but failures happen and are an interesting party of the hobby. Failures are pretty cool, especially uncommon ones. I totally agree that larger shafts make joints/connections a lot easier and stronger. That's reason enough to use them in my book.
Got some of the garage dealt with. Definitely need a tool box to get tools sorted out. But at least my bench is up and I can start working on stuff. Waiting for parts to show up so I can start working. The mess on top of the bench is all my electrical stuff. I ordered more batteries off Amazon, I have to just solder on the connector. One will be getting Dean's and being put over to my car stuff, but the other 4 will be XT60s for boats. Eventually I'll be making something up to hang my charger on the wall to charge batts off of the bench. Plan is to start getting some B6 chargers and slowly build up to having enough to charge half my batteries at a time, and regulate my currect charger to cars, if it's still around by then. I'd make up some kind of Bus system for the DC power run, so I can add on and just plug in the next charger. Still have to go get the power supply from my dad and make sure it works. Might also just get one though The tiny electric radiator kept it pretty warm in there yesterday. Took a while for it to heat up, I let it run overnight pretty much. Was also a warmer day out yesterday too. But I'm fairly certain that the garage is insulated, there's spots in the concrete where there was flooring glued down, and looking at old pictures there were French doors in place of the garage door now (garage door was also new and installed in 2019) my guess is it was a 4 seasons room or something at one point. The history of this house is quite odd and hard to put together. I know at one point it was apartments, that was at least 7 years ago, back when I was delivering Pizzas I remember delivering here a lot. But at least it's been pretty much completely remodeled with a lot of new stuff in here, so it should be trouble free for hopefully a long time *knocks on wood* letting me spend more on boats.
Looks like a cool boat room! (Add a DVD and tv to watch while you work and you'll never come out... Ask my wife, lol! BrianK
Out of curiosity, you are using stainless steel shafts right? That is an interesting data point and something to really consider in my next build if so. I was planning on a very potent brushless drive train in a Tennessee.
Pretty sure @Kevin P. is running stainless shafts. I would like to drop a small endorsement for metric shafts. The gears we use are all metric bore, the props we buy are metric bore (if you get the nice cast ones). Skip the middle man and go metric. Either a 4mm shaft with a bushing for the common 5mm bore gears, a 5mm shaft (m5 props are huge, just a warning), or a 5mm shaft that has be turned down to 4mm for the prop. 4mm is still beefier than 1/8", and 5mm is even beefier than 3/16.
My bad, hard to tell if snarky or inquisitive. It would be interesting to test out. I might make a test rig with a traxxas mount, constrained shaft, on a board where the shaft could be held by vice grips. Probably would not prioritize over builds for this year. yes on the stainless. I build my tenn class with brushless, wasn’t impressed. If I battle it again I’d probably go to 550’s with props flipped
So I know it's more work to get the ship on the water, but I'm really leaning towards replacing the shaft, rudder, and prop. Right now Baden has a 1.5" prop. To put in a motor mount and use a gearbox with the current setup, I'd have to offset the motor and run the gearbox sideways. It could be done, and just balance it out, but I'm still using a dogbone, 1/8" shaft and a 1.5" prop. Since I haven't installed anything yet to get the motor in, I think now would be the time to change the ship up. I'd go 5mm shaft with a traxxas villian gearbox. For a prop I'd go at least a 1.75" prop. A question I have is on the rudders though. With a 1.75" prop I'd use 1.75" rudders of course. But going with a 2" prop and 2" rudder, what does the extra height, shorter length of the rudder change? I was actually thinking 2 inch rudder with a 48mm (1.89") prop. I'd imagine that would give the prop very good coverage. But would a 1.75" rudder turn better than a 2" rudder? I'd assume that the shorter rudder would be longer, so what does that do for the ship?
For exact rudder size it’s something that is best done looking directly at the boat. I cut out index cards of various dimensions, hold them up the the boat, and pick whichever one looks like it’ll give the best coverage. I typically increment the dimensions by 1/16 (holding area constant) to get a number of rudders to check. Baden has the most optimal rudder/prop setup so turning will be great regardless. The exact dimensions will be less critical than on a 2 drive prop, one rudder boat
Had I thought about it before, I would have hung my 32" spare tv out there. I hung it in my "lounge" as I'm calling it. I plan to at least get a laptop out there, if not a full tower. Probably a laptop though
I used an 1/8” shaft in Warspite starting in 2003 with 1.75” Dumas 3 blade props. Same shafts until 09. Then new 1/8” shafts with Kort props. That ship has seen a lot of battles. No failures. I have several cruises with 1.25” props and 1/8” shafts. No failures. The Bikes shafts are thinning a lot. It’s had a lot of battles since 1999.
