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I am new to fe boats. My 8yo son decided he wanted to get into rc boats. I am a carpenter by trade. We decided to scratch build a mystic that's 36 inches long. The question is what size motor and esc should I run in it. We will be running 3s batteries to begin with since we already have those from our electric truggies. Thank you
You can run two 3S packs in series to get 6S, which will give you enough voltage for some speed, or possibly RPM, to get a less than optimal hull design on plane. Not talking trash about your building skills, I just have no idea where you're starting point is. I would recommend a 40mm motor, with a length in the 74-82mm range, for which there are several manufacturers to choose from. Motor kV (RPM) would be in the 1600kV range for a sport setup. You could probably squeak by with a 120A ESC, but I'd recommend a 180-200A to give you some headroom.
Ok thank you. Here's another question. Remember I'm new to boats. Why such a low kv motors. I'm use to high kv motor in our truggies
Here's the boat
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I'm guessing I misunderstood you, and you did not actually build this hull. What's the make/model?
As for kV, no gearing in boats. 1600kV on 6S would put you around 35,000 RPM, reasonable for sport running. You can run upwards of 50,000 RPM for straight line (SAW) passes.
You didn't misunderstand me. I have been raised around but my whole life built several boats that I fished out of and built other model boats from scratch the are just to be pretty. So that being said I'm not going to ague with you about my ability to build something out of wood and fiberglass. I have been doing it all my life. Maybe you should assume what a new members ability is without knowing the person or having seen there work.
I guess next you'll tell me I'm not building this one at the same time as a just to be pretty boat in my house. Without knowing me. You just ruined this group for me on my first question
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Your craftsmanship is second to none, my friend. fweasel probably saw your pictured boat and thought the same thing I did; that you bought that hull. You're a very skilled builder and I'm sure that'll be the consensus for anyone that sees this thread.
I hope you'll stick around and share your future builds with us.
Thank you.Quote:
Originally Posted by jingalls007
I simply reacted to the photo of your hull, and thought it was a production piece. I suppose that could be considered a compliment. I'm sorry you saw it otherwise and took offense. None intended. Good luck on your project with your son.
Kv's are similar to gearing and lower Kv's allow a larger diameter and pitch propeller. Motor size and amps potential are directly proportional. More motor, more amps, bigger and more cost to an ESC. Certain hulls have more water drag and cannot tolerate higher KV's, a rigger vs a mono or cat have different hydraulic drag and prop blade area needed to push the hull efficiently.
As was stated 3S times 2 in series is an easy 6S setup. Going to 6S and a relatively mid size motor, (36X74, 40X74) will keep amps under 150. That allows ESC's at reasonable and economical cost. Plus decent performance. What is your budget and what are your performance expectations?
Mic
Thank you for the explanation. Really don't have a budget when it comes to me and my son having fun. But with that said I would like to stay around 300-350 for motor and esc if possible. I would like to be able to run fast for when I'm running it. But on the other hand be able to slow it down for when my son is running it. If that's even possible.Quote:
Originally Posted by HTVboats
completely possible, run for you on 6s using your 3s packs in series, run for the kid on 3s.... LOL best of both worlds with what you already have, very nice work BTW, i am working on a Dumas Kit criscraft 19ft racing runabout off and on, i wish my craftsmanship was up to your scratch build skills....
That's great. And thank you. I have been working with wood and my hands since I was 8 or 9. Have always loved working with wood and see just what all I can make it do and learning its limitations.
same here, started woodworking about 8, but kinda took a hiatus since i moved from chicago to upstate NY, ad i dont have the funds to buy all the tools that i had access to when i lived with my parents (dad was a woodworker and has a full shop setup in the basement that i learned on) for senior year woodshop i built an acoustic guitar.... after that i used an electric to teach myself how to veneer.... walnut crotch grain, bookmatched, with abalone purfling and cream binding
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Those are sweet. No I don't know that I could do that.
its not much different than a boat, just bigger pieces for the acoustic, and for the veneer, purfling and binding, the hardest part was getting everything laid out right with the router to get a double step for the purfling to sit on behind the binding...
I bet
So piggy backing on this thread, what i want to understand better is what does the difference in motor size(the can..36/40/56) do for performance? I get the kv thing with higher vs lower kv, but i am still not sure on the can size and how that effects power? speed? amp draw(something else i don't quite fully understand either). Oh and motor length too.
Thanks!!!!
For a given motor quality, the bigger the motor mass the more torque the motor will have, and thus the bigger the prop it will be capable of swinging. If you choose to swing that bigger prop the motor will draw more amps.
For a given motor quality, the bigger the motor mass the Lower the RM (internal resistance) will be for a given KV, which means fatter wires and the motor will be capable of handling more power and will be more efficient under higher loads.
For a given motor quality, the bigger the motor mass the higher the IO (unloaded current draw) will be for a given KV, so even if you don't choose to swing the bigger prop the amp draw will be a little higher with the bigger motor (although not nearly as much higher as if you did swing the bigger prop), so bigger motor are less efficient under light loads.
I talk about mass rather than size as there are so many length and diameter options, and for practical purposes it makes little difference whether you get the motor's bigger mass from a longer can or a fatter can, For a given motor quality a 180g 28mm diameter long can will produce similar power and torque figures as a 180g 36mm short can, as will a 300g 36mm long can when compared to a 300g 40mm short can, and a 650g 40mm long can will when compared to a 650g 56mm short can. In most cases packaging constraints and commercial availability will dictate length to width ratio rather than any theoretical benefits to bigger diameter or longer cans.
I will explain KV as it is often misinterpreted, KV (velocity constant) is the RPM (usually quoted unloaded) that the motor will spin for each volt applied to it, for instance a 1000KV motor will spin at 10,000RPM at 10V and 20,000RPM at 20V.
As the KV increases the KT (torque constant) decreases proportionally, a lot of people misconstrue this as that low KV motors have more torque than high KV motors, but that is not quite the case. If you take 2 motors of similar quality and mass, one with high KV and one with Low KV, the one with the low KV will have a higher KT, but KT is not torque, it is torque per amp; While for a given current level the low KV motor will have more torque, the high KV motor will have fewer turns of thicker wire in order to achieve that higher KV, which decreases it's RM and increases its current handling capability, if you increase the current of the high KV motor to its limits its torque increases to the same as that of the low KV motor.
Love you explanations Paul, especially "For a given motor Quality" this is often not considered when comparing the different brands of the same can size.
In your kv explanation above, there's one to many zeros in 10,000RPM, or one to few zeros in 1 KV.
Thanks Don, edited with the "10V" that I meant.
"For a given motor quality" is another reason why I prefer to use motor mass rather than motor size, while a motor with a bigger can volume (whether through length or diameter) is generally capable of more power not all motors are stuffed to the hilt with wire, or even rotor sometimes, so a heavier motor is a better indication of power as it indicates how much copper is stuffed within the can.
Agreed, weight of the motor tells you more about the motors power potential, than do the numbers, that the manufacture gives it. Although I have see a few where the stator was huge and heavy, but had small holes for the wire to go through. So there are different kinds of "Quality" and I,m not saying that weight is the best indicator of high quality, but rather that a heavier motor might stand a better chance of having the quality that you want.
Second most important (most important to me) is Rotor Displacement (rotor diameter x diameter, divided by .7854, x magnet length). In my modified limited motors, displacement seem to matter more than ANYTHING! And Bigger, is always better! Displacement is even more powerful than copper content. But I am talking about making POWER, and nothing else.
Make sure your Truggy batteries are up to the task of high current from a boat. Please let us know what batteries you are using and let us know their specifications are so you don't have a bad first experience if they are too low of a C rating, etc...