17" mono motor, speed control and drive line

[Propwash]

Just got a 17" mono hull and looking for a motor and wire drive setup for it. Used to fast nitro boats but this the smallest boat I have ever had. Many yrs in rc cars trucks boats. Just bought to make it good and fast but not ballistic play boat. Looking for the right size brushless outrunner motor and mount for it. Water cooled speed control 40 amp. Also thinking .062 wire drive. Do I go 1/8 propshafy or 3/16. Should hsve more selection in 3/16 but good with either size... thoughts?
Hull is a gelcoat glass layup off ebay and actually looks pretty good. Very very slight hook in the bottom which will be fixed.
Thsnks in advance
Mark

[Propwash]

Thinking a barbwire 2 motor to go in it but not sure if yhere is something better since I have not ever seen specs on the motor on the interweb.

[Dr. Jet]

0.062" wire dive is probably overkill in something that size. Furthermore, any appreciable bends in the wire will create radial loads in the strut which equal friction. I'd go with an Octura 0.098" flex drive and a 1/8" prop shaft. Steve has everything you need right here.

It's real easy to overpower a little boat like that, so think carefully about your options. A 26~29mm motor would be the most I'd be comfortable installing in something that small. 3500~4500Kv on 2S, a bit less if you plan to run 3S. Props in the 27mm~32mm range would probably be a good start.

Start a build thread and I'm sure Paul and some others with more real-world experience will chime in with valuable advice.

[eehess81]

I use a 1/8 flex cable, 3000 kv 3840 prop drive outrunner with 3s, 60amp seaking esc, 32mm prop, on my 17" mono. Goes about 40 on glass, 30ish in chop. Fun boat

[Propwash]

Thanks for the responces. I am really lost in the brushless motor sizes and where to get them. I do understand the kv rating but the rest is a bit crazy. I am guessing outrunners make more torque.
This boat needs to be fast enough for me to have some fun with but my wife can still kind of learn a little with. Once I get this one done may build one just for her. I know not always a great idea...lol.

[eehess81]

This is the motor I am using. I got the motor size wrong..it's 2836(28mm wide 36mm long)
https://hobbyking.com/en_us/propdriv...ner-motor.html
You can run it on a 2s instead of 3s to slow it down.

[eehess81]

Yes..outrunners produce more torque than inrunners.

[NativePaul]

What boat is it and what do you want from it in terms of speed and or runtime?

I think .062" is a little big, racing boats this size we generally use 1.2mm if it needs any significant bend in it like a cat, a hydro, or a mono with a rearward mounted motor; but best for a mono is 1.5mm with the motor forward of the CoG, the thicker shaft is needed to eliminate shaft whip when there is little to no flex in the wire. .062 is 1.6mm which sounds like a marginal difference but it adds noticably to the wire's stiffness, and if you want to use it you will have to get the motor as low and as forward as possible to increase the radius of the bend. Flexshafts are not as efficient as a well set up wire, but an .098 flex will also work fine, and they are more tolerant of imperfect setups.

Don't pick a 3/16" shaft as 3/16" props will be too big for the boat. For maximum prop choice in the size range you will be using you want 1/8" if you are going to be balancing and sharpening your own BeCu props, or 4mm if you are going to be buying CNC alloy props.

If as it sounds like you don't have any rules to conform to, go for 3s, it is a bit easier on the electrics than 2s, and almost every model shop has a variety of 3s 2200mAh packs for parkflier planes. A 3s setup is also good in that you can buy a 2s pack and that backs off the speed a good chunk without having to do anything mechanical, which is great for letting learners have a go and build confidence/competence with much reduced risk of crashing and much reduced risk of damage if crashed.

Apart from on startup where an outrunners generally much higher pole count takes less angular movement before the ESC can work out which way round it is turning and starts making any meaningful torque, there is no practical difference in torque between an inrunner and an outrunner. I have raced with both and by far the biggest difference is in cooling, an inrunner can be water cooled much more effectively, and an outrunner can be air cooled much more effectively. As water cooling in the closed confines of a boat hull is more effective than air cooling, inrunners are usually the best choice for boats (maybe interestingly, the exception to that can be Mini and Micro boats, where the mass of the water cooling system can be greater that the extra mass added by an oversized ESC and Outrunner that don't need water cooling, thus resulting in a net weight loss). Motor KV, motor mass, and motor quality have a much bigger real world effect on torque than its type, pole count or wind. A motor between 60-90g is good for a boat that size, and due to the cooling differences I would go low to middle of the range for an inrunner or mid to high end of the range for an outrunner. 2800-3500 is good, if you want several minutes runtime go 2800-3000, for a minute or 2 of sprinting go 3000-3200, and if you only want a few passes go 3500. Props will be in the 27-32mm range for oval or general running but can go up to 35mm for SAWs.

[Alfa Spirit]

Regarding the size of the hull you can have a 37000 - 38000 RPM unload setup.

[eehess81]

I had issues using an inrunner on my setup..the esc lvc got set off all the time on 32mm prop..if you use an inrunner probably need a much smaller prop. The outrunner turns the 32 no problem without causing enough voltage drop to set off lvc.

[NativePaul]

I had issues using an inrunner on my setup..the esc lvc got set off all the time on 32mm prop..if you use an inrunner probably need a much smaller prop. The outrunner turns the 32 no problem without causing enough voltage drop to set off lvc.

Was the inrunner of the same KV, mass and quality as the outrunner?
If you install a higher KV inrunner, a heavier inrunner, or swap out a crappy RTR outrunner for a decent aftermarket inrunner, you can expect to see higher currents being pulled, but that is not due to the fact that it is an inrunner, but due to the increased KV, mass or quality; and if you had of replaced it with a similar outrunner you would have got similar results.

When I swap between an inrunner and an outrunner of the similar KV, mass, and quality, I get similar amp draws and performance on the same prop. Theoretically I should be getting slightly worse acceleration and higher amp draws on acceleration with the outrunner due to its larger moment of inertia and moving mass taking more energy to spool up, but in practice the difference is not enough to tell. The only noticeable differences are a higher motor temp on the outrunner due to the inferior air cooling, and in monos the increased torque roll under hard acceleration due to the aforementioned larger moment of inertia and moving mass is noticeable.

[eehess81]

The inrunner was a 2836 3000kv just like the outrunner and similar weight..was twice as expensive so I assume it was atleast of similar quality or better. Lot of variables that are tough to quantify though so I can't say 100% that outrunners have higher torque due to limited experimentation. The inrunner also got noticably hotter, probably due to being overloaded with the 32mm prop.

[Alfa Spirit]

Very good quality outrunner brushless motors : https://fr.aliexpress.com/item/33004...79700644%22%7D

[Propwash]

Thanks for the info from everyone. Busy week. The hole motor size ghing is still escaping me after days of slapping myself in the forehead. May need to go inrunner for ghe extra cooling. But... 2860 or 3650 or something in between. I just still have no idea what to pick but wa nt it around the 3000kv mark. I thought a 40 amp speed control would be enough but maybe 60.
This wont be a race boat. Just a fun fast play boat. This will be a forward mounted motor set up. I am pretty fussy about having a really free driveline, that and weight is the reason I am looking at wire drive. I also dont like end loading the prop load into the motor bearings. Prefer single or double ended square drives but that doesnt seem possible in this size range. It will be run a number of times in arow so cooling may be important for the motor.
Again thanks for the responces.
Will post a couple hull pics this weekend

[eehess81]

Those motors sound kinda big for a 17" boat. I have a 2860 3000kv in my 24"mono. Might wanna go a bit smaller in length.