Help -- motor KV specs

[T-Man]

Can someone explain the KV ratings on motors and how that number relates to which ESC and battery setup I would select? I've read everything I can find and still don't really understand.

Thanks!

[domwilson]

http://forums.offshoreelectrics.com/...read.php?t=271

Hope this helps.

[T-Man]

Thanks.
I had already read that thread a couple times, and I still don't understand. I will need the "KV selection for dummies" version, I guess.

[T-Man]

OK, for more clarification...

I know that "KV" means the motors unloaded RPM output per volt of input, but how do I select the proper motor KV rating for a given battery setup and vice-versa? What do I need to look for to determine which motors are a good match for which battery and ESC combinations? How do I know what RPM output is appropriate for a given hull size? Where is the correct balance between RPM and torque and how does that relate to the KV number?

Sorry for the number of questions, but there are so many numbers, terms, and abbreviations being tossed around when folks talk about spec'ing out a FE setup that I'm totally confused. Reading all the info I get in searches doesn't help much in clearing up my confusion.

[m4a1usr]

Kv selection is more importantly defined by speed desired and voltage limitation. I.E. you cant stuff 8S in a 24" cat. Thats just an oversimplification but you get the point.

If you are unsure of motor applications it might be prudent to look at what others are choosing for similar size hulls and power. Its common to find folks putting way too much motor in sport builds. I'm guilty of it. But I tend to correct once I find I have gone beyond reasonable. Because under powered builds tend to smoke ones esc.


John

[vasy]

Here is a good one: http://forums.offshoreelectrics.com/...ead.php?t=4159

[eboat]

some one beat me to it

[T-Man]

Thanks, John!

To use a specific example I posed in another thread, I have an Aeromarine Popeyes .21 cat, which is 29" X 11". The motor/batt/prop chart on this forum suggests that a 1512/ 4s or 1515 / 6s and a prop in the neighborhood of 38 - 40mm dia might be a good choice for that size hull...

BUT, there are multiple KV rating options for each of those 2 motors, so which are the proper choices?

I'm thinking I might go with the 1512 / 4s setup for my boat. Is this a good combination for my hull? If so, what KV motor would you choose?

[m4a1usr]

BUT, there are multiple KV rating options for each of those 2 motors, so which are the proper choices?

I'm thinking I might go with the 1512 / 4s setup for my boat. Is this a good combination for my hull? If so, what KV motor would you choose?

The 1512 is not a bad choice. Actually has more power then a 540 XL size can. And 4S is a good voltage for that size hull because of space inside. But you might want to get the 1515 if you want ulitmate speed. It is addicting. Seems like once we hit 50 mph we need 60, then 70 and on and on. A 1515 goes well in bigger hulls too if you get burned out with hulls less then 30". Bigger hulls usually mean higher top ends. Not in every boat but with larger size comes better control. Your going to have to looks at your speed goal (or desire), physical size limitations for component layout, and realistic props for that size hull. Dialed in, your hull with the 1512 should run mid to upper 40's, maybe low 50's. But I'm pretty sure thats the wall. With the 1515 the 60's look very promising. But thats just my opinion.

A 1512 in 2D or 2.5D would be your better choices based on 4S. A 1515 1Y the alternate.

John

[T-Man]

If I can get 40 mph, I'm good with that. I already have a nitro boat that gets me in the 50's and it is all I can handle. I'm more concerned with run time. I would much rather have 7 - 10 min of run time and 40 mph than 3 min of run time and 55 mph.