Motor kv

[Old School]

With reference to the OSE store recommendation for sport running and racing RPM (25,000 - 30,000), I have noted recently in several posts that members recommend a kv value considerably higher than required to fall within the range specified on the OSE store site.

A higher kv may be suited to SAW passes and perhaps a lower kv for a larger propellor. 2200kv is a "sweet spot" for 4s, however, what is an ideal value when running 6s, please? 1330kv will give approximately 30,000 RPM on 6s and yet in two recent posts I have seen recommendations for 1500 plus kv. My son runs a TP Power 2860 with 1770kv on 6s but limits his running to a few quick passes with minimal temp rise. I would be looking more towards fast continuous and not SAW passes.

[properchopper]

This has helped some of us

kv_voltage[1].pdf

[Old School]

Many thanks

[JohnZ]

Thanks for the chart. I needed this to figure out what the heck I needed. Was looking to use a 3S pack in a 21" mono and had no clear idea what motor to use.

[Fluid]

Realize that the final rpm values listed are at zero load. Multiply by .85 to obtain closer to a real-world prop rpm.



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[CraigP]

Realize that the final rpm values listed are at zero load. Multiply by .85 to obtain closer to a real-world prop rpm.



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Question: I was wondering if the OSE calculator used 3.7V/cell as a good, all around value for heavy loads? When I first saw that, I thought that was very conservative... But as I started to data log my boats, I began to see that it did represent a good average. I know the boat is a bit faster at the top of the charge, and I can hear the small drop in speed from the pitch change. But it seems this value has been very close to estimated run times based on current flow. Is that the thinking behind that voltage value?

[CraigP]

This has helped some of us

[ATTACH]156990[/ATTACH]

Wow, all of my boats have motors almost halfway in the green chart! I wonder if that is the sweet spot for KT too? I’ve got two 4s boats, one 6s and one 8s.. That character is handy... Thanks for sharing

[Speed3]

I think offshore electrics recommendation is good.

30000 rpm unloaded in my opinion is a good rpm to work with 1800kv for 4s.

In my opinion it is better to choice 1800kv for 4s than say a 2200 because it is much easier on the electronics.

And you can use a bigger prop and get the speed the 2200kv will give while at the same time having longer runtime. Or go even faster than the 2200 with the same runtime or more speed and more runtime.

[Fluid]

High Kv motors might give the average boater a bit more speed, particularly if the hull can’t handle a larger prop. That said, one of the fastest P Limited race monos I’ve seen runs a 1500 Kv motor. I set a Q Sport Hydro SAW record with a 99 mph pass running a 1500 Kv motor. Most folks would insist on at least a 2000 Kv motor for that use. With the props available today we don’t always need to spin them at insane rpm.


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[JohnZ]

Thta's obviously to be the case but with the hull I'm using, 21" BBY Oval Master, I don't have room nor would it be practical to use anything more than a 3S pack especially just for running up and down the river.
I realize there are certain methods to achieve such speeds but one also has to be practical about it as well and since I won't be racing with this boat, I don't need to resort to anything exotic.

[Speed3]

For your oval master a leopard 2860 2550 kV or 2730kv. A x632 or x435 and a 4500mah 3s with around 50c or higher would be a good combination for runtime and decent speed. Or the 3650 same kV, suggested prop and battery.

SMC have a 4500mah 3s 90c battery that is light and powerful.

[JohnZ]

I've run that same hull before on a Trinity Speed gems which is about the same size as the 3650 . Sold the boat so I bought a new one.
Going to go with the Leo 3650 2930 KV and 3S pack for now. I don't know SMC but I'm checking into Dinogy and a couple others.