Motor for MHZ Chaparral

[Skeet]

I have done searches and a lot of reading here on motor choice for large monos. I am still a little confused on motor choice. I plan to run on 12s and would like your opinions on motor choice. I prefer to use TP motor and have been looking at the 600kv and 720kv. Four or 5 minute runs are fine with me. Would also like to run in the 60s. Thanks

[jkflow]

Almost copied this from another answer I just gave but edited for your numbers.
Typical recommendation I see is that you want ~ 25-35000 rpm on the prop, and you should dial in with prop size.

In simple math, you can multiply the kV by the voltage (12S = 12*4V) 48*600 = 28800 rpm. You actually get roughly 90-95% as it's a theoretical value.
Roughly 26000 rpm for a 600kV. I would go a little higher (720-800kV).
Can't advise on prop size. Above is based on simple math, others might have better ideas on your specific need.

[Alfa Spirit]

This is not a small mono, lenght is 1310mm, with one motor TPPower 5670 - 5Y - 768kV with 12S Battery.

[donhuff]

"You actually get roughly 90-95% as it's a theoretical value."

Can I ask what you mean by that statement? If we need to start a new thread, please do so.

[RaceMechaniX]

On a big mono like this you want to run a lower kv and use larger props that align with gas boats. So 60-75mm. I would shoot for 20-22kRPM loaded with a KV range between 580-650Kv. I use a more conservative KV calculation using 3.7V per cell under load and multiply by .85 to take into account average motor efficiency.

The TP5670 would be a good choice. A 10D is on the higher KV side, a 6Y would be ideal but it's a special order based on what I see in stock today.

[jkflow]

kV rating by definition is applying a mechanical force until the motor (acting as a generator) reaches a 1V output.

We use kV in the reverse and need to take all the losses into account. Typically, that is within 5% of the listed rating.
In addition, the motor itself is manufactured with ~ 5% tolerance on the kV rating, unless it's a super precision custom build version.
Hence, the 5-10% approximation on kV rating.

[Alfa Spirit]

Almost copied this from another answer I just gave but edited for your numbers.
Typical recommendation I see is that you want ~ 25-35000 rpm on the prop, and you should dial in with prop size.

In simple math, you can multiply the kV by the voltage (12S = 12*4V) 48*600 = 28800 rpm. You actually get roughly 90-95% as it's a theoretical value.
Roughly 26000 rpm for a 600kV. I would go a little higher (720-800kV).
Can't advise on prop size. Above is based on simple math, others might have better ideas on your specific need.

Why do you count 4 Volts?
4Volts is the voltage after charging process. When the battery is loaded and deliver current the voltage goes down to the nominal value = 3,7 Volts.

[jkflow]

Pick whatever voltage value you want. The 4V was just an example to keep it simple.
Usually people subtract an entire cell to account for drops.