Help in understanding FE?

[jmdmbsc]

Back in the hobby after 20 years. I need help in understanding electrics. Hoping some folks can lend some thoughts. I'm trying to understand the relationship of batteries to ESC to motor. My batteries are 5000Mah, 50C, 3 cell. I run 2 in series for 6s. Specifically I have a new TFL Pursuit carbon fiber with Seaking 180A, need to purchase a motor. The prop is 42mm 1.6 pitch. Is there a math formula that would help in understanding the relationship or can someone put it in layman's terms? I'm missing something, maybe it comes down to amp draw?

I'm trying to maximize run time and top end speed. I have a TRX M41 with Seaking 180 & Leopard 4082 1600Kv, runs 48-50mph and lets call it around 10 minutes, I also have a Proboat UL 19 stock with the 120A ESC & 2000Kv motor running 62mph for around the same run time. I know props are part of the equation, start out smaller, based on heat go up from there.

[Jesse J]

A pretty simple rule of thumb for sport running is to keep unloaded rpms between 25-35,000.
So for example, so for 25 volts , a safe range is 1200-1500 kv motor. That formula should work with your prop and hull size. The main advantage of 6s in lower amp draw, so don’t go wild with motor kv.

[properchopper]

This may help visualizing the safe range Jesse mentions. Stay in the green

kv_voltage[1].pdf

[jmdmbsc]

This may help visualizing the safe range Jesse mentions. Stay in the green

[ATTACH]167039[/ATTACH]

Thanks! I guess if you run higher RPM's like 40,000-45,000 your generating more heat? so where do Amps come into play with an ESC?

[larryrose11]

Thanks! I guess if you run higher RPM's like 40,000-45,000 your generating more heat? so where do Amps come into play with an ESC?

Heat comes primary from amp flow.
Power dissipation (heat) = Resistance*(Current)^2.
Power = Volts*Amps,
So, higher voltage systems have less amps, and in general run cooler.
The problem come in when you select a motor that is too high in KV for a given voltage, or too much prop.

System load is what draws current.
Typically, this is putting too aggressive of a prop on a boat. Current generation of controllers have no way to limit how much current is pulled. The motors just try their best to spin, and the load on the prop is what will determine how much current is pulled.

Higher KV motors (for a given voltage) are more prone to creating current spikes, which can fry a controller that is not up to the job.
Putting in 2 motors means that the load on each is lower, which is why you can see some setups around here the seem pretty hot compared with a single motor setup.
An example is a twin catamaran running a 1800-2000 KV motors on 6S. No one here would ever suggest a single setup like that. it may work, but it wont be robust.

[jmdmbsc]

Heat comes primary from amp flow.
Power dissipation (heat) = Resistance*(Current)^2.
Power = Volts*Amps,
So, higher voltage systems have less amps, and in general run cooler.
The problem come in when you select a motor that is too high in KV for a given voltage, or too much prop.

System load is what draws current.
Typically, this is putting too aggressive of a prop on a boat. Current generation of controllers have no way to limit how much current is pulled. The motors just try their best to spin, and the load on the prop is what will determine how much current is pulled.

Higher KV motors (for a given voltage) are more prone to creating current spikes, which can fry a controller that is not up to the job.
Putting in 2 motors means that the load on each is lower, which is why you can see some setups around here the seem pretty hot compared with a single motor setup.
An example is a twin catamaran running a 1800-2000 KV motors on 6S. No one here would ever suggest a single setup like that. it may work, but it wont be robust.

Thank you !!