Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: ferny on October 06, 2019, 12:31:08 PM

Title: Water cooling
Post by: ferny on October 06, 2019, 12:31:08 PM
I will be using 2x 1250kv out runners and hobbyking 50amp Esc's in a slipway 1/16 tamar running on 3s lipo, will the Esc require water cooling?
Title: Re: Water cooling
Post by: TomHugill on October 06, 2019, 02:04:19 PM
I would water cool the esc at least
Title: Re: Water cooling
Post by: ukmike on October 06, 2019, 03:38:20 PM
I totally agree with Tom.


Remember that Chinese Amps rating tend to be exaggerated somewhat, especially HK, be safe and water cool them.


Mike.
Title: Re: Water cooling
Post by: ferny on October 06, 2019, 04:09:51 PM
I totally agree with Tom.


Remember that Chinese Amps rating tend to be exaggerated somewhat, especially HK, be safe and water cool them.


Mike.


Very true have seen some wild claims on Ebay for cheap esc's less than a tenner and 350 amps 🤣
Title: Re: Water cooling
Post by: kinmel on October 06, 2019, 04:51:34 PM
My 1:12 Tamar and latest Shannon use the same setup as you propose and they have never needed water cooling, the ESCs don't even get warm.
These boats don't achieve 25 amps, never mind 50.
Title: Re: Water cooling
Post by: Taranis on October 06, 2019, 05:14:36 PM
Likewise  :-))
Those out runners are meant for turning large aircraft propellers and the 50 amp rating will not be reached anywhere near turning boat propellers
Iíve not succeeded in blowing 25 amp fuses
Title: Re: Water cooling
Post by: TomHugill on October 06, 2019, 07:49:12 PM
Likewise  :-))
Those out runners are meant for turning large aircraft propellers and the 50 amp rating will not be reached anywhere near turning boat propellers
Iíve not succeeded in blowing 25 amp fuses


Till you stall the motors!
Title: Re: Water cooling
Post by: JimG on October 06, 2019, 09:08:56 PM

Till you stall the motors!
Not even then, brushless behave very differently in this case, the current does not rise when stalled. When a brushed motor is stalled it becomes a near short through one winding so the current will soar. In a brushless this cannot happen as the esc is always pulsing the power to the windings. I just tried stalling an outrunner used in a plane with a wattmeter in line. Full throttle gives a current of around 25A but when I held the propeller to stall the motor full throttle gave only 6A which dropped to 0 after a few seconds as the feedback from the motor to the esc was lost causing it to become confused and stopping power.
Jim
Title: Re: Water cooling
Post by: kinmel on October 06, 2019, 09:17:56 PM
If the system develops a fault you want the fuse to blow quickly, instead of trying to cool overheated electronics !  The fault will not cure itself, so we kill the power supply.

That is why I use 50amp ESCs with 25amp fuses, rather than 30amp ESCs that are more than capable of handling the motors in normal conditions.

On twin props we also have completely independent port and starboard radio and electrics, so that we can still get home if a fuse blows.
Modern electronics are so cheap that we build resilience into the design,  rather than trying to manage problems such as overheating
Title: Re: Water cooling
Post by: ferny on October 06, 2019, 09:34:51 PM
Thanks for all the good info! When you separate electronics and radio do you mean 2 recievers?
Title: Re: Water cooling
Post by: kinmel on October 06, 2019, 10:22:26 PM
Yes, in fact both power lines are fully independent. Battery, switch, fuse, receiver, Esc and motor.
Title: Re: Water cooling
Post by: ferny on October 07, 2019, 07:26:42 PM
Re the above do you also run 2 servos, 1 for each rudder as I cant get my brain around 1 servo operating off 2 rx?!
Title: Re: Water cooling
Post by: kinmel on October 07, 2019, 08:34:06 PM
Re the above do you also run 2 servos, 1 for each rudder as I cant get my brain around 1 servo operating off 2 rx?!
Each side is utterly independent, each rudder has it's own servo operating from the appropriate Rx.

On my Shannon lifeboat the additional cost of doing it this way is less than £40 on top of a total build cost of about £1400, it's a no brainer.

Title: Re: Water cooling
Post by: Taranis on October 07, 2019, 08:44:22 PM
In our case not actually rudders but steerable water jets and of course you need a transmitter that will operate two receivers https://www.modelboatmayhem.co.uk/forum/index.php/topic,63576.msg675407.html#msg675407 (https://www.modelboatmayhem.co.uk/forum/index.php/topic,63576.msg675407.html#msg675407)


I made sure this could never be repeated  {-)
https://youtu.be/YVHRWCUKObI
Title: Re: Water cooling
Post by: kinmel on October 07, 2019, 09:15:23 PM
Any transmitter can control more than one receiver, but on standard radio sets the channels on each Rx simply mimics the other.
The redundancy design is still valid though.
Title: Re: Water cooling
Post by: ferny on October 07, 2019, 09:43:55 PM
I'm sold on the redundancy issue!