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[TheLongBuild]

Does anyone know what the purpose of the white block is on this type of speed controller ?.

[chas]

Blimey, that takes me back a long time. It's a resistor, probably just a few ohms and is the bit that drops the voltage to the motor and slows it down. That type of controller had to be matched to the battery and motor to work properly, yours is almost certainly made for a 540 and a 7.2  battery.  Similar ones used to be advertised on the back of model boats magazine decades ago. I  had one back in the day and hated it.

[DocMartin]

What do the markings on the top of the component read??


It appears to be a dual value ceramic cement resistor.

[T888]

It’s a resistor, be careful they do get very very hot





Tamiya Part #7305015, Mechanical Speed Control Resistor

[TheLongBuild]

Thanks, not sure of the writing as that is an old picture of a model I no longer have, however at the lakeside today we were looking at one in a medium sized tank and wondered what it did, the one in the tank is in the heat sink as per the last picture posted by T888.


The speed controller seemed to do the job in the model I had so did not bother to change it as it worked..


Thanks.

[ColinB]

I have one in my Nordkap. Hoping to get rid of it. I was sold it to reduce the power to the motor

[unbuiltnautilus]

For the lowest speed the voltage is fed through the whole resistor, for mid speed the voltage runs through half of the resistor, and for full speed the voltage bypasses the resistor completely. When used correctly they worked fine, when the servo geometry was off they were a right royal pain!

[Martin (Admin)]

Yes.... very old skool !

Nearly everyone use Electronic Speed Controllers  ( ESC ) these days:
https://www.modelsport.co.uk/electric/electronic-speed-controls

.... waterproof ones are best for boats

[Colin Bishop]

If it gets hot then your precious battery power is being diverted to global warming instead of driving the boat and your run time dramatically reduced!

Colin