Oh no, you're right, if it doesn't have space you can't put gears on it.
I have never activated rotating radar antennas, because the ships I built are older.
I'm thinking about how you could resolve this but I don't have your view.
For example, couldn't you hide the engine in the hull and reach up to the radar antenna with a long, thin rotating axis?
In the plastic tube instead of the motor you could pass the axle.
In this way you could opt for an engine with lower rpm and equipped with reduction gears.
I'm guessing because I don't have any images to look at.
Since I have no experience in this field, I make general reasoning, think of them as thinking out loud.
I hope a modeler who has already installed rotating radar antennas can help you.
On a brushed motor everything is easier, because you can reduce the rpm by acting on the voltage. In this case a resistance (adequate in ohms and watts) can create a voltage drop useful for your purpose.
However, within certain limits, because under a certain voltage the engine no longer turns without having managed to reach the desired number of revolutions.
However, brushless motors (I know their working principle but I never use them) are different. If I'm not mistaken the number of revolutions is determined by the electronic controller. Without the electronic control it wouldn't even turn, unlike the brushed motor which just needs to be connected to a DC voltage.
Do you have a photo of this engine? Does it have two or three cables?
I've never tried with brushless motors, because I don't have them.
Start from a very high value of 48,000 rpm, which seems like a lot to me.
There are brushed motors on the market, even smaller and cheaper ones with lower rpm than yours.
Are you tied to this engine for a particular reason or could you change your choice?
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