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Inside the Arri IIc variable speed motor


GeorgeSelinsky

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ArriMotor.jpg

 

Here we're looking at the inside half of the speed regulator of the variable speed motor. Can anyone tell me what kind of electronic device this is? Is it a resistance device or something else? I gather the way it controls the speed is by increasing or decreasing the DC voltage supplied to the motor.

 

- G.

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Guest Sean McVeigh

It's a high-current power resistor, hence it's size. I believe it ranges from something like 2 ohms through to 5 or 10. The wiper arm is that cute spring-loaded fellow in the middle that is connected to the rotating bottom cap.

You could essentially call it a "heater" if you'd prefer :)

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That's what it looks like to me. The tip of the contact would be what slides across the other points varying the resistance. You might be able to check this with an ohmmeter by measuring from that point to either side of the circle. It would vary as you turned it. It would also be a higher resistance on one side compared to the other unless you had it dead center.

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