Prop

[peter_g]

I am in the process of building a prop for an up-and-coming film. I am modifying something called a megger ? a device for measuring the electric resistance of insulation in electric motors ? for my own ends. I have a vintage megger that I believe first came into service in about the late 50?s or early 60?s. Pictured below is something similar to what I have:




My only problem is that after so many years of service, my megger is damaged beyond repair. I need the needle to fluctuate on demand. I tried to use some kind of mechanical way of getting the needle to move (i.e., attaching a piece of copper wire to the internal mechanisms such that when I pulled on the wire the needle would move), but this makes the needle move jerkily. I?ve come to the realisation that the only thing to do is to completely gut the megger and replace the existing mechanisms with something that works. I was thinking of something along the lines of those hobbyist kits that have tiny electric motors powered by AA batteries. Does anyone have any experience with this kind of thing?

[TJ_the_director]

find an old volt meter for cars and rig it up under the glass faceplate. hmm?

[Tasty Fish Lips]

How bout using magnets?

[eidde]

yep Ive made similar things.
our simplest bet is probably to get an electric motor, and a variable resister (potentiometer - dont know a 0 - 10 K resistor...?). that has a knob on it to adjust the resistance.
I assume the meter itself is broken?
Whatever, it'll be some sort of volt or amp meter.
If its broken get another one from a second hand (so it looks old and fits in with the rest oif the look) electric shop or car boot sale.
Connect the handle directly to the spindle of the electric motor, wire the variable resistor over the terminals of the motor.
Then wire the meter (like a voltmeter - you are measureing the voltage across the resistor produced from the motor) to the same terminals.
Now wind the handle, you should see the needle move. You may need to adjust the knob on the resistor to tune it.
Just experiment a little and you should get the desired result.
You can also wire the meter in series (like an ameter) with the resistor rather than in parrallel (like a voltmeter) -
Connect one motor terminal to the meter. The other terminal on the meter goes to the resistor, the other termnal on the resitor goes to the other terminal on the motor.)
Will give you much the same sort of results, but might be more sensitive.