I have an unusual motor which I am trying to identify - or at least gain some information about. I hope this is the right forum to use - there does not seem to be a Motors section.

The motor is a small 6cmx2cm can motor, with three contacts and a 2mm shaft. It came in a box marked 'Mitsumi M1G20', addressed to Marubeni Corp, and dated 1964. So we are talking about an old Japanese industrial motor. There is no data on a Mitsumi M1G20 on Google, but a Mitsumi M1G10 is a straightforward 5V geared motor.

The motor is 7-pole, with ball bearings. The brushes are fairly hefty - 2mm cubed - and connect to a seperate slip ring each. Each brush is connected to one of teh external contacts, and the third contact disappears into the motor going elsewhere. There is a 7 ohm resistance between each brush and the third (return?) contact, and when 1.2V is placed between either brush and the return contact the motor turns fairly briskly. I'd love to know what voltage might be appropriate for it... and why it has three contacts...

Above the brushes is the oddity - a disk mounted on the shaft holding some kind of centrifugal apparatus. It does not seem to be electronic - it looks more like a drum brake, with a chunk of copper pivoted so that it will fling out and contact the inside of the metal end cap.

I enclose pictures - and would be very grateful if anyone could hazard a guess at to what this might be....

 

I see that Marubeni Corp started out in 1858 !
I would say the mechanism on the end is possibly a RPM governor.

 

I see that Marubeni Corp started out in 1858 !
I would say the mechanism on the end is possibly a RPM governor.

I know that we're talking about the 1960s - but would they really control a motor speed by rubbing a chunk of copper on the end cap?

I was wondering if it was some kind of brake, to stop the motor spinning once it had powered down. I've found out that one set of contacts has teh motor running faster than the other set - so the motor appears to be a two-speed one - that would mean that only the fastest speed could be governed. All in all, it's an odd motor. Possibly for a belt-drive turntable?

 

I know that we're talking about the 1960s - but would they really control a motor speed by rubbing a chunk of copper on the end cap?

I was wondering if it was some kind of brake, to stop the motor spinning once it had powered down. I've found out that one set of contacts has teh motor running faster than the other set - so the motor appears to be a two-speed one - that would mean that only the fastest speed could be governed. All in all, it's an odd motor. Possibly for a belt-drive turntable?

A mechanical governor usually works by having a mass spin with the motor and held back by a spring or gravity. As the centripetal force exceeds the spring force (or gravity force) the weight moves away from the spinning shaft and mugs more strain on the motor to slow it a bit. The motor speeds up as the weight moves closer to the axle. Look up, flying governor as well.

 

I'm pretty sure this is a centrifugal switch; I think I see an electrical contact on it.

Centrifugal switch for what? I have no idea.

 

A mechanical governor usually works by having a mass spin with the motor and held back by a spring or gravity. As the centripetal force exceeds the spring force (or gravity force) the weight moves away from the spinning shaft and mugs more strain on the motor to slow it a bit. The motor speeds up as the weight moves closer to the axle. Look up, flying governor as well.

Yes. The copper mass you see there is mounted on a springy strip of beryllium copper. It will move outwards when rotated, although not much, because it will hit the side of the casing.

 

Could it be a motor for a record player? I remember taking an old portable record player apart many years ago that had a motor with a speed governor that used a weight and a pair of contacts.

 

Yes. The copper mass you see there is mounted on a springy strip of beryllium copper. It will move outwards when rotated, although not much, because it will hit the side of the casing.

Then it could be that the springy thing is not exactly a governor that adds an additional strain but, instead, a switch to disconnect the motor power as @strantor suggests. The switch simply controls over-speed situations.

 

I'm pretty sure this is a centrifugal switch; I think I see an electrical contact on it.
View attachment 278444
Centrifugal switch for what? I have no idea.

Yes. There is no wiring, so I was confused, but a multimeter gave me this ODD connection diagram. Wiring must be internal to the shaft. I hope I have it right. It looks like it would just short, so I suspect there is some extra resistance in there somewhere!

There are no split rings. There are two brushes with a (spark suppressing?) resistor between them. A third contact just disappears into the motor casing. If volts are applied between contact 1 and 2, or between 3 and 2, the motor rotates. One contact set gives a slower speed than the other.

If the centrifugal switch is jammed shut, both contact sets give the same (slower) speed.

I cannot understand how the motor works, or what its application might be, and I cannot find any mention of a Mitsumi M1G motor on the Web. It seems to have a lot of torque - perhaps it was tor a record or tape deck?