8mm Forum: New Carbon Brushes for GS1200 Take up Motor

This is topic New Carbon Brushes for GS1200 Take up Motor in forum 8mm Forum at 8mm Forum.

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Posted by Thomas Knappstein (Member # 6134) on July 23, 2018, 10:38 AM:

Hello at all!

Does anyone here change the Brushes in the Take up and Rewinding Motors of an Elmo GS 1200? Where can I get them?

Posted by Phil Murat (Member # 5148) on July 23, 2018, 02:17 PM:

Hi,

Sure you ll find what you need there :

CARBON BRUSHES

Posted by Paul Adsett (Member # 25) on July 23, 2018, 06:36 PM:

Which one fits the GS1200 reel motors?

Posted by Phil Murat (Member # 5148) on July 24, 2018, 12:48 AM:

Hello Paul,

Depending on size of original brushes (recorded with a good caliper) , choose the more approaching one and adjust (with a file/Sandpaper) as necessary.
Generic ones are only supplied with copper mesh alone (springs and contacts have to be picked up on former brushes)
2 kind of copper mesh : straight fitted and angular fitted.

However, I assume the more important is :
- hardness of brushes (avoid hard ones to prevent from premature rotor contacts wear)
- Spring load (avoid strong spring load to prevent from premature brushes and/or rotor wear)

I've already done that with some electric motors and it worked....

Posted by Paul Browning (Member # 2715) on July 24, 2018, 06:54 AM:

If needed we would make these brushes out of graphite, drill the hole and super glue the wires in, make sure its conducts, and there you go. When cars had dynamo's the brushes would arc a lot or burn down, better to try and get a diameter on the inside and make sure its not too hard. We used old electrodes from the spark erosion section, its the same material.....

Posted by Winbert Hutahaean (Member # 58) on July 24, 2018, 10:05 AM:

I have zero knowledge on electronic stuffs... so what is the function of these brushes?

Will they wear after years? Do we really need to change it regularly?

Thanks

Posted by Steve Klare (Member # 12) on July 24, 2018, 10:37 AM:

A DC electric motor is a set of electromagnets on a shaft inside a permanent magnet held in place. When current flows in the coils of the rotor, a magnetic field is established that the permanent magnets attract (and/or repel). This turns the rotor until the magnetic fields align.

Here it could stop, so to keep going, the next set of coils at the right spot need to be energized and the first set turned off: this is good for another fraction of a turn.

This means somehow you need to keep applying power to the rotor and turning it on and off to the right coils at exactly the correct angle of rotation. (-kind of like all those cylinders in a car engine firing at the right time to keep it turning.)

So you have a set of copper contacts on the rotor wired to the coils and two stationary brushes sliding on them. The operating voltage is applied to the brushes Everything is set up at the correct angles to make it work correctly. This acts like a very sophisticated synchronized switching system, but it's just angles and wiring.

-These days they'd be writing and debugging code for weeks!

Being that the brushes slide, there is friction, so there is wear. They are softer than the copper, so they wear to the right shape to make good contact (less arcing). They are much easier to replace than the copper commutator, so they have their service life and then get replaced by the next set (-for the greater good!).

It's a wonderful, simple idea that changed the World.

Posted by Winbert Hutahaean (Member # 58) on July 24, 2018, 07:34 PM:

Thanks Steve for an excellent explanation. I just knew it.

So what is the impact of bad brushes to the motor? become slower?

Posted by Thomas Knappstein (Member # 6134) on July 24, 2018, 11:51 PM:

Thank you for this great statemants.
I have changed the complete Motor. I have one of them bought for replacing many Years ago.

But I will try to change the Brushes in the other one next time.

Posted by Adrian Winchester (Member # 248) on July 25, 2018, 08:16 PM:

I'll offer one comment on this:

I have two GSs; one has had considerable use over many years; the other is virtually like new, and has probably been used for no more than 20 hours. I have only ever had a problem with the brushes on one of the four motors on these projectors. Guess the projector?

Answer: the 'like new' one!

Posted by Bill Brandenstein (Member # 892) on July 27, 2018, 01:14 AM:

A description of the symptoms would be greatly appreciated!

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