F120 Gear Motor R-291

[TCW]

I was wondering if anyone new how many ohms should I see across the windings of the R-291 motor? I noticed the record carriage stopped and the motor case was warm and it smelled a bit. When removing the motor cover it stinks. I'm getting 80 ohms. My gripper motor (same motor model) is 30 Ohms.

[jukenorman]

Hi Tom,
That will be a single winding that you are measuring. I would recommend stripping the motor to check its condition and service it. You will probably be able to see if any winding looks a bit burnt and you can then measure the resistance of each winding. They should all be about the same.

Norman.

[TCW]

The brushes seem to be a worn down and oily. I found them to be 5/32 square by 7/32 long. Where to find new ones or if need be cut down a set to fit?



I tested the motor armature with the commutator. It did 180 degree test of the commutator segments(a bit flawed because of the uneven number of segment bars). Also segment to adjacent segment test and lastly bar to armature stack. The results are listed left to right.

1) 13.7 Ohm, 4.5 Ohm, Infinite
2) 13.7 Ohm, 4.6 Ohm, Infinite
3) 13.8 Ohm, 4.8 Ohm, Infinite
4) 13.3 Ohm, 4.8 Ohm, Infinite
5) 13.2 Ohm, 4.8 Ohm, Infinite
6) 13.9 Ohm, 4.8 Ohm, Infinite
7) 13.8 Ohm, 5.0 Ohm, Infinite
8) 13.7 Ohm, 4.1 Ohm, Infinite
9) 13.8 Ohm, 4.1 Ohm, Infinite
10) 13.8 Ohm, 4.2 Ohm, Infinite
11) 13.9 Ohm, 4.3 Ohm, Infinite

Upon reassembly with existing brushes I had 14.4 ohms at the motor power plug. A little extra Ohms for the wire and brush assemblies I think is OK seeing they haven't really seated fully yet though I did spin the armature through the little door a bit.

[Ron Rich]

Hi Tom,
My GUESS is that it's probably still OK -- "ACE is the place----- " most stock, or can get small motor brushes ! Ron Rich

[jukenorman]

Yes motor looks OK. I did an AMi magazine motor quite recently and I used Hitachi power tool brushes (CB56). The original brushes would have been 3/16" square and 13/32" long - Jukebox World gives the sizes but I cannot do small orders there any more because of Brexit (Booo!), hence the Hitachi part. I've done the conversion from millimetres just to show my age.

Norman.

[TCW]

Apr 28, 2021 16:27:06 GMT jukenorman said:

I did an AMi magazine motor quite recently and I used Hitachi power tool brushes (CB56).

Norman.

Hi Norman,

CB56 Motor Carbon Brush 10 x 5 x 5mm for Hitachi Power Tool. Fractional conversion in 64th., Original dimension converted to 64ths in parentheses.
25/64(26/64) x 13/64 x 13/64(12/64). Did the extra 1/64 require sanding or did it fit OK straight away? 

Thanks,
Tom

[TCW]

By the way I ordered Rannb Carbon Motor Brushes for Power Tool 10mm x 5mm x 5mm - 10 Pairs $8.49 on Amazon, be here Saturday.

[jukenorman]

LOL Tom, how many lifetimes are you looking for from your AMI? Yes they did fit OK although I was prepared to shave them slightly!

Norman.

[Ron Rich]

Hi Tom,
Yea--just noticed --"10 pairs--" ? Ron Rich

[TCW]

Well the price was right but who knows, maybe I'll offer the spares up here...  ?