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[dodgy geezer]

I think you'll find high frequency digital storage scopes are needed to pick up that stuff.

100MHz are cheap - Gigahertz less so... :(

Next best pondside tech toy after a handheld scope is a dc current capable clamp meter. £14.34 is the discounted price for those new to the store. I don't need another, but I checked that is a hall effect type that does d.c.
Some reviewers have not sussed you have to store a reference zero reading before each true reading.https://www.aliexpress.com/item/1005005757085279.html

Shows £20 for me. And when do you need to measure 600A?

[dodgy geezer]

Here are a few pics of the Comet.  First the brushes, and to me they don't look too bad at all.

Brushes don't look too bad - commutator less so.


Check the thickness of the Beryllium copper strip brushes where they contact the commutator. They might be worn thin, and if so could break, then snag on the commutator.
The commutator tends to arc where the brushes cross over to the next section. Annoyingly, this is exactly where the holding tab into the backing paxolin is situated, so the tab conducts heat that makes the paxolin eventually crumble.
Do you fancy making up a new commutator? It's fairly easy if you use a Dremmel to sand the small pieces to size.


The Comet looks like a later one. The earlier Comets did not have the metal armature slices very well aligned, since they were hand-assembled. Yours are quite even.

[HMS Invisible]

100MHz are cheap - Gigahertz less so... :(




Shows £20 for me. And when do you need to measure 600A?

This happened when I posted a link to a dual esc. For my privacy I stripped off the url cookie before posting. As a result everyone sees the default option which can be changed at the page foot. There can be several stocked variations which can mean as little as a more popular colour, or a "pro" option, a carry case or more features. Aliexpress shopping means you have to put in the hours to know the process. So I'd recommend looking through the spec list and comparing with other Aneng meters after hitting the "find similar" button.
 It isn't so much the 600 amp range but frequency counter, true rms etc and you'd pay well over a hundred quid for a dc current type if you needed to rush to a trade counter in an emergency.

[DJW]

Hi Martin


I did run one, the one that's now in parts...  See post 11 above. The other one doesn't feel free enough to spin so I didn't try it.


David.

[dodgy geezer]

An article describing the repair of a set of Torpedo brushgear (which is the same as the Comet brushgear) is available on the web site here. You can see the kind of wear that is typical, and the creation and replacement of the commutator.. Sorry about the dark pictures...

[Circlip]

And beware when dealing with Beryllium Copper.   


 Regards   Ian

[DJW]

Haha...  this was meant to be a not too tricky side project. Now we have at least a few ways listed to cause serious injury by electric shock or poisoning. Well. I did ask for input so no one else to blame..!


Thanks for the brush and commutater refurbish link, ill have a good look over that. I'll also strip that second motor and see what it looks like. Might be able to make up one good motor from the two. We'll see.


Thanks to all.
David.

[dodgy geezer]

Might be able to make up one good motor from the two. We'll see.

No reason why you should not have two good motors. Just need to get some paxolin and spring copper...

[roycv]

Hi Dodgy PM sent
Roy

[dodgy geezer]

Having done a bit of experimenting, I can recommend the use of neodymium to boost the Comet's magnet. I tried a magnet from an old hard drive, and found that I could demagnetise and remagnetise the iron horseshoe easily. All you do to improve the magnetism is stroke the horseshoe with the North pole of the neodymium, going north to south on the horseshoe, about 10 times. To demagnetise, go the opposite way (South to North)...