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Thread: Does this comm need cut, etc? W/Pics

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Old 02-01-2010, 07:44 AM   #1
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Default Does this comm need cut, etc? W/Pics

This thread is not meant to bash Holmes Hobbies products, it is purely to help determine how badly the motor is damaged, and what I need to do to repair it.



This is the comm on a Holmes Hobbies 7T Cobalt Puller that I got in a used LCC package deal.
It doesn't live up to the hype. It's going in a Night Crawler, in an effort to get some wheelspeed. My eyes tell me that the cheap Integy 35T that I have runs the car faster, and the 35T definitely runs cooler, according to my calibrated finger tips. I have tried these motors with the stock 20T pinion, and a 26T pinion. So far the 35T w/20T pinion runs coolest and fastest. I had alot higher hopes for the puller, and haven't given up on it yet.
The 7T seems torquey but slowish, and it got hot faster than I expected, seeing how well the 35T handled the 20T pinion.
This is all on 2s lipo, hopefully getting what I need to safely start running 3s today.

Got excited when I saw this stuck spring, thought that might be the prob. Sprayed everything out with motor cleaner, lubed the bearings, set the end play, then timing to neutral(eyeballed it, and ensured no sparks), and bam! Same crappy performance. I think I accidently did it while disassembling the motor, as the brushes look to be very similar in length.


My questions:
1. Does the comm need a cut? Couldn't get my cam to take good pics, so here are a few, hoping one of them has the detail you need to make a decision.





2. Do these brushes look worn? I will replace them regardess if I get the comm cut, just need to know what to look for in the future.

Last edited by shelljeep; 02-03-2010 at 11:50 AM.
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Old 02-01-2010, 08:09 AM   #2
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I doesnt look like it to me, but I've never cut a commutator.....I just clean them up and maybe sand them down occasionally.

It's hard to tell on the brushes. If it were me, I'd clean up the comm and replace the brushes and springs. It cant hurt since you've already got the motor torn apart.
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Old 02-01-2010, 08:15 AM   #3
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Do you use something like 220 emory cloth to do that? The pics were taken after I hit it with motor cleaner, it did nothing to the black glaze on it.
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Old 02-01-2010, 08:33 AM   #4
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I would start by using a pencil eraser. You can put the armature in your drill and spin it, then use the eraser to clean the surface. If you are still having troubles, then use some really fine grit sand paper or, as you mentioned, emery paper. Attach it to one of your wife's emery boards (she'll love this ) and spin the drill again applying pressure from the emery board. Then clean it up again with that pencil eraser.
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Old 02-01-2010, 08:53 AM   #5
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Thanks. Going to have to tell the wife who suggested this if she finds out. :-P
(I'm in enough hot water already, gotta share the load...)
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Old 02-01-2010, 08:59 AM   #6
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Haha.....you could always use one of her old boards.....

BTW, I would definitely try just cleaning the comm with an eraser first, then put some new springs and brushes in and see how it runs. Remember to run the motor for a while outside of the truck to break in the brushes.
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Old 02-01-2010, 09:08 AM   #7
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What's the break in procedure?
Do I keep it low rpm or vary it? How long should I run it?
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Old 02-01-2010, 09:12 AM   #8
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Yeah, I will usually just either run the motor with it not installed in the truck at low speed for a minute or two.....or intall it in the truck and run it at low speed with the tires off of the ground. I'm sure there are other methods, but I've had pretty good luck with this method.
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Old 02-01-2010, 09:20 AM   #9
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Thanks!
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Old 02-02-2010, 04:57 PM   #10
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I just had my comm cut and brushes cleaned what a difference. The motor sounds totally different. From the looks of it either that motor was beat on bad or it was ran with negative timing.
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Old 02-02-2010, 05:19 PM   #11
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I would advise not using an emory board or sandpaper to try to 'cut' the comm. Honestly, that doesn't even make sense!

Without a lathe, your doing nothing but maybe taking a glaze off the commutator. You might even make things more out of round that way.

Looking at the commutator, it appears you could use a cut. Notice the brush marks aren't the same width across every comm slot? Makes me think they're not in the round.

I've not looked, but I wonder if the HH Pullers will even fit in a comm cutter? I could look I guess...
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Old 02-02-2010, 05:28 PM   #12
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Quote:
Originally Posted by EeePee View Post
I've not looked, but I wonder if the HH Pullers will even fit in a comm cutter? I could look I guess...
not the normal lathes ...... arms are to long.
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Old 02-02-2010, 05:39 PM   #13
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Quote:
Originally Posted by EeePee View Post
I would advise not using an emory board or sandpaper to try to 'cut' the comm. Honestly, that doesn't even make sense!

Without a lathe, your doing nothing but maybe taking a glaze off the commutator. You might even make things more out of round that way.

Looking at the commutator, it appears you could use a cut. Notice the brush marks aren't the same width across every comm slot? Makes me think they're not in the round.

I've not looked, but I wonder if the HH Pullers will even fit in a comm cutter? I could look I guess...
I completely agree with EeePee.

Not sure what lathe could cut them, I will have a hudy lathe tomorrow and find out.
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Old 02-02-2010, 06:32 PM   #14
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Come on, I'm good with an emory board... you should see my nails.

But seriously, called the lhs today, Big Boys Toys and Hobbies, and they don't cut coms, much less puller comms. So, it looks like I'll be buying a new armature or sending this off to get cut.
I have new brushes coming from HH, where can I send this armature to have it cut? What's it cost typically? Wondering if it's worth it after shipping, etc.
Thanks for all the info.
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Old 02-03-2010, 09:55 AM   #15
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Quote:
Originally Posted by EeePee View Post
I would advise not using an emory board or sandpaper to try to 'cut' the comm. Honestly, that doesn't even make sense!
Nobody said that the emery paper would cut the comm....just used to clean up any nicks or grooves.
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Old 02-03-2010, 10:16 AM   #16
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something like 1000grit and wet would help take the glaze you see off but its not gonna take the grooves the naked eye cant see out.

using anything but an eraser or diamond bit to properly cut the comm is just gonna cause more damage then its worth.
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Old 02-03-2010, 10:20 AM   #17
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So who do you guys get to turn your comms?
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Old 02-03-2010, 10:25 AM   #18
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I bought a com lathe so I can do it myself, though the puller won't fit. Been thinking of modifying it so it will...

You might try asking JRH if he can do it. He's got a feedback/question thread going in the vendors section.
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Old 02-03-2010, 10:31 AM   #19
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Will do. Gracias.
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Old 02-03-2010, 10:33 AM   #20
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Quote:
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Will do. Gracias.
Bwenos nachos.
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