RCCrawler Forums

Charlie-III · 10-12-2011, 08:07 AM

Quote:

Originally Posted by Onebdgti

^^^ Thats purrrdy

I have a few arms laying around and they say 11x3 and 12x2 are these equal to a 33t and a 24t.

I don't believe so since the double or triple winds are paralleled so the turn count stays the same. They do it to pack in more copper with the small wind count which makes a better field.

WIDELOAD · 10-12-2011, 06:33 PM

As Charlie-III said, they don't count as a 33t or 24t. They are still a 11t and 12t, its just there are multiple stands wrapped around the segments.
So an 11x3, has 3 pieces of wire wrapped 11 times around the segments, and the 12x2 is 2 pieces of wire wrapped 12 times.

Make sense?

Onebdgti · 10-12-2011, 07:04 PM

Oh yeah makes perfectly good sence

prusik333 · 10-16-2011, 07:53 PM

my motor stop working, just sent sparks out the can

took it apart and the wires weren't even connected to the brushes, on either side?

this is what it looked like after 4 passes, that hole is like that on the other side

after the 12th pass, brass went flying, only thing that sucks, is i was on my last pass....not sure if i would have stopped, if that thin coat of brass would have held up or not?

Well i learned a few things
1. always check your brushes, make sure they are long enough & your wires still connected to the brushes

2. I thought you could make as many passes on a comm, just long as you have lines still on the comm. i thought the brass went all the way through (keep making passes until nothing left)....freakin new guy on a lathe

Hulksta · 10-16-2011, 08:01 PM

You cleaned that up

Hulksta · 10-16-2011, 08:06 PM

Heres a brOOd motor that was not loved for a year before the rebuild (it came to me with broken brush wires from rock damage.

Start..

First pass..

Second and last pass..

ickabob · 10-16-2011, 11:37 PM

Picked this up on ebay, cut my first motor today with it and it works great. Im learning at this point and have read most all the post on this thread. Thanks for all the info here.

Charlie-III · 10-17-2011, 07:15 AM

Quote:

Originally Posted by ickabob

Picked this up on ebay, cut my first motor today with it and it works great. Im learning at this point and have read most all the post on this thread. Thanks for all the info here.

On your first cuts (hopefully on a junk armature) check the diameter of the cut part on both ends and compare the size. This will tell you if it's set-up correctly and NOT cutting a taper.

A tapered comm is almost as bad as an out of round/burned comm.

ickabob · 10-17-2011, 09:07 AM

Quote:

Originally Posted by Charlie-III

On your first cuts (hopefully on a junk armature) check the diameter of the cut part on both ends and compare the size. This will tell you if it's set-up correctly and NOT cutting a taper.

A tapered comm is almost as bad as an out of round/burned comm.

Thanks for the info I will be picking up the right tools for every step of rebuilding a motor, unless I missed something here in the posts. thanks again

DiggyStyle · 10-17-2011, 10:02 AM

Quote:

Originally Posted by EeePee

There's a minimum diameter you can cut down to, and I don't know exactly what it is. EddieO (brood) says 0.270, which is just under 7 millimeters.

EddieO is absolutely right, the standard minimum diameter of the comm should really be no less than 0.270". There's not much more it can go, there won't be much material left and you don't want to risk cutting it any smaller or you may kill the armature early. Once you get below that, it's time to get another armature. You should only cut off just the bare minimum amount in order to get the comm back to true (it should look clean as new by then) and you should be able to this sequence of use and re-truing (cutting) quite a few times before getting down to the 0.270" mark, which should give you a nice long lifespan from your motor. A digital dial caliper is the best tool for monitoring the diameter of your comm. If you don't have one already, you can get a decent one at Harbor Freight tools for around 20 bucks. Good luck!

EddieO · 10-17-2011, 10:40 AM

The following is a safe guide...

7.5mm Small Comm/.300 can go to .270 safe
9mm Mid Comm/.350 can go to .320 safe
10mm Large Comm/.393 can go to .360 safe

I've seen suggestions a 7.5mm comm can go to 6.5mm, which is nuts....that's like .255...good luck with that. While we had some crazy fast stock arms we kept running into the .26x range, they didn't last long and blew up quickly....

So while you can go below the above chart, you are playing with fire.......don't be surprised when stuff goes BOOM.

Later EddieO

prusik333 · 10-17-2011, 03:20 PM

Quote:

Originally Posted by EddieO

The following is a safe guide...

7.5mm Small Comm/.300 can go to .270 safe
9mm Mid Comm/.350 can go to .320 safe
10mm Large Comm/.393 can go to .360 safe

I've seen suggestions a 7.5mm comm can go to 6.5mm, which is nuts....that's like .255...good luck with that. While we had some crazy fast stock arms we kept running into the .26x range, they didn't last long and blew up quickly....

So while you can go below the above chart, you are playing with fire.......don't be surprised when stuff goes BOOM.

Later EddieO

thanks for this info, i guess it would be a good idea for me to get a digital caliper

DiggyStyle · 10-17-2011, 04:46 PM

Quote:

Originally Posted by EddieO

The following is a safe guide...

7.5mm Small Comm/.300 can go to .270 safe
9mm Mid Comm/.350 can go to .320 safe
10mm Large Comm/.393 can go to .360 safe

I've seen suggestions a 7.5mm comm can go to 6.5mm, which is nuts....that's like .255...good luck with that. While we had some crazy fast stock arms we kept running into the .26x range, they didn't last long and blew up quickly....

So while you can go below the above chart, you are playing with fire.......don't be surprised when stuff goes BOOM.

Later EddieO

Excellent info Eddie, thanks! Yeah I've run some, in the past, down around 0.268 or so, just to push the envelope, and had them detonate. I stick to the 0.270 mark as gospel! You can't go wrong staying on the safe side. And yes, I would highly advise anyone who is going to use a motor lathe to also invest in a pair of digital dial calipers.

DiggyStyle · 10-17-2011, 04:53 PM

Quote:

Originally Posted by prusik333

thanks for this info, i guess it would be a good idea for me to get a digital caliper

A very good idea! You don't even have to spend a ton of cash (ie: a 'Mitutoyo' brand caliper, even though they rock!

) to get a decent caliper that will serve you well. You really shouldn't have to spend more than 20-30 bucks (unless you just want to). Digital display is the way to go. You will thank yourself.

JohnRobHolmes · 10-17-2011, 05:15 PM

Although 6.5mm is nuts for mission critical installations and doing laps, I have ran many crawler motors down that far without failure until the very end. It is one thing to pop an armature running 30k rpm into a can with such a small comm, it is another thing to use a worn 35t spinning on 2s or 3s in a scaler. I like getting the most life from my motors, and as they get passed down from my high performance rigs to my every day play rigs I certainly let them wear all the way out before tossing in the towel.

The old racing figures are great standbys for keeping up motors, but things just aren't quite the same when motors spin slow and are mostly at low rpm to stall situations.

EeePee · 10-17-2011, 05:36 PM

Quote:

Originally Posted by prusik333

after the 12th pass

12 passes is quite a lot.

Quote:

Originally Posted by Hulksta

You cleaned that up

Call it a practice arm... well, call it trash now. Probably took 10 passes to get the outer part anywhere near the middle part.

Good stuff.

JohnRobHolmes · 10-17-2011, 05:39 PM

Must have been one sexy curvy comm before you got ahold of it

EeePee · 10-17-2011, 05:42 PM

I bet those springs were getting a workout.

Wonder if the brushes were so short the leads were grinding into the comm for a while until they broke free.

JohnRobHolmes · 10-17-2011, 05:43 PM

Sadly I have had motors come back like that. Little brushes shaped like triangles from getting so short they fall into the motor.

EddieO · 10-17-2011, 05:59 PM

This isn't an old racing thing, this just straight physics. The internal diameter of the copper on a 7.5mm comm is about .255 on the money. There is no copper left really at that point. Depending on the heat during the soldering/welding, the expansion can push this out even farther.

And while we can argue that getting the "most life out of your motors" cause they go so slow is one thing, not every person is using their motor in a crawler. Should a wraith user, who is at full throttle on 3s 90% of the time let his comm go down to 6.5mm?

Keep in mind folks, when a comm plate explodes, often they take out other stuff with, namely brush hoods. Some motors, such as the Checkpoint, V2, or Trinity cobalt often require an endbell replacement when you blow a plate.

Just for shits and giggles, I grabbed a unused 7t arm that was done by Fantom. I just kept cutting until it threw the plate..........happened at .258. That's with a diamond bit.....that's meant to cut. A brush riding up against its edge every millisecond will lift it sooner. RPM has little to do with this, in fact, repeated stopping and starting is probably worse than a motor spinning at 30k......there is a reason I have seen more hung brushes in crawling the last few years than I saw in 20+ years of racing...

Racers didn't do it because we were racing, we did it because it was simply past the ability of the comm under any circumstance.

Later EddieO

10-17-2011, 05:15 PM	#1175
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	Although 6.5mm is nuts for mission critical installations and doing laps, I have ran many crawler motors down that far without failure until the very end. It is one thing to pop an armature running 30k rpm into a can with such a small comm, it is another thing to use a worn 35t spinning on 2s or 3s in a scaler. I like getting the most life from my motors, and as they get passed down from my high performance rigs to my every day play rigs I certainly let them wear all the way out before tossing in the towel. The old racing figures are great standbys for keeping up motors, but things just aren't quite the same when motors spin slow and are mostly at low rpm to stall situations. Last edited by JohnRobHolmes; 10-17-2011 at 05:18 PM.

10-17-2011, 05:59 PM	#1180
EddieO I wanna be Dave Join Date: Apr 2007 Location: Arlington, Washington Posts: 2,303	This isn't an old racing thing, this just straight physics. The internal diameter of the copper on a 7.5mm comm is about .255 on the money. There is no copper left really at that point. Depending on the heat during the soldering/welding, the expansion can push this out even farther. And while we can argue that getting the "most life out of your motors" cause they go so slow is one thing, not every person is using their motor in a crawler. Should a wraith user, who is at full throttle on 3s 90% of the time let his comm go down to 6.5mm? Keep in mind folks, when a comm plate explodes, often they take out other stuff with, namely brush hoods. Some motors, such as the Checkpoint, V2, or Trinity cobalt often require an endbell replacement when you blow a plate. Just for shits and giggles, I grabbed a unused 7t arm that was done by Fantom. I just kept cutting until it threw the plate..........happened at .258. That's with a diamond bit.....that's meant to cut. A brush riding up against its edge every millisecond will lift it sooner. RPM has little to do with this, in fact, repeated stopping and starting is probably worse than a motor spinning at 30k......there is a reason I have seen more hung brushes in crawling the last few years than I saw in 20+ years of racing... Racers didn't do it because we were racing, we did it because it was simply past the ability of the comm under any circumstance. Later EddieO Last edited by EddieO; 10-17-2011 at 06:18 PM.

LinkBacks (?) LinkBack to this Thread: http://www.rccrawler.com/forum/electronics/223989-cutting-motor-commutator-motor-tweaks.html
Posted By	For	Type	Date
Hiilimoottorin kunnostaminen	This thread	Refback	10-04-2011 03:19 PM

10-12-2011, 06:33 PM	#1162
WIDELOAD Rock Crawler Join Date: May 2009 Location: Queensland, Australia Posts: 610	As Charlie-III said, they don't count as a 33t or 24t. They are still a 11t and 12t, its just there are multiple stands wrapped around the segments. So an 11x3, has 3 pieces of wire wrapped 11 times around the segments, and the 12x2 is 2 pieces of wire wrapped 12 times. Make sense?

10-12-2011, 07:04 PM	#1163
Onebdgti Rock Crawler Join Date: Jul 2010 Location: St. Albans Posts: 507	Oh yeah makes perfectly good sence

10-16-2011, 07:53 PM	#1164
prusik333 RCC Addict Join Date: Feb 2008 Location: Nevada Posts: 1,267	my motor stop working, just sent sparks out the can took it apart and the wires weren't even connected to the brushes, on either side? this is what it looked like after 4 passes, that hole is like that on the other side after the 12th pass, brass went flying, only thing that sucks, is i was on my last pass....not sure if i would have stopped, if that thin coat of brass would have held up or not? Well i learned a few things 1. always check your brushes, make sure they are long enough & your wires still connected to the brushes 2. I thought you could make as many passes on a comm, just long as you have lines still on the comm. i thought the brass went all the way through (keep making passes until nothing left)....freakin new guy on a lathe

10-16-2011, 08:01 PM	#1165
Hulksta RCC Addict Join Date: Dec 2009 Location: Newcastle, Australia Posts: 1,784	You cleaned that up

10-16-2011, 08:06 PM	#1166
Hulksta RCC Addict Join Date: Dec 2009 Location: Newcastle, Australia Posts: 1,784	Heres a brOOd motor that was not loved for a year before the rebuild (it came to me with broken brush wires from rock damage. Start.. First pass.. Second and last pass..

10-16-2011, 11:37 PM	#1167
ickabob Quarry Creeper Join Date: Mar 2010 Location: murrieta Posts: 390	Picked this up on ebay, cut my first motor today with it and it works great. Im learning at this point and have read most all the post on this thread. Thanks for all the info here.

10-17-2011, 10:40 AM	#1171
EddieO I wanna be Dave Join Date: Apr 2007 Location: Arlington, Washington Posts: 2,303	The following is a safe guide... 7.5mm Small Comm/.300 can go to .270 safe 9mm Mid Comm/.350 can go to .320 safe 10mm Large Comm/.393 can go to .360 safe I've seen suggestions a 7.5mm comm can go to 6.5mm, which is nuts....that's like .255...good luck with that. While we had some crazy fast stock arms we kept running into the .26x range, they didn't last long and blew up quickly.... So while you can go below the above chart, you are playing with fire.......don't be surprised when stuff goes BOOM. Later EddieO

10-17-2011, 05:39 PM	#1177
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	Must have been one sexy curvy comm before you got ahold of it

10-17-2011, 05:42 PM	#1178
EeePee MODERATOR™ Join Date: Jul 2004 Location: Ohio Posts: 18,928	I bet those springs were getting a workout. Wonder if the brushes were so short the leads were grinding into the comm for a while until they broke free.

10-17-2011, 05:43 PM	#1179
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	Sadly I have had motors come back like that. Little brushes shaped like triangles from getting so short they fall into the motor.

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