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Old 04-08-2007, 09:08 AM   #1
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Default smallest usable comm diameter

How for can the comm be cut, as in, its smallest usable diameter before it is considered no good anymore ??
Thanks
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Old 04-08-2007, 09:30 AM   #2
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I'd say under 7 mm it's near crap.
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Old 04-08-2007, 10:08 AM   #3
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Quote:
Originally Posted by Bdegan
How for can the comm be cut, as in, its smallest usable diameter before it is considered no good anymore ??
Thanks
Hi Brad,

It all depends on the motor that you are using. The Reedy quad-magnet motor requires a larger com - whereas some of the Top motors can be cut as small as 7mm and still offer some good performance.

Keep in mind, as your com-size decrease, the rpm of the motor increases - equalling an adjustment needing to be made to your gearing.

Hope that helps.

Last edited by duckman996; 04-08-2007 at 12:10 PM.
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Old 04-08-2007, 10:39 AM   #4
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Quote:
Originally Posted by duckman996
Hi Brad,

It all depends on the motor that you are using. The Reedy quad-magnet motor requires a larger com - whereas some of the Top motors can be cut as small as 7mm and still offer some good performance.

Keep in mind, as your com-size decrease, so does the rpm of the motor - equalling an adjustment needing to be made to your gearing.

Hope that helps.
realy
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Old 04-08-2007, 11:05 AM   #5
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Quote:
Originally Posted by duckman996
Hi Brad,Keep in mind, as your com-size decrease, so does the rpm of the motor - equalling an adjustment needing to be made to your gearing.

Hope that helps.
First I've heard that one. I thought it increased the RPM's, guess I was wrong.
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Old 04-08-2007, 11:10 AM   #6
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Quote:
Originally Posted by John Warner
First I've heard that one. I thought it increased the RPM's, guess I was wrong.
well what dose your motor do when the com gets small
dose your motor get faster or slower
theres a sweat spot where the motor is fastest then when you make it smaller the performance go's down.
depending on how you cut you brush too.
but its still easier than a damm nitro motor.
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Old 04-08-2007, 12:09 PM   #7
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Quote:
Originally Posted by John Warner
First I've heard that one. I thought it increased the RPM's, guess I was wrong.
You are correct... the RPM DOES increase.... typo on my part - I fixed it.

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Old 04-08-2007, 12:17 PM   #8
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Quote:
Originally Posted by wallyedmonds
well what dose your motor do when the com gets small
dose your motor get faster or slower
theres a sweat spot where the motor is fastest then when you make it smaller the performance go's down.
depending on how you cut you brush too.
but its still easier than a damm nitro motor.
I found that as long as you geared properly the Epic based motors get faster as the com decreases to about 7.2 mm - then they just overheat and run strong for 2-3 min... after that, they die off quickly in a race.
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Old 04-08-2007, 12:23 PM   #9
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Quote:
Originally Posted by wallyedmonds
well what dose your motor do when the com gets small
dose your motor get faster or slower
theres a sweat spot where the motor is fastest then when you make it smaller the performance go's down.
depending on how you cut you brush too.
but its still easier than a damm nitro motor.
Small Comm = More RPM, Less Effenciency, Less Torque

Bigger Comm = Less RPM, More Effenciency, More Torque.

Small Track = Bigger Comm

Large Track = Smaller Comm
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Old 04-08-2007, 12:28 PM   #10
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.270 on the small comms is really the safe point, though I have seen people run them smaller.......yer playing with fire, certainly something I would not do in the A main at a big race....

.310 on the large comm (reedy stuff, like quad mag 19t)....

We have never really messed with cutting the stuff to some magical diameter like other companies have claimed at big races....we cut tills its round and run it......

Just remember, as it gets smaller.....you may need to adjust your gearing some....not always, but sometimes.

Later EddieO
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Old 04-08-2007, 01:00 PM   #11
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You can go to 6.8mm but after that you're probably screwed

It will still be fast until 7.0 or maybe 6.9. This is from my experience from Orion armatures during the last few years.
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Old 04-08-2007, 02:04 PM   #12
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From my experience .270 is pretty much the cutoff point. If the comm doesn't start to flake at the grooves it's still not worth risking damage to your lathe to cut it smaller.

I have seen a few motors peel up the copper off the comms at .275 though.
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Old 04-08-2007, 02:09 PM   #13
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Quote:
Originally Posted by EddieO
.270 on the small comms is really the safe point, though I have seen people run them smaller.......yer playing with fire, certainly something I would not do in the A main at a big race....

.310 on the large comm (reedy stuff, like quad mag 19t)....

We have never really messed with cutting the stuff to some magical diameter like other companies have claimed at big races....we cut tills its round and run it......

Just remember, as it gets smaller.....you may need to adjust your gearing some....not always, but sometimes.

Later EddieO
For us living in the metric world:

.270 = 6.86 mm
.310 = 7.88 mm

Personally - when I cut a comm to around 7mm that motor turns into a practice motor. I've had too many die-off during a race for my liking at this size.
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Old 04-08-2007, 02:33 PM   #14
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Quote:
Originally Posted by duckman996
I found that as long as you geared properly the Epic based motors get faster as the com decreases to about 7.2 mm - then they just overheat and run strong for 2-3 min... after that, they die off quickly in a race.
yep at that point you have gone past the sweat spot.
and the arm is junk.
the trick is to fined what a given motor likes
magnet
com size
brush
and rollout
all motor's are different and to find what a given motor wants is an art form
and you duckman have that little extra touch to find it prity good
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Old 04-08-2007, 02:40 PM   #15
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.275
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