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smallest usable comm diameter

smallest usable comm diameter

Old 04-08-2007, 02:40 PM
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Originally Posted by superspeed
.275
common be brave .264!!!
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Old 04-08-2007, 03:48 PM
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I stop at .270 or ealier if the comm starts to chip.
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Old 04-08-2007, 04:04 PM
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If ya can't peel the copper segemnt up with your finger nail then there another run in her....

or... keep grind'n till ya see daylight...
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Old 04-08-2007, 04:14 PM
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Originally Posted by 2-Bad
If ya can't peel the copper segemnt up with your finger nail then there another run in her....

or... keep grind'n till ya see daylight...
thas correct@!!lol
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Old 04-08-2007, 04:27 PM
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Originally Posted by 2-Bad
If ya can't peel the copper segemnt up with your finger nail then there another run in her....

or... keep grind'n till ya see daylight...
I used to true them till the comm peeled off.
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Old 04-08-2007, 04:55 PM
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Default Checkpoint 19T

we have run a Checkpoint 19T motor at 6.86mm with Infinity brushes for the last 3 weeks - very quick.

regards

Don
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Old 04-08-2007, 07:50 PM
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Thanks Everyone,
Thats a lot of good info.
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Old 04-09-2007, 07:54 AM
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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.
That is the same experience I've had with the common Trinity motors. However, you can get around this by shaving both the leading and trailing edges of the brushes. As the comm gets smaller, the edges of the brush wrap around more comm surface area. This causes more overlap of the brush between the comm segments as the comm rotates. Another simplified way of looking at it is that more overlap usually means more heat with the increased RPM.

Shaving the edges of the brushes will reduce the comm overlap back to a level where the efficiency picks back up and the motor doesn't overheat. But you have to keep in mind that you also need to increase the spring tension some as the comm gets smaller. All of these things can be quite hard to master for consistency though.

donwhit is correct about the CP motors. I can run the comms AND brushes quite small without losing power. I'm not sure, but I think the CP motors don't heat up with the increased overlap since the amount of brush edge touching each segment changes as the comm rotates (round face versus rectangle face with long flat edge). However, I do have to spend some time with each motor on the CE dyno to find out how much to change the spring tension as everything gets smaller.
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Old 04-09-2007, 08:23 AM
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Originally Posted by teamgp
That is the same experience I've had with the common Trinity motors. However, you can get around this by shaving both the leading and trailing edges of the brushes. As the comm gets smaller, the edges of the brush wrap around more comm surface area. This causes more overlap of the brush between the comm segments as the comm rotates. Another simplified way of looking at it is that more overlap usually means more heat with the increased RPM.

Shaving the edges of the brushes will reduce the comm overlap back to a level where the efficiency picks back up and the motor doesn't overheat. But you have to keep in mind that you also need to increase the spring tension some as the comm gets smaller. All of these things can be quite hard to master for consistency though.

donwhit is correct about the CP motors. I can run the comms AND brushes quite small without losing power. I'm not sure, but I think the CP motors don't heat up with the increased overlap since the amount of brush edge touching each segment changes as the comm rotates (round face versus rectangle face with long flat edge). However, I do have to spend some time with each motor on the CE dyno to find out how much to change the spring tension as everything gets smaller.
I have tried shaving the leading/trailing edges as well... however, still see a noticeable drop within the last couple minutes in TC. In 1/12 - not so much - leading me to think that the voltage running through the motor has something to do with it as well. As the comm does get smaller - I have also adjusted spring tension by up to 2-points on the Trinity spring-thing and did notice RPM increase. I have also tried reducing spring tension and found that with a small comm, cut brushes, the motor is more reactive to spring changes.

I think that CP motors don't heat-up as much since the design is much more effecient (round brush)... but I also think that the brush tubes are far superior to the convensional design for minimizing brush movement - reducing arching on the comm = less heat.
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Old 04-09-2007, 01:37 PM
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Originally Posted by duckman996
I have tried shaving the leading/trailing edges as well... however, still see a noticeable drop within the last couple minutes in TC. In 1/12 - not so much - leading me to think that the voltage running through the motor has something to do with it as well. As the comm does get smaller - I have also adjusted spring tension by up to 2-points on the Trinity spring-thing and did notice RPM increase. I have also tried reducing spring tension and found that with a small comm, cut brushes, the motor is more reactive to spring changes.

I think that CP motors don't heat-up as much since the design is much more effecient (round brush)... but I also think that the brush tubes are far superior to the convensional design for minimizing brush movement - reducing arching on the comm = less heat.
i agree
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