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Old 08-24-2011, 10:56 AM   #1
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Default Does ON resistance in speed controls still mean anything?

Back in the old days of running brushed motors with sub-Cs, ON resistance meant a lot in regards to power, gearing and making time. We ran 4 minute heats and as the capacity of sub-Cs increased, we ran 5 minute heats. Now we all are running brushless motors (more effiecient than brushed) and Lipo batteries with a HUGE amount of capacity (5500mah+) and the heats are still 5 minutes.

So with all the voltage and capacity in the batteries and the efficiency of the motors, does the ON resistance really have a factor in performance that is noticeable in a 5 minute heat?

BTW, I'm talking in regards to 1/10th scale. For 1/12th scale, its been 8 minutes since the old flex-plate stick pack days with Sanyo 1200s. Something to think about.
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Old 08-25-2011, 09:42 AM   #2
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Amazing, no one seems to have a comment on this. I guess it really doesn't mean anything anymore. So the difference between .0006 ohms and .0003 ohms is just too little to bother with.
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Old 08-25-2011, 10:09 AM   #3
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Amazing, no one seems to have a comment on this. I guess it really doesn't mean anything anymore. So the difference between .0006 ohms and .0003 ohms is just too little to bother with.
I think it has a place but I am unsure how much. I only run 1/12 Mod & 13.5.

I usually don't see a fade until the 7min mark. The batteries (PowerPush) are so good now that I think the loss on the speed control is not as much of an issue anymore.

It's a hard question to answer?

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Old 08-25-2011, 10:17 AM   #4
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It's there at the top levels in blinky mode. When you're down to simple "losses" yes it could be a factor.
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Old 08-25-2011, 11:19 AM   #5
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Old 08-25-2011, 08:24 PM   #6
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Originally Posted by Randy_Pike View Post
It's there at the top levels in blinky mode. When you're down to simple "losses" yes it could be a factor.
That's been my thinking on it. When using boost, I don't think on resistance has been a big deal, but with the move to non-boosted ESC's, I think on resistance will start to make a bigger difference, much like it did in the brushed motor days...
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Old 08-25-2011, 08:55 PM   #7
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That's been my thinking on it. When using boost, I don't think on resistance has been a big deal, but with the move to non-boosted ESC's, I think on resistance will start to make a bigger difference, much like it did in the brushed motor days...
In the old brushed motor days with sub-Cs you had to worry about making time as your batteries start to get flat about a minute before the end of the heat. Nowadays with lipo and the efficiency of brushless, no one ever has an issue of dumping or going flat within the final laps.

On average for me after using a fully charged lipo in a 5 minute heat, the charger will show about 1800mah was used to re-peak it again. With most packs nowadays that are 5500+mah any loss would have no effect on the supply of charge necessary to make 5 minutes.

So does the ON resistance have an effect on the voltage output? Or does the FETs regulate that as long as there is an ample enough supply of charge in the battery?
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Old 08-25-2011, 09:26 PM   #8
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Quote:
Originally Posted by YR4Dude View Post
In the old brushed motor days with sub-Cs you had to worry about making time as your batteries start to get flat about a minute before the end of the heat. Nowadays with lipo and the efficiency of brushless, no one ever has an issue of dumping or going flat within the final laps.

On average for me after using a fully charged lipo in a 5 minute heat, the charger will show about 1800mah was used to re-peak it again. With most packs nowadays that are 5500+mah any loss would have no effect on the supply of charge necessary to make 5 minutes.

So does the ON resistance have an effect on the voltage output? Or does the FETs regulate that as long as there is an ample enough supply of charge in the battery?
Hard to say really when you have some other factors involved such as the resistance on your connectors, solder joints, wires, batteries etc.
Add to that other things such as the rolling resistance of your tires, the friction of your bearings, gears, belts, drag from your body shell/wing, weight of the car and many other factors.
The above alone would make it very difficult to pin point the difference in ON resistance effects on your car during a race.

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Old 08-25-2011, 10:11 PM   #9
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Surely , given the almost unmeasurable resistances quoted in spec sheets, any esc resistance would be TOTALY swamped by Internal resistance of batts , motors & reactance .
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Old 08-25-2011, 10:13 PM   #10
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Unless you're running every lap in every race with a consistancy of 0.20 or lower, it's not really worth worrying about!
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Old 08-27-2011, 08:39 AM   #11
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MOSFET resistance is also calculated @ 25degC (i think).

Once temperature is outside of that 25degC... all bets are off.
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