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Old 04-18-2013, 10:55 AM   #1
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Default 14mm rotor and motor current question

I have a tekin redline 2.5 that has been sitting around for a long time. I used it once and quickly learned that this motor is only good for overloading batteries and speed controls. I was wondering if i bumped up the rotor to the 14mm HT if that would help mellow this motor out by reducing current draw (and therefore keep everything cooler) or if I should stick with something more reasonable like a 4.5-6.5 turn motor.

I intend to put this into a team associated 12r5 along with a 7.4v shorty pack and run it around on an 1/8 on-road track for science . Any other opinions or ideas?
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Old 04-18-2013, 10:56 AM   #2
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What speedo were/are you using?
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Old 04-18-2013, 10:59 AM   #3
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RS pro

edit- nothing was damaged by running it but everything pretty hot after about 2-3 mins of running. i think 140-170F if i remember correctly. i would like to be able to run a good 5-10 minutes without getting past 150. This may also have been because of running ni-mh batteries and/or texas summer heat. its been a few years so I dont remember all that precisely.

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Old 04-18-2013, 11:14 AM   #4
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It seems that the only contribution the HT rotor would have on decreasing current draw is that that comes from the the use of a softer throttle finger to keep the tires from spinning.

I'd recommend getting either a higher turn motor and/or a different speedo. The rs pro won't fair well with a 2.5T on 2S power, even with a fan. 2S 2.5T will most likely push the limits of any speedo that'll fit on a 12th scale chassis. I cannot imagine a 2S 2.5T powered 12th scale being driveable, even on an 1/8 scale track. Your thoughts of 4.5-6.5T seem more reasonable and it'll still be wicked fast.
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Old 04-18-2013, 11:36 AM   #5
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Use a different speedo, put a fan on said speedo, and start with no boost so you can check temps. A 2.5t on 1s in a 12th scale will be crazy fast, and I would really recommend that you try that out before attempting the 2s malarkey. I really can't even imagine trying to drive a mod 12th on 2s...

Max K and I were actually joking about this exact same thing at MHIC recently, and I believe his words were along the lines of "it would be ridiculous and nearly impossible to drive". That, coming from someone who has won carpet nats...

To put it in perspective, a mod 12th will already typically turn faster laps than a mod sedan, even despite the 1s vs 2s voltage difference. Direct drive, half the weight, foam tires, etc. Now imagine doubling the voltage in the 12th... If you want even more sobering news, think about pro-10 cars...10.5, 2s, and even heavier than a 12th scale...
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Old 04-18-2013, 01:39 PM   #6
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I guess I will just get both a rotor and a higher turn motor. Thanks for the feedback.

I am not sure if I should be ashamed or impressed with myself that I have also fit an eagletree eLogger in my rc12r5 to watch current. For Science!
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Old 04-18-2013, 02:13 PM   #7
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Contrary to popular belief, a bigger rotor will draw more amps, and in 12th scale, a 12.3mm rotor will fare alot better with your RSpro timing down around 40 to 50.... You can make it Work with a 2.5t , but you have to be very smooth... The 2.5t comes with a 13mm rotor which is too big for 12th scale and draws too much current: smaller 12.3mm rotor is better and will turn more rpm.....
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Old 04-18-2013, 03:02 PM   #8
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hmm, not sure that's true. The torque transmitted to the rotor is due to the magnetic flux coupling in the air gap. The smaller the air gap, the greater the flux density and the more efficient the power is transferred. Hence, why a larger diameter rotor is considered "high torque." In theory, the larger diameter rotor would feel more "torquey" while the smaller diameter smoother.
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Old 04-18-2013, 05:28 PM   #9
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Quote:
Originally Posted by samnelso View Post
hmm, not sure that's true. The torque transmitted to the rotor is due to the magnetic flux coupling in the air gap. The smaller the air gap, the greater the flux density and the more efficient the power is transferred. Hence, why a larger diameter rotor is considered "high torque." In theory, the larger diameter rotor would feel more "torquey" while the smaller diameter smoother.
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Old 04-18-2013, 05:42 PM   #10
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Correct, but a larger diameter rotor also has a bigger magney, which demands more current to energize it ...
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Old 04-18-2013, 05:46 PM   #11
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Bigger magnet = more current draw and less rpm !
Smaller magnet = less current draw and more rpm !
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Old 04-18-2013, 05:57 PM   #12
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The best way to reduce the air gap and gain efficiency is to move the stator plates closer to the 12.3mm rotor rather than using a bigger rotor... I don't think the motor manufacturers make the stators like that though, so you'll have to play with rotor sizes intead, but I think the 12.2mm to 12.3mm rotors are the best choices out there....
In addition, with the high rpm of a 2.5t motor, the closer the mass of the rotor is to its centerline, the better... The further it is, the more the rotor will fight itself and explode inside.... In high rpm situations, smaller rotor is always better !!!
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