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To determine what the bearing and windage losses are, you can measure no load current at, say, 6V and at 10V. The difference (usually very small) will be the contribution of bearing and windage losses. |
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This is the same reason why high electrical resistance is a good thing -- the eddy currents that do form will be lower in power if the resistance of the steel is high. Silver is a better conductor than copper, but costs so much that it's not practical. And it's only a little bit (I think about 20% or so) better than copper. And it's not just the cost of the metal -- it's the processing too. There are very few manufacturers that are setup to process silver into electrical wire, and there are a few applications which demand it (some space applications.) So they command a HUGE premium. After processing, silver wire is around $2500 a pound. That would make a 1515 cost somewhere in the $600.00-$800.00 (just an estimate!!!) range. :lol: |
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Have you ever thought of making a limited run of like "ultimate motors" Like a batch of 150 1515's with silver angel hair wire, 1mm air gap, monster magnets and low drag bearings.. expensive yest. but with your PR you could market it and it would probably sell out.. ...not to mention that the motors would be absolutely INSANE! |
Since we are discussing motor designs I have a few questions...
I had 2 of the old feigao xl can motors. 2 pole and cheap!!! I had a 14xl that I ran on 8s, and a 7xl that I ran on 4s. In the same weight vehicle with the same gearing (thus load) the 14xl ran cooler. I am guessing the motors use the same materials and construction techniques. Are lower kv motors more effecient just due to design? Higher turn motors use thinner wire and more of it, is that inherently more effecient? Just wondering. The 7xl was very gearing sensitive to keep temps down to "reasonable" levels. while the 14xl did not seem to mind. Amp draw must have some bearing, as less amps means less heat. |
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#1. Lower kv - more torque to overcome the the mechanical resistence. #2. Higher Voltage - This goes back to the Watts = Amps X Voltage law. Think of it this way. It takes X number of Watts to accelerate the test vehicle. Less Amp Draw equals less heat. The 14xl was taking advantage of the higher voltage, thus the amp draw was substantially less. Probably 50% of what the 7xl was drawing to do the same amount of work. |
Theoretically no. The 14XL has necessarily THINNER windings, therefore the windings heats more than the 7XL for the same amp. The thickness is lower as the turns is bigger, or the Kv lower (same space, longer windings ==> thinner windings). So theoretically a 8S 14XL setup will produce same heat than a 4S 7XL setup.
For example, a 1515/1Y and a 1515/2Y, both 4S. The 1515/2Y will run a lot hoter in current buggy or truggy setup. The 2Y needs higher voltage (8S) to run efficiently. But therefore, the resistive losses are smaller in the ESC, but you need a 8S ESC... Higher Kv means less torque per amp (torque said alone means nothing). Maybe, when the windings are thinner (14XL) they better fulfill the motor ? Just weight your two motor and see wich one is heavier ? |
You have to remember the resistive losses come from I^2*R. True, resistance is higher in a higher turn motor because of the added turns and thinner wire, but less current makes a bigger difference because that is the squared part of the equation. So, as long as the top speed is the same (load), a higher voltage on a lower kv will result in the same amount of work and same overall power as a lower kv/voltage setup.
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Briang, you forgot that the resistance depends of the length AND the surface of the wire ;) For the same volume of matter (or same weight for both motor), a wire twice more more long have a resistance four times higher.
R = R0 * length/surface and you have to keep length*surface equal for both motor (volume or weight). So the multiplication R*IČ would be exactly the same. For example, I am sure that the 1515/2Y motor resistance is average 4 time higher than the 1515/1Y one. |
Geared for the same speed the 2 motors should "see" the same load. I just wondered why the 14xl ran cooler. I just figured the amp draw thru the motor (if there is such a thing) was around half as much with the 14xl than the 7xl, and that accounted for the addl heat created. Higher amp draw seems to produce more heat as the wires and such have to transmit it.
I may be completely wrong on this, so that is why I asked! Thanks for the replys. |
Cool thread lots of info here. Thanks a bunch.
Also, I am surprised to see so many copies, I was only aware of Leopard. Now there seem to be tons of them. |
Does the no load current increase as the volts increase?Also does the kv effect the no load current.
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The 14xl has two things keeping it cooler: 1. The more surface area allows it to cool off better, especially over time. This is why larger, more powerful ESC's require heat sinks with more surface area (typically larger or finer fins) 2. More mass requires more heat (energy loss) to get it up to the same temperature (especially in a short amount of time). Looking into specific heat, the equation is: heat added = specific heat x mass x change in temperature In this case, the specific heat should be equal for both motors (same materials), canceling out. Same heat added and greater mass = lower temperature. Edit: Sorry for awakening a dead thread, I just now saw the dates |
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BTW -- we are planning some limited edition (very high cost) motors for sale in the near future -- watch for 'em. |
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