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Thread: Rotor KV on a TP

  1. #1
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    Default Rotor KV on a TP

    Is there a certain KV rotor say on there 40x110 mm motor ,, for a 2080-2200?1700?etc ,, thanks


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    I don't quite understand your question "KV rotor"

    The rotors are exactly the same for all the 40mm diameter motors, except for the length of the different sizes, ei 40 50 60 70. And BTW that number is the actual length of the rotor magnets.

    What determines the different KVs is how many times the wire goes through the slots, making a loop/turn (coil) in the stator.

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    Quote Originally Posted by donhuff View Post
    I don't quite understand your question "KV rotor"

    The rotors are exactly the same for all the 40mm diameter motors, except for the length of the different sizes, ei 40 50 60 70. And BTW that number is the actual length of the rotor magnets.

    What determines the different KVs is how many times the wire goes through the slots, making a loop/turn (coil) in the stator.
    Hi Don I think you answered me by telling me the rotors are all the same KV on the 40MM motors as long as so is the lengths thank you !

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    ??? your reply still makes me think you don't understand it just right.

    The rotor has nothing to do with kv. the number of turns, of the wire, going through the stator, is the only thing that determines the kv.

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    Quote Originally Posted by donhuff View Post
    ??? your reply still makes me think you don't understand it just right.

    The rotor has nothing to do with kv. the number of turns, of the wire, going through the stator, is the only thing that determines the kv.
    I understand, the KV is determined by the winding,,,,, not the rotor Don thank you

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    Woow, very interesting ..... LOL

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    I wasn't trying to be a smarty pants. It's just that your wording sez "the rotors are all the same KV on the 40MM motors".

    The rotor CAN have an effect on the kv of a motor. But it is a big job to alter the rotor . A smaller rotor will raise the kv, IF, the stators rotor hole stays the same. A larger rotor will lower the kv. A tighter air gap between stator/rotor will lower kv, AND increase torque a lot, a whole lot! Stronger magnets will lower kv and increase torque, and so weaker ones will raise kv.

    And that last one is a scenario that all of us have experienced, but most of us didn't know what was happening. When neodiddyum magnets (that's what I call them) get hot, they lose some of their strength. This raises the kv of your now hot motor. It probably got hot in the first place because let's say you were using a prop one size to big for the power of the motor at the rpm it is turning (KV). So NOW, with the hot magnets your KV increases, and within a second your prop is 2 sizes to big! Heat is starting to build rapidly at this point. Give it a few more seconds and your 3 sizes to big!!! It doesn't take but a very few seconds running like this and you will reach the temp where the wire insulation breaks down and wires short out.

    I bet that this is one of the reasons that NEU motors use samarium cobalt magnets. Even tho they are a little weaker than Neo magnets, they do not lose but very little strength when they get hot. But NEU makes up for the lower strength by using BIG honking magnet in all their motors.

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    Hey Don,

    I don't think Neu use SmCo magnets unless they recently changed magnets. Based on the Gauss measurements I have taken on 15 and 22 series rotors, they are beyond the magnetic field strength of SmCo magnets even the best ones I test regularly. They might be using a lower grade N42 or N45 magnet instead of N52 which is pretty common. As you point out heat has a lot to due with performance and it is why it's so important to keep the motor temps (both stator and rotor) are reasonably levels under 200DegF or 90DegC. This chart below the different grades or Neo and SmCo magnets versus their performance at temperature.

    NeoEnvelope.jpg
    Tyler Garrard
    NAMBA 639/IMPBA 20525
    T-Hydro @ 142.94mph former WR

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    Quote Originally Posted by donhuff View Post
    When neodiddyum magnets
    Please tell me I'm not the only one reading that in Bill Murrays voice. Neeeeo ditty diddydum diddy doo. RrrrrAZZZLE DAZZZLE!

    We don't always get rain at the Michigan Cup race been when we do.....we make Don dance in it. There may well be singing this time.
    Noisy person

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    You would know better than I do Tyler. I thought that they were the cobalts, based on the way they look. They sure do not look like all the other neos that I have seen. Square corners and black coating, not the nickel coating like most neos.

    I read up on the neos that most manufacturers use, and seems like the normal was N38s. Reason for doing so was that the 52s while the strongest, they lost power with heat quicker than the lower powered ones do. And the 38s were about the best comproise.

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    ??????? did I dance in the rain? It must have been after Miller time had started!

    Yeah, you don't want to hear me sing. That's not pretty.

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    Nothing beats showing some examples and differences so here we go. For each rotor I find the strongest north or south pole and hold the Gauss meter for the pic. The meter will also show the peak and measured value. First rotor is a Neu 1521, it shows 3624G

    Neu 1521 rotor.jpg

    Next rotor is a Aquacraft 2030 6-pole rotor. It measured an impressive 4441G max

    AQ 6-pole rotor.jpg

    Next rotor is a Lehner 2240. It measured 5228G max.

    Lehner 2240.jpg

    Next rotor is a Lehner 2280. It measured 4215G Max.

    Lehner 2280.jpg
    Attached Images Attached Images
    Tyler Garrard
    NAMBA 639/IMPBA 20525
    T-Hydro @ 142.94mph former WR

  13. #13
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    Biggest rotor I have is a Lehner 3080. It measured 5614G max.

    Lehner 3080.jpg

    The last rotor is a special Titanium sleeved 2-pole rotor designed to run up to 150,000RPM. This has a SmCo Grade 28 magnet. It measures quite a bit lower around 2200G. Using the latest Grade 35 SmCo magnets you can measure around 3000G through a thick containment sleeve.

    Ti Rotor.jpg

    This particular rotor will produce about 12kW continuously above 120kRPM and operating at 180DegC. Very HOT!

    So it's plausible that Neu are using very high grade SmCo magnets but I suspect they are using lower grade Neo magnet's.

    The coating on the magnets is typical for rust prevention and in some high end assemblies to reduce the eddy current losses on the skin. Nickel is very popular, but there are quite a few types of coatings.

    -Tyler
    Tyler Garrard
    NAMBA 639/IMPBA 20525
    T-Hydro @ 142.94mph former WR

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    So, it looks like "size matters" (pun intended) or actually mass, on the gauss readings? Since the biggest rotor, and I assume the largest magnets too, has the largest reading on the scale. And with that, I guess to get truly accurate readings for an honest comparison you'd have to have all the magnets the same size.

    And one thing for sure on the Neu magnets, they are thick. About 2 to 2.5 times thicker than a typical TP or Leopard or most any China motor.

    One thing I have noticed when test a motor after rewinding it is that the kv will creep up as the motor warms up. And if I hold one until the point where I can no longer stand the pain of the heat. The kv will have gone up maybe 50 to 100 rpm. Then yesterday I rewound a Neu motor and test ran it and held on to it, because of this thread, until to hot to hold again. And the kv never varied more than 5 or 15 rpm, and actually went down instead of up! There is something different inside of the Neu motors.

    12kw (16HP)... 120,000 rpm... 356*F sounds like an electric turbo motor. And that rotor doesn't look to be all that big.

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    Size and shape definitely matter. All of the Lehner inrunners use segmented disc magnets that are bonded in the unmagnetized state, ground, balanced and lastly magnetized. All of the 4-pole and higher pole count motors use pre-magnetized segments that are bonded in place. That's one of the big differences between most of the 2-pole rotors and 4+ pole motors. The two poles are assembled unmagnetized and often use a disc or tubular magnet with thick cross-section. The 2-poles often will not have any "iron" or steel underneath the magnet, they are simply bonded to the shaft or a thin spindle. The 4+ pole motors use a steel core to which the magnets are bonded to. This helps route the magnetic flux through the core of the shaft. 2 pole rotors are fairly straight forward to magnetize. They are put in a fixture surrounded by a large copper coil and "zapped" with a lot of energy from a stored capacitor bank which produces a very strong magnetic field in one direction. The processes can be repeated in till the magnet reaches saturation. Magnetizing a 4+ pole motor is very difficult in the assembled state as it requires a much more complicated coil assembly. So typical process is to magnetize the tiles in a batch all with the same orientation and then assemble the tiles onto the rotor core. The magnetic field produced by a singe tile in a 4+ pole motor is very unidirectional. i.e. the field lines all point in the same direction. If you mapped the field strength by rotating the rotor one turn you would see a nice sinus curve with a 2-pole. A 4+ pole rotor would generate a field diagram closer to a square wave with rounded corners.

    Have a look at the field strength of the AQ motor, those have very powerful magnetic tiles and pretty thin. The cross-section of the magnet does help as does a good yoke underneath the magnets.

    And yes, that Ti rotor is from an eTurbo. The rotor is not that big maybe 28mm x 50mm so similar to a 1521, but you have to remember power=torque x speed. So triple the speed for the same torque and you get quite a bit more power. Obviously there are losses and a lot of heat to get rid of but that's a whole different discussion.
    Tyler Garrard
    NAMBA 639/IMPBA 20525
    T-Hydro @ 142.94mph former WR

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    I have noticed before that the AQ magnets seemed to be very strong, for their size.

    Is the eturbo used for the purpose of reducing turbo lag? And then when the thermal expansion of the exhaust gasses catches up to, or exceeds, the speed of the electric drive, the emotor turns off. If running on electric continuously, I would suspect that the alternator capable of driving 15 HP would have to be huge and would consume so much of the engines power as to make the whole thing not worth it.

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    Don, for the eTurbo it's used for boost assist to negate any lag and also used for recuperation. So instead of opening a wastegate to dump the energy, you close the wastegate and harvest it. There are also many special modes for emissions and lambda control where the ability to control the turbo speed or boost pressure comes in very handy. The motor is "on" continuously during operation but the amount positive or negative power is adjustable from -100% to +100%. The losses are very low "idling" the eTurbo so not much of a concern.
    Tyler Garrard
    NAMBA 639/IMPBA 20525
    T-Hydro @ 142.94mph former WR

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    That is a very interesting graph, thanks for posting it Tyler.

    For some reason I was assuming that neodymium magnets maintained their strength statically, then fell off a cliff when they got to a certain temperature, I would never have guessed that the strength was linear with temperature.

    I was also assuming that the fall of in magnetism was permanent, was I right in that or does it or some of it come back when it cools down?

    It is making me rethink my cooling policy, I've always tried to keep my stuff under 60 degrees, but never been too worried about temps as long as it was below that, but if a n52 magnet that has once been to 60 degrees has the same strength ad a n48 magnet that has never been over 30 degrees, I should be more concerned about running temps, and also cars and shade on hot days.
    Paul Upton-Taylor, Greased Weasel Racing.

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    Paul,

    I believe what you are talking about is the Curie temp of the magnet. This is the point where non-reversible damage occurs. If we operate below the Curie temp the magnet will come back to its original strength when the temperature returns to room temp. All magnets reduce their field strength with increasing temperature and this causes the KV to increase and torque per ampere to decrease. The slope of this change is more drastic for Neo vs SmCo magnet. That is to say, SmCo will produce more consistent torque over a wider range of temps. Compared to Neo which produces best torque at lower temps. So it is very important to try and keep the rotor cool.

    I try to keep mine below 100DegC and verify my measuring the coupler temperature after a run which is a good indicator.

    permanent-magnets-chart.jpg

    I did find a tech article from Novak that some of their rotors are constructed from SmCo. So perhaps Neu is using SmCo, but Neu would need to use a metallic containment sleeve instead of the Carbon or kevlar wrap they use today. The epoxy resin used to hold the filament winding in place needs to withstand the same temp as the magnet and most epoxies will start to reflow around 120DegC.

    https://images.amain.com/images/Link...al_article.pdf
    Tyler Garrard
    NAMBA 639/IMPBA 20525
    T-Hydro @ 142.94mph former WR

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    This is a killer thread fellas. Thanks for filling my head with additional data. Much appreciated.
    Noisy person

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    Ah yes curie point is what I was thinking of, but couldnt remember the name. Never knew about this temporary effect, grate info.

    It sounds like I don't have to worry about motors n hot cars, but I should try to seek out shade at events.
    Paul Upton-Taylor, Greased Weasel Racing.

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    Pre-cooling motors for trials makes more sense to me now than it did.
    Noisy person

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    Quote Originally Posted by T.S.Davis View Post
    Pre-cooling motors for trials makes more sense to me now than it did.
    Along with that statement, Should be preheating your batteries also.

    Larry
    Past NAMBA- P Mono -1 Mile Race Record holder
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    Quote Originally Posted by TRUCKPULL View Post
    Along with that statement, Should be preheating your batteries also.

    Larry
    Yeah, I got a little carried away once pre-heating. I used to do it for heat racing too but it's such a PIA.
    Noisy person

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    I use a Coolatron cooler, once warmed up it stays at about 100F all day long.
    So once that your packs a recharged, you put them in there with the rest of them,
    So when you have a heat coming up your packs are all ready to go.
    This is very good in the spring or the fall.

    Larry
    Past NAMBA- P Mono -1 Mile Race Record holder
    Past NAMBA- P Sport -1 Mile Race Record holder
    Bump & Grind Racing Props -We Like Em Smooth & Wet

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    Wonder if I could plug that right in to my power supply.
    Noisy person

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    Quote Originally Posted by T.S.Davis View Post
    Wonder if I could plug that right in to my power supply.
    12V - it's good.
    I have a 12V plug in the back of the SUV, so I can get things warmed up on the way to the pond.
    I also have a 110V adapter, so right into the jenny.

    Larry



    Larry
    Last edited by TRUCKPULL; 03-10-2022 at 06:14 AM.
    Past NAMBA- P Mono -1 Mile Race Record holder
    Past NAMBA- P Sport -1 Mile Race Record holder
    Bump & Grind Racing Props -We Like Em Smooth & Wet

  28. #28
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    That makes more sense Larry. I'm gonna git one too.

    I've done heating pads. That's not worth a crap. I also had a similar cooler/heater from Black and Decker that totally sucked. Also tried a great big roaster. hahaha Wayyyyy to hot. Even on the lowest setting. No fire but super close.
    Noisy person

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    Or you could just put the batteries in your pants. 98.6 degrees.

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    Quote Originally Posted by Shooter View Post
    Or you could just put the batteries in your pants. 98.6 degrees.
    With Larry's internal combustion it could be really dangerous !

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