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  #1  
Old 04-21-2009, 12:45 AM
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How many poles in brushless motors?

I got a few questions for you brushless motor gurus out there.

How do you tell with 100% certainty (short of taking the motor apart) how many poles a brushless motor has?

If you turn the shaft by hand, can you count how many cogs there is in one rotation and divide or multiply or whatever, to find out exactly how many poles there are?

Also, does the number of poles directly relate to the potential torque and power output of a motor. For example, with all other factors being equal, would a 2 pole motor of 4300kv have less torque than a 4 pole 4300kv, or a 6 pole 4300kv?

Also, what is the general rule of thumb when figuring out what timing to use on motors of more poles?

Thanks in advance.
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Old 04-21-2009, 02:00 PM
kufman kufman is offline
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These are pretty touch questions.

# of poles. You can try and count the number of cogs per revolution, but it will not work for air core motors (lehner, castle, feigao, etc.) I believe you will feel 6 cogs for a two pole, 12 for 4-pole and 18 for 6. I could be wrong on this.

There is a lot of debate on the number of poles vs torque question so I think i will leave that one be.

Generally, you need higher timing for more poles. This is what the Schulze manual says at least.
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Old 04-21-2009, 04:47 PM
SpEEdyBL SpEEdyBL is offline
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The biggest determination of power is motor size and motor efficiency. i.e you can only get a certain amount of torque with x amount of magnetic material and y amount of wire and the rpm can only be so high. The motor also has to be efficient so it can run long enought without overheating.

The number of poles does not affect the size of the magnet or the total amount of wire. Actually its easier to make a small 2 pole motor than a small 4 pole motor, which is why small motors are generally 2 pole. It's more practical to make big motors with more poles because you can get more phases per revolution for smoother operation and the load is better distributed spatially among the magnet/coils (you don't have all the magnetic attraction/repulsion on one side of the rotor). Same reason why most motorcycle engines are 2 cylinder and truck engines are 8 cylinder.

Last edited by SpEEdyBL; 04-21-2009 at 04:59 PM.
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Old 04-23-2009, 03:24 AM
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Thanks guys for the knowledge.

Brushless motors are confusing beyond the simple KV rating. I bought a 4300kv motor, which feels like a traditional brushed motor when turning the shaft. It cogs 6 times, each cog is very tight and a very strong magnetic feel to each cog. It doesn't feel anything like a Mamba CMS36 motor, which has 2 cogs but very vague cogs.

The funny thing is, the Mamba Max can't really drive it. It cogs like crazy at a slow speed. I was thinking maybe it's a 6 pole motor and needs high timing or something.
The same motor runs perfectly with no cogging in my cheap EZrun ESC - that is what puzzles me.

So, nobody knows exactly how many cogs you'd expect to count when turning a shaft to determine how many poles a motor is?

Thanks again.
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Old 04-24-2009, 01:02 AM
SpEEdyBL SpEEdyBL is offline
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Kufman is right on;
12 cogs = a 12 slot, 4 pole motor
6 cogs = a 3 slot, 2 pole motor

Your CMS36 motor is slotless (the coils are not wrapped around anything, just air) so the will be very little localized magnetic attraction. Therefore it is very difficult to tell how many poles it is just but spinning the shaft. If you have a good volt meter, you might be able to tell by measuring from any two motor leads and counting the number of "blips" per revolution.
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Old 04-24-2009, 02:10 AM
GSMnow GSMnow is offline
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The way the Mamba Max ESC starts the motor is not well suited to motors with a heavy iron stator. The latest firmware did help a lot, but it is never going to be perfect. The MM ESC relies on the back emf generated voltages as the rotor turns past the non energized stator winding. It the air core motors like the CM36 and Feigao etc, there is virtually no lag in this signal because the magnetif field is directly passing right over the winding wire. In a motor with an iron stator (any one you feel strong cog stops as you turn it) the rotor magnet has to actually magnetize the stator iron as it moves, and the change in magnetic field in the iron stator generates a voltage in the winding around it. Sensored ESC's don't care and work fine. Some sensorless ESC's are engineered with the motor to compensate, but will only run certain motors well. The Mamba Max is designed for very high current and accurate high rpm running so they could only tune it so far for these low and slow signal motors. The Medusa dn Neu 4 pole motors do have stators in them , but they are using very high quality magnetic laminations that transfer the rotor field very quickly to the windings so they actually run very well. I had a few stutters with the older software, but once I updated to the new version developed alnog with the monser (1.21 I think) I have not had a stutter start on my Medusa 3300 KV motor on 4S.

The CM 36 motors do have a steel band in them to help focus the magnetic field in the windings. It there is a gap in the band, I could see it having a slight magnetic cog feel in 2 spots when either of the rotor's 2 poles goes by the gap. My 5700 one does not seem to have any cog point at all though, so this is only a guess why you feel a 2 spot detent.

Check which firmware you are running, if it is lower than 1.17, certainly upgrade it. 1.17 was very good, but I still had a few false starts on the Medusa, it would pull very high current and heat up the esc fast without rolling the car. The newer version has not done this at all. Triple check all your battery and motor connections. If you are using the bannan plugs, do yourself a big favor and change them. I am now using Medusa's 5.5 mm connectors. They are overkill but they work. I fried 2 sets of the original style 4 mm ones. Castle is also selling the 5.5's like I got from Medusa, and I think the Monster uses 6.5s. Then set start power to med or high, see which works better. Set timing low to begin, it will not effect startup. Make sure you are geared reasonably. This is a 4300 you are dealing with, right? How many cells are you running? How much weight is it pushing? How fast do you expect to go? Overgearing will make startup much worse. The Mamba Max startup makes the motor turn open loop like a stepper motor until it reaches a high enough rpm to generate sufficient back EMF. Most "cogging" people complain about is whn the motor slips and drops back 2.3 of a turn or so to get back in sync with the ESC stepping before it reaches back EMF feedback speed. Lower gearing and higher start power will greatly reduce this issue.

I hope this helps, the Mamba Max is one of the best driving sensorless ESC there is. Sensored systems may be a tick smoother at low speeds, but few crank out the power like the MM can. My biggest issue racing with it is that it really is more power than my ability can control on the race track. It is super easy to just over drive the conditions. My 4S Mamba Max / <edusa setup in the 8.5 pound 1/8 scale is just about a perfect balance, of power to weight. I would say it is nearly as smooth and predictable as any sensored 1/10 I have driven. I would love to find a 1/10 motor that scaled to my 1/10 buggy to match the driving character of the 1/8 setup.
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  #7  
Old 04-24-2009, 08:57 AM
Glocked2 Glocked2 is offline
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Brushless in E-Maxx

I'm awaiting arrival of a new E-Maxx and am planning on changing to Brushless power as soon as OEM is worn out.

I do not care about increasing speed in this truck above 25mph or so (I wish to keep the handleing realistic for just low speed bashing, running on a tight tech. track by my house, no big air but some)

The reason I will change to brushless is to gain some runtime and decrease maint.

I do not plan on running lipos and will initially run 4600 MaH NiMh's (6 cell)

What is the difference on Brushless Sensored vs. Sensorless? Which will be better for this application? Pros? Cons?

Any recommendations? Castle, Novak, Trinity, Tekin, AE, or LRP, or Excelorin?

Any help much appriciated. Thanks.
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  #8  
Old 04-24-2009, 11:01 AM
kufman kufman is offline
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Quote:
Originally Posted by Glocked2 View Post
I'm awaiting arrival of a new E-Maxx and am planning on changing to Brushless power as soon as OEM is worn out.

I do not care about increasing speed in this truck above 25mph or so (I wish to keep the handleing realistic for just low speed bashing, running on a tight tech. track by my house, no big air but some)

The reason I will change to brushless is to gain some runtime and decrease maint.

I do not plan on running lipos and will initially run 4600 MaH NiMh's (6 cell)

What is the difference on Brushless Sensored vs. Sensorless? Which will be better for this application? Pros? Cons?

Any recommendations? Castle, Novak, Trinity, Tekin, AE, or LRP, or Excelorin?

Any help much appriciated. Thanks.
If you plan on doing any crawling or slow speed running with your E, you should probably look at a sensored system or a hybrid system (one that switches to sensorless after startup). Tekin's new systems, the RX8, is a hybrid system. The claim is that they have the good startup of sensored and the efficiency of sensorless.

If you have no plans for going slow, then any of the systems you have mentioned will work great. The castle systems are very popular, but be sure you are getting version 3 of the ESC if you do decided to go this route.

Novak's system is descent especially for dual battery setups. They are coming out with a new rotor that makes their motor much more efficient and cooler running. The motor is completely rebuildable so that it nice for long life.

The Losi system is getting better. The first revision of the software kind of sucked, but that has been fixed. The motor isn't really serviceable.

There isn't too much from LRP yet for larger scale cars, but there is supposed to be something comming soon.

In general, you will be looking for a motor with a Kv rating of around 2000 rpm/v for 4s/12 cell operation. Novak's closest motor at this time is the 7.5. The new rotor is supposed to make the 7.5 slower but more powerful so it may get closer to the 2000 rpm/v range. Higher rpm can be used, but the gearing must be compensated. I originally bought a 2480 rpm/v motor and it was much to fast for my E-maxx, in my opinion.

By far, the most powerful controller on the market is the Mamba Monster Max. The RX8 from Tekin should be just as good and even better because of it's ability to use sensors.
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  #9  
Old 04-24-2009, 11:15 AM
Glocked2 Glocked2 is offline
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Will those you've mentioned also be able to run 7 cell NiMh in the 4500Mah to 5000 Mah variety?

By the way, thanks.
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Old 04-24-2009, 05:40 PM
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Quote:
Originally Posted by SpEEdyBL View Post
Kufman is right on;
12 cogs = a 12 slot, 4 pole motor
6 cogs = a 3 slot, 2 pole motor

Your CMS36 motor is slotless (the coils are not wrapped around anything, just air) so the will be very little localized magnetic attraction. Therefore it is very difficult to tell how many poles it is just but spinning the shaft. If you have a good volt meter, you might be able to tell by measuring from any two motor leads and counting the number of "blips" per revolution.
That's a test I like
I just hooked it up to my multimeter, and it has 2 blips per revolution on the 4300 motor in question. This is the motor that has 6 distinct strong cogs per RPM. What exactly am I measuring when I do this test? I have the multimeter on DC voltage.
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Old 04-24-2009, 06:14 PM
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I pulled that 4300kv motor in question apart

Well, I decided curiosity killed the cat, and I just HAD to pull apart the motor.

If one of you good guys could please look at the photos and tell me what composition this motor is made up of, like how many slot, poles, and type of stator and everything, then I would forever be indebted to you.

Considering I paid $30 for this motor, I am happy enough with it's performance when paired with my EZrun ESC, but it would be nice if I could run it on the MM as well.

GSMnow, I am running the latest firmware for the MM. I hadn't tried this motor using the 1.17 firmware, so I don't know if it is any better with the latest. All I know is it goes quite poorly compared to a $35 Chinese ESC, which kinda p's me off.
I am still using the 3.5mm bullet plugs that came on it, and to hook up to the MM, I made an adaptor to convert the 4mm ones to 3.5 for this motor. It could be the adaptors, but I don't believe so. I've used those exact same adaptors on my other ESC (which is also an EZrun) to use this motor, and it worked perfectly (the adaptors). So, the only thing that seems to not perform well is the MM or the fact that it is essentially running 3.5mm plugs when coupled with adaptors.
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  #12  
Old 04-25-2009, 02:33 PM
SpEEdyBL SpEEdyBL is offline
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That right there is a 2 pole 3 slot motor, with an iron stack. When you hooked up the voltmeter to the motor, you were detecting whenever a magnetic pole passed by a given phase, hence two detections = 2 poles. It's more complicated for higher pole motors. Fore example, a 12 slot 4 pole motor, has four slots to designate a phase (there are always 3 phases in any brushless motor) and you would get a "blip" every time one of those poles passed one of those four slots. In this case it just so happens to be 4 blips per revolution since each of the magnetic poles pass by a slot in the same phase at the same time. Confusing? Basically if its not a 2 pole motor (all 2 pole slotted motors have 6 cogs), then you can safely assume its a four pole motor, since I don't think there are any motors built for r/c cars that have more than 4 poles. If it did have more than 4 poles, it would surely say so on the label.

Rules of thumb:
The # of coils = the # of slots
If the coil looks like a basket of just wire, it's slotless.
I'm not sure, but I think it goes like this: cogs per revolution = the # of slots times the # of poles divided by the greatest common multiple of the # of poles and slots. I think Neu has a 27 slot 14 pole motor. That would be 378 cogs per revolution by my math! Probably too hard to count by hand!
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Old 04-25-2009, 03:01 PM
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timie1 timie1 is offline
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WOW, thanks a lot Speedy. I really appreciate your help.

Yes, all the poles and slots and coils and cogs and blips and phases and highest common multiples are confusing

Now that we know what type of motor it is, is there any reason why the MM would have trouble on this motor, but no other motor?

And, if so, is there a way it could be remedied by changing the settings in the ESC? I had the MM hooked up and changed a few things, but none of them seemed to get rid of the cogging altogether. I just didn't want to continue experimenting in case it was killing my ESC. I really don't want to blow a cap or something.
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Old 04-25-2009, 07:03 PM
kufman kufman is offline
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On the left is a slotless lehner 4200 that runs a 2 pole rotor. On the right is a slotted Plettenburg can that runs a 4 pole rotor. Below are the two rotors.

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Old 04-25-2009, 07:27 PM
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Thanks Kufman for taking apart your motors.
I took apart a big 75mm motor I have and I can see the difference. That one is a slotless motor like your lehner. Here is the link to that motor. (Post #12 by the bottom of the page)
So it's generally considered that the MM prefers the slotless motors? Is slotless the same as air core? If the CM36 motors are air core, does that mean they are slotless as well?

Thanks again for you help. I knew there were brushless guru's out there!!
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Old 04-25-2009, 10:26 PM
kufman kufman is offline
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Originally Posted by timie1 View Post
Thanks Kufman for taking apart your motors.
I took apart a big 75mm motor I have and I can see the difference. That one is a slotless motor like your lehner. Here is the link to that motor. (Post #12 by the bottom of the page)
So it's generally considered that the MM prefers the slotless motors? Is slotless the same as air core? If the CM36 motors are air core, does that mean they are slotless as well?

Thanks again for you help. I knew there were brushless guru's out there!!
Slotless and air core are two terms for the same thing.
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Old 04-26-2009, 01:48 AM
GSMnow GSMnow is offline
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With my experience with the type of connectors on that motor, I would say they are certainly not helping matters at all. The start routine of the Mamba Max does use some very high current pulses to get the rotor to align with a pole, and this makes it very sensitive to the connections. The fact that it is also using those same wires to read the very tiny back EMF pulses at low rpm makes it even more picky about having rock solid connections to the motor. When my system was a few months old, it started coggin horribly, this was a Mamba Max ESC and a Castle CM36 5700 KV motor which was working flawlessly the day before. Everything seems fine looking it over, I even pulled and re-seated the motor banana connectors and didn't see any sign of damage, but I did note that 2 of them were much easier to unplug than the third one. I drove it for about 6 minutes, with the only issue being a cogging off of the start, once rolling it seemed fine, but when I checked over the car, I noticed the bullet (banana style) connectors were quite hot. I broke down and soldered the shell to the base of the insert for a test, and sure enough the cogging was gone. If the connectors get warm at all the connection is bad and will cause issues with the way the Mamba Max starts up. Those connectors on your motor in the pics may look fine and seem like a good design, but look closer. All of the current has to flow through those thin strips of metal that only touch the pin and barrel in tiny points. Those fingers end up getting heated from the current through them and then they lose tension making them make and even worse connection which then causes more heat.... You get the idea. Take a look at Castle CC Bullets or the Medusa 5.5 mm connectors. Those can take current. I run them on my 1/8, and will be adding them to both my 1/10 brushless setups, I already bought them, just have not soldered them on yet, I have the motors hard wired without connectors for now. If you are pretty good at soldering you may be able to tack solder the motor plugs together for a test and still be able to pull them apart later, just a blog of solder (heated so it flows on)across the base of the banana pin to the sleave of the socket. To take it apart, just heat the connector and tap it on a surface that can take flying melted solder. That got me through a few races. I replaced the banana connectors with crimp barrels on my XXX-4, but I will be changing them out to the 5.5's soon.

Did you adjust the start power to high and the timing to low like I wrote last time? Also, what are you using for batteries? This does make a difference. Onca again, the high start current demanded by the Mamba Max makes it very tough on the battery for the first few seconds of every startup.

If you have the motor out of a car or with no gear or other load on it, it may feel like it is shaking quite hard. Have you actually geared it up and driven it? The mass of the car rolling on the ground does act like a flywheel to smooth things out as it rolls off. If you pull the trigger very slow, there will be a point where the car lurches and may even kick backwards before it actually rolls. Raising the start power will help this portion quite a bit. The idea is that it will use a stronger magnetic field to align the rotor to the coils while still clocking to then next coil slowly. Lower start power settings will have less torque during the rotor finding time. This can make it smoother, but only if the motor has enough power to actually start running.
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Old 04-26-2009, 11:48 PM
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Today I had the time to put some new connectors on the motor. I put some 4mm ones on, and it made no difference at all I do not want to use anything bigger than 4mm connectors because I find they work fine, and most of my setups there isn't the room for a big massive bullet taking up such large amounts of space that the bullets require. I don't think any bigger connectors would make this motor magically work. I've come to the conclusion this issue is an incompatibility of the motor and ESC.

I really fiddled with all the start power settings, timing, punch control and so on to no avail. I'm running a 4000mah 2S 25C lipo - so it should be fine.

I just don't know. I don't think the MM will ever drive it properly. I mean, it goes fine when it's going, but getting it going is just not good. And one thing I noticed today is that it rarely would go into reverse. It goes into reverse fine with the 5700 CM36 motor, just not with this motor in question.

So, I think I'll just designate my $35 EZrun to run the motor. It goes better in EVERY respect (for this motor). Strange how a cheapo ESC is far less picky!!!!!

By the way, the car I'm running it in is a B4.
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Old 04-27-2009, 10:33 AM
GSMnow GSMnow is offline
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I agree, just run it with the ESC that works on it.
My guess here is the back EMF is just very low or noisey. The Mamba Max tries to go into closed loop (back EMF timing) at a very low rpm, and maybe that motor is just not making enough signal yet. I have messed with my Mamba Max 5700 setup that drives completely smooth, even at a crawl, and I have been able to make it do some very odd things. With no gear on the motor at all, turn the trim on the transmitter until the motor just starts to turn, then hold the shaft back to slow it down. The motor will fall out of closed loop, then the current climbs up and jerks it to turn again, but then it eases the power back down to the original low trigger position, and this repeats with the motor slowing then bucking. With the rolling mass of the car on the ground, it seems totally fine, even if I slow the car til I hear the tone change. It just ramps up current to try and keep it rolling. Making a brushless motor drive nice with no position sensors is not easy. If you can design it around a specific motor, it is much easier, but there are still compromises. Castle designed around their motors first, and then opened up the control routine to improve the performance on the ROAR style slotted motors. I will bet that EZ-Run was designed using a motor like the one you have. If it needs to be clock run like a stepper to a higher rpm, that is what they did. Without a scope on a test bench, I can't say for sure, but obviously, there is some anomoly of that motor the Castle programming does not like that the EZ-Run is programmed for. I have tried 5 different motors on my Mamba Max so far, and every one has been totally driveable, but the amount of start line buck differed slightly between them, with the worst being a higher turn stator equipped slotted 2 pole motor. The Medusa 3300 I have has a heavy stator in it, but being a 4 pole, each pole is only 2 or 3 turns, so it is like a 6600 KV turning through a 2:1 gear reduction. This makes the rpm where it goes stable, very low, it pushes my 8.5 pound 1/8 scale like it is nothing at all, even at a super slow crawl. I did have to go to high start power for it though.

As far as being less picky...This is only guessing, since I don't have one to test....
Maybe it just uses a lot of start current and stays in open loop clocking to a higher rpm. This will turn most motors without bucking, but it also is sucking far more current than a closed loop system will. This is why a brushless servo is so much more efficient than a stepper motor for robotics. For normal racing use, it should not make much difference as long is it does manage to go to closed loop at any race speed on the track, but for low speed creeping around, it could be a current pig and suck your battery much faster.
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Old 04-27-2009, 07:18 PM
SpEEdyBL SpEEdyBL is offline
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Quote:
Originally Posted by timie1 View Post
Today I had the time to put some new connectors on the motor. I put some 4mm ones on, and it made no difference at all I do not want to use anything bigger than 4mm connectors because I find they work fine, and most of my setups there isn't the room for a big massive bullet taking up such large amounts of space that the bullets require. I don't think any bigger connectors would make this motor magically work. I've come to the conclusion this issue is an incompatibility of the motor and ESC.

I really fiddled with all the start power settings, timing, punch control and so on to no avail. I'm running a 4000mah 2S 25C lipo - so it should be fine.

I just don't know. I don't think the MM will ever drive it properly. I mean, it goes fine when it's going, but getting it going is just not good. And one thing I noticed today is that it rarely would go into reverse. It goes into reverse fine with the 5700 CM36 motor, just not with this motor in question.

So, I think I'll just designate my $35 EZrun to run the motor. It goes better in EVERY respect (for this motor). Strange how a cheapo ESC is far less picky!!!!!

By the way, the car I'm running it in is a B4.
Have you ruled out radio interference? This can exagerate cogging. You should probably check to see if cogging occurs when your setup is very close to you. Before I switched to 2.4 ghz, it would talk a bit more effort to get my cars moving when they were far away. Sometimes they would start and then stop very abruptly, or reverse before ultimately moving forward.
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Old 04-29-2009, 02:37 PM
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Thanks Speedy, you bring up a good point. However, I can safely say it cogs just as much when it's 2 feet in front of me as it does when it's 100 feet away.

To tell you the truth, I've given up on it. I'm not going to spend any money trying new things for this setup. The motor goes fine on the EZrun, and the CM36 motor goes fine on the mamba. That is good enough for me!!

I've decided that I probably could use this motor on the Mamba max at a pinch - because it's only getting it going from a dead stop. Otherwise it's fine, so racing wouldn't be an issue after the start.

Thanks for your help.

At least now I know exactly what sort of motor it is
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Old 04-29-2009, 09:02 PM
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I feel no notch in my Mamba MAx motor. But at the RCX I turned the rotor of this HUGE brushless motor and I coulden't get it past the notch.
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  #23  
Old 05-04-2009, 02:33 AM
GSMnow GSMnow is offline
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The Mamba Monster motors (CM220 and CM2650) are 4 pole stator equipped motors designed by Neu but built in Castle's own factory. The rotor magnets are incredibly strong and there is virtually no air gap. This makes them pull very hard into the stall positions. They will have 12 detents per rotation, but you will likely need a gear on the motor to turn it. I have not driven one yet, but I would not be surprised if they show very strong drag braking, even with the ESC drag brake dialed to zero.
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Old 05-05-2009, 04:08 PM
SpEEdyBL SpEEdyBL is offline
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I have the CM2650 motor. Yes, it is pretty hard to turn the shaft by hand without a pinion gear, much harder than turning the shaft of a novak motor. Surprisingly though, drag break is not nearly as strong as one might expect. This is because after a certain point, it propels itself to the next position with almost as much force as when it resists. So, once you can get the shaft going its pretty easy to keep it spinning.
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