6s Lipo on a Feigao 8xl?? help pls

Is 6s Lipo too much voltage for a Feigao 8xl motor?

I have a MGM compro 16018 on the way, as well as two 3s 4000HV lipo packs. When I was using BrainG's parameter calculator, it came up saying 22.2 volts exceeded the 40000 rpm limit of the 8xl motor, and overheating would result.

Since the unloaded kv rating is 1875kv x 22.2v = 41625 rpm.

Is that calculation correct??

Is this the unloaded kv? (Calculator says 2084kv, but the rc-monster store says 1875kv)

If it is then it's not that much over the rated rpm of the motor. Would this still produce too much heat? Will a fan help any?

But then what is the loaded kv rating?? Wouldn't it be lower? If so then the rpm's might be within the motor's rated rpm limit?

I know thats alot of questions I asked, but I'm really confused!
Any help or knowledge here would be much appreciated!!

[joeling]

Hi,

I have run the 8XL successfully with 5S 4000mah with average run time between 10 to 20 minutes geared 13/46 for buggy.

Once upon a time, I have also run a 7XL on 6S without issues on the motor again geared 13/46 (there were other issues - plastic spur melting...)

So I guess running 6S on 8Xl is probably ok but not recommended. If I'm not mistaken, the bearings of the 8XL is rated up to 50k rpm only.

Oh, I have also run 6S on 7XL in a savage successfully using a 60mm fan + heatsink on the motor but the gearing is not as high as that of a buggy's.

I hope this is of help.

[jnev]

You are lookign at this motor, right? http://www.rc-monster.com/proddetail...WAND_XL&cat=20

BrianG's calculator is right. The 9xl motor is in the 1800KV range, and the 8xl is in the 2000KV range. The data in the RCM store is just wrong and it has been like that for the as far as I can remember. Don't pay attention to the ratings. Just buy the right XL number.

[BrianG]

For the record, the kv numbers listed in Mike's store is the "loaded" value. I did not like this since who determined what the load was? So, I use unloaded kv values (wherever I can). This lets you enter in an estimated amperage and if the motor resistance is provided, makes for a more accurate "loaded" calculation based on the vehicle, not some fudge factor.

As an aside, the last letter in the motor list dropdown, L or U, denotes if the KV value listed in loaded or unloaded, respectively.

Ok, thanks for clearing that up, about the kv ratings.


So, will 6s be too much for my 8xl feigao? Around ~41625 rpm max on a 40000 rpm rated motor?

I guess I can get away with it for a while with fan on top of my rc-monster heatsink. But will it eventually take its toll on the motor?

[BrianG]

Well, expect some hot temps. The general rule of thumb is to keep those motors at or under 35k rpm. But that depends on how much top speed running you plan to do. If you hit max speed rarely, then you might be ok. If you're doing speed runs, there might be issues. If the motor gets too hot, you will demagnetize the rotor and then you'll have no power and the motor will get hot for apparently no reason. Also, I don't know how much centrifugal force the magnets will take before flying apart, not to mention the bearings.

Hmmm that doesn't sound very good at all! I will most likely be hitting max speed alot.

So my only other options really, are getting a 10xl feigao (which RCM does not currently sell), a Neu 1515 1y or 1.5d, or lowering my voltage by getting another set of lipos, to say 4s or 5s by getting some 2s packs.

Well neither way seems very cheap. And I already went ahead and order those 3s lipos from maxamps. It won't be a complete waste because I can run them in my Ruslter.

If they only sold 4000hv 1s lipos for a cheap price...... or some kind of high current, voltage reducer to place in between the batteries and the ESC..... oh well.

Thanks for the info everyone.

[lincpimp]

If you gear the setup for around 40mph, the higher motor rpms may not be an issue. I have run my 7xl on 4s, considered a "hot" motor, in an 1/8 buggy geared for 37mph and never had any issues. I had a RCM heatsink on the motor and decent ventilation, but no fans and it never beat 160f. Feigao run hot, but it never gave me an issue and the buggy is heavy with a 10000 4s pack in it. If you have everything, give it a try and keep an eye on temps during the first runs. You may have to put a 12 tooth pinion, or less on it to get the correct speed, but the motor will not work as hard, due to the gearing.

Once I get my ESC and Lipos in the mail, I will try it out for sure.

According to the Parameter Solver, a gearing of 12/51 on 6s Lipo will yield 38.9 MPH. But the warning still comes up saying it may cause overheating.

[lincpimp]

A 12/51 gearing is low, so it may help the motor out. Guys doing 10s systems are using 1400 kv motors and low gearing. Of course those are high end motors, but the same may be true for the feigao. We can all agree that an xl motor in a rustler would never get very hot, just not enough load on it. So relieving the motor with lower gearing may help the heat situation. Let us know what you find. I may try my 7xl on 5s(wow)! In a tower terror mt!!! 10lbs or less!

Ahh I gotcha now. Its like when you switch to a low gear on your bicycle you don't have to push as hard with your legs?

Do people actually buy those Tower Terrors? I know nothing about them, but they look cheap in the pictures...

[BrianG]

Yeah, because of the high motor rpm for that specific motor....

[BrianG]

I was wondering about that truck. Was a little shy about buying a "generic" R/C though. Does Tower actually make it, or is it a rebadged version of something else?

[lincpimp]

Yep, rebadged version of a european vehicle IIRC. Diffs are a little harsh, but should be fine after a little break-in. Truck is slightly smaller than an emaxx, and uses a body that would fit a crt.5, looks funny from some angles, but not bad. Diff cases and arms look very sturdy, not much else save the TVPs and wheels, truck is very simple. Ctr gear is mod 1 and it doubles as the brake disk! Has a straight shaft to the diffs from the spur, no cups or dogbones to wear out. Spur has a large square cutout that mates with a square portion of the center shaft. Radio box makes a good mount for the esc, with the lid removed. Servo is directly below it, hooks to a double belcrank steering with beefy turnbuckles. Not HB/Ofna quality, but no worse that traxxas or duratrax and alot beefier than an emaxx IMO. Only real problem is that the tires do not have foams in them. No one on the terror forum seems to care, the truck only weighs around 9lbs with fuel.

[tashpop]

i maybe new to this, but maybe i'm missing something. can the MGM compro 16018 even handle 6cells (22+volts)?