Thats what I wanted to know

Can that be right, since the XL motors are rated at something like 1200-1800 watts, but the HV motors are only something like 375-800watts.....:032:

EDIT: I doubt the two motors pull the same amps, but finding out how much they do pull is beyond me.

Now there are two things that determine the efficiency of the motor. 1. The resistance, and 2. amount of amps the motor pulls unloaded. Ideally, a motor spinning unloaded should pull 0 amps because it is doing no work, but in reality, motors pull current unloaded because this isn't a perfect world and motors cant be made ideally. Multiply this amp value by the volts and you get the power automatically lost as heat. This is called iron loss. Then there is resistance. Energy created as heat = resistance x amps squared. To find efficiency, subtract the (resistance x amps squared) and the iron loss from amps times volts and divide that whole thing by amps times volts. So efficiency = (IE - rI^2 - I0)/(IE) where I = amps E = volts, r = resistance and I0 = iron loss. The resistance and IO for the feigao motors are given at feigao.com. But anyhow, all that really matters in terms of how powerful a motor is, is how efficient it is, because heat is the only thing that really prevents you from gearing up. I think the HV4.5 has more resistance, but much lower iron loss than the 8xl, and that is why the HV motors run cool at smaller loads and considerably warmer or hot at higher loads, while the feigao runs warm/hot at all loads, but only gradually increases in temperature has the load is added. There are some things I may need to clear up, but those will come later.

But the statisfaction of the magnet is reached pretty soon on the hvmaxx.

It's got a tiny 12mm rotor;

You said a hvmaxx was more efficient than an XL;

but that's quite familiar on partial load with segmented/sintered magnets;

Did you take this into consideration;?

a 1000 watt setup at 93% eff. gets 70 watts of heat;
a 1500 watt setup at 95% eff. gets 75 watts of heat; while the 1500 watt setup is more efficient, though it will get more hot.

His point is simple Zero;

a motor delivers 50Ncm of torque at 2000Kv;
a motor that does 25Ncm at 4000Kv would have the same power.

Again; i used an 8XL on my 6Kg heavy savage without ANY heat issues on 16 cells, it's beyond the power a hvmaxx is ever capable of..

thats not true. the motor will more torque is pulling more amps.

I never made my point clear enough... it sounded like you were talking about Kv. determining torque constant, when Kv. is not what determines torque constant. That's all I meant.

Also, just because a motor pulls more amps, does not mean it has more torque either. There are a lot of factors your not taking into account.

he's right. i bought my hv4400 system just a month prior to novak releasing the 6.5 system. i called novak and spoke to a technician. i asked, 'would it be better to upgrade my system with a new 6.5 motor, or the new sintered rotor?'. the tekkie said that by upgrading my rotor, i essentially had a 6.5 motor - just without the ribbed endbells.

Actually that is my point. kv DOES determine kt. Kt is the torque per amp pulled, not just the torque. If two motors each pull x amps on y volts they will both have the same power if they have the same efficiency. That means kt multiplied by kv is a constant, ONE number for all brushless motors, because ultimately power = rpm x torque. So yes, for every kv value there is a kt value to get that number. The only thing that changes btw when a motor is inefficient is rpm. A motor that is 50% efficient at x amps and y volts will have 1/2 rpm as it does unloaded. Torque is uneffected by efficiency. If you disagree, I'd like to know your reasoning before you just tell me im wrong.

Maybe we should do some tests before we keep arguing. Those numbers are purely speculation. I realize that the higher power system will create more heat even if its more efficient, but where did you come up with those numbers? I think the HV motors actually have 14.5 x 45 mm rotors while the feigaos have 19 x 45 mm rotors. Thats about 1.31 times the magnetic surface area and 1.31 times the leverage, so the 8xl should have about 1.72 times the physically possible force as the novak. An 8xl on 4s spins at 31000 rpm. The novak motor only needs to spin at 31000 x 1.72 = 53000 rpm to have the same power and the novaks seem to be able to handle 50-60k+ rpm just fine. So both motors are physically capable of the same amount of power without the rpms getting too high. Motor resistance is a totally different factor, it is that that determines how many amps the motor will draw and how powerful it is, not the size of the motor. It could certainly be possible to design really small motor with a big heatsink that can spin safely at 200,000 rpm and be more powerful and more efficient than an 8xl.

Buy a hvmaxx and get an XL, and do some tests yourself.. this is starting to sound like a useless discusion at the traxxas boards about the hvmaxx.. did you even read the thread griffinru made about his 7XL?

btw; magnetic volume is ~1.75 times bigger, that and the leverage..

I thought you agreed the xl was stronger in terms of torque?

Get both setups, and test it yourself, please report back.

Intriquing. The one thing that gets me though is gearing the two systems. In 12-13lb truck (IE:mine), I need to gear the HV4400 at 30:1 using 14.4v. Any higher and the thing just gets slower and slower, and tries to pull too many amps from the batteries, hence why a cell in a pack went pop. With an 8xl however it seems you can gear much much taller, say 15-20:1, using the same 14.4v, and although the motor may get warmer, it doesnt toast your batteries or speedo (usually anyway).
Is this simply because the XL motors have more torque for the same voltage/amp draw/kv rating? Its mainly like trying to read Irish looking at the equations....

Get a new rotor for your HV. It will solve all heat and current problems.

@Serum, I think I will end up testing both systems. Are there larger than 20 tooth pinions for mod1, because that's what I would need for the 8xl to even reach 50 mph in the buggy im getting. Novak claims their HV 4.5 can do 60 mph in a 1/8 buggy and I only need a 12 tooth pinion for that. I'm probably going to go with two max amps 3000 mah 4s packs in parallel. That should be enough since it takes less than twice the power to get a 1/8 scale moving as fast as a 1/10.

While you are at it, get an eagletree datarecorder as well, they tell you exactly what your setup does.

Will the MM handle the 7xl? I may rather test against that instead since the rpm I can reach with the 8xl seems to low with the gearing options I have.

Yeah, it can handle the 7XL, no problem.

Glad we got that little discussion sorted, I was worried I might have to bitch-slap a few people for a minute. At my end, I WILL get the new sintered rotor I have decided, and some good 7 cells packs. Last night, due to the fact Im an insomniac, I ordered some 12 gauge deans wire, 5.5mm gold plugs, heatshrink tubing in red & black, and some cvd boots. Im counting on the HVMaxx esc not thermalling with 14 cells- shouldnt do, but if it does I think it was Griffinru showed how to do the internal mod for better current flow, so I miay do that too if needed. I also figured it was time to ditch the tamiya plugs, so I ordered enough 5.5mm connectors to do 3 pairs of batteries, and thus all my chargers & esc too.
In 6 weeks I breakup from work, and get 4 weeks off! Thats the beauty of working in the naval college- all the students get leave for the summer, so no students = no customers = holiday! Good luck with testing the setups Speedybl, should be interesting to see your findings.

Do you remember where that mod was showed? the sintered rotor is about 25-30 bucks, so that's not a big problem either. If it doesn't get hot because of it, it's a wise investment IMO.

I've already spun the 3.3 center shafts with a 5700 Mamba Max and 3S. The plastic 3.3 shafts are much bigger and you have to grind the frame to make them fit, but they are not nearly strong enough for brushless power. Get the metal CVD's.

What size dogbones for the stock e chassis? Do they make sizes for e-revos with the e tranny?

Stock chassis takes like a 70 mm front and back.
That is measured center of pin to center of pin.

E-revos require custom centre dogbones due to the non-stock measurements. Mike sells them, or can make them.