HV-Maxx 4.5 or MM and 9xl?

[Serum]

That didn't take too long to have answered; yes, the novak motors rate their kv-values unloaded.

[suicideneil]

Originally Posted by SpEEdyBL

Try and calculate the power of ss5800 using the advertised values (.45 oz*in/amp kt, 5800 kv) and you get more output power than input power (volts x amps). I wont go into the math now, but you see my point. sorry im in a rush. Ill explain why im brought this up initally later

Please do! Im not a maths person really, but I would be very interested in seeing how much power in oz*in/amps the HV motors have compared to the Xl motors- the 7xl & 8xl in particular. Might prove very useful in calculating gear ratios- IE how much more I can gear up an XL motor, compared to a HV to make the most of the extra torque.:024:

[zeropointbug]

You might want to try contacting the manufacturer about the torque constant value You should also ask for each motor, the torque at peak power. EDIT: I guess that depends on voltage...

[SpEEdyBL]

First there are many things to consider and i wont explain all of them in this post. Ideally, if a motor were to be 100% efficient, it would put out the same amount of power (force x velocity) as power from the battery (volts x amps). As you know, more volts = proportionally more rpm and more amps = proportionally more torque. Torque is measured from a certain distance away from the pivot point so lets take our measurements 1 meter away from the center of the shaft to make it simple. Now kv values are given for all motors and torque values are not explicitly given, but you will see why it doesn't matter in a minute. First, kv must me converted in to velocity. 1 rpm = 2pi/60 radians per second = 2pi/60 meters per second 1 meter away from the center of the shaft. All you have to do now is find what torque value multiplied by that velocity will equal the volts x amps. For instance, if you had a 1000 kv motor and applied 10 volts and it drew 10 amps, power would be 100 watts, velociti (radians per second) would be 2 x 10000pi/60 ~1047 meters per second. Solve the equation 100 = 1047x and x ~ .0955 newtons of force 1 meter away from the shaft. If you do this equation again for a 2000 kv motor on the same volts and amps, you get half the torque. So, torque in newton meters per amp (nm/amp) ~ 9.55/motor kv. Once converted to oz*in/amp, kt ~ 1350/kv. This works for all brushless motors. To put this in perspective, the 8xl which has roughly 2100 kv will have more than twice the kt as the HV4.5 which has 4800 kv. That means if both motors pulled the same number of amps, the 8xl would have more than twice the torque and ideally (assuming equal voltage also) both motors would have the same power output.

[zeropointbug]

Brushless motor Kv. is irrelevant in torque constant value... you can have two motors of the same Kv. and both can worlds difference in torque constant.

It's kinda hard to follow your post though...?

[suicideneil]

Originally Posted by SpEEdyBL

To put this in perspective, the 8xl which has roughly 2100 kv will have more than twice the kt as the HV4.5 which has 4800 kv.

Thats what I wanted to know

That means if both motors pulled the same number of amps, the 8xl would have more than twice the torque and ideally (assuming equal voltage also) both motors would have the same power output.

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.

[SpEEdyBL]

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.

[Serum]

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..

[SpEEdyBL]

Originally Posted by zeropointbug

Brushless motor Kv. is irrelevant in torque constant value... you can have two motors of the same Kv. and both can worlds difference in torque constant.

It's kinda hard to follow your post though...?

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

[zeropointbug]

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.

[ClodMaxx]

Originally Posted by SpEEdyBL

Suicideneil, again HV4400 does not have 4400 kv. I still have no idea how novak came up with those numbers. I know for a fact that the HV6.5 is the exact same motor as the HV4400, but with a sintered rotor and a ribbed can...

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.

[SpEEdyBL]

Originally Posted by zeropointbug

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.

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.

[SpEEdyBL]

Originally Posted by Serum

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..

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.

[Serum]

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.

[suicideneil]

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....