Very interesting Setup from Mega Motors - RC-Monster Forums

GriffinRU · **Very interesting Setup from Mega Motors -** 11.18.2006, 04:55 PM

sleebus.jones · 11.18.2006, 05:36 PM

Well, it seems to defy the laws of physics at first glance. The amp draw goes up as the battery voltage goes up...that doesn't make sense. All things being equal, higher voltage should equal less amp draw.

Also, the back-calculated Kv rating varies with voltage, another weird thing:

1. 3S = 1306Kv
2. 4S = 1250Kv
3. 5S = 1281Kv
4. 12v = 1320Kv

Something's not right, or someone's being sloppy.

Sleebus

GriffinRU · 11.18.2006, 08:52 PM

Quote:

Originally Posted by sleebus.jones

Well, it seems to defy the laws of physics at first glance. The amp draw goes up as the battery voltage goes up...that doesn't make sense. All things being equal, higher voltage should equal less amp draw.

Also, the back-calculated Kv rating varies with voltage, another weird thing:

1. 3S = 1306Kv
2. 4S = 1250Kv
3. 5S = 1281Kv
4. 12v = 1320Kv

Something's not right, or someone's being sloppy.

Sleebus

I was more intrigued with motor mount; math might work if you take efficiency into consideration and power constant.

Artur

crazyjr · 11.18.2006, 09:31 PM

that would be cool, but it would take a lot of gearing or batteries to wake it up. I'd like to see that heatsink as a bolt-in for any XL, I'd definetly go brushless if it were possible

glassdoctor · 11.18.2006, 10:06 PM

Quote:

Originally Posted by sleebus.jones

Well, it seems to defy the laws of physics at first glance. The amp draw goes up as the battery voltage goes up...that doesn't make sense. All things being equal, higher voltage should equal less amp draw.

Actually this is not true at all... their numbers are correct.

Amp draw increases with voltage. Given the same motor, etc... more voltage always means more current.

The high voltage/low amp draw thing is due to using a different motor/gearing setup with the change in voltage.

This is how a system can operate on lower amp draw and still make the same power (watts). You use a much milder amp draw motor and just feed it more volts.

BrianG · 11.18.2006, 10:21 PM

I don't know, 1300kv seems a bit low. You'd almost have to use 5s to get the RPMs out of it. I'm not really crazy about the looks either, although that is a minor consideration.

coolhandcountry · 11.18.2006, 11:07 PM

It looks like a xl motor with a weird heatsink. Should run cool though.

sleebus.jones · 11.18.2006, 11:08 PM

Quote:

Originally Posted by glassdoctor

Actually this is not true at all... their numbers are correct.

Amp draw increases with voltage. Given the same motor, etc... more voltage always means more current.

Sorry, no it doesn't. As voltage goes up less amperage is needed to do the same amount of work. That is because of this relationship here:

Amps = Watts / Volts

Say for instance, we have a 1000w motor on a 6 cell pack:

139A = 1000w / 7.2v

Now, let's upgrade that to a 10 cell pack:

83A = 1000w / 12v

See? The amps went down, not up. If the amps stay the same when the voltage went up, that would mean the motor somehow make more power...which can't happen, because the motor is unchanged.

What this vendor is asserting with their numbers is that the same motor can do more work with more voltage. That makes no sense.

Sleebus

GriffinRU · 11:21 PM

Quote:

Originally Posted by sleebus.jones

Sorry, no it doesn't. As voltage goes up less amperage is needed to do the same amount of work. That is because of this relationship here:

Amps = Watts / Volts

Say for instance, we have a 1000w motor on a 6 cell pack:

139A = 1000w / 7.2v

Now, let's upgrade that to a 10 cell pack:

83A = 1000w / 12v

See? The amps went down, not up. If the amps stay the same when the voltage went up, that would mean the motor somehow make more power...which can't happen, because the motor is unchanged.

What this vendor is asserting with their numbers is that the same motor can do more work with more voltage. That makes no sense.

Sleebus

What happen to the motor when you apply more volts?
Hint -> Power=torque*RPM
Torque and Amps are twins...

Artur

GriffinRU · 11.18.2006, 11:24 PM

Quote:

Originally Posted by coolhandcountry

It looks like a xl motor with a weird heatsink. Should run cool though.

How they fix motor inside? Is it a clamp style?
It helps in fixing motor in 2 planes, but still requires to align with differential, which is usual.

Artur

squeeforever · 11:31 PM

Alot of this is over my head, but for instance, the XL motors are all rated for around 1800 watts (I think), so if the dimensions, etc of the motor stays the same, but the wind/RPM's change, the watts is gonna be a constant. Example:

1800W / 22.2V = 81A

1800W / 14.4 = 125A

But what if the KV changed? The watts would be the same, but wouldn't the amperage change alot with the KV? Yes, it would. A higher wind XL motor (like a 9XL) on 18 cells will pull less amps than a 7XL on the same amount of cells, will it not?

Basically I see it like this. The formula you gave would work if the RPM's were a constant between each motor. That formula might work for other things without the extra variable...Now this may be wrong...But this is the way I understand it.

sleebus.jones · 11.18.2006, 11:35 PM

Squee, you've got it spot on. Motors are designed to do a specific amount of work. It's just like a horse, no matter how hard you whip it, once it's going as hard as it can, it's not going to work any harder. If you need more work done, you either need:

1. A different horse

or

2. More horses!

Yes, if the KV changes, you've changed "horses" and the draw will be different for the same work done. It's not as over your head as you think! :)

Artur: When you apply more volts, you get more RPM, up to the limit of the work the motor is able to do. It's the same analogy with the horse, you'll only get so much out of the motor, regardless of what you do.

Sleeb

squeeforever · 11.18.2006, 11:41 PM

Ok, so after reading this thread several times, it seems as though you and glassdoctor are both correct depending on the situation...

GriffinRU · 11.18.2006, 11:47 PM

Quote:

Originally Posted by sleebus.jones

Squee, you've got it spot on. Motors are designed to do a specific amount of work. It's just like a horse, no matter how hard you whip it, once it's going as hard as it can, it's not going to work any harder. If you need more work done, you either need:

1. A different horse

or

2. More horses!

Yes, if the KV changes, you've changed "horses" and the draw will be different for the same work done. It's not as over your head as you think! :)

Artur: When you apply more volts, you get more RPM, up to the limit of the work the motor is able to do. It's the same analogy with the horse, you'll only get so much out of the motor, regardless of what you do.

Sleeb

I will make it simple...

If you get light bulb rated at 12V and apply 16V you won't get more light but it will draw more amps and won't last long. Why? Because of fixed resistance. But how much light it will produce will be based on how big is the light bulb. Now apply the same to the motor...

Artur

squeeforever · 11:53 PM

Yup. And going down below that rating will decrease the light output as well as the amount of amps it uses, but this still doesn't have the extra variable like the motors (I don't think, or does it?). Please excuse me, I am kinda tired, and very confused :p.