torque voltage correlation

HI
I have a 2200kv brushless motor and use it with 3s lipo. When I increase the input voltage, motor speed (rpm) will increase too. But how about the torque will it increase or decrease at higher voltage? how? why?

[BrianG]

If all else is the same, increasing voltage will also increase current. And since motor torque is a function of kv and current, that will go up too. You could also increase torque at the axles simply by gearing down, but obviously speed will do down.

Are you sure that increasing voltage increase the current too? my motor is 36-60-2200 medusa. will 3s 5000mah lipo last longer than a 6s 5000mah lipo?

[BrianG]

Think of a motor like a resistor. As you increase voltage, current goes up. Of course, a motor is not a simple resistor because it's resistance changes with frequency, load, etc. But the analogy works for this.

Now, if you gear down a 6s setup to have a similar speed as 3s, then current will be reduced because gearing down reduces the load on the motor (effectively increasing the resistance).

Also, you might find yourself applying less throttle on 6s than on 3s, so that may help too.

Thanks for your bare explanations. At last I want to ask something else.
I'm at the overgearing limit of the motor (because of heat) on 3s. I want a little more top end but not more torque. My Truck is a little bit overpowered and more torque can damage my tranny. Is there any other solution for me aside from getting a higher Kv motor?

[snellemin]

If voltage increases than motor current consumption decreases, when gearing stays the same. With a decrease of current, there is less motor torque. But you won't see the difference driving around as motor horsepower has increased a bit. If want the same amount of torque at the wheels while keeping the increase in horsepower, you need to drop a couple teeth on your pinion. Your car will be snappier of the line and have about the same topspeed.

Why not just loosen up the clutch to reduce stress on your drivetrain?

Originally Posted by snellemin

If voltage increases than motor current consumption decreases, when gearing stays the same. With a decrease of current, there is less motor torque. But you won't see the difference driving around as motor horsepower has increased a bit. If want the same amount of torque at the wheels while keeping the increase in horsepower, you need to drop a couple teeth on your pinion. Your car will be snappier of the line and have about the same topspeed.

Why not just loosen up the clutch to reduce stress on your drivetrain?

You and brian-G saying opposite things. Can one of you provide a datasheet of a motor company or someting like that to prove his argument? That will be a more concrete data

[snellemin]

You can play around with numbers with BrianG speed calculator and see what I'm talking about. Play with the voltage and current values.

on the link if you increase voltage, current increase too
http://scriptasylum.com/rc_speed/_bl_comparison.html
But on that link on the same website it's opposite
http://scriptasylum.com/rc_speed/_power.html

Here are some graphix from neumotors but I din't understand them:( Maybe it helps you o explain your argument
http://www.neumotors.com/Site/Dyno_data.html

[BrianG]

Originally Posted by snellemin

If voltage increases than motor current consumption decreases, when gearing stays the same...

Yeah, I'm a little confused on this as well. Was that a typo?

If voltage increases on the same gearing, current goes up. The higher voltage will cause the motor to try to reach a higher rpm faster, and so current will go up.

If voltage increase with reduced gearing, current can remain the same, but that depends on how much gearing changes.

BrianG on that link http://scriptasylum.com/rc_speed/_power.html if you fill in the blanks for example 11.1V, 5000mah, 20minute and calculate the current and power. Under the results of the calculation stays mah values for higher voltage for the same run time and this mah values are lower on higher voltage. That means on higher voltage current will decrase.
Which is wrong? you or you calculator

[BrianG]

lol, there is a note at the very bottom that says speed (ie: gearing) and weight do not change. So, if you apply higher voltage to the same kv motor, and keep the same speed, the gearing has to change.

OK. Now at last I get it:)
Thanks a lot for your interest BrianG you have been very helpfull

[J57ltr]

As voltage and current are proportional to one and other. I think what Snellemin was saying was that through a run that as you start out that the current is going to be high and voltage will drop. As rpm increases the amount of time that the motor is Pulesd starts to decrease because of he lower and lower the ESC has time it has to comutate the windings, thus the Impedance (think variable resistance) goes up and the and the motor draws less current, as an effect the voltage starts to raise so at higher rpms the motor has less torque. Just about every DC motor makes maximum torque at 0rpm and as the rpms increase the motor has less torque. But I think that's what he was saying.

Jeff