Voltage and current question
 

Only if you gear down...

If you do go up in voltage, does the amperage increase? (keeping the same gearing)

Yes.

If you gear so that the motor produces the same output (wattage) on both 4 and 6 cells you should produce the same top speed. The higher voltage setup will be more effecient, due to the higher voltage drawing less current (amps) to produce the same output (volts x amps = watts), in turn the lower draw produces less heat in the wires, motors, esc, etc. Small gain but still there, plus stuff runs cooler, so it should last longer too...

There's one simple law that explains it all: Ohm's Law, which states that V=IR (voltage = current x resistance). If you don't change the gearing, then R (resistance) remains the same. So by Ohm's Law, current will increase proportionally with voltage. This doesn't always hold true, however, because you could change your driving style.

Changing the gearing has no effect on the electrical resistance.



If you go up from 4s to 6s, your motor will draw less current if the total motor rpm is the same, for example a 3000kv motor on 4s (= 44400rpm) is drawing more amps than a 2000kv motor on 6s (also 44400rpm).

Right, changing the gearing affects the mechanical resistance. But since a motor converts electrical energy into mechanical energy that mechanical resistance is a factor here.

We're talking about increasing the voltage on the same motor, and its effects.

Oh no, here we go again! Griffin and I had this discussion a while back.

The vast majority of a motor's "resistance" comes from the back-EMF. A slower turning motor under heavy mechanical load reduces the BEMF, thus lowering the "resistance" and increasing current flow. By reducing the gearing, you are allowing the motor to spin faster doing less work for each rev. Since the motor is spinning faster with less load, more BEMF is generated, thus increasing resistance and lowering the current.

I remember it well; talk about clash of the titans... :whistle:

And even though it looked like we disagreed, we were actually saying the same basic thing; it was the terminology that was getting in the way. :smile:

I'm actually loving my 8S 60A or so spikes truggy set up now :lol:. I still haven't charged my 2 4S packs and tomorrow I'm going to run some more testing my 6 pole 36 x 60 1300Kv motor. This will be good to see if a smaller motor does actually need more AMPs to get the truggy moving then a larger motor.

Thanks for all the info guys. I am an electrician so I am familiar with ohms law which makes this hobby a little easier, but very new to brushless and did not know if you could use the same theorys with the esc and brushless motor.

There seems to be many people here with some incredible knowledge and can always count on an intelligent answer!!! Thanks again. I will post pics when I am done.

Are their any good reference sites I could visit????

Depends what you want to reference exactly- BrianG's website is great for electrical setup and gearing info (in his sig), and I have a nice FAQ in my sig, though its aimed more at the noobs on the traxxas forum- still some good links in there however.

Been to your site....AWESOME!!!!!!!!!!!!!!!!!!