how could one determine what batteries are needed to feed a specific motor?
with that i mean; how does one know how many amps a setup will pull?
before you have it up and running?

Jolly, I'm curious about the same question. It really comes down to Watts and how much of it your car needs. Looks like a 1:8 buggy will see peaks of 2000 Watts, so 70A peaks @ 30V.

Can anyone point us to graphs of some electric setups? So far I've only found this one.

what i also wanna know is this:
lets say battery has these specs: 100A continu, 150A peak and 200A burst
but the motor wants for example 150A continu and to start he wants 250A.
what happens then to the battery?
this is about lipo or li-mn?!?

If the battery can't supply the current the motor wants, then the battery will drop its voltage, which in turn lowers the current draw. This is why you want a battery that is able to handle the motor you choose.

Well, I would hook up a set of good NiMHs of the voltage I was looking at running just to get a baseline reading. Install the eagletree, and run it like you would at worst-case conditions (lots of stops and starts and heavy acceleration). After a few minutes, you should have enough data on the logger to see what your currents are. I'd probably look for a lipo whose continuous C rating is equal or more than the peak rating on the logger. A little overkill maybe, but the voltage drop will be more stable and the packs will run cooler.

i have yet another question.
if you want to crawl or so, would your best bet be running a 90/1 reduction or so and 20k rpm or run around 15/1 and only a few 1000 rpm's?

Good question! My reasoning tells me 1000 RPM and 15:1 would be better.

wouldnt it have a huge lack of torque?

Electric motors have max torque right at 1rpm. The problem with running at slow rpms with a sensorless brushless motor is maybe a little cogging since there are less rpms for the controller to sense.

thanks.
also, what would happen if you stall a 2 pole inrunner?

Gearing down allows you to increase torque. By running the motor at a high RPM and gearing down further, you are increasing the amount of torque available at the wheels.

My vote would be 20k RPM for max torque, but 1k RPM might provide enough torque for the job and be more efficient.

Lots of cogging, lots of current (no back-EMF to impede current flow), and possibly a blown controller if it doesn't know how to deal with that condition properly.

I tend to lean towards the higher rpm choice and gear down. Very slow speeds will be smoother.

darn, dangerous huh?!?
or would a crawler be better with brushed motor?:032:

At the risk of being flamed, I would say yes. Or maybe a sensored brushless motor...

or an outrunner maybe?!?
but i know squat about outrunners, anyone got links?

I done some reading on the out runner in a crawler.
The man ran a mamba 25 esc in it with a little aevox motor.
He compared the combo to the power of a 55t lathe motor.
It was on rccrawler but not sure where.
I will be playing with different combos before long. I hope to know more.

I made my post based on the brushed motors that are more popular (55t lathe motors). With sensorless motors I agree that the higher RPM would be a better choice.

I think an Outrunner would be much better suited. Main downside of them is keeping dirt out, but in a crawler I would guess that is not a problem.

i found good ones, hyperion z30 serie.
what does this mean; 12 Statoren (CNC gefertigt) und 14 Magneten?
does it mean 12 poles?

hehehe, i'm bringing this up again.
this time, for your pleasure, with more questions.:D
let novak hv 4.5 in a monster you need to run 25/1 or so, right.
so it runs 40mph and does 70k rpm, and doesnt run to hot. ok?!?
why on earth wouldnt this work with lehner or so other high-end BL without heat problems? :032: