Quote:
Originally Posted by johnrobholmes
I can barely imagine what kind of power a 4030 will put down. It will be interesting to see if the gearing or rollout threshold for startup will can be changed much with the extra motor size. Getting any more speed from your revo as-is takes a taller tire,hotter wind motor, or higher voltage. I really think the simplicity will help understand the limits of sensorless motor control.
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I think I am right at the threshold for startup with the 4120.
It was surprising to see that the 4130 was only generating 2.9 volts at 930 rpm. I wonder what the lower and upper limits of the EMF feedback "window" really is?
I'm sure the design of the ESC has some reasoning in it that matches most setups out there. There is a resistor in each of the 3 lines on the EMF feedback leads going to the brain board. I'm sure those are there to raise the upper limit of the EMF "window", but it also raises the lower limit that can be seen by the ESC. I wonder what would happen if those were removed? I believe they traded some "lower" to increase voltage operating range. The Quark tends to cog more on fresh fully charged 6S Lipo. I'm sure it has to do with this. Removing those would probably make for better startups, but also might lower the voltage operating range to perhaps 4S or 5S.
I have a Quark 125 Monster Pro on the way now. Once it gets here, I may try to bypass those resistors on my 80 amp ESC as a test. Do something that is reversible just to see. I need to ask Griffin about this.
Vehicle weight has alot to do with this also. The ESC blindly (no EMF feedback) sends a "kick in the pants" to the motor for startup. If vehicle weight or gearing is so great, that the motor doesn't give the vehicle enough movement to get some EFM return, the ESC is "lost" as to armature position. This is when cogging occurs.
The 4130 did startup better than the 4120, but the top speed wasn't there so I switched. This leads me to believe that kv and stator length has something to do with this.
Aaaah, look at this.
"Kv = RPM / voltage"
I spun the 4130 at 930rpm with a drill. It was feeding 2.9 volts into a volt meter on the AC scale.
930rpm/2.9volts= 320kv"
With the higher kv of 660, using this formula, the 4120 at 930rpm is only going to generate 1.4 volts.
The first EMF pulses must be VERY small and hard to see. Longer stator/magnets/winding changes that.
Hmmmm............This is where experimenting with different winding configurations could pay off.
