Direct Drive to Diff E Revo Build

[johnrobholmes]

Originally Posted by sikeston34m

Outrunner motors are different creatures with more magnets floating around.

They act no different than any other motor type. They are just permanent magnet motor and abide by the same rules as inrunners and brushed motors alike.

Even if one of us is wrong in our assumptions, it is still a great conversation! Until we get some real quantitative testing done we can't do much more than chat about it anyway.

[sikeston34m]

Yes it is a GREAT conversation. You bring things to the forefront that I haven't considered.

I would like to stick with the AXI motor because of the cooling fan that I've mounted to the rear of it. Hopefully, AXI will answer my email soon.

Even if I can just get a Delta wound 4130 that makes 700kv, it will outperform this 4120 since it's stator/magnets are 10mm longer. It will make more torque.

The Revo runs well. It's powerful and efficient. I'm happy with top speeds and even the low speed driveability. I just want some more torque with the same top speeds. Along with the extra torque will come more acceleration.

With the 4S 5000mah Lipos, RTR weight is 10lbs 3 ounces.

I think more outrunner power can be had on the 4S setup with a custom higher kv wind on the 4130 motor.

The 4130 motor would match the top speed of the 4120, possibly even more, if I had the ESC and Lipo's to put it on 8S to 10S. But even then, we are talking more weight.

I'm really considering going with the Quark 125 amp Monster Pro. I should see a performance improvement because of the increased current handling ability. It also has less resistence accross it's power board.

[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.

[sikeston34m]

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.

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.

[sikeston34m]

AXI emailed me back!

"both ways are possible to provide you with set of parts for this motor. This we make really rare but in case you have it for some special application it is possible. Or if you tell use the winding we can make for you custom made winding."

What wye wind should I get to make 700kv?

Here's what I wrote them back.

"With a Wye wind, the torque is 1.73 times greater than the Delta wind but the kv is 1.73 times lower. If we negate the kv loss with fewer turns, will the torque bonus still be there?

Excellant! How much for the custom wind 4130? How much will the kit be?"

This should be interesting!

[BL_RV0]

get a vid when shes done!

[sikeston34m]

Well the custom wind from the manufacturer is pretty much out of the picture. I can buy two regular motors for what they want for that.

I have a second 4130/20 here that I can use to experiment with different windings. But how do I get this stator off the bearing holder?

Hmmm, I wonder if I could trim the stationary endbell down to allow enough room to do the winding and make the terminations?

I was thinking about modifying a pair of needle nose pliers to aid me in this. Grind the teeth off the jaws, then wrap them with black tape. I know I can't tear the insulation on the winding wire as this will create shorts.