Direct Drive to Diff E Revo Build

[johnrobholmes]

Originally Posted by BrianG

Isn't there some kind of rule-of-thumb that states the motor has to spin a certain minimum percentage of its kv rating for the ESC to get the proper back-EMF pulses?

Patrick del Castillo told me it was 10% of the kv. With a rollout of 6.5 inches that would put this rig at a min speed of .3 mph or so, but I would at least double that figure or more to be conservative. The startup speed of the ESC is not the same as the minimum sensing speed however, so it might be trying to start the motor up much faster. Once you put the new diffs in your startup issues should go away, especially when you volt up.


Volting up right now might even help the startup, if only making it more abrupt and violent.


I really dig the build, I love how low and clean it looks. I still want to try this, but I sold my revo a while back and the emaxx isn't getting parted out yet. I have a 3032 I want to try, should be about like a 4020

[sikeston34m]

Originally Posted by johnrobholmes

Patrick del Castillo told me it was 10% of the kv. With a rollout of 6.5 inches that would put this rig at a min speed of .3 mph or so, but I would at least double that figure or more to be conservative. The startup speed of the ESC is not the same as the minimum sensing speed however, so it might be trying to start the motor up much faster. Once you put the new diffs in your startup issues should go away, especially when you volt up.


Volting up right now might even help the startup, if only making it more abrupt and violent.


I really dig the build, I love how low and clean it looks. I still want to try this, but I sold my revo a while back and the emaxx isn't getting parted out yet. I have a 3032 I want to try, should be about like a 4020

Aaaaaaaah, so there's some confirmation about what's going on here! I'm VERY sure that with lower gearing, this thing is going to be a BEAST!

The reason why I want to switch to the 4120/14 is the higher kv to work with the Quark. It will have more than enough torque to work with the lower gearing.

I'm wondering something about the new 4120 motor. It's 15mm shorter than the 4130. Is there enough room to put the mechanical brake back in there and go with a HV forward only ESC? An ESC like the Phoenix HV 110amp version might be a good choice then. The Voltage could be cranked up as high as motor temps would allow. I think that would be pretty high, since this setup gets rid of the heat well. Is there such a bracket for the brakes though? Before it was mounted on the transmission, which is obsolete with this setup.

Thanks for your compliments. The low center of gravity that this has, REALLY sticks it to the ground. It's gonna high speed corner VERY well. I know on gravel, I could turn the wheel sharp at 30+ mph and it would just go round and round like it was on ice, instead of tripping/flipping over it's front tires. LOL

I don't think I like the Revo tires very well. Will prolly be changing out to something else. The E maxx's gator tires grip really well for off road.

John, I'm sure you are looking at the Scorpion 3032, correct? I put a 3032/10 in a Direct drive to transmission setup in an E maxx. It was a great performer for the first pack.

You gotta think about how much we are pushing, jerking, and tugging on that stator with this type setup. I ripped the stator from the bearing holder. In other words, the stator spun loose and ripped the windings from the power leads.

At the factory, sometimes I think they don't loctite the stator on both ends. This appeared to be the case. Even on the AXI 4130 that is in this one. Same thing. A prop doesn't have brakes like we use constantly or the resistence of acceleration that we are asking.

I used Red Loctite between the stator and the bearing holder on the endbell side. I had to slow "bake" it at 100 degrees for about 6 hours to get it to set. Green Loctite is the Better choice. It weeps into the microscopic holes and sets quicker with no temperature increase. I would make a puddle there and it would soak in, then I would do it again. About 3 "puddles" soaked into that crack, so I think the void was completely filled.

I know you plan a custom wind, I just don't want you to learn the hard way like I did. Let me know how it works out.

[sikeston34m]

Waahhooooooo Mike is gonna build me some Hybrid Diffs!

Seems like the 4.3:1 ratio was the least in demand, so he thinks he has some gears laying around and he's gonna check on the rest.

Me thinks this project won't be held up for long.

[squeeforever]

I think the MM will work with some, but not all outrunners. If I remember correctly, Serum posted a video of his G2R with a MM and outrunner and it didn't cog whatsoever.

[sikeston34m]

You know, come to think of it, you could be onto something Brian.

JohnRobHolmes uses them with his outrunners and Rock Crawler setups. Way LOW gearing but they work for him.

Perhaps the Quark has a different "kick in the pants" startup routine. I'm not sure.

[BrianG]

The Quark definitely has a different startup routine than a MM. Actually, I made a thread about that a while back noting the differences.

[lincpimp]

Originally Posted by BrianG

The Quark definitely has a different startup routine than a MM. Actually, I made a thread about that a while back noting the differences.

Also seems like the quark, when turned all the way up, can really provide some starting power. I had mine set for the outrunner in the redcat and then moved it into my ls10 with a feigao 12l on 5s lipo and it would lift the truck completely off the ground and flip it over. And that was with smooth throttle input, no stabs! I turned it down quickly, as I could see that I would be snapping some driveline components soon!

[BrianG]

linc: The difference I noticed was with what happens if the motor doesn't get started (geared too high, too much load, etc). The MM progressively adds more and more power until it starts. While good to a degree, this could end up causing the ESC to go up in smoke if there is too much trouble getting that motor started since a motor can pull a LOT of current in its stalled state. The quark OTOH simply keeps trying to move the motor, but not with any more power than the "start power" setting. IMO, this is safer for the ESC.

ZPB: Yeah, that's why I wasn't sure if the same percentage applied to outrunners. I'm sure there is still some kind of value, just different. Makes sense that the motor would have to spin a certain speed to generate the needed EMF signals since a coil induces a voltage while in motion only.

[MetalMan]

I run a 14pole outrunner in my rock crawler on 3s Lipo using a Mamba 25. The motor's rated at 45amps continuous, and the little Mamba 25 runs it very well. Granted, the gearing is low, but I've run the truck geared for higher speeds as well. However, the Mamba 25 doesn't like that so much, and does sometimes have difficulty starting the motor. I blame that problem on the Mamba 25 being so small...

[Mod Man]

I can tell you that the HV110 has no cogging and runs phenominal with outrunners. Part of that is due to being designed for aircraft use (the brakes suck, though).

If you do not mind parting with some coin, the MGM Com Pro is the best running car ESC I have ever had. They have the best start up, are reverse capable, and run cool. But, they are super expensive and tough to get serviced if need be.

Matt

[aqwut]

I find that outrunners don't cog too often, except when using some cheapo ebay ESCs.. Seen the size of that motor, had a lot of batteries coming.. and couldn't resist picking one up.. and as for the 10mm and 12mm shaft, I now have a taig lathe.. so I can do something with it....

Sikestorm, that truck you have is just beautiful man..

what are the maximum RPMS an outrunner can take?.... about 12000rpm?

I got lost when you guys started talking about EMF pulses....

[zeropointbug]

It's more of a sine wave than a 'pulse', but while in operation, it is probably distorted somewhat... if it were running as a generator, then it would for surely be a sine wave.

[sikeston34m]

Originally Posted by aqwut

I find that outrunners don't cog too often, except when using some cheapo ebay ESCs.. Seen the size of that motor, had a lot of batteries coming.. and couldn't resist picking one up.. and as for the 10mm and 12mm shaft, I now have a taig lathe.. so I can do something with it....

Sikestorm, that truck you have is just beautiful man..

what are the maximum RPMS an outrunner can take?.... about 12000rpm?

I got lost when you guys started talking about EMF pulses....

You must be looking at Modman's truck Aqwut. I haven't shown my truck here yet. LOL

Yes, around 12,000 max. rpm's for this style outrunner. There are outrunners that are high speed though capable of 40,000rpms.

[Mod Man]

Most outrunners are capable of around 20,000 RPM. That is true for most Orbit outrunners as well as AXIs. That is due to magnetic saturation. Beyond that heat tends to build up and efficiency goes way down.

Much depends on each individual motor, though.

EMF is "Electro-magnetic-fequency". Back EMF is the back pulse the motor creates as it rotates. A motor requires voltage to run, but it also creates voltage as it spins. This voltage is read by the ESC to give a rough calculation of the motor's RPM thus eliminating the need for position sensing. Software is EXTREMELY important in eliminating cogging as is high torque capability of the motor. High voltage normally reduces cogging as well.

Matt

[sikeston34m]

Hey Modman Was that the AXI 4120/18 that you were running?

It's the only one that I see with a 515kv rating.