Lowering BL Revo CoG.

[suicideneil]

I dunno if an outrunner for racing would be ideal- the spool up time is much slower compared to an inrunner I believe, so that would mean poor acceleration down the straights and out of corners, just when you need it most. I might be lying though...

[zeropointbug]

Hmmm, all I need is 4 digital scales now... ... I have one legal for trade 10lb unit, which I just weight the components and place them on the chassis and hold the truck in the center of the skidplates and see if it holds level. I do it by eye as well. There has got to be more to weight distribution than just static balance me thinks... a sort of 'dynamic' balance, where even though it is balanced for weight, components might be all wonky all over the place that it causes certain 'inertial' effects when in action, thus not being 'truly' balanced.


Neil, true, that might be a valid point... it might be unbearable going from a fast spooling 1512 to a high inertia outrunner. Although, I don't think it would affect it in the straight, I would think more in the tight technical parts where you need quick power to the wheels for mere milliseconds.

Sike! Calling Sike on this one!

If I could get an outrunner to work well in the Revo for racing, and lowering the batteries... I am pretty sure I could beat all the truggy drivers except two at our track.

[sikeston34m]

Hi Guys,

Always glad to lend a hand when I can.

Here's some reference material. http://www.rc-monster.com/forum/show...ect+drive+diff

Am I still using the outrunner in my truck? No, but I still have all the parts here.

I ran into two problems with the direct drive to diff setup:

#1. 4.6:1 final diff drive ratio gears would NOT hold up to the torque being made. The diffs use ball bearings not thrust bearings on the pinion gear. I could trash the pinion bearings in less than one packs runtime. Yes, they were shimmed properly. It would always punch the center race right through the outer race. Little balls everywhere. LOL

#2. In an effort to get the kind of speed/power I wanted, a custom wound outrunner was created. An AXI 4130 was made into a 4 turn motor. Hot Thing! but would pull HUGE amp spikes on startup.

It still wasn't too shabby:

http://www.youtube.com/watch?v=dFDrYXLkcGg

Check out the video, then ask yourself if this has "spool up" problems.

Spool up time is required or negated by final drive ratio. It all depends on how much torque the motor makes. High Revving motors use very low gearing to make up for their lack of torque. The same applies in reverse for outrunners.

How do you plan on gearing your setup Seth? And what voltage do you plan on running?

[sikeston34m]

Thanks for the PM Seth. Please feel free to include me on ANY discussions of this sort. I LOVE it. LOL

[sikeston34m]

More Reference Material:

http://www.rc-monster.com/forum/show...light=axi+maxx

Check out the setup and the vids in this thread.

Such Torque from such a small outrunner.

[zeropointbug]

beauty, thanks for posting Sike.

I would run 6s, so the 330 Kv. of the scorpion motor would equate to 45mph, not too much faster than the 40mph it's geared for at my track, which is perfect. (we have a long straight section)

If they have a 300Kv., that would be ideal, but they have a big gap in their Kv's to choose from.

I was also thinking about a truggy center diff, but the Revo diffs are too high of a ratio to be used with one, you would need hybrid diffs.

Q1: What diffs were you using to blow the bearings? And how would an inrunner/trans setup be any different in that respect?

Q2: Simply, what do you think of the motor in question? Think it will be suitable?

If this did work, then the handling on the truck would be in short, sick. I would be able to keep up with truggies no problem, as I can keep up to most of them even with the high CG as it is now.

[sikeston34m]

Originally Posted by zeropointbug

beauty, thanks for posting Sike.

I would run 6s, so the 330 Kv. of the scorpion motor would equate to 45mph, not too much faster than the 40mph it's geared for at my track, which is perfect. (we have a long straight section)

If they have a 300Kv., that would be ideal, but they have a big gap in their Kv's to choose from.

I was also thinking about a truggy center diff, but the Revo diffs are too high of a ratio to be used with one, you would need hybrid diffs.

Q1: What diffs were you using to blow the bearings? And how would an inrunner/trans setup be any different in that respect?

Q2: Simply, what do you think of the motor in question? Think it will be suitable?

If this did work, then the handling on the truck would be in short, sick. I would be able to keep up with truggies no problem, as I can keep up to most of them even with the high CG as it is now.

Q1. I was using the RCM v2 Hybrid Diffs. Difference = Direct Drive. No Slipper. Diff Torture Chamber!

Q2. Scorpion Motors are well built, but they have little or no fan. This makes it harder for them to shed their heat, especially in a rolling application. Flyboys mount them behind the biggest fan possible, so it works well.

Any Motor makes heat especially when pushed. If your mount and frame are aluminum, you might have enough mass to shed heat.

This is why I went with AXI. They do sell a fan that mounts to it's rotating endbell. It moves alot of air too.

I've been tempted to go with Mike's Slipperential. Put that together with regular straight cut gears in the diffs. An Outrunner geared properly would work very well.

For gearing, think outside the box somewhat. Go by the gearing calculator and even then, the outrunner has the torque to pull higher gearing than it suggests.

[zeropointbug]

You are blowing diffs without a slipper? I have my slipper tightened all the way down and I have not had any problems yet. Just have to let off throttle at the right time I guess? It took me 2 years to blow a diff with slipper tightened 100%.

-Have you ran a scorpion motor in the direct outrunner project? If so, which one?

I am sure the outrunner will get enough cooling to keep it within the safe temp range... I don't really care about temps at this point, I just want to test the waters and see if I like the concept, as I always have wanted to do this, but am reluctant in the end.

One thing I don't get is the power rating, 2400watts cont. for a 440g motor? Come on, doesn't a 1515 weight almost that, and it has a 1500watt rating. Unless it's typo, or it's the max watts rating, I highly doubt it.

So the motor/trans that is in the truck now is 470g, I would save a small 30g, but the CG would be very low.

If I can find a way to lower the trans (G1 single speed) and make a seperate motor mount to lower the motor, then I would obviously keep using the Neu. But the outrunner just seems alot easier to accomplish this.

It's times like these when you just hate the setup of the Revo with the shocks taking up over half the room.

[sikeston34m]

[COLOR=[/B][/COLOR]

Originally Posted by zeropointbug

You are blowing diffs without a slipper? I have my slipper tightened all the way down and I have not had any problems yet. Just have to let off throttle at the right time I guess? It took me 2 years to blow a diff with slipper tightened 100%.

We're talking some explosive High Geared Torque coming from an Outrunner here. So Yes, the lack of a slipper is partially to blame for the problems. If there were a slipper, it could have been utilized with the setup. Inrunners don't have this type of Torque Period.

-Have you ran a scorpion motor in the direct outrunner project? If so, which one?
No I haven't. When you choose your Outrunner, whichever one it is, seep some additional RED or GREEN Loctite in between the Stator and the Bearing Holder. This is a weak spot if you run it as is. They don't put enough.

I am sure the outrunner will get enough cooling to keep it within the safe temp range... I don't really care about temps at this point, I just want to test the waters and see if I like the concept, as I always have wanted to do this, but am reluctant in the end.

One thing I don't get is the power rating, 2400watts cont. for a 440g motor? Come on, doesn't a 1515 weight almost that, and it has a 1500watt rating. Unless it's typo, or it's the max watts rating, I highly doubt it.

There's a difference in the "flyboy" rating and our Land Vehicles. The Most Major one is airflow. The ability to shed heat is one thing that affects ratings alot.

So the motor/trans that is in the truck now is 470g, I would save a small 30g, but the CG would be very low.

If I can find a way to lower the trans (G1 single speed) and make a seperate motor mount to lower the motor, then I would obviously keep using the Neu. But the outrunner just seems alot easier to accomplish this.

It's times like these when you just hate the setup of the Revo with the shocks taking up over half the room.

Yes, the Revo is VERY cramped.

It's alot to think about isn't it?

[zeropointbug]

We're talking some explosive High Geared Torque coming from an Outrunner here. So Yes, the lack of a slipper is partially to blame for the problems. If there were a slipper, it could have been utilized with the setup. Inrunners don't have this type of Torque Period.

-IMO, I don't think that would matter would it? I mean if it's an inrunner of equal power is geared for the same speed, then the torque to the diffs would be the same, as all brushless motors have to the same torque curve (straight line)... and yah, it's too bad that any type of slipper can't be used with a setup like this.

There's a difference in the "flyboy" rating and our Land Vehicles. The Most Major one is airflow. The ability to shed heat is one thing that affects ratings alot.

-Completely agree with you on this one, cooling is basically the limitation to the continuous wattage rating (to a point), the better the cooling the closer the continuous rating will be to the peak rating. But still, that said, 2400watts for 440g is huge, so maybe the rating is taking into account that the components they use can handle high temperatures? However, that does not mean the efficiency would be very good at that output, if anything below average, maybe 85% or lower, whereas a Neu, IIRC, is roughly almost 90% efficient at it's rated output.


Another thought... I was just moving stuff around on the truck and was tilting the transmission 45 degrees one way and putting the motor centered in the chassis. Now if only I could make it work that way without heavily modifying the chassis to make room for it. If it could be done, then the motor would be centered, trans tilted to the left with steering servo on left as well, with Rx/rx batt on right side, and then twin packs on each side, should be 99% balanced then. Still thinkin on the ideas though.

[sikeston34m]

Originally Posted by zeropointbug

-IMO, I don't think that would matter would it? I mean if it's an inrunner of equal power is geared for the same speed, then the torque to the diffs would be the same, as all brushless motors have to the same torque curve (straight line)... and yah, it's too bad that any type of slipper can't be used with a setup like this.

I think there are some major differences between outrunners and inrunners in how they make power. The Gap between the two used to be large when I first got into discussions about this. Those were the days of the two pole inrunners.

The Gap has been closed somewhat with the rising popularity of 4 pole inrunners. (I LOVE 4 pole motors btw)

Ok, Let me explain my thoughts as best I can, this way.

What makes power in an electric motor? Any motor?

It is the repelling/attracting forces of the magnetism. Correct?

How much power we can make depends on the strength of the attracting or opposing magnetism. Correct?

So in the Engineering World for Motors, one would think the bigger/stronger the magnets AND the stronger the electromagnetic field is, then the more overall power is going to be produced.

Bigger is More!? Well yeah. But we only have so much space to work with, right?

This is where I feel the outrunner shines.

Measure the stator on an outrunner. I believe an inrunner would be required to have a rotor almost this big to make the same amount of torque simply because of the obvious leverage advantage.

Now, consider the total mass of the magnets spinning inside the outrunner's can. Think about how large an inrunner's rotor would have to be to contain the same magnet mass.

Then let's add up the poles. A 12 pole motor shaft shifts 30 degrees for every commutation from the ESC. This is where the lower kv comes in, BUT there's a torque multiplier at work here too.

How many degrees does the shaft shift on a 4 pole motor? To be honest, I would have to look it up, but it's alot more.

Long Story Short, the outrunner makes its power at a much lower rpm, but it's still all there. Condensed Power at a much lower rpm. This is what I was calling "Explosive".

Where as, the inrunner makes it's power through it's ramp up (spool up) time, and much higher rpm.

Another thought... I was just moving stuff around on the truck and was tilting the transmission 45 degrees one way and putting the motor centered in the chassis. Now if only I could make it work that way without heavily modifying the chassis to make room for it. If it could be done, then the motor would be centered, trans tilted to the left with steering servo on left as well, with Rx/rx batt on right side, and then twin packs on each side, should be 99% balanced then. Still thinkin on the ideas though.

I think what you're doing is great. Please share more and take some pictures.

[zeropointbug]

Well, I don't know what you think 'kind' of power an outrunner has, all I know is that an electric motor has watts, and the wattage is a product of speed vs. torque, and every motor has 100% torque at zero rpm and drops from 0rpm to max rpm. I really don't think there is anything different in an outrunner, except for motor inertia (although it's spinning alot slower, so that is near canceled out), it has many times more torque, but spins many times slower, so power ends up being the same as well.

Unless I didn't get the idea you were trying to convey? Explain in more detail?


On a side note, I posted some pics of roughly what I was thinking of when I said tilting the trans and making a mount for the motor in the center of the chassis, and lowering it. Check it out. Looks like a pretty balanced setup?

[zeropointbug]

The batteries would be mounted on CF angle mounts and will be sitting 1 inch lower than in the picture.

[sikeston34m]

Originally Posted by zeropointbug

Well, I don't know what you think 'kind' of power an outrunner has, all I know is that an electric motor has watts, and the wattage is a product of speed vs. torque, and every motor has 100% torque at zero rpm and drops from 0rpm to max rpm. I really don't think there is anything different in an outrunner, except for motor inertia (although it's spinning alot slower, so that is near canceled out), it has many times more torque, but spins many times slower, so power ends up being the same as well.

Unless I didn't get the idea you were trying to convey? Explain in more detail?


On a side note, I posted some pics of roughly what I was thinking of when I said tilting the trans and making a mount for the motor in the center of the chassis, and lowering it. Check it out. Looks like a pretty balanced setup?

yep, Watts is Watts but could there be something more? LOL

KV versus gearing versus final efficiency rating. I get that.

That's an interesting way to look at tranny position. I like that, but how are you going to secure it?

This should be good.

[zeropointbug]

Isn't there a website that is going to be doing dyno tests for popular motors in R/C? That would put this debate to rest I think, just to see a torque/power curve of some of these motors. Another thought, maybe it's the ESC firmware that is causing a different 'feel' or level of power between a in and outrunner type?

As for the mounting of the transmision, I was thinking about getting a small bracket made that screws into the aluminum plate on the trans and goes around and mounts like the regular plastic stand-offs. I would have to grind the plastic mounts away of course.