Diffrunner concept

[zeropointbug]

To bring back my old idea on the integrated-inline-differential-motor package concept (IDM?).

I am not sure who remembers this from the fall, but here is a sketch of what I mean. It would improve efficiency of the powertrain (theoretically), and would allow more space on either side of the chassis for things like batteries, while pushing everything towards the center line of the chassis, thus improving handling characteristics.

[TexasSP]

Okay, first off I like this idea I am just trying to wrap my brain around it.

It looks in my mind as though due to the shaft running through the motor it would only give you diff action in one direction as the other end of the motor (where the mounting face is in your drawing) would still be controlled directly by the motor shaft.

I guess I am trying to understand how the motor shaft would give you the diff action independently of the motor shaft without a way for the motor to spin the diff like in a center differential setup and allow the two drive shafts some independent movement.

I could very well be missing something.

[lutach]

The Outrunner part of the motor will act like a spur gear and the shaft will run inside the motor to the other side. This is basically bolting the motor to the diff case which seems to benefit outrunner style motors. When will the final unit be built? It looks very easy, but I know there will be challenges with it. I think a new diff case will have to be built for quick access in case things needs to get changed. I also think a larger bearing would be nice to support the outrunner case in place better. Things can twist and bit and jumps will put a high load on it as well.

Maybe I got it all wrong, but it was worth a try . Awesome idea to exploit the torque available in outrunners.

[BrianG]

Makes sense. The motor is tied to the diff cup itself and the shafts run through the motor without being attached to it at all.

[sikeston34m]

Yes, I remember this discussion.

I believe what the picture fails to illustrate is:

The back of the can is attached only to the diff housing. The can is attached to the shaft running through it by a bearing only. No longer a press fit with a set screw.

It would effectively spin the diff housing just like a spur gear spins a center diff.

I believe this design WILL work, but............there's always a but.

Current diff designs do not support this setup. Both in available gear ratios and toughness.

The lowest toughest gear ratio on the market currently is the 13/43 diff setup. I do know MT tires in the 5.75" size won't work with this without cogging. Perhaps a smaller tire size will.

Granted, the diff unloading to the front will cut down on some of the abuse. This then switches the game into trying to not make the diff unload.

This center diff will need the thickest grease you can find, and then some.

One other thing this setup needs, is a good HV ESC with the Mamba Car Software. Come on Castle. LOL

Some thoughts need to be spent on Motor Cooling also. A fan made into the endbell along with an Aluminum motor mount/chassis will help things greatly.

A Really Low KV Motor on 8S to 12S would be hard to beat.

[What's_nitro?]

Yep I remember this! Have you made any sort of prototype yet?

[zeropointbug]

Originally Posted by sikeston34m

Yes, I remember this discussion.

I believe what the picture fails to illustrate is:

The back of the can is attached only to the diff housing. The can is attached to the shaft running through it by a bearing only. No longer a press fit with a set screw. Yes, the shaft would basically be traveling through the hollow body of the motor with no coupling whatsoever, besides the bearing at the end.

It would effectively spin the diff housing just like a spur gear spins a center diff.

I believe this design WILL work, but............there's always a but.

Current diff designs do not support this setup. Both in available gear ratios and toughness. But wouldn't this depend on the Kv. of the motor and Volts used? I am sure the ideal unit could be found to match a good racing speed and the correct torque loading to match diffs capacity.

The lowest toughest gear ratio on the market currently is the 13/43 diff setup. I do know MT tires in the 5.75" size won't work with this without cogging. Perhaps a smaller tire size will. This is what I am wondering myself, but haven't you tried this with pretty good success?

Granted, the diff unloading to the front will cut down on some of the abuse. This then switches the game into trying to not make the diff unload.

This center diff will need the thickest grease you can find, and then some. I don't understand why very thick oil would be needed? Standard high viscosity center diff oil will work just as good as in a normal setup, no?

One other thing this setup needs, is a good HV ESC with the Mamba Car Software. Come on Castle. LOL Yeah, the verdict is still out on this one, I think the new ICE controllers might a good choice, if not, maybe the MMM will do just fine with an outrunner?

Some thoughts need to be spent on Motor Cooling also. A fan made into the endbell along with an Aluminum motor mount/chassis will help things greatly. Fins like a Neu would prob work best yeah, planar fins slicing through the air.

A Really Low KV Motor on 8S to 12S would be hard to beat.

I also like the idea of a special inrunner motor of relatively high pole count and low Kv. with a large diameter hollow shaft be used. This would take MUCH technical design as the motors output shaft needs to house the diff output, couple to the diff for power transfer, and somehow support the diff all at the same time.

[zeropointbug]

Originally Posted by What's_nitro?

Yep I remember this! Have you made any sort of prototype yet?

Nope not yet, I usually shut down completely from R/C come fall and then get re-inspired in late winter, such as now.

Luc, supporting the outrunner housing is a challenge as well, as there is alot more leverage on it that if you would just use it normally, roughly twice it would seem? Just trying to imagine the forces.

[TexasSP]

Okay, I see what I was missing. I knew their had to be more to it. I am just tired, and brain is not fully functional.

[sikeston34m]

"Current diff designs do not support this setup. Both in available gear ratios and toughness. But wouldn't this depend on the Kv. of the motor and Volts used? I am sure the ideal unit could be found to match a good racing speed and the correct torque loading to match diffs capacity."

The outrunner shines in the Torque department. Diff design is advancing. I'm impressed with the New E Revo Diffs. I have put my MT through hell and back over the past two years and I'm only on my second set. LOL

I like one members quote. "I don't use a slipper clutch, I use Tires".

We NEED drivetrain parts tough enough to transfer Explosive Torque Levels of power to the wheels. It's getting there.

"The lowest toughest gear ratio on the market currently is the 13/43 diff setup. I do know MT tires in the 5.75" size won't work with this without cogging. Perhaps a smaller tire size will. This is what I am wondering myself, but haven't you tried this with pretty good success?"

Yes, with a AXI 4130/20 305kv motor. It did work pretty well, but it did cog some on start up. It needs slightly lower gears. Top Speed was lacking. A good Castle HV Controller would take care of this.

Castle has improved startup routines. They may have practically solved this problem themselves. More testing would answer this question OR a lower kv motor and higher voltage.

The Diff will unload to the front wheels. Yep, just like over powered center diffs do now. Be prepared to stiffen things up.

The MMM works fine with outrunners but limits things to 6S operation.

[sikeston34m]

Originally Posted by zeropointbug

Nope not yet, I usually shut down completely from R/C come fall and then get re-inspired in late winter, such as now.

Luc, supporting the outrunner housing is a challenge as well, as there is alot more leverage on it that if you would just use it normally, roughly twice it would seem? Just trying to imagine the forces.

Scorpion answered this problem with their press fit endbell bearing. On the large end of the motor, by the mount.

Three bearings to support the diff/endbell. A large bearing on the mount side, one at the center to the shaft, then the last bearing would support the end of the diff.

[zeropointbug]

Understandable Texas, most people at the track didn't understand it when I drew it out for them either.

Here is the inrunner variant of the concept, obviously more work and design issues. I am still trying to come up with a good connection between hollow output shaft and diff housing. There would have to be some sort of adapter plate screw onto the diff and then that to the motor shaft. Maybe even a slipper clutch could be implemented with this setup?

[sikeston34m]

Originally Posted by zeropointbug

Understandable Texas, most people at the track didn't understand it when I drew it out for them either.

Here is the inrunner variant of the concept, obviously more work and design issues. I am still trying to come up with a good connection between hollow output shaft and diff housing. There would have to be some sort of adapter plate screw onto the diff and then that to the motor shaft. Maybe even a slipper clutch could be implemented with this setup?

This would work also, but would require even lower diff gears to multiple the available torque.

Enlarge the hollow output shaft and use a flange that bolts to the diff housing.

Here's an inrunner that impresses me and makes me curious. If it weren't so spendy, I would have one. It's "only" a 8 pole though. LOL

http://www.aero-model.com/Hacker-Hel...0mm-720mm.aspx

[zeropointbug]

Originally Posted by sikeston34m

Scorpion answered this problem with their press fit endbell bearing. On the large end of the motor, by the mount.

Three bearings to support the diff/endbell. A large bearing on the mount side, one at the center to the shaft, then the last bearing would support the end of the diff.

Oh, that sounds good. But what is the second bearing supporting? Doesn't make sense putting a bearing in the middle if it's to support the rotor? Am I missing something?

[sikeston34m]

Originally Posted by zeropointbug

Oh, that sounds good. But what is the second bearing supporting? Doesn't make sense putting a bearing in the middle if it's to support the rotor? Am I missing something?

It's to eliminate flex.

You don't want the diff housing and the larger span trying to tame the magnetics of the motor, do ya?

Hmmm............trying to visualize everything here.

If the diff housing were thick aluminum, and the bearing on the diff end was enlarged, then the center bearing wouldn't have to support the endbell at all.

Two shaft bearings inside the motor would help hold everything true.