Possible Center Diff Revo
 

After some thought I have decided to build an outrunner powered revo. I have a pair of the Hybrid diff cases with buggy ratio (43/13) gearing and a brand new 3.3 chassis. I have most of the suspension parts and other necessary items.

I would also like to put a center diff in this and power that diff with an outrunner via a pinion gear. I have an ofna k-series diff, the one that uses the 51t plastic gear.

Motor choice would be this one: Scorpion 3026 1400

I would stick with stock height tires and stock drveshafts. Power would be from a pair of 5s 2200 20c lipos wired in parallel for 4400mah. A quark 125b would be my esc of choice.

Heres the speedcalc with my setup, went with the k-series diff for two reasons. I have one here and the 51t gear will allow me to use my current selection of pinions to get the gearing right.

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Spur Tooth Count: 51
Pinion Tooth Count: 16
Total Voltage: 18.5
Motor KV: 1400
Tire Diameter (inches): 5.75
Tire Ballooning (inches): 0
Spur/Pinion Ratio: 3.19 : 1
Total Ratio: 10.54327 : 1
Tire Circumference (inches): 18.06 inches (458.83 mm)
Total Motor Speed: 25900 RPM
Vehicle Speed: 42.02 mph (67.5 km/h)
Effective Speed Rate: 2.27 mph/V (3.65 kmh/V)
Estimated Adjusted Speed: 40 mph (64 km/h) - 5% loss
Effective KV Value: 1400

Hopefully this motor can hold up at 25k rpm. Being a 10 pole motor it should have quite a bit of torque, and it has a built in fan to stay cool. Since it is a higher kv and geared down it should start without cogging. I am also hoping that the use of a center diff will help the front and rear diffs handle the power better.

Battery trays will be custom made, I may even weld some extra al to the stock chassis so the trays are built in. I am going for the lightest weight I can, so I will stick to as much plastic as possible.

Any thoughts, ideas or critisisms are welcome!

25k RPM is a bit much, I think. Being 10 poles, that can work an ESC pretty hard at that RPM. With the same size motor, how about the Scorpion 3026 1210kv?
It would spin up to about 22k RPM, and with a 18-19t pinion would hit the same speed (~42mph).

The 1200kv motor is an 8 pole to, so the lower rpm and lower pole count would be easier on the esc. Do you think this size motor would be powerful enough to move the revo around? I know that the 10 pole would have more torque than the 8 pole motor, but is it a big difference?

IMO, the 3026 1400kv has advantages over the other ones.

Higher kv, more gearing options that are readily available for inrunner use.

The built in cooling fan. This isn't an option with alot of outrunners.

25mm motor mount spacing - it's compatible with most mounts.

It has the highest continous amp rating. It's tough. :yes:

Center diff
 

You'll never look back from that center diff. Handling and control are way better than a locked center can deliver. Once you get tired of burning wheelies that is.:whistle:

Just saw the other thread with Mike's custom center diff that has the slipper built in. That looks perfect for this conversion. I will wait and see what size spur it has and then buy the motor. I think that the 1400kv motor will be fine with the quark esc, even with the high pole count and motor rpm. Does quark spec max rpm with various pole motors? I do not remember seeing that info, but have never specifically looked for it.

I was wondering about that, I never did see the slipperrential for sale?

There are much cheaper ESC's that boast such max rpm figures as 210000rpm (2 poles), 70,000rpm (6poles), 35,000rpm (12 poles).

I really don't see the Quark's switching ability has being a problem.

The max. rpm of 25,000 on 5S is also being figured unloaded isn't it? I doubt the motor will ever hit that unless you're jumping at WOT. :surprised:

I did not think it would have issues either. WOT jumping, that sounds like fun, and flipping and tumbling. And most likely some broken parts! HAHA