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FC5687

Ball diff with brushless?

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Rumour has it that brushless motor is no good for 4WD (both belt @nd shaft drive) with "ball differential".

Any thoughts?

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What car? I had a Kyosho Lazer ZX6 which is 4wd and came with ball diffs and plenty of people ran brushless motors in them, in mod, so 6.5T brushless with ESC timing. It had a centre slipper though. It looks like 4wd are going away from ball diffs though, but 2wd still favour ball diffs for low traction surfaces.

Also, brushless motors can be mild too, a 21.5T sensored motor will be slower than a 23T Super Stock brushed motor.

What car and what application?

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Racers run ball diffs on dirt tracks. All run brushless, including low turn mod motors.

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I think that is a misconception in that if they are not built and setup correctly they can be easily damaged.  However a brushed motor will do the same to a poorly constructed ball diff

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In modern cars, you tend to have the slipper set, so that slips before the diffs do ,well rear diff, the front diff only really takes a load under braking, (and I can adjust the front brake bias on my K1, running a separate belt to the front)

My shaft drive ,Dark Impact is running a 7700kv on 3s, and the diffs (with mods) have been fine

My K1 , belt drive ,is running 4.5t (9500kv ish) 2s, and been fine (apart from understeer, so gone to a gear diff at the front). The k1 is quite nippy.

 

I think the key, is the slipper clutch, and proper diff parts (tungsten balls, solid metal shafts, set up right etc). If you can set the slipper, so it slips just before the ball diff does, it shouldn't give you any bother.

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4 hours ago, Jonathon Gillham said:

What car? I had a Kyosho Lazer ZX6 which is 4wd and came with ball diffs and plenty of people ran brushless motors in them, in mod, so 6.5T brushless with ESC timing. It had a centre slipper though. It looks like 4wd are going away from ball diffs though, but 2wd still favour ball diffs for low traction surfaces.

Also, brushless motors can be mild too, a 21.5T sensored motor will be slower than a 23T Super Stock brushed motor.

What car and what application?

Top Force with TA03 ball diff for front and rear. Recently thinking a rebuild with GPM alloy parts and aluminum gearboxes cover.

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6 hours ago, FC5687 said:

Top Force with TA03 ball diff

I think you'd need to run the diffs tight and as above make sure all the 'consumable' parts are top quality, i.e. ceramic / tungsten carbide balls, smoothed plates, best grease you can buy, new springs. Then build them to the manual spec but make them...tighter. So when you spin them unloaded you get a quarter of a turn free rotation rather than half a turn. Might not give you the turning characteristics you want but they won't slip. 

If you were running on very high grip surfaces and you are jumping the car a lot you'd probably have issues fairly quickly so buy some spare diffs. If not on astro then it should be OK. People were running pretty hot motors in the Egress and that has the same issue regarding slipper compatibility. You might find you can fit a slipper pinion but I've never used one. 

Ultimately without a slipper clutch the transmission is exposed somewhere to shocks and stresses and if the diffs don't give a bit to handle that the stress moves up the drive train and you will wear out gears faster. Driven aggressively on high grip surfaces, buggies with no slipper, geared diffs and very hot motors will eat themselves fairly quickly unless heavily built with an emphasis on durability. 

 

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7 hours ago, FC5687 said:

Top Force with TA03 ball diff for front and rear. Recently thinking a rebuild with GPM alloy parts and aluminum gearboxes cover.

Where can you get the alloy gearbox covers?  Is this the whole case or just the bottom cover

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I have read online the gpm gearbox covers for the top force dont always fit and sometimes leave a gap. Not really needed in my opinion.

Also you should be ok with brushless just don't go crazy something like a 8.5 to 13.5 should be plenty quick.

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If I'm running / racing on high grip, like carpet, I use a gear diff. Mainly as a ball diff will try and push the car straight on, putting power to both (all) wheels.

It's on the lower grip surfaces, where the inside wheel spins up, that ball diffs shine, sending power to both (all) wheels.

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