Originally Posted by
syndr0me
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As for the diff balls on the outer edges of the rings, this is actually becoming the preferred style in on-road, as the diffs stand up much better to the torque of brushless motors, and last longer between rebuilds. It's the same design they use on their flagship 416, though with aluminum diff halves. I believe Tamiya first introduced this, though, on the 501x off-road buggy.
Not quite. Kawada and Corally had the diff balls riding at the edge of the diff rings for a while now. And other probably (Yokomo and Robitronic Avid for instance). But I think this trend appeared out of the need to use the same diff rings with larger diameter diff pulleys (which more or less all cars use these days) which can accomodate more balls. The Avid however was the only to have purpose-designed rings with a very large diameter, so in their case I think it is a calculated move. This improves torque transmitting efficiency, so I expect it is a feature that will stay.
What i am looking forward to is to see a diff where the balls don't run down the same track on the rings but are a little oiffset in groups of three (four groups in a 12 ball diff). Thius would help the diff last a while between rebuilds. I have designed and made one by hand for my Kawada Sigma2 out of delrin (before Tamiya introduced their 37 tooth pulley in the 501 that has only htree balls offset outsied the others) but couldn't find anyone to cheaply manufacture it. I have also found a way to make the pulley out of one piece of material rather than have to glue/weld/attach somehow one side ring which I think is an improvement over conventional designs.