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« on: October 22, 2015, 07:11:10 AM »
Since I have about a week left before my 2010 DS goes to the great trade in crusher, I have been taking my last chance to experiment with the Agni motor, before I never see it again... Hence building an experimental brush carrier from what was left of the original BBQ'd carrier....I hope what I have learned can help others that still want to use a brushed motor like the Agni.
Agni never should have made the carrier just from Bakelite, good for high voltages and low current, crap at taking extreme heat, like that of an arc or of a melting pigtail, that is glowing under 100 s of amps, due to a momentary brush mismatch, due to contamination etc.
In the picture you will notice the heavy copper wires that go into the carrier, to feed the new copper brush holder tubes. Copper tubes wont melt and burn like the originals did. This should avoid the pigtails and springs from taking too much current and melting and the need for constantly matched brushes. The copper also acts as a heat sink to keep the brushes cool. You will notice that I have used larger screws for the connections. There is also the addition of two screw terminal blocks that are wired to the dual temperature sensors, the red for the Positive tube and the other is the Negative. I have soldered where it was needed...
You can heat these tube with a butane gas torch and they can take it, try that with the original tubes and they burn up really quickly! The tubes carry the current to within 2 mm of the commutator slots, so the current only needs to travel through 2 mm of brush material to the commutator, that avoids heating. The wider tubes than the original carry more air past the brushes to cool them and offer greater lateral support for the tubes. It is using PMG Perm 132 motor's brushes that wear slower and offer a greater contact area than the originals. The copper bit at the connector end of the brush, sitting on the pigtail is a spring retainer, pigtail guide and brush tensioner (I have the bike for another week so I don't care how fast the new brushes wear out), They will also help to cool the brush directly via the pigtail. If I had the bike for another month I would have experimented with adding an advance on the fly function to reduce current draw at all speeds...
Theoretically, this carrier should be able to handle double the amps at a conservative estimate, based on doubling the copper to the brushes but really, it should handle far more than that. The brush carriers are demonstrably the weak spot in an otherwise amazing little motor, in terms of the power to weight for a KISS, system, not requiring any fancy electronics to make it all happen. Had Cedric used a decent material and approach to the carrier design, this motor would have been able to take the real world application that it was intended for, without the high risk of premature failure..... It should have really been a sealed design too, as those magnets are just "magnets" to ferrous dust.
Cheers,
Cam
