From tyounger@csc.UVic.CA Sun Mar 7 17:27:10 1999 Date: Sun, 7 Mar 1999 17:24:22 -0800 From: Tom Newsgroups: rec.models.rc.land Subject: Re: Stock motor brush Q's: On Mon, 8 Mar 1999, Michael H. wrote: > What's the difference in the different shaped brushes? > I have ones that are flat (ie. rectangular/square shaped head) and also > ones with a sideways "H" shaped surface. And I have seen ones with > horizontal grooves. > Do some make more power? The most power is made with full brushes. > What's the ups/downs if any of the different shapes? There are many different styles of cuts for brushes. Timed brushes (brushes which are trimmed on one edge) are used to change the timing on an otherwise fixed timing motor (specificaly stock motors). Some brushes are cut on the top, or both sides, or the top and both sides. This is used to reduce the brush/commutator contact area. Reduced contact area will increase the contact resistance, thereby reducing peak current draw of the motor. More cutting will reduce peak current draw more. Motor power output is proportional to current draw, so this will also reduce the peak power output of your motor as well. Cutting both edges of your brush will reduce the time each armature coil is energised, cutting down on the power your motor uses due to reduced time the coils are energised as well as increasing contact resistance; if you just cut your brushes on the top or bottom, all you do is increase the contact resistance which reduces the maximum current draw/torque of your motor. There are some other more complicated cuts (like the H cut) which combine the full brush dimensions with reduced contact area. The problem with brushes which are not full height is uneven commutator wear. To combat this, some people run their brushes one right side up the other upside down so that the full height of the commutator is used. Cutting both sides of a brush helps minimize this problem, however the commutator will wear more in the middle than at either edge.. Cuts like the venturi cut and the H cut have no practical advantages over more traditional cuts, but they are rather nifty looking. There is a rather nifty alternative however, the slash or X cuts. These cuts have either one or two slashes cut from corner to corner. This has the advantage of a cut brush (if that is what you are after) with even wear over the whole commutator surface. Other cuts tend to wear the commutator unevenly, since they do not have a constannnt surface area the whole way down the brush. > Is there a particular one suited for 1/10 4wd touring car (esp. rs4)? > High power applications benefit the best from full contact brushes. Smaller contact area will create higher brush temperatures than a full brush. High temperatures are bad, but if cutting brushes doesn't raise the temperature too much, it is a valuable tuning aid. ___ TTTTT OO M M The sixth sick shiek's sixth sheep's sick. |~~~| T O O MM MM @o o@ T O O M M M So if it is in or if it is on it is as it is, * T OO M M be it in or on. `-'