Brushes

[HauntedMyst]

I generally have my comm cut after 3 days of racing (I'm open to unput if this should be more or less) but I haven't changed my brushes yet on my stock motor. Why? I simply don't know when to change them and they never actually have looked worn out. I changed them on past motors just to more silver content but they didn't look worn out.
How do I know when they look worn out and how often should I change them? I race every other weekend about 4 races and 2 practice runs not counting any running I do during the week for fun.

[Grizzbob]

Well, a lot depends on the particular brushes you're running, but as long as they're still at a good length(so they will still make good contact with the comm)& haven't changed color then you should be able to keep using them. As for the comm, I would say that it'd be a good time to cut it on a lathe, most of today's brushes are kinda hard on the comm, & the more runs you do the faster the comm will wear away.(you should also keep an eye on the color of the comm, if it seriously darkens or turns red, then you need to cut it). When the brushes discolor, they've already lost most of the lubricants molded into them, so they won't work very well, & just accelerate comm wear. I know it seems excessive, but a big reason why many racers cut their comms every race day(myself included) is because doing it that often keeps it true for longer, so the brushes bounce on it less, thereby keeping the wear to a minimum. You can actually get a motor to last longer by doing it very regularly than by waiting a real long time between comm cuts(the accelerated wear over time more than makes up for the lower number of comm cuts on a lathe), & of course the motor will run it's very best for more of that time too..... :)

[jeepinator]

I am not sure when the OPTIMAL time to change the brushes is, but I do know the indications when it becomes very important to:
1) Discoloration (expecialy a purple hue - very bad)
2) When they get short. I usually side-by-side compare the used ones with new ones to get an idea of how much they are worn. 3 to 4 millimters is enough for me to change them.
3) When they wear in an uneven fashion. Like the center of the radius is not the center of the brush.
4) When the comm wears very quickly (usually a sign that all the lubricants have been "cooked" out of the brush.

When one of the above criteria is met I change them. I realize that I may not be getting full potential out of my motor by running them so long, but I try to ballance performance, fun, cost and convenience.

Some folks simply use the "X number of runs" rule. For the sheer performance this may be good advice, but I realy try to avoid rules like that. There are just too many variables.

[HauntedMyst]

Thanks for the feedback Grizzbob and jeep! I will check them for color. Unfortunately, I don't have a comm lathe but one of the guys at the track does and he does it for $5. My understanding is that the more silver, the better the performance but the quicker the wear. Is that true? I actually like simple rules, they make things easier for an imbecile like me even if it costs me more. Hold on, its 3 o'clock, time to watch Wapner...

[Grizzbob]

Yup, that's the case, Haunted. The silver in them is the best thing for power, but that's also what chews up the comm the quickest, so they have to try to balance it out with copper & graphite for lubrication.... :)