Motor tuning and brush cutting

[FrankW]

I was looking back at an old thread that I started a few years back about timing advance cut brushes for stock motors. It was a pretty interesting debate on whether they did effect the timing of the motor or not.

I was thinking that it might be time to open a discussion on motor tuning and brush cutting again.

Recently I started racing 12th scale again. 4-cell 19T "Super Stock"; and I would think that similar tuning tricks for stock motors would work for these 19T spec motors. I tweeked my springs to reduce the tension on the comm and narrowed a set of brushes by cutting the trailing edge. I noticed a pretty significant rpm increase (I sold my old dynos so i don't know the exact rpm numbers), and a no-load amp jump from about 2.5 amps to about 7. I'm hoping these modifications will show an improvement on the track.

Anybody have any good tuning tips for locked endbell (or even adjustable endbell) motors?

-Frank

[highroller]

The tuning tricks are still used today but it varies with type of racing, track and motor used.
Almost any type of modification you do to the surface area of brush has some effect on motor power. Any surface area removed from brush usually increases rpms at some loose in torque. So what you gain in acceleration, may be lost on the bottom end - sometimes changing the spring tension offsets it a little - increase the spring tension to gain back some of the torque. The increase in amp draw is usually attributed to an increase in RPMs. The same setup doesn't always work with the same type of motor.
For example two Chameleon2 may work great with that setup, while the third works better with a full or hollow brush, and a different spring tension. The Reedy Quad like a narrow type (1/3 of leading and trailing edge is removed) then using spring tension according to track layout. Tight racing lines go heavier wide sweeping layout (gently rollout on and off throttle) lighter spring. Heavier spring also helps slow the car quicker. Just as I was finding the sweet spot to the 19turn Specs, I went to 19 turn Mod which is a different beast, you now having timing to change power.

I use a dyno but only to get other motors to produce close to the same power as my best motor. There's been too many occassions that I've had six motors of the same type with one particular one producing the highest numbers (watts, rpm.torque - amp draw) and not perform as well on the track as those with lower dyno numbers - that's still making compensations in gearing.

[WheelNut]

Check out these 2 links:

http://www.rccars.com/forums/showthread.php?threadid=74

http://www.hobbytalk.com/modules.php?op=modload&name=Sections&file=index&req=listarticles&secid=3

According to the late big jim Greenemeyer the springs used on your motor should be as light as possible all the time, that is as light as possible but without going so light that excessive arcing occurs. The only purpose of the spring is to hold the brush to the comm, so if you use a spring that is to stiff it will result in unnessacary friction, and increased wear. If you go to soft on the spring though the brushes can burn up easily and possibly be ruined in only one run. A 4 cell 1/12th scale car doesnt put much load on the brush, so there it very little arcing, therefor you should use a spring on the light side of the spectrum. He also does not recommend running a narrowed brush. In the 19T thread there it talks alot about spring tension and what brushes to use on the 19T spec motors.

[TEM]

I played with timed brushes a long time ago in spec racing (trinity street spec motors, spec brushes, etc). Like highroller said; increase in timing increases rpm but you lose torque in return. Maybe I didn't find the sweet spot for the conditions, but I didn't think it was worth all that trouble.

A question I have for you is what exactly are you trying to achieve with the motor? I don't question your driving skills, but I find it very easy to get a 19T motor setup (with good cells ofcourse) on a 12th scale thats faster than most of us can drive!

My motor advice won't sound as pro as highroller, and you probably seen similar info before but here goes. 19T motors. Out of the package; dissemble, blast bearings and re-lube, cut the com, align hoods, shim armature, install brushes (ALWAYS 787's or 4499's), springs red/green +/- to start, run in brushes, cut comm again, clean motor, reassemble, lube bearings. Hope I didn't miss anything. Looking for around 10amps at 3 volts on a turbo charger. Very straight forward, no "tricks" no "magic". I use the same scheme in TC and 12th only thing I play with maybe springs. Making sure the car has a very free drive train and cells are good (high V, low ir), if you can drive it well, you're probably with a VERY tough crowd of racers not to make the A.

[highroller]

While Big Jim did clear up many motor misconceptions much of his tuning tips were already being used or had been posted on the Trinity Forums. Thing is if I had said use a such and such no one believed it worked but because Big JIm said do it - everyone was willing to try it. Plus what worked with a P2K doesn't work with todays motors. While P2K2 where only making .98 watts a Monster Stock2 is producing .108, Epic Roar Stock .112 on average. RPM are a different level altogether. Where the Red/Green springs worked with P2K (2) the higher rpm ranges require a slightly stiffer spring tension 2 red or Purple/Red and sometimes 2 purples.

Two methods can be used to reveal when spring tension is adaquate one is amp draw (how slow or quick amp draw builds or if amp draw remains stable) the other is to use a dyno (flywheel) levels of power should increase, remain steady in the shortest possible duration - slow increase, quick dropoff or unsteady readings are indications spring tension is improper (improper brush breakin may be a second case). On slave motor dynos past experience with one motor is about the best indicator or when spring tension is generally in the right area but again numbers should remain constant at the testing loads and voltag setting.

For laydown motors brushes I use Reedy 767 (tried 769 hollow) but drill or cut 767s, Putnam Green and Blue shunts brushes non race motors old Kyosho Stock Brushes. Standup Brushes Putnam X brush or Trinity 4383, or Reedy 737 or 732, while the 728 is used in some 4cell motors. Springs are Trinity Blue, Green, Red, Purples.

Most of my racing is oval now, with some offroad or TC when extra time permits in most cases I find the brushes remain pretty much the same but spring tension may vary a small amount.
In 19turn spec again either Reedy 767s or Putnam Green or Green/Blue made the best power, springs could be either two reds, or Purple/Red (oval) and sometimes putting the heavier spring on negative helps probably like in /12th racing. The heavier negative spring would act as a brake on tight tracks, producing good torque, while lighter spring on positive would produce better acceleration (rpm). But again you may run into situations where a particular motor doesn't respond and have to try something different. Recently I stopped running the MS2 motors and use the Epic Roar Stocks for oval. Tried different motor setups, gearing etc and couldn't break 47 lap with the Epics went and practiced tried a different gearing , tweaked on chassis (something I had already done) found of the the two EPic one worked with 1 32 pinion while the other ran better with 31 pinion turning 49 in first qual, 51 second 51 third finishing first is all but ended up third due to tangling with another car but still stayed on same lap finishing 50laps sometimes running quicker laps than leader or seond place but could never regain the distance.