Post by Eagle Racing on Jul 18, 2020 5:17:19 GMT -7
This is an article I found and thought it had some good info to share here. I don't know who wrote it.
To put it briefly, here's basically what happens with DC motor timing...
There is a brush position on all motor comms where you get maximum voltage potential across the brushes and minimum commutation arcing. This is called the brush neutral postion and on typical 3-pole slot car permanent magnet motors is generally around the center of the comm segment (but not necessarily there). This is a static setting for the motor. All this is fine and good, but when you apply current to the armature windings with their magnetic mass, they become electromagnets with their own magnetic fields. The armature's magnetic field is out of phase with the magnetic field created by the permanent magnets. These two fields interact in a process called "reaction." The "reaction" causes the total magnetic field to rotate to the point that the effective comm timing is no longer at the neutral postion. This causes arcing and sparking of the brushes, limiting the overall performance of the motor. If the timing is way out of whack brush life will decrease drastically, 100x-1000x worse.
Having adjustable timing allows you to move the brushes back to the neutral position when the motor is running and under the effects of armature reaction. On large brushed motors (and generators) there are quite elaborate ways to compensate for reaction, but for small brushed DC motors the usual fix is to have adjustable brush rigging. The Tomy endbell is a form of adjustable brush rigging. Moving the comm plates instead of the brushes is another way to compensate, and that's how the Super II and Patriot Storm arms do it.
Here's the rub and the reason I don't lose too much sleep over the constant "high timed arm" arguments that seem to plague other slot boards: Armature reaction is directly proportional to the armature current. If you run a motor over a very narrow range of currents the timing can be set for optimal performance - end of story. But slot cars tend to be run over a wide range of currents, so putting in an arm with fixed off neutral timing is a compromise solution, at best.
The timing adjustement must be well chosen for the particular armature winding, motor magnets, and motor load, and even the power supply capability. Overly advancing the timing is as bad or worse as not advancing it at all. The Tomy adjustable timing strategy is nice because it allows some degree of tuning for the total racing situation. Trial and error and testing. On the other hand, putting in a fixed off neutral timed arm is kind of a crap shoot. Hopefully the guys who sell cars with off neutral timed arms have done their homework and have picked a timing value for their cars that deliver a net improvement over a wide range of operational scenarios. No matter what you do to set the timing, it's unlikely that you'll pick a perfect setting for the entire racing situation unless you're running flat out on a banked oval or something like that. But even if the timing adjustment only improves the performance for certain parts of the race scenario, it can still deliver a net if somewhat subtle improvement. Whether this makes the difference between winning and losing is the point of many an argument.
Note that there are other timing related factors involved besides reaction, but it's probably the biggest factor for the simple 3-pole motors in most HO slot cars.
To put it briefly, here's basically what happens with DC motor timing...
There is a brush position on all motor comms where you get maximum voltage potential across the brushes and minimum commutation arcing. This is called the brush neutral postion and on typical 3-pole slot car permanent magnet motors is generally around the center of the comm segment (but not necessarily there). This is a static setting for the motor. All this is fine and good, but when you apply current to the armature windings with their magnetic mass, they become electromagnets with their own magnetic fields. The armature's magnetic field is out of phase with the magnetic field created by the permanent magnets. These two fields interact in a process called "reaction." The "reaction" causes the total magnetic field to rotate to the point that the effective comm timing is no longer at the neutral postion. This causes arcing and sparking of the brushes, limiting the overall performance of the motor. If the timing is way out of whack brush life will decrease drastically, 100x-1000x worse.
Having adjustable timing allows you to move the brushes back to the neutral position when the motor is running and under the effects of armature reaction. On large brushed motors (and generators) there are quite elaborate ways to compensate for reaction, but for small brushed DC motors the usual fix is to have adjustable brush rigging. The Tomy endbell is a form of adjustable brush rigging. Moving the comm plates instead of the brushes is another way to compensate, and that's how the Super II and Patriot Storm arms do it.
Here's the rub and the reason I don't lose too much sleep over the constant "high timed arm" arguments that seem to plague other slot boards: Armature reaction is directly proportional to the armature current. If you run a motor over a very narrow range of currents the timing can be set for optimal performance - end of story. But slot cars tend to be run over a wide range of currents, so putting in an arm with fixed off neutral timing is a compromise solution, at best.
The timing adjustement must be well chosen for the particular armature winding, motor magnets, and motor load, and even the power supply capability. Overly advancing the timing is as bad or worse as not advancing it at all. The Tomy adjustable timing strategy is nice because it allows some degree of tuning for the total racing situation. Trial and error and testing. On the other hand, putting in a fixed off neutral timed arm is kind of a crap shoot. Hopefully the guys who sell cars with off neutral timed arms have done their homework and have picked a timing value for their cars that deliver a net improvement over a wide range of operational scenarios. No matter what you do to set the timing, it's unlikely that you'll pick a perfect setting for the entire racing situation unless you're running flat out on a banked oval or something like that. But even if the timing adjustment only improves the performance for certain parts of the race scenario, it can still deliver a net if somewhat subtle improvement. Whether this makes the difference between winning and losing is the point of many an argument.
Note that there are other timing related factors involved besides reaction, but it's probably the biggest factor for the simple 3-pole motors in most HO slot cars.
