Tuff Love for Tuff Ones: Exploring “Brush to Commutator” Issues

I’ve mentioned previously that on my small Model Motoring track I am currently using these old-skool “cruise control”-style controllers. While it’s true that this track is about to be the subject of a significant re-engineering project, said project calls for the retention of these controllers because I enjoy them. Some people will say that setting a car at a particular speed and leaving it there is boring, and I can understand that in concept, since doing so requires setting the speed of the car to the fastest rate at which it can negotiate the tightest and most difficult turn, necessitating slow action all the way around. That’s not racing, for sure, but I personally think its quite fun to sit back and watch a pair of cars chase each other on the track and see what happens. Like it or not, you can see that this type of “model motoring” requires a low amount of power, so that the cars run at less than half the speeds they are capable of achieving. I was surprised to find that doing this is not as cut and dried as it sounds: there are some challenges to this which one might not think about until you try it, but it led me down one of those rabbit holes that I live for, and which I will write about in this here post.

As most T-jet fanatics know, there are 3 different gear ratios available on the original Aurora chassis. The highest ratio-the original standard 9-tooth pinion-is by the far the most tolerant of low-speed cruising. Just like a real high-strung, high compression performance car, the lower gearing of the “hop up” 12-tooth and the “Tuff Ones” 15 tooth pinion doesn’t like to putter around at low speeds as much. These motors require a higher level of energy input to get them moving, and although most of them seem fine once they get going, they are also far less tolerant of voltage drops and have a tendency to stall out (which is say, come to a stop) at low speeds at spots on the track where the power dips.

Of course the natural automatic reaction to this is, “well, add more power taps!” And more are coming for this track, rest assured! But regardless of the number of power taps, its interesting to note that the lower geared cars exhibit this trait consistently: when power is applied, they either sit still or barely crawl until the power reaches the point at which the resistance to move them is overcome, at which point they take off and shoot across the room; using these cruise control terminals, it is very difficult to dial in the power for these cars so that they will cruise happily along the track without stalling or de-slotting. Not only are most of the “Tuff Ones” chassis particularly difficult in this area, but the few cars in The Road Crew that run with the very high performance Dash Motorsports “T-Dash” chassis are even worse. Over time, I’ve been able to observe which of these lower geared, high performance cars behave more predictably on this track and which are the most recalcitrant. These observations have led to me to realize that, although there are probably multiple reasons for this behavior (including, foremost, the laws the physics), there is also some tuning that can be done to alleviate this problem by paying attention to the brushes and their contact with the armature commutator plate.

Frequently on this blog I’ve talked about the design evolution of the T-jet chassis through the years and the various companies that have made them. One of the key components which has been improved over time is the shape of the commutator brushes. Originally just a “barrel” that was smooth on the top and the bottom, these were later modified with a notch in the bottom so that the electrode of the chassis can anchor them in place and prevent them from spinning in their sockets as the armature rotated. As far as I know (please correct if I’m wrong, T-jet historians!) it was Playing Mantis-later Auto World-who had the brilliant idea to taper the top of the brush. The combination of the notch at the bottom and the taper at the top really improved the performance of the “pancake” motor design, allowing both less friction and more consistency at the brush to commutator contact point. Although the original style brushes seem to work fine in most of the original chassis with the higher rear gears, I have found that changing out the brushes in the Tuff Ones chassis for the newer style of brushes, which can be bought affordably online from Auto World, can really make a difference in the tractability and consistency of their performance, especially at lower speeds.

It is the Dash Motorsports “T-Dash” design that is the “odd duck” here, as I have seen these assembled with brushes that are both smooth and with the notch in the bottom, although I have yet to see a T-Dash chassis with a tapered brush. Even more strangely, it is the chassis without the notched brushes that seem to offer me the best low-speed control. One particular T-Dash chassis in my fleet-the one under the teal ’69 Boss Mustang-is so fast that it can’t be effectively used with these “cruise control” terminals because it will just fly right off the track, even though I have installed the Auto World tapered-brushes in it. I’m still trying to figure this dynamic out and won’t pretend to understand everything that’s happening here, but I have seen enough consistency in changing the brushes in the Tuff Ones chassis to know that there is a difference.

In the video above you can see the difference this change made to one car in my fleet, namely the blue Cheetah I profiled here. Prior to this video, I made the same change to the white GT 40 you also see on the track here; initially this car was impossible to use on this track, as it would either stand still or shoot across the room with no middle ground, until I replaced the brushes with the newer style, giving it a much more controllable power band, so I decided to do the same thing to the Cheetah, since both cars are running with original Tuff Ones chassis with the aluminum threaded wheels.

Of course there are other things that can be done to address performance problems; some people gently bend the electrode to strengthen the pressure of the brushes against the commutator (although be careful, as this can easily be overdone, and you don’t want to break the ends of the electrodes off!) And of course cleaning and maintenance is also a big help; running the brushes along a light abrasive to remove oil and carbon deposits and cleaning the commutator can also help performance issues a lot.

I’m not an expert on the behavior of electricity so I’m sure there’s more at issue here than just the type of brushes, but I’ve head pretty good results so far using the new brush design in the older chassis; if you have some older Tuff Ones that aren’t running the way you want, this upgrade may be worth a try!