I tend to be wordy in explaining some of these processes; sometimes it seems I type as long as we actually tested! But if you are not interested in the process, the last paragraph will get you the info in concise terms.
This update refers to the R5, R6, R7 editions in 8.0, 8.5, 7.5, 7.0, 6.5, 6.0, 5.5, and 5.0 winds. The 'stock spec' winds and my 'outlaw' 10.5 and 13.5 motors work well as setup and require very little change except for gearing at the track. We used the R7 as the test article this year as it is our current motor series.
This year I intended to only make small changes to the R7, I was happy with this configuration mechanically. In fact I just made another sensor board fixture (ROAR approved) which makes it much easier to center the rotor and maintain close tolerance for the rotor to sensor board. Some motors had a compromise that was not ideal and the new fixture was the fix, but fortunately this was not often.
Early in 2024, some of the most consistent and fast team guys came to me with a dilemma. On slick tracks they were needing to peddle the throttle mostly at 2/3rds of an average length of a straight. Watching these guys you did not see this issue but it was pronounced enough for them to ask for a solution. The problem was with the open sprints using 7.0 wind and open late model with 8.0 wind; they did not want to give up on the big torque out of the corner and great top end the 7.0 wind affords. To a lessor extent, they also commented about the same problem with the 8.0 wind in late model.
As I have not done purchases of competitor motors for a year or so, and I wanted to take a look at them again, I gathered up the close competitors motors, did multiple setups with a variety of rotors in their motors on my dyno; I wanted to see what the rest of the world was doing. After the dyno work, to the local track we go, with my local development racer doing a lot of runs. By April we were doing 400 laps a week (every week) to make sure what these motors felt like on a variety of surfaces and then racing the motors on Saturday on local tracks. By June or so, I was travelling twice a month to be with the real fast guys testing on a variety of tracks in Oklahoma and Texas. I am getting too old to do that much travelling but it was fun, and glad I am done for a while! We tested motors from multiple competitor motor designs, especially during low traction situations.
This is what I have learned. To me, there are two 'camps' of motor design. I am in the minority in design type as my goal was to build as much torque into the stator as I can, moderate it with ESC. The other camp builds the stator to make it low torque and use a lot of timing on the can and in the ESC. We all have very good rotors with massive increase in magnetism the last three years; more than 28% increase. The rotors have basically the same dimensions by rules, the material is just better. The result is that the low torque stators have easier time of controlling rotor spin up and torque application for less grippy tracks; my stator excels on very high bite tracks, so we tune them down to be manageable on slick surfaces. As a result, with the low torque design you make your motor tuning decision using small rotors, low torque stator as standard setup and then tune before practice and warm up with your ESC tuning box. Making a change during warm up is dicey as it takes a minute or so to make a box connection if you think you need a change. My high torque stator is tuned by selecting from the collection of rotors to put you in a range of power, and then you can dial up and down your output from the radio by percentage of throttle. This is my opinion of what is happening with the other motor manufacturers as I observe during the race and feedback from my race guys.
I did find the problem with tire spin up about halfway down the strait on slick tracks with the R7, the issue the fast guys were complaining about! Honestly, the dyno did not show this, but in watching the throttle trigger movement as they drove, I could see they had to momentarily dial back the throttle trigger somewhere down the straight. The problem was consistent. In essence, we were able to fix the tire spin up on slick tracks with the R7 7.0 & 8.0 (applicable to the 6.0 and 5.0 series) by:
SLICK TRACK SETUP
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Use the 12.1mm mod rotor with 31 degrees of timing.
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Use some torque moderation in the ESC to control acceleration from a corner; 10% or more if the track is very slick.
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Make adjustments using throttle percentage in your radio during warmup to the race as needed; set it at 92% for the starting point.
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After a few laps, make final adjustment on your radio in the throttle percentage, you are ready to race!
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As the track gains more and more traction, to the point the car can high side, we change rotor to a 12.3mm mod edition to keep the power/torque range for the throttle around 92%. We eventually go to the 12.5mm mod rotor when the track is at high bite.
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What we attempt to do is apply the rotor to keep the throttle range around 92%. This allows you margin to add power/torque both up and down quickly at warm up with your radio.
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For medium to large dirt tracks, use the even series of motors (such as 8.0, 7.0). For small tracks use the odd series motors (such as 8.5 or 7.5 winds).
We are prepared for the RC Chili Bowl again! Whether it is slick and bumpy (we will use the 12.1mm rotor) or if the track becomes a traction monster, blue groove surface, we have the combination which has he capability to win. We will see how well our year long test session pans out!
Hope to see you at the races!
Mark Fulton