Well...
It was an interesting, educational, and ultimately disappointing day testing our proposed VTA combo (1s / 13.5) yesterday.
To recap, we're TRYING to find a LiPo / Brushless (or, heck, LiPo / Brushed) combo that we can run that is TRULY equivalent to the incumbent 4-cell / 27T brushed combo that is all we have ever run here. Saturday we tested three cars that under the incumbent formula were all front runners and ran lap times very comparable to each other. I was running the 1s / 13.5 combo and had gotten the gearing down as low as an FDR of 5.0 and had the car turning times that were equivalent to the 4-cell / 27T car (running consistent 10.8's)and about a half second behind the 2s / 21.5 car. My temp was about 110* after 10 minutes running so I was pretty sure I had a fair bit more "in the bag". As it turns out, I was correct.
On Sunday we continued to drop the FDR on my car, a TC4 "Tubby". First step was that I had to put on an even smaller spur gear as I'd gotten as far as I could with the 88T gear we'd installed Saturday. The largest pinion the Tubby would accomodate without grinding relief into the chassis webbing was a 46T and that wouldn't quite get us to the next step which was going to be 4.5FDR.
At a 4.5FDR (actually 4.53) my car gained another 4 tenths, top five laps averaged 10.4 seconds and the temp was only up to 115*. Time to add some more gear. At this point I could feel the loss of acceleration and was taking somewhat more sweeping lines through the turns to gain the time. This is absolutely A-OK in a practice situation, but that's not always possible in a race situation where you are (potentially) giving away the inside line. I wasn't having to swing WAY wide or anything, just had to drive a bit further to maintain more corner speed than I'd had to. The improved top end, though, was more than enough to offset this minor loss of acceleration.
To get to a 4.0FDR, though, I finally had to break down and grind away at the webbing for pinion clearance as I was going to need a 49T pinion. This was easily accomplished with a cordless Dremel and a cutting bit. Using this combination I started having some radio problems, intermittently "losing" the car in one particular place on the track. Did some playing around with the antenna positioning, etc, but still found a couple tenths. The top 5 laps averaged 10.196 and the top 10 laps averaged 10.26. Car came off the track with a motor temp just under 120*.
Next step was a 3.5FDR, accomplished by going to a 56T pinion (actual was 3.48FDR). At this point the radio problem was showing up pretty consistently in two locations on the track and the car was pretty much impossible to drive. What I figured out was that the Spektrum was falling below voltage threshold under acceleration at the higher-draw sections of the track where there might be weaker reception areas as our track is in a windowless basement with a low ceiling and LOTS of fluorescent lighting, radio problems (even with Spektrum) aren't unheard of here. I happened to have one of Spektrum's power capacitors in my radio case so I popped that in and POOF, problem solved. YEAH!!
At 3.5 we'd passed the "sweet spot" so testing was, for all intents and purposes, over. The car ran it's top 5 at 10.4 and top ten at 10.5, and to get those numbers I was having to "sweep" the turns as much as possible which would REALLY be giving away the inside line in a race situation. Motor temp had also jumped to 155*, another indicator that the sweet spot had been passed.
The ultimate gearing may lie between 3.5 and 4.0, and it may lie between 4.0 and 4.5 as we saw our peak times at the 3.98FDR actual and had been making comparatively big jumps either side of that. Unfortunately for our purposes finding that "perfect point" for this track didn't matter--it was too fast. As might be expected, after more than 2 years of running the 4-cell / 27T combo that car was pretty much at it's peak lap times after learning the layout. 10.8's was where it was going to run. The 2s / 21.5 car continued to play with it's gearing a bit (optimum was at about 4.4FDR on the Xray 007 that was testing this combo for us) and ended up running best 5 laps at 9.9 and best 10 laps at 10.0. This means the 1s / 13.5 was a fair bit closer to the 2s / 21.5 combo than the 4-cell / 27T combo we'd hoped to run it with. Bummer. We COULD mandate a minimum FDR at 4.5 but we'd really like to stay away from that--my own feeling is that precious few folks really understand what FDR is or represents and fewer yet can accurately calculate it.
I should also point out that to make sure what we were testing was differences between power systems none of the three of us did any suspension tuning beyond balancing the cars out with the LiPo systems to weight at the stated 1450g minimum. These cars already lapped pretty much on-the-nose with each other using the incumbent 4-cell / 27T spec. Fiddling with the suspension Shawn might have been able to optimize a bit and gain a tenth or two with his 2s / 21.5 combo car. My car really probably stood to gain the most if I was to actually make suspension adjustments but it's been a matter of pride that I have (for example) never even opened the shocks since I dug the chassis out of the basement when we started experimenting to create the VTA class. To this day I can't honestly tell you if there's even any oil in the shocks much less what weight it is. The rest of my "set-up" similarly follows the "ignorance is bliss" rule. It is not at all unimaginable that with a little tuning the 1s / 13.5 combo could have been as fast as (or even faster?) than the 2s / 21.5 combo. My car is REALLY "lazy" with a lot of roll and resistant to changing direction. The old Z590 servo really serves to exagerate these tendencies and was clearly too slow at the 1s power even with the booster to 5v. That said, it is as stable and predictable as a cruise ship in a duck pond--I can put it on a time and keep it there all freakin' day absent hitting, getting hit, or something in the way. Or all three.
What are we going to end up doing? I'm not 100% sure, there are a few folks in the club who weren't present for the test sessions who we need to talk to about it yet. The consensus of those involved in the test, though, was that we aren't going to be able to mix the LiPo / brushless in with the existing 4-cell / 27T racers and not have some folks keenly disappointed. It absolutely KILLS me to "split" a class (we aren't a terribly large club) but the solution seems to be that we maintain the existing 4-cell / 27T spec for a "Club-Spec" VTA class and implement a LiPo / Brushless class to run separately. Then the question becomes "which LiPo / Brushless spec to we go with?". This isn't quite the slam-dunk it seems...keeping in mind that one of the reasons WE started down the VTA path initially was to create a distinctly slower class and, while a bit slower, the 2s / 21.5 VTA spec isn't a ton slower than the 2s / 17.5 Rubber TC cars we were running between tests. In the end, though, the three of us feel that if we're going to split the class that we may as well go with the existing national spec and offer a "full" USVTA class here at long last. Unfortunately, this renders everything we learned about 1s / 13.5 in VTA absolutely moot...other than the learning exercise it was.
Something else we're seriously discussing is phasing "technology" into the "Club-spec" VTA. It seems a pretty well accepted fact that round cells aren't going to be very available for much longer...the market is shifting very rapidly to the LiPo (and other alternative) power sources. The second pillar VTA was created upon was the idea of "cost containment" and wholesale technology shift doesn't meet that criteria very well. What we MIGHT do (probably will do?) for the upcoming season is allow brushless 17.5 in with the 4-cell class which would allow folks who chose to start investing to go ahead and purchase a brushless system now and get going with that tech (because they'll also be buying new pinion sets in the range allowed by the brushless, etc) this year and then can look at purchasing LiPo (and chargers, and balancers, etc) down the road either a) when they choose to join the "full" USVTA-spec class, or b) when they can't reliably source round cells anymore.
Another area of discussion among us was whether or not to limit esc technology. As (honestly) no one has purchased esc's for VTA yet no one would be "stuck" with a speedo they couldn't use. We were pretty much split on whether to do this or not so we'll probably leave it open. I'd be 100% for mandating the Havoc / 21.5 as it is honest to the original cost-containment intent of the class but I'm afraid I'll be over-ruled. We'll see.