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RCX 2011 Setup: Batteries and Electronics

Posted 06-19-2011 at 05:39 AM by color0
Updated 06-19-2011 at 05:52 AM by color0
In the past couple weeks of detailing my RCX 2011 Stock (80t) setup, I should have covered everything except batteries, body and electronics I believe, so I'll cover batteries and electronics (including ICS settings) this time since I've already covered my body modifications in prior posts.

At RCX I alternated (and still do) between TRP 900's and R1 990's, and I honestly cannot tell which one is better. I have charged both at various rates between 1-2A, finding no significant laptime differences; the only real difference is a lot more false peaking when charging above a certain current per pack. So far I have found that my TRP's do not like being charged over 1.2A, and the R1's don't like being charged over 1.5A (charger: PN S6, using the PN aluminum charging tray/heatsink). At these settings, both cells have excellent punch, the R1's have better initial punch and the TRP's lower punch lasts a couple minutes longer. Interestingly, charging the R1's at 1.2A does not change its characteristics at all in my experience, so I've just been charging them at 1.5A (it's faster, lol...). I only discharged the TRP's and R1's for the first three cycles, after that I just ran them, let them cool, then pop back on the charger. I run the cells for several cycles a day if need be, I don't seem to have any punch problems after the 2nd cycle, as other racers have warned me about for years. In fact I ran the same TRP cells four times on RCX Sunday, for Q1, practice, Q3 and the main! I don't think I ever lost my punch or top speed advantage (granted that advantage was at least partly the motor's credit). So I personally don't buy into all the battery charging and discharging religions there are out there -- I just take good care of my cells, cycle them consistently and expect that they get used to and perform well for the duty cycle they're responsible for. On the plus side, it also means that I can use the same cells for Mod racing without having too much punch.

OK, onto the electronics then. First of all I should of course mention that I'm still using the original MR03 PCB -- although I think other electronics might be allowed I find that the MR03 PCB is hands-down the smoothest, most positive-feeling electronics system for Mini-Z. The servo is so fast that the fastest digital servos, costing hundreds of dollars each, are barely equal to it! Anyways, for Stock racing the question is always power, so Philip convinced me to get a 3x2 FET stack using his AN0113 FETs. The car definitely feels a little punchier (not excessive, thankfully), top end has increased, and overall I don't know a whole lot about FETs but I like the ones I have.

Now for ICS settings, Philip and I worked out the following settings back when I first got the car that should be fairly optimal for Stock-class racing.

GAIN: Medium
SPEED: Fast
PNCH: 2
D.BAND: Narrow
DUMP: Over
D.FREQ.: 1.2kHz
NUTRAL: Mid
VINERTIA: Off
BAKTIM: 1
ST.GAIN: 250
TH.GAIN: 250

GAIN describes the amount of force the servo motor will apply to hold the servo at a certain position: obviously, to have positive servo feel and inspire confidence in the driver, we should have the strongest servo action possible unless it reduces the amount of power going to the drive motor. I thought I had the GAIN set to Strong, but it seems that somewhere along the line it got changed back to Medium, so please excuse my prior mistakes. No adverse effects so far with this setting: I haven't broken servo gears yet, though I do have a prototype aluminum 4th gear as a safety envelope.

SPEED describes the max speed the servo will move: given how small and quick these cars are I saw no reason to limit the car's own reaction times, hence Fast was the setting chosen.

PNCH describes the initial movement strength of the servo: I wanted my car to feel linear, not twitchy, and thus I left this setting at its stock, very mild-feeling setting. PNCH actually affects the feel of the car quite a bit! With high steering punch the car will actually feel much more aggressive, whereas mine, with a low punch setting, is very mellow despite having fast turn-in and high corner speed.

D.BAND describes the deadband of the servo movement: to get minimal response time you always want the narrowest deadband possible, hence I had mine set to Narrow. It doesn't affect the car's stability down the straight at all, also thanks to the low steering punch setting.

DUMP is a strange setting to me, basically it dictates whether the servo stops its centering action just before hitting center (Smooth), or just after (Over). I left it at Over, since I normally don't let the steering wheel center fast enough to hit that braking limit anyways. If you have fast hands, I suggest you try both settings and see which one you like better. I have heard in the past that Smooth makes the servo a little sluggish compared to Over.

D.FREQ is the drive frequency: the lower your drive frequency the more power you can apply to the motor, that is the theory taught to me by 1/10 scale racers. So for Stock Philip and I set the drive frequency to the lowest one Kyosho allows, 1.2kHz.

NUTRAL describes the throttle deadband: I didn't want to reduce my capability to reverse so I've left it at Mid for now. Making it Wide could potentially reduce the initial throttle response at tip-in so I didn't want that either, hence it is still set at Mid.

VINERTIA is a "virtual inertia" setting which keeps providing a little power to the motor even after you lift off entirely. I think this feature is useless, as I rely on weight shifting to rotate the car and really, unless you're a habitual user of the brakes typically lifting off is the only way you slow down a Mini-Z in a race. Hence, OFF is the setting of choice here.

BAKTIM is a limiting setting, to keep you from accidentally engaging reverse if you pump the brakes. I don't even brake, so I put this setting all the way down to 1 (basically zero reverse lockout -- a quick double-tap instantly engages reverse) and I can reverse as quickly as I need to in order to get back in the fray after I screw up.

ST.GAIN and TH.GAIN are technically supposed to be gyro settings, and are not supposed to take effect when there's no gyro in the car. HOWEVER, what Philip and I found was that ST.GAIN and TH.GAIN could be tuned for each individual servo to reduce the servo jittering that plagued many early MR03's such as my own. 250 and 250 are just five points short of the max on both settings and I found that this is what worked to stabilize my servo after setting the GAIN to Strong. Your mileage and results may both vary on these last two settings, so please experiment as I really can't tell you anymore about these two settings.

The final component to the electronics setup I guess are my transmitter settings. I use a KO Propo EX-1UR, which is a fantastic transmitter with extremely fast, if sometimes twitchy, response. I know a lot of racers have migrated away from the EX-1UR precisely because it's twitchy, but I love the way it works for me, and the only other thing I'd ask for is a drag brake setting (for now, bumping the Throttle Trim back a couple steps is sufficient). So let me just lay out all my settings here and explain them as I go along:
  • Steering Travel: 70
  • Steering Travel: L70/R70
  • Steering Dual Rate: 82%
  • Steering Trim: R5
  • Steering Subtrim: R1
  • Steering Trim Rate (step size): 2
  • Steering Config: Normal (not reversed)
  • Steering Punch: 0%
  • Steering Curve: 0%
  • Steering Quick-Response: OFF
  • Steering Speed: L100%/R100%
  • Throttle Trim: 0
  • Throttle High Point: 60
  • Throttle Brake: 45
  • Throttle Subtrim: 0
  • Throttle Trim Rate (step size): 10
  • Throttle Config: Normal (not reversed)
  • Throttle Punch: F0%/R0%
  • Throttle Curve: F0%/R0%
  • Throttle Quick-Response: OFF
  • Throttle Speed: F100%/R100%

Special things to note: the steering travel and end point settings are actually the recommended ones from KO Propo, for the particular module (ASF, RF-901SM) most serious Mini-Z racers are using today. So don't set these to 100%! You will run a risk of burning out the servo motor, or stripping the mechanical components inside the servo. The recommended throttle end point settings are forward 60 and backward 60, but I didn't need full reverse anyways so I left it at 45 to provide a usable brake in case I ever needed it (nope, didn't).

My steering dual rate was set to 82% as a last-minute desperate attempt to calm the rear end. As you may have read from my race report, by the time the main rolled around my 911 was feeling extremely loose, so I took a couple clicks out till the car felt safe -- it came out to be 82%.

You'll note that my steering and throttle both are not limited by the speed settings, left at 100% for both. This way I can always react quickly to things in front of me, and under normal circumstances I train my hands to be smoother instead of using the transmitter as a crutch. I also set steering and throttle curves to 0, i.e. perfectly linear. This lets me better judge what the chassis is doing per degree of my actual input, and helps me set up a car to be linear and neutral, (just feels nicer to me).

So to quickly condense the points I consider in my batteries and electronics setup:
There you have it -- I am no electronics guru, Mini-Z or otherwise, and all I claim to do in this post is to inform you guys and gals what was in my setup for RCX Sunday. In the next post I'm just going to sum up everything that went into this setup and then we'll be done!
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