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Color0's Micro RC Blog -- A technical brain dump from the mind of yours truly...
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Transmitters (aka Radios) Explained, Pt. 1

Posted 04-20-2009 at 05:40 AM by color0
Updated 03-08-2011 at 09:35 AM by color0
As most readers of this blog will know, there are many raido transmitters (also known as "radios") in existence that can control an RC car, and not all of them are made equal. The stock Mini-Z's radio, for example, is on the opposite side of the universe from a high-end one like the KO Propo EX-1 UR. But its actually respectable for what it has to do: it's not fast, but it's not horribly glitchy, and it offers enough features to get your average customer started (and hooked) on the cars. The EX-1 UR, on the other hand, has one of the fastest response times ever (seriously, it feels dang near telepathic), with almost no glitching from the ASF module, and it has more adjustments than I will ever need: steering and throttle trims and subtrims, balance, step sizes, initial punch, response curves, heck, even ABS and traction control, from a radio transmitter?! It's ridiculous, it's cool, and if you didn't understand the last couple lines of what I've written, then the rest of this article is dedicated to you.

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Let's get started with the choices offered... I'm just going to write about the most well-known and/or widely-available ones for Mini-Z, so if you would like to know about a specific radio, just leave a comment and I'll try to help.

I also assume the reader has knowledge of the different frequencies RC's can be run on: AM, FM, and 2.4GHz. Some of the features you may not know about, but don't worry, I'll explain everything at the end.

First, the basic radios. These are the ones that Kyosho offers us as "stock" radios. Features aren't a lot, just throttle and steering trim, and steering dual rate.

Perfex KT-2/KT-5 (AM): Response time is relatively the slowest of all. Signal is OK; you can race with these but you'll notice small glitches. Price: can be free (just ask an MZR member with 4+ cars).

Perfex KT-18 (ASF 2.4GHz): This is the "stock" radio that Kyosho offers with the ASF 2.4GHz Mini-Z's. Same basic features, but with independent left and right steering end-point adjustments (I'll refer to these from now on as EPA). Response is excellent, close to that of a high-end radio. However, its power source -- 4.8V -- is extremely low, and its signal is prone to getting drowned out against other higher-powered radios. Price: $80


And then the mid-range ones (there are a LOT of these, I'm only going to cover a few). In addition to the basic features, mid-range radios add on steering and throttle EPAs, and usually subtrims too (explained later), and model memory. I think these all have a small number of programmable buttons too, for you to customize.

JR XR2i (AM): Standard mid-range features. The XR2i has two-model memory so you can save different settings for two cars. Response and signal quality are much faster than the KT-5's. Price: ~$86

Airtronics MX-A (AM): Standard mid-range features, and with 12 model memory (quite enough). Response and signal quality are also great. Price: ~$60

Futaba 2PL (AM): Standard mid-range features minus subtrims, but plus ABS! 10 model memory. Response is supposedly a tick faster than the MX-A, and signal quality about the same. Price: ~$75


And now the high-end players. These are all feature-packed: In addition to the standard mid-range features we see things like ARC/Punch and Expo/Curve for both steering and throttle, steering and throttle response speed, throttle hold position, ABS, traction control, built-in lap timers, and LOTS of model memory. They also all use frequency modules instead of being locked into a particular kind of frequency (AM, FM, or 2.4GHz), so you can use them for both AM and ASF Mini-Z's.

Airtronics M8, M11: These are BIG, but in return you get a BIG LCD screen on which to make transmitter adjustments (this is actually a good thing, given the complexity of some of the adjustments). I believe they both have a data-logging built-in, pretty nifty. Requires KO Propo's ASF module as well as a PN Racing module adapter to drive an ASF Mini-Z with. As with the other high-end radios, response is the best you'll get. Price: ~$270 for M11, no module. (This seems way high, I don't think it's accurate.)

Futaba 3PK: Smaller and lighter (the lightest of the five I'm covering), and with your standard high-end radio features. The steering wheel's position and angle are changeable for even more customization. Like the M8/M11, the 3PK requires a PN Racing module adapter to use the ASF Mini-Z module. Price: ~$200 without module.

KO Propo EX-10/EX-1 UR: These are the radios I most often see at a Mini-Z track. They weigh in between the 3PK and the M8/M11, with the EX-10 being mid-sized and the EX-1 being relatively small (and thus, dense). Standard high-end radio features, but given that you can clip the ASF module in directly to these two radios, I reckon the response time should be the best in these two -- and probably the fastest in the EX-1 UR given its newer software. Price: $240 for EX-10 and $195 for EX-1 UR, no module.

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Yes, that long passage above was just an introduction to the spectrum of radios you can use with a Mini-Z. Now, what about all the crazy features I mentioned? Let me begin a glossary of sorts...

Steering Trim: Sets the center point of your car's steering. Most important radio feature, period, as your car's gotta go straight before you can race!

Throttle Trim: Sets the center point of your car's throttle control. Not as useful since neutral normally means neutral, to any electronics system.

Steering Dual Rate: Sets the maximum travel (angle) your steering can go. Very useful, it can instantly add or reduce your car's steering, and you definitely want the servo to stop steering before it hits the stops and damages itself.

Steering/Throttle EPA: Sets the maximum travel in a certain direction that the steering or throttle can go. The best part of this is, the adjustment doesn't have to be symmetrical, i.e. you can set steering throw farther in one direction or limit the maximum amount of brake you can apply (good for RWD Mini-Z's). This is the second-most important adjustment (behind steering trim) on a radio for racing purposes.

Steering/Throttle Subtrims: Convenient feature. Instead of moving the steering/throttle trim in one direction, and then adjusting the EPA to suit, you can just move the subtrim instead of the trim and it will automatically take the EPA's with it. Extremely useful if you're running an aftermarket servo off of a Mini-Z PCB.

ARC/Punch: Semi-useful feature applicable to steering and throttle. As far as it's normally implemented, ARC/Punch raises the initial value of an input the moment you turn the wheel or touch the trigger. (Ex. Suppose I set Throttle Punch to 30%; the instant I touch the trigger I'd be giving it 30% gas instead of 1%. The rest of the trigger travel goes linearly to 100%.) Useful only if your car is extremely unresponsive, or if your motor only wakes up at 50% throttle and above (happens with some powerful motors). I do not recommend using this feature on the car's steering, rather use Expo/Curve.

Expo/Curve: Keeps the initial and end-point outputs the same, but raises (positive Expo) or lowers (negative Expo) the output during the midrange. The input-to-output graph is curved almost exponentially, giving this feature its name. Expo/Curve is extremely useful for quickly tuning a car's steering characteristics. (Ex. Suppose I set Steering Curve to +20%; the initial half of my steering movement will be faster (less wheel movement for same steering), and the last half will be slower (more wheel movement for same steering). So initial turn-in will be faster, but mid-range steering adjustments can be made more accurately.)

Steering/Throttle Speed: Sets the speed (usually a percentage of the fastest possible) that the steering and throttle will reach the user's desired input. I personally set everything to 100%; while you could use this to smooth out your driving, it's not as great as driving smoothly yourself.

Throttle Idle/Hold: Don't worry about this, it's only used for nitro/gas RC's.

ABS: This is one of the most over-the-top features I have ever seen in a radio transmitter. It works quite similar to real ABS, once you pass a certain braking "threshold" (user defined), the radio will help you pulse the brakes, with the duration and frequency of the pulses being user-adjustable. Personally I rarely brake hard enough to require this but it's a REALLY cool feature to think about.

Traction control: ABS, in reverse! When you get back on the throttle, if you pass a certain threshold (related to the speed at which you squeeze the trigger, instead of a set braking level as in ABS), then the radio will help you pulse the throttle to maintain traction at the wheels, with the duration and frequency of the pulses being user-adjustable. Probably useful for some outrageously over-powered Mod cars, and again a really cool feature to think about.

Built-in lap timers: Useless compared to an actual lap timer at your local track, but if you don't have such a thing you can easily set up a button-activated lap counter/timer on your radio to get a ballpark of your lap times.

Model memory: Allows you to store different settings for different cars. The mid-range radios have from 2 to 12 models, while the high-end ones have as many as 30. Use one for your RWD racer, one for your AWD racer, one for your drift car, etc...

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I'm actually out of space for this article now so the rest will have to wait for next week. Hopefully this part 1 helped give an overview of what's out there, what some of the radios offer, and what kind of radio you will want/need in your Mini-Z career. Next week I'll be explaining how to use the features you've got.
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