Airtronics MX-3 & JR Racing XR3i
Everyone wants a top-of-the-line FM radio system, but not all of us can afford one. And truthfully, most drivers (even the pro’s) use very few of those high-end systems’ more esoteric features. For most racers and performance-oriented drivers, a midlevel FM system is ideal; with a lower price and the critical tuning features required for high-performance driving, the onestep-down systems are a perfect match for the wallet and the racetrack. We examine two of the hottest new pistols in this category: the Airtronics MX-3 and the JR Racing XR3i. Both transmitters rival the most expensive pro radios in features, yet they cost much, much less. See for yourself!
With a five-year lock on the transmitter category of our annual “Readers’ Choice Awards” and a clear dominance the pro racing scene, it’s hard to believe that Airtronics has never followed up the wildly successful M8 with a lower-priced computer radio. Well, the wait is over! The MX-3 is here, and it’s loaded; all the important features you could ever need for competition are in place, and all are easily adjusted by means of an LCD screen that uses the same no-brainer navigation as the M8 does. But here’s the really good news: the MX-3 is also the least expensive FM system with an LCD display on the market!
The MX-3 is available in 27 or 75mHZ and with a variety of servo combinations that range from basic (a pair of 94102 “standard” servos) to race-ready (highspeed, high-torque servo combos); all MX-3s include a switch harness, spare servo horns and grommets, a 4-cell battery holder, instructions and a frequency flag (Yes!).
The MX-3 test began as soon as I plucked the transmitter out of its Styrofoam shell and gave it a quick “How’s it feel?” appraisal. The wheel and transmitter both operate smoothly and feel solidly connected, and the case is well-balanced thanks to the placement of the batteries in its “foot,” The shallow thumb rest molded into the grip is comfortable and unobtrusive, and the wheel and trigger are positioned comfortably relative to the grip. I found the dual-rate lever counterintuitive; I instinctively pushed it to the right to increase the dual-rate setting, but this actually reduced dual rate. Also, some drivers may wish the dual-rate switch was on the grip, where it could be adjusted with a thumb while driving, but since I don’t tweak the radio once the race is on, I don’t mind the switch’s top-mounted location.
For practical testing, I installed the MX-3 in a Traxxas T-Maxx, and I didn’t have any trouble zipping through the radio’s menu of adjustments as I dialed in the brake and throttle throws and fine-tuned the steering. I also used the third-channel endpoint settings to adjust the reverse-mechanism’s servo to obtain the correct amount of travel.
After I had run a few tanks through the T-Maxx, I forgot all about the MX-3, and that’s exactly what I had hoped for. A good radio lets you concentrate on driving and doesn’t distract you with an uncomfortable grip, an unbalanced feel, weird ergonomics, or-worst of all-glitches and “hits.” None of that from the MX-3! I only had to think about it when I needed to shift the T-Maxx into reverse; instead of flipping a thumb switch (as you do on the Traxxas TQ3 radio), you have to flip the third-channel switch with your finger. It quickly became second nature for me to hit the switch with my right middle finger without taking my hand off the wheel.
Great radio. For an incredibly low price (about $120 with two “standard” servos), the MX-3 has the most used functions of Airtronics’ MS, plus the same excellent reception and mini-receiver as the flagship transmitter. I looked for a downside that might explain the MX-3’s low price, but I just couldn’t find one; it’s fully adjustable, easy to use, has a nice feel and is totally reliable. How do you top that?
JR RACING XR3i
The new JR Racing XR3i replaces the XR3 as the company’s mid line 3-channel FM computer radio system, and it’s loaded with hot racing features that are normally found on more expensive, flagship systems. The XR3i bridges the gap between middle-of-the-road and top-of-the-line with features such as adjustable exponential, throttle deadband, channel mixing and a built-in lap counter. That’s not all: the XR3i includes two premium race servos and carries a low $169 street price. Let’s take a closer look at this affordable and feature-packed radio system.
The XR3i radio system is available in either 27 or 75MHz models. Both include a JR Racing R-135 3-channel FM receiver, one standard 270 servo and a 1590 high-torque, metal-gear servo with 85 oz.-in. of torque and a 0.15-second transit speed. A 4-cell AA battery holder, a switch harness, spare servo horns and rubber servo-mounting grommets are also included along with detailed instructions.
I installed the XR3i radio system in my Team Associated Factory Team GT. The relatively large R-135 FM receiver fit snugly inside the RPM receiver box that I had installed on the truck. Setting up the radio system was easy, thanks to the XR3i’s straightforward programming. I actually adjusted the steering and throttle-reverse functions, subtrims and endpoints without even opening up the instruction booklet. Of course, I read the instructions later to learn how to exploit the radio’s many other features.
The XR3i’s unique ergonomics are very well thought out. I was particularly impressed with the lap– counter function; pressing the lap button (grip button “C”) with my thumb became a natural response and did not interfere with my driving in any way. The transmitter feels solid and well balanced, and the throttle trigger is wide to accommodate not-so-slender fingers. The narrow handgrip with its molded-in thumb rest provides a natural and comfortable grip. Monster truckers will love the easy-to-access auxiliary third-channel switch, that’s just above the thumb rest; it can be programmed to perform various servo-actuated shift functions. The foam– grip steering wheel is positioned in-line with the handgrip to help reduce wrist fatigue during long driving sessions. All the buttons and levers are easy to access and memorize-important for making subtle trim adjustments while you drive-and the large, angled LCD has big, easy-to-read symbols. It takes only a quick glance at the screen to clearly see your lap times when you use the timer function.
The XR3i performed flawlessly during testing, and I never encountered glitches or other interference problems. I didn’t exploit the radio’s third-channel operation during track testing, but I did set up a third servo on the bench and confirmed that the function works as JR promises. I’ll definitely use it in a future project!
The XR3i is stylish, has a long list of impressive features and is easy to program. It provides exceptional reception, and the included premium race servos are a definite bonus. JR has put together an affordable and feature-packed 3-channel FM radio system that is a must-see for anyone in the competition radio market.
GLOSSARY OF TERMS
Deadband. All transmitters are designed to have a small area of trigger travel that will not transmit a “forward” or a “reverse” command; this is done to prevent the trigger from being too touchy. The JR XR3i’s deadband is adjustable, so you can set the transmitter for a hairtrigger feel or make it more forgiving if you have a nervous trigger finger.
Dual rate. This function allows the total servo throw to be altered, and it’s most often used for the steering channel. Unlike endpoint adjustments, which are made independently for left and right throw, dual-rate adjustments affect servo throw in both directions.
Endpoint. Unlike the dual-rate function, which is used to adjust total servo travel, endpoint adjustments allow you to set left and right servo throw independently. Adjustable endpoints are particularly useful when you adjust a nitro car’s throttle/brake servo, where you may need significantly more travel to operate the throttle than you need to operate the brake.
Exponential (expo). This allows you to adjust the servo’s response around neutral. For example, if the expo Is set for a negative value, the servo will respond less quickly to steeringwheel or trigger movement near neutral and more quickly as the limits of travel are reached. A positive expo setting does the opposite: It’s faster near neutral and slower as the servo nears its travel limit. The greater the expo value, the greater the difference in servo speed from slowest to fastest.
Frame rate. Frame rate is the speed at which the transmitter “fires” bundles of Information to the receiver. The XR3i allows a faster than usual frame rate to be selected to better exploit the superior processing speed of digital servos.
Mixing. As the word implies, this feature allows you to “mix” the transmitter’s channels so that the throttle will also influence steering or vice versa. This function is rarely used with cars, but it is popular with boats, where a little rudder is often mixed with the throttle to prevent the boat from pulling to one side when it accelerates.
Servo-reversing. With the exception of the trigger and wheel, this is the oldest transmitter feature, and it’s arguably the most important. Back in the bad old days, if your car went right when you steered left, you were stuck; you either had to rewire the servo or invent a linkage that would allow the servo to operate the steering system correctly. Servo-reversing lets you reverse the servo’s operation with the touch of a button.
Subtrim. This is simply a very fine trimming function. If one “click” of trim is too much, the subtrim will allow you to make a more precise, smaller adjustment.
Trim. When you adjust the neutral position of a servo’s output arm, you are adjusting its trim, or “trimming” the servo.
AIRTRONICS (714) 978-1895; airtronics.net.
JR RACING distributed by Horizon Hobby Distributors (217) 355-9511; horizonhobby.com.
Copyright Air Age Publishing Feb 2003
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