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The Spektrum DX4S brings a ton of cool features to car radios that can make racing or playing more fun. Click image to enlarge

The Spektrum DX4S DSMR Surface System

Spektrum’s near-magic applied to four wheels

Text, photos and video by Tom Hintz

Posted - 8-4-2016

When I returned to the RC hobby world after a 30-some year sabbatical the frequency hopping, computer-based radio systems shocked me with their lack of frequency issues and the loads of computerized bells and whistles they featured. The Spektrum DX4S DSMR™ 4-Channel AVC™ surface radio system brings many of the creature comforts from aircraft radios to the four-wheel ground-based crowd. Now everyone from entry-level back yard bashers (me) to the finest on-track aficionados can benefit from the impressive list of programming features plus the amazing stability of AVC (Active Vehicle Control™) technology. Actually, the Spektrum DX4S can be applied to virtually any ground-based vehicles including boats.

In basic appearance the Spektrum DX4S resembles the first pistol-grip car radios that appeared over 30 years ago. The Spektrum DX4S comes with three different rubber grip sets you can use to give your hand the warm fuzzies. I guess way back 30 years ago we were not sophisticated enough to blame the grips on our radios for a poor driving performance.

The transmitters steering wheel has evolved from simple black plastic to a f aux carved aluminum street wheel with a low profile tire that serves as the grip surface. It looks very cool but steers the car the same way. Where some radios feature wheels that are either mounted lower on the head portion of the radio or can be adjusted to a similar position the Spektrum DX4S keeps the wheel in what seems to be the logical place. I don’t have a clue why some manufacturers/racers think the wheel needs to be offset like that. My Spektrum DX4S feels just fine to me and the position of the steering wheel does not appear to be what is holding me back from fame and fortune in RC car racing.

The DX4S is built around frequency-agile, DSMR 2.4GHz technology. This exclusive Spektrum™ technology can be used in any type of surface application. Its range and response, particularly in noisy 2.4GHz environments is dependable and interference free. It's also backwards compatible with DSM2® Spektrum receivers. Longtime Spektrum users won't need to replace the receivers they have unless they want the frequency-agility of a DSMR receiver or AVC functionality.

The Spektrum DX4S has programmable switches (left) that let you set the radio up best for you. Even the old metal antenna is gone, now replaced with a small plastic blade (right) on top of the transmitter. Click images to enlarge

The Spektrum DX4S has a 30-model memory with the familiar ModelMatch™ that also made the jump from Spektrum’s aircraft radios. This kit comes with a waterproof SRS4210 AVC receiver and a Free SR410 receiver. There are 2 user-defined mixes and pre-set mixes including dual and 4-wheel steering.

Internally the Spektrum DX4S has all of the bells and whistles originally developed for airplane radios. Dual rates, exponential, adjustable end points and centering are all available as are mixing and more. Since most ground vehicles only use two channels for throttle and steering the remaining two channels of the Spektrum DX4S can be used for other critical functions like making a driver raise an arm and/or flash a “salute” of sorts. Of course there are more legitimate uses for the other channels and I am sure you will figure those out if you need them. I just have more switches to point at and wonder.

The LCD screen provides a graphical representation of the adjustments being made from trims to mixing. Just how the manufacturers figured we would be able to program anything reliably without an LCD screen is beyond me. To find your way around the LCD screen Spektrum’s SimpleScroll™ programming interface is built in. The Spektrum DX4S screen isn’t fancy but it is larger than I expected on a surface radio and bright enough to be read in sunlight. Spektrum even included the roller/switch for scrolling through the menu of available functions and programming.

Though most of us will only use the throttle and steering channels those who employ the AVC system often use the remaining two channels to adjust the level of steering and throttle help the AVC system delivers. You can assign those extra channels to whatever switches you like to make the adjustments accessible during a race.

Active Vehicle Control

The AVC system is essentially a gyro that keeps track of the car wanting to yaw (drift sideways) so it can apply counter steering and reduce throttle until the car straightens out. All this is a huge over simplification but it works because the AVC system is so simple to use. You dial in some numbers on the AVC screen to tell the system how much help you want it to provide and that's it. Play with those numbers until you get the feel you like.

The large LCD screen (left) on the Spektrum DX4S makes using its many capabilities fast and easy. The Active Vehicle Control (right) lets you dial in the amount of "help" you want to stabilize the car at all speeds. Click images to enlarge

By the second day I had my Associated RC10 B5/B5M broad sliding corners on my "test track" that runs around the flower bed in the back yard. The hardest thing I had to learn was to let the AVC system do it's stuff. I learned to pitch the car into the corner, tap the brakes to shake the back tires free so it went into a drift, then nail the gas and let go of the steering wheel for a second and the car digs through the corner in a nice and slowly correcting drift, building speed all the way. You can also steer during the slide to correct the line as needed. the whole AVC system is adjustable, you just need to get used to it!

High Tech ABS System

The AVC isn’t the only electronic assistance available in the Spektrum DX4S. A nifty ABS (anti-lock braking system) lets you program how the braking is applied so you can fine-tune deceleration for changing track conditions. For me using the ABS took some trial and error to get a feel for it on the loose dirt surface I mostly run on. I did find that I can use nearly the stock settings when you enable ABS and get very controllable straight line braking. However, when I want to Toss the buggy into a broad slide I can run it in hard and just flick the trigger into braking and the rear tires break loose and as the rear end swings out I hit the gas and the AVC helps it dig through the corner. Looks great, probably not the fastest way through the corner but I am a big fan of fast and sideways all at once.

The first downside I found with the Spektrum DX4S is that it is powered by four AA batteries. You can buy a LiPo pack but there is no built-in charging port like a real radio. That is just weird coming from someone like Spektrum. True, the batteries tend to last a long time but you know as well as I do that “a long time” always maxes out at the worst possible moment.

The other design flub is the alarm that you can set for things like the timer reaching that magic moment when the LiPo pack is in danger of drawing down too low. You can choose from a tone or vibration, or both. Once again Spektrum took a minimalist approach and just has the alarm in my case give me one little beep and a vibe (not long enough to be a vibration) and that’s it. Unless you are really focused on what the radio is doing (rather than your car) you are likely to miss the “alarm”.

In the Dirt

This system came with two receivers, the SRS4210 (left) with th AVC system and a SR410 (right) that has no stabilization. Click images to enlarge

I installed my Spektrum DX4S and SRS4210 receiver in my new Associated RC10 B5/B5M. After minimal setup I took my new combination out to my special test oval surrounding the flowerbed behind the house. Part of it is low grass, the rest is loose powder type dirt that looks cool coming off the back tires when the Associated RC10 B5/B5M digs out of a slide.

Somewhere between the superb chassis/suspension on the Associated RC10 B5/B5M and the feel of the Spektrum DX4S I was turning decent laps almost immediately. This radio just feels very natural in the hands and the responses are smooth and predictable. I have not enabled any expo or dual rates just yet and even though my “track” is very short I don’t feel like I am getting behind the car when slinging it through the dirt side of the circle/oval.

An important thing I discovered about the AVC is that it works best when you don’t try and help it. I was doing way better just pitching the car into the turn, maybe tapping the brake to swing the back end out but then just nailing the gas without adding steering until the car gets father through the turn when a bit of correction from me sets a better line out. AVC lets you tweak the steering while it is holding a prolonged power slide. With some practice that makes for some impressive sideways git-a-longs.

As I would suspect adjusting anything in the Spektrum DX4S produces reasonable changes that make this system easy to tune for your vehicle and driving style. Small and big changes are available, you just need to learn how to apply this system to your car and style.

Conclusions

The Spektrum DX4S is a very nice system for modern RC cars and trucks with a list of features that will make controlling virtually anything on wheels easier than ever before with an accuracy and consistency that will make you a better driver. The Spektrum DX4S feels great to my hand with the standard grips installed but you can go bigger or smaller to get the feel you want.

When I bought this system I paid $229.00 (8-3-2016) with the SRS4210 AVC receiver and a SR410 receiver. That is not bad money for a first rate system that has all of the features you need to get more out of just about any car or truck you may be thrashing. With the reasonable cost of compatible Spektrum surface receivers and the 30 model memory the Spektrum DX4S can extend its economy as your fleet of surface vehicles grows. Any way you look at it, owning a Spektrum DX4S looks like a great investment.

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