REVOLUTIONARY RADIO BREAKTHROUGH

by Greg Vogel

THE BIRTH OF A NEW ERA

During our meeting with the Spektrum Team, we spoke primarily with the Spektrum engineering manager at Horizon, John Adams. We picked his brain, then probed it, threw it in a blender till his head was spinning, and came up with this in-depth interview all about the system’s technology. We didn’t leave a technological rock unturned, so meet the Spektrum system ...

RC Driver: When did your team decide you were going to design this system?

John Adams: Believe it or not, the concept to do this started about six years ago and we started on the actual project four years ago.

RCD: What’s this technology all about?

JA: Well, I’m sure you guys can figure out a little by playing with the system you have, and I bet you’ll think it’s kind of magical. I guess that’s the best way to describe the technology—magical. It is used by NASA as well as government services and the military for ultra-security-level radio communications.

RCD: What was the chain of events that made the Spektrum happen?

JA: We consulted with several companies active in this arena, and the people we are with now are probably the fifth group. Fortunately, we came across a group in Silicon Valley, Cyprus Semiconductor, that is a true leader in Spread Spectrum Technology. Paul Beard, an engineer at Cyprus and a modeler, worked closely with Horizon product managers, and we became the team that could make this happen. In May 2004, they achieved a significant breakthrough in hardware manufacture; we actually had a working system prior to that, but the receiver was of excessive size and a bit too expensive. That breakthrough allowed us to build a system at a size and cost that made the Spektrum what it is.

WHAT IS SPREAD SPECTRUM?

JA: The spread spectrum technology uses different formats—frequency hopping and direct sequencing. I’ll explain each and why we landed on direct sequencing. First, you need to understand that the 2.4GHz band actually spans 2.400-2.4835 GHz. That means there is about 1 MHz of bandwidth available for each channel. That bandwidth has been sliced into 79 useable radio frequencies. This technology has been successfully used in myriad applications. It has also been agreed to by international agencies and governments. Everyone plays by the same rules.

FREQUENCY HOPPING SPREAD SPECTRUM (FHSS)

This is where the transmitter and receiver simultaneously jump from frequency to frequency within the 2.4GHz band, in perfect tandem on the same channels, spending only milliseconds on each, each following an identical algorithm. We set out to use this technology because we felt it was the most secure. But when we got into it, we found there were some inherent issues like response time, which is called latency—basically the delay from, let’s say steering wheel input till the time the wheels turn. We got our initial frequency hopping system down to a 24-millisecond rating, which is kind of slow compared to, for example, your Airtronics M8, which has a rating of 12 milliseconds. We also had to overcome another frequency hopping issue; if the receiver momentarily lost the signal, it would take a certain amount of time for it to find the signal again and for the transmitter and receiver to confirm they were back in perfect unison within the frequency hopping protocol.

DIRECT SEQUENCING SPREAD SPECTRUM (DSSS)

In a direct sequencing system, as soon as you turn on the transmitter, the radio scans various frequencies within the 2.4GHz band and locates one that is not in use. The FCC requires that any direct sequencing system include collision avoidance mechanisms. So, when you turn on the system, it scans the 2.4 band for an open frequency and locks onto one; it will not lock onto a frequency already in use. Our new DSM system uses DSSS and has 79 potential channels. One of the benefits of DSSS is that the latency period is reduced to 5.6ms. How fast is that? If a person eight feet away claps his hands, the sound takes about 7Ms to reach your ears—no perceivable delay. There is another awesome benefit. Other factors being held equal, DSSS provides a stronger signal than FHSS that, in effect, allows a far more robust radio frequency (rf) link to the receiver. You get a rock solid 3,000 foot range at a significantly lower power output—which also conserves battery power.

TOTAL SECURITY
GLOBALLY UNIQUE IDENTIFICATION (GUID)

After the transmitter finds the frequency and you turn on your receiver, the transmitter module identifies its GUID to the receiver. The GUID is a unique code that exists in each transmitter module. The receiver “binds” to the transmitter module based on the GUID. The two are linked together indefinitely until you turn the system off. They remain bound until you choose to rebind the receiver to another module. The receiver will only listen to the specific module it has been bound to. There are 4.2 billion possible GUIDs, so you will never see any DSM receiver listening to the wrong transmitter.

The buttons that are pushed, and the lights that flash and then go out during the binding process, are shown on the receiver (left) and the transmitter module.

The binding process is very easy. Simply turn on your car while holding the little button below the LED light on the receiver. When the light blinks, you know it’s ready to bind. Now do the same with the transmitter. Hold the button down on the module and turn on the radio. The light should blink, then both lights should go out; the two are now bound and you’re ready to use the system. You only need to bind once unless you are adding another receiver; then you only need to bind that one new receiver. You can bind any number of receivers to a transmitter module or you can rebind a receiver to a new module.

RCD: A question about binding: For instance, if you are binding a new system in the pits and there are drivers running a system on the drivers’ stand, will the receiver want to bind to one of the other driver’s systems?

JA: Good question. The binding process of the receiver to the module needs to happen within five feet; this is known as close proximity binding. The binding mode is much different from the actual running mode. You can actually be in the same room as a bunch of other operating systems and bind your system without fault; when it’s binding, it simply doesn’t recognize any other system. If two people, however, were binding at the same time, everything would work flawlessly unless the two were within five feet of each other.

FAILSAFE. During the binding process, the system actually does two things: first the receiver and module bind; second, the failsafe is set. As you go through the binding process with the transmitter, you also set the failsafe. This is cool: the radio inputs that you transmit during binding become the default settings in the unlikely event (e.g., from a battery failure) of a signal loss. You can push full brake in the binding process and when the signal is lost, the receiver will engage full brake on the car. If you do not touch the wheel or trigger in the binding process, the car will simply go to the neutral points when the signal is lost.

The failsafe positions are stored in the receiver, which allows you to turn on the car in the pits safely. Suppose your car has turned wheels and is set at full throttle before you turn it on; with the transmitter off and in the impound, simply turn on the receiver only and it will instantly move the servos and throttle to the failsafe pre-set positions. What’s cool about this feature? You can start up the vehicle, place it on the side of the track, let it warm up while you get your radio from impound and get up on the stand, then turn on the radio system and you’re ready to run. There is no chance for your system to receive interference that would cause your car to run off; the receiver has complete and constant control of the steering and throttle servos.

RCD: Is there a voltage cutoff where the system becomes inactive?

JA: Well, between 3.2 and 3.4 volts, the integrated circuits in the receiver would start to shut off, so that’s when it would happen. The transmitter module actually uses 40% less power than the conventional module in your radio, so your transmitter batteries will last longer. The receiver draws 40mA, a standard receiver draws 10-12mA, and the difference comes in because the Spektrum is both transmitting and receiving.

2.4GHz ADVANTAGE - The spectrum transmits on 2.4GHz instead of 75MHz or 27MHz like the ground radio systems in the United States. All model-generated RF noise such as that resulting from electrically noisy bearings, motor arcing, power surges, clutch bells banging on metal spurs, whatever the source, this all happens below 300MHz. Such model-generated RF noise is not sensed by the Spektrum’s receiver, which operates on the 2.4GHz or 2400MHz frequency—so there’s absolutely no glitching.

RCD: Is there any noise that can interfere?

JA: So far, we haven’t found it. In fact, we’ve rented a frequency generator and even tried to trick multiple systems into being on the same frequency, and because the system is on such a wide band, the two conflicting is very unlikely. We’ve also used things like computers and cell phones that operate near 2.4GHz and have not had any conflicts. A 2.4GHz baby monitor transmitting an image to a video screen within two feet of the Spektrum causes absolutely no interference.

RCD: The antenna is kind of stubby: Any chance of hiding it altogether?

JA: (laughing) The production antenna for the receiver will be 8.5 inches long and you can cut it, which is a no-no with regular receivers, down to 3.6 inches. It still should be vertically oriented, and you really shouldn’t coil it up inside a receiver box because it could reduce range. There are also two holes in the receiver so you can either have the antenna run out of the top or out of the end of the case. Basically, if you use the same mounting system as you normally do with your antenna, you’ll have great radio performance. If you do, however, bundle the antenna up with the servo wires, you won’t have any problems; again because of the high operating frequency.

As far as the factory antenna on the radio is concerned, it simply isn’t used and only the stubby antenna on the module is used. So you can actually remove the radio’s factory antenna.

RCD: We noticed a lot of drivers at the On-Road Worlds using the system, and some had their factory antennas up.

JA: Yup, it’s hard to break the habit. A lot of drivers so far can’t get used to not having that fishing pole in front of them! We were actually fortunate enough to have run the systems at the Worlds. Bob Novak, IFMAR and others were great and allowed us to run the system. 21 drivers on the Losi team and selected drivers on other teams used the system with great success. We had a hard time getting them back! The pro drivers said they couldn’t detect any difference in response and the rf link was flawless—a real testament—and the very high resolution of DSM actually gave them better control than that provided by any previous radio modulation type.

TELEMETRY

JA: We’ve been calling this a receiver throughout the conversation, but in fact it’s a transceiver. Not only does the module talk to the receiver, but the receiver talks to the module.

RCD: So it’s a real-time system?

JA: Kind of, we get about 16 frames per second back, so it’s not real-time, but very rapid.

In early spring, we’ll have a telemetry module that will plug into the battery port and this module will be about the size of a personal transponder. The system will have sensors that can plug into it, and the first sensor we expect to have out is a temperature sensor. It can read head temps on nitro engines or battery or motor temp. We also plan to have an rpm and speed sensor, a “quality” monitor to tell you how well the system itself is working, battery voltage sensor, and a lap time system.

LAP SYSTEM THAT WILL MAKE YOU A BETTER DRIVER

The lap system will work like other popular systems as far as the information it records. The counting unit will be a small box you’d set next to the track with a directional antenna, and as the car passes, it would record the lap. The information will be displayed on a 4-line handheld unit that your pit guy can hold, and he can see your information and give you guidance.

What’s cool about the lap data recordings is that you’ll be able to take that information and compare it with other drivers. So you can actually download Masami’s lap times and transmitter movements on a PC and compare them to yours. You can see when his throttle positions change and when he inputs his steering and use that info to improve your lap times.

RCD: Assuming he’d give up that info.

JA: True. We’re also toying with other options such as amp draw, EGT temperature, servo position, and we’re also working on a method that measures fuel by electronic resistance because floats and devices are not very reliable and can impede fuel flow. Traction control, ABS and possibly even an accelerometer may also become part of the system.

RCD: What’s the time frame for these features?

JA: By spring we should have a module with five options available. I’m not sure when the others are coming, but they are on the drawing board.

RCD: We bet this product is going to get great response.

JA: Since it was announced, it’s getting outstanding response. I’ve never had so many calls from dealers, racers, even robotic people—it’s just amazing. Everyone is just blown away, especially in the racing environment. No longer do you need to wait for a frequency clip to practice; no longer do you need to impound radios; no longer do you have to wait for a break in the race to adjust your car and transmitter in the pits. We got together with ROAR to re-do the rules to accept the system, and the unit is internationally approved.

RCD (Erich): Well John, I see a problem with the DSM System.

JA: You do?

Erich: Yeah. What am I going to blame my driving mistakes on? I can’t yell out, “Who’s on my frequency?” or, “My car was glitching!” You guys put me in a real bind.

JA: (laughing) I guess that will be a problem for some drivers.

THE BIG TEST–UNBELIEVABLE!

So far, we were sold on the DSM system, and the interview left us with the drive to go out and do some testing. We installed the system into the TTR S3 also reviewed in this issue. If we were going to beat up the receiver, an insanely fast buggy that goes through a ton of abuse would surely be the perfect test. It took only minutes to swap out the old receiver and module and install the new Spektrum system in our Airtronics M8 and to the Airtronics digital servos. The binding process was simple, and we even set it up with a little brake for the failsafe. With both car and transmitter on, the buggy’s servos responded as normal.

We fired up the buggy—no glitches. We ran a screwdriver over the heat sink head and near the needles—no glitches like we sometimes had with our old system. Then we started driving—again, no glitches. Finally, we took the buggy out as far as we could see in at the paved lot where we speed-test cars. The S3 was operating under my controls, although there was some operator error—my not being able to see what direction the car was pointing.

Our next subject was a Losi XXX-S fitted with a Novak Super Sport Brushless motor system. Installation was easy: We didn’t have to bind the system again, so it was off and running. On our indoor track, we didn’t notice any difference in operation between the DSM and our previous 75MHz radio gear. With one exception: there were no hesitations, no glitching, and just perfect worry-free running.

CONCLUSION

If you are a racer or just race against friends, there’s no doubt that you may have encountered some frequency conflicts. The Spektrum DSM System totally eliminates that possibility; there is no chance you’ll conflict with another driver’s car. There are also no chances of glitching, and there’s even a failsafe option that would prevent damage to your car just in case the signal was ever lost. Just turn it on and go. That’s it—no worries, no hassle. How could you say no to one of these units? The DSM is simply one of the best products ever to hit the RC market.

Links

Spektrum, distributed by Horizon Hobby, www.spektrumrc.com, www.horizonhobby.com, (800) 338-4639

For more information, please see the source guide in the magazine.

return to the sample articles list