Radio Control and Slot Car Blog

 

  

When talking about breakthroughs in Radio Control (R/C or RC) technology, quite a few things come immediately to mind. From the first wheel radio, first electronic speed controller, first computerized radio, and first synthesized radio, there have been a number of milestones. Spektrum’s DSM 2.4GHz Spread Spectrum Technology can now be added to this list since this technology has forever changed the world of Radio Control.

Spektrum’s DSM (Digital Spectrum Modulation) technology is based on an optimized version of Direct Sequence Spread Spectrum. Spektrum’s DSM and DSM2 technologies provide users with pure digital control that provides an impenetrable radio link immune to interference. Providing exceptional resolution and impressive response times, Spektrum Technology offers RC enthusiasts the accuracy, reliability, and locked in feel necessary to provide a totally connected and crystal-free RC experience.

What Is Spektrum Technology?

While in development, Spektrum engineers looked to create a radio system that provided the end user with the same locked in feel as a crystal-based radio while eliminating interference and glitching. Spektrum engineers sought to improve both the modeling experience and safety all at the same time. Just a few years ago, the thought of eliminating crystals and frequency control was not even on the horizon. Now, thanks to Spektrum Technology, this is not only a possibility, but it is a reality.

 

  

What makes Spektrum Technology a reality is a combination of two factors: the utilization of a frequency in the higher 2.4 GHz frequency band and Direct Sequence DSM (Digital Spectrum Modulation) technology. Moving to a broadcast channel in the 2.4 GHz range moves the broadcast signal up beyond the range of model generated noise from motors and vibrations. This is the first step in eliminating glitching and interference. From here, unlike current narrow band 27 and 75MHz systems, Spektrum’s Direct Sequence Spread Spectrum (or DSSS) spreads the data over a wide range of spectrum, which helps to minimize narrow band interference. The encoded information is broadcast to the receiver with its own Globally Unique Identification number (called GUID). The GUID code is what makes it virtually impossible for any other receiver to recognize the transmitted information.

How Spektrum Works

Before operating a Spektrum controlled car or plane, you must first bind the receiver to the transmitter or module. Binding is the process of having the receiver recognize the GUID code of the transmitter or module. Every receiver you plan on using with a particular Spektrum radio or module must go through this binding process to allow a receiver to only recognize one specific module.

Once a receiver is bound, collision avoidance software prevents a Spektrum equipped radio from transmitting on a frequency that is already in use. All Direct Sequence Spread Spectrum systems are required by the FCC to incorporate active collision avoidance, making it impossible and illegal for more than one transmission on a single frequency.

Why Use Direct Sequencing Spread Spectrum?

There are two main broadcast methods that spread spectrum manufacturers can utilize. One format is called Frequency Hopping Spread Spectrum (FHSS). With an FHSS system, the transmitter transmits a narrow band signal and rapidly jumps from one frequency to the next, spending a few milliseconds on each frequency. Originally, Spektrum engineers started their development with FHSS based systems because they were relatively easy and inexpensive to develop. However, they soon discovered that FHSS had several limitations that would prevent it from being the optimal solution for RC. While more difficult and costly to develop, our engineers began experimenting with Direct Sequence Spread Spectrum (DSSS) and optimized the modulation scheme to overcome critical response and re-link issues. DSSS systems transmit on a single selected frequency but on a very wide band. Only a small portion of that band is used for specially encoded information. In addition, DSSS offers an increase of processing gain for significant improvements in range. With years of development and testing, the DSSS modulation scheme was optimized for RC car and airplane use, and Spektrum’s DSM 2.4GHz Spread Spectrum Technology was born. DSSS provided engineers and hobbyists with the safety, security, and locked in feeling that is necessary to maintain total and complete control in any vehicle or aircraft.

DSM2 Technology

Above and beyond the basic features of DSM, there has been a technological breakthrough for both air and surface applications thanks to Spektrum. An updated version of DSM technology referred to as DSM2 (second generation protocol) makes it possible to fly any size model with the convenience, safety, and peace of mind of Spektrum. With DSM2, the total latency of your radio system has been greatly reduced, while the bit-rate has been increased. When combined, these improvements provide hobbyists with a faster and more locked-in feeling when compared to traditional 27MHz, 72MHz, or 75MHz radio systems. DSM2 also provided a new opportunity when separating the two receivers. By providing superior path diversity, the DSM2 receiver can now see a broader RF environment.

What Does Latency Mean To The End User?

Latency refers to the time it takes a radio system to translate your transmitter inputs to the appropriate responses in your car or plane. Every radio system on the market has some sort of latency built into it - there is simply no way around this. While latency cannot be totally eliminated, it can be reduced. The original Spektrum surface module system featured a latency of 5.6ms. For example, lets say that your transmitter has a built-in latency of 15 ms and you equip this radio with an original Spektrum receiver and module system. When you turn the wheel on your radio, your servo would begin to move 20.6ms (.0206 seconds) later. While the radio systems latency is part of the overall reaction time of your vehicle, it is not the entire equation. Whether you use analog or digital servos, servo response time, receiver pack voltage and more all factor into the responsiveness of your radio system. As development continues, the latency of radios and radio systems will continue to drop, but latency will never be totally eliminated.

Understanding Resolution

The resolution of a radio system can be one of the most over-hyped and misunderstood terms out there. Resolution refers to the number of steps your radio has in its range of motion. A higher resolution means that your radio has more steps in its range of motion. One would naturally think that the higher number would be better, but there comes a point where the numbers lose relevance. Yes, a higher resolution number is better, but there comes a point where the resolution of a radio surpasses the resolution of the servos or ESC, making incredibly high resolution claims irrelevant. In other words, resolution is only one element in a series of events that have to happen - the system will only ever be as fast as its weakest link.

Advanced Spektrum Features - Air

Spektrum’s AR7000 and AR6000 air receivers feature DuaLink technology. Each receiver features two separate receivers and antennas built into one device. The transmitter transmits on two frequencies simultaneously while the receiver receives and decodes both sets of information. Should one signal be blocked or corrupted or should one receiver malfunction in flight, the other frequency or receiver will take over. DuaLink offers the security of having two radios operating simultaneously on two separate frequencies. This is called dual path redundancy. Regardless of the plane’s orientation, you will still enjoy that same locked in feeling to your model thanks to DuaLink.

ModelMatch prevents you from flying a model while the transmitter has the wrong model selected. When you bind your receiver to a Spektrum DX7 transmitter, the transmitter remembers the specific memory location that you’ve selected for that aircraft’s profile. In the event that you try to fly a specific model with the wrong model memory selected, the transmitter will not broadcast your transmitter inputs until you change to the proper model memory. Since it is transmitter based, ModelMatch works with all Spektrum air receivers when combined with a DX7 Transmitter.

Finally, there is ServoSync. With ServoSync, the DX7 transmitter’s signal is re-sequenced to best suit the type of mixing you select. This comes in handy in a number of applications, such as if you have a dual elevator on your big Extra or a 3-servo CCPM setup on your heli, ServoSync will see to it that those servos working together receive their impulses together. The result is more synchronized servo movement that translates into an undeniable, locked-in feel when you fly.

Advanced Spektrum Features - Surface

Spektrum Pro Series modules and receivers offer performance enthusiasts the speed, durability, and precision that is necessary to win at all levels. A special conformal coating, ReliaKote, has been designed for the receivers, along with all-new cases. These updates make Spektrum Pro Series receivers both water and fuel resistant. Another update that debuted in the Pro Series receivers and that since has been incorporated into the Original Series receivers is updated firmware that eliminates the possibility of an Electro-Static Discharge (ESD), sending the receiver into Fail-Safe mode when racing on carpet. Finally, for those looking for the smallest receiver possible, a new SR3500 Micro Receiver has been developed. Weighing in at a scant 6.5 grams and measuring just 1.06 x .78 x .48 inches, the SR3500 is perfect combination of performance and reliability in a miniscule package. All the SR3500 Micro Receivers features are identical to the Spektrum Pro series receivers, minus telemetry capability.

Racers who equip their vehicles with Spektrum equipment can take advantage of real-time telemetry for the ultimate competitive edge. With Spektrum Telemetry Modules, racers can keep track of RPM, voltage, signal strength, and temperature all from the convenience of the hand-held unit. The addition of the Telemetry modules to any racecar will make testing even more valuable and provide more relevant data. For nitro racers, your pit man can now make the appropriate carburetor changes on the fly thanks to knowing exactly what the running temperature of the head is.

Commonly Used Terms And Phrases Within The Spektrum Arena

• Analog - A voltage method that is used to represent data.
• Binding Process - Programming a receiver to recognize the GUID code of only one specific transmitter or transmitter module.
• Channel - Refers to the number of devices that you can plug into a receiver and control; also references the frequency a transmitter broadcasts on.
• Collision Avoidance - A protocol which eliminates the possibility of more than one Direct Sequence Spread Spectrum system from transmitting on the same frequency.
• Conformal Coating - A special treatment applied to the PC Board of Spektrum Pro Series receivers to aid in making them water proof and fuel resistant.
• Crystal - In tradition radios, the crystal is what determines what frequency a radio broadcasts on.
• Digital - A numerical method that is used to represent data.
• Dipole - A twin antenna setup that makes DuaLink possible.
• DSM - Digital Spectrum Modulation; DSM is the 2.4GHz technology that makes Spektrum possible.
• DSM2 - The second generation of Digital Spread Modulation. DSM2 offers significantly reduced latency and a faster response time than any brand of 27, 75, or 72MHz PCM system.
• DSSS - Direct Sequence Spread Spectrum. DSSS broadcasts on the 2.4GHz frequency band and generates a wide signal on a single frequency.
• Dual Link - Spektrum designed architecture that provides increased RF link diversity. This combined with DSM2 is what makes the full range system possible.
• ESD - Electro-Static Discharge. These are extremely high voltages that can build up on various surfaces.
• Fading - The term used to describe data that does not reach the receiver. DuaLink minimizes this possibility.
• Failsafe - A safety feature designed into Spektrum receivers that drives the servo positions to a preset location in the event that signal is lost.
• FHSS - Frequency Hopping Spread Spectrum. These systems usually transmit a narrow band signal and rapidly jump through a fixed set of frequencies, spending a few milliseconds on each frequency.
• Frame Loss - The simultaneous loss of information to both antennas in the aircraft system.
• Frame Rate - The time interval at which the servo data is updated on the receiver.
• Frequency - The specific channel or RF spectrum that a radio broadcasts on. In a traditional RC radio, the transmission crystal resonates when voltage is applied; the rate of this resonation determines the frequency that is broadcast on.
• GHz - Gigahertz. One hertz represents one cycle per second, and a gigahertz is 1,000,000,000 hertz.
• GUID - Globally Unique Identification Code. Each individual module or radio is factory programmed with its own unique serial code. In the binding process, the receiver is programmed to only recognize the GUID code of one specific radio or module.
• ISM - This is another name for the 2.4GHz frequency band. ISM was originally intended for Industrial, Scientific, and Medical use.
• Latency - The time it takes for a servo or ESC to react to an input made on a radio.
• MHz - Megahertz. One hertz represents one cycle per second, and a megahertz is 1,000,000 hertz.
• ModelMatch - A safety feature that prevents a pilot from flying a model when the model selected in the radio is not correct.
• Module - A device that plugs into the back of many radios that determines the broadcast frequency and band.
• Monipole - An antenna with a single wire.
• Packets - A set or group of data that is sent from a transmitter to a receiver in a digital radio system.
• PCM/PPM - Pulse-code modulation and pulse-position modulation. PCM is a method of sampling an analog signal to convert it to a digital one. PPM systems use pulses to transmit specific transmitter inputs. Each pulse represents a position or position change of the controls.
• Pro Series - The second generation of Spektrum surface modules and receivers. With the Pro Series, the receivers feature a conformal coating, latency has been reduced, and new firmware has been developed to prevent ESD issues.
• Receiver - A device mounted into a car or aircraft that receives and decodes a signal sent by a transmitter. Servos, ESC, and other devices are plugged into the receiver.
  Resolution - Refers to the incremental step size of the data transmitted to the receiver.
• Servo - An electronic device used to actuate steering bellcranks, throttle and brake linkages, or control surface.
• Servo Sync - A resequencing of the data the DX7 transmits based on the type of mixing you select. This feature helps to sync control services that are connected (such as a swash plate on a helicopter) and is used in radios that have many channels.

Checkout Spektrum RC Radio to see what Spektrum Technology products RCSLOT has available.