Tuesday, June 27, 2017
Home » Product Reviews » Spektrum DX7 SE

Spektrum DX7 SE

When the original Spektrum DX7 was introduced, it was nothing short of revolutionary. Being the first full-range 2.4GHz radio, modelers from all over the world snatched them up like hotcakes. The new 2.4GHz systems offered features such as glitch free operation, eliminated the possibility of frequency conflicts, and prevented operation with the wrong model selected. While these features alone made the DX7 worth its weight in gold, some discerning modelers happened to notice another benefit. They felt more connected with their model, as ifthere was a hardwired connection between their transmitter and their model. The reason for this newly found responsiveness was due to the fact that, at the time of its introduction, the DX7 was one of the fastest radios on the market. Since then, top pilots have been pushing their helicopters harder and harder, performing insane maneuvers such as tic-tocs, cracking, and funnels just inches off the ground and faster than ever before. At these speeds and altitudes, milliseconds matter. Improving on the already excellent performance of the original DX7, the DX7 Special Edition (DX7se) improves on it by having lower latency and twice the resolution, making it one of the fastest and most precise radios on the market today.WHAT IS LATENCY?The measure of a radio’s speed is referred to as latency, which is the response time from the instant a stick is moved, to the time the receiver outputs that command to a servo. The first factor that contributes to a radio’s latency is the speed at which it processes all the data internally within its processors. This is what I will refer
to as processing latency. This is a normally a fixed time for a given radio and basically includes everything the radio does from the instant you move the sticks to the time it has the data ready to be sent out to the receiver. The DX7se is one of the fastest radios on the market in this respect. The other factor that contributes to a radio’s latency is the rate at which the radio sends data out to the receiver and servos. This is called the frame rate. For as long as I have been involved in R/C, the frame rate has been fixed at roughly 22 milliseconds (0.022 seconds, or about 45 times a second), to maintain compatibility with the servos at the time. Even today, most analog servos are designed to be updated at a 22-millisecond frame rate. This means that every 22 milliseconds, the servo is looking to the receiver to provide it with new positional data.The downside of a fixed frame rate is that it causes the overall system latency to vary. If a stick input is made the instant before the data is sent out to the receiver, the latency is composed of only the processing latency. However, if a stick input is made the instant after the data is sent out, the system has to wait another frame or 22 milliseconds before the servo will be updated with the new position. For you mathematical types, the actual system latency will be as follows: processing latency < actual system latency < (processing latency + frame rate) The amount of latency variation is directly equal to the frame rate. Another thing to notice, is as the processing latency
approaches zero, the latency due to the frame rate becomes the major contributor.With the advent of digital servos, the rate at which the servo can be updated has greatly increased. It is not uncommon for a digital servo to be capable or receiving data and updating its position every 4 milliseconds (.004 seconds or 250 times a second). However, since the receiver is outputting data at a much lower rate, the digital servo’s capability to be updated more frequently is wasted and the servo still updates at the 22 millisecond rate.HERE COMES THE DX7SETo improve upon the DX7’s already speedy performance, the engineers at Spektrum have cut the frame rate in half, to 11 milliseconds. This has the effect of reducing latency range by 50%, further improving the responsiveness of the transmitter to receiver link. This higher frame rate is applied to the cyclic and collective servo channels. The folks at Spektrum have wisely maintained the original 22 millisecond frame rate on the other channels to maintain compatibility with existing gyros, governors, and throttle servos that have the potential of not working properly with a higher frame rate. The higher frame rate on the cyclic and collective channels requires that you use digital servos on these channels. The DX7se’s manual clearly states that you risk damage to the servos if you use non-digital servos on these
channels. To get the maximum benefit of the higher frame rate and improved resolution, the manual recommends using strong and precise servos, such as the JR DS8717 high torque, high speed servo. Whereas the original DX7 had 1024 steps of resolution, the DX7se doubles that to 2048 steps for maximum control precision. This extra resolution means that your controls will function with glass-like smoothness, making precision maneuvers such as FAI style flying that much easier. While the DX7se operates with all Spektrum and JR DSM2 receivers, the DX7se offers these advanced features when used with the following receivers: AR7100, AR7100R, AR9000, AR9100, JR R921, R922, R1221, R1222. Included with the DX7se is a 1500mAh NiMH battery, which should provide several hours of flight time, as well as a wall charger, instruction manual, binding plug, and DX7se label neckstrap. Since the
DX7se is aimed towards heli pilots, it comes pre-configured with non-ratcheting throttle stick. It can be user configured to have a racheting throttle stick if desired, and comes with the required ratchet part. Other functionality includes a 20-model memory, both heli and airplane programming, 5-point throttle and pitch curves, CCPM mixing, and many other features. For more information, you can refer to the Spektrum website at www.spektrumrc.com.FLYING THE DX7SEFor my testbed, I used my Miniature Aircraft Fury Extreme 90 helicopter, equipped with JR8311 servos on the swash and JR770 Gyro and JR8900 servo on the tail. I had been flying it on a JR9303 with a Spektrum 2.4GHz module and Spektrum AR9000 receiver. For this test flight, I manually copied over the settings from the JR9303 to the DX7se and rebound the receiver to work with the new transmitter. While flying with the DX7se, I felt more connected with the model, especially during hard and fast maneuvers close to the ground where it matters most. The coordination of tic-tocs, piro-flips and other timing-intensive stunts, seemed easier, as it required less leading of the controls to get the desired effect. The speed of my 6 year old JR8311 servos is relatively ‘tame’ compared to some of the latest servos, but I was still able to notice an improvement in control feel. With modern high-speed servos such as the killer JR8717 heli servos, the control response will be phenomenal.

CONCLUSION

The DX7se combines the robustness of DSM2 with enhanced speed and precision to provide the most connected feel between you and your model. With one of the fastest and most reliable connections between you and your model, the DX7se deserves serious consideration!

Links

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

FEATURES

Spektrum DX7se transmitter Channels: 7 Model Memories: 20 Model Type: Heli /Air Modulation: 2.4GHz DSM2 Battery: 1500mAh NiMH Weight With Battery: 28.6 oz. Current Drain: 200mAh 2048 resolution 11-millisecond frame rate (original DX7 is 22ms)

SYSTEM FEATURES

Full-Range 2.4GHz DSM2 Spektrum System Compatible with models of all size and speed including giantscale and turbine jet 20 Model Memory Compatible with all Spektrum and JR DSM2 receivers 1500mAh 9.6V NiMH Battery and charger Fully Digital trims Improved programming with more mixes and better interface Innovative Model Match and Servo Synchronization technology

PROGRAMMING FEATURES

Sub trim Travel Adjust Dual Rates, three axes Exponential, three axes Servo Reverse Trainer system select Throttle Recovery Input Select (Switch Select-ability for Aux 2 and Gear) Dual Rate Switch Select Fail Safe Servo monitor

HELICOPTER SPECIFIC FEATURES

4 Swashplate types Swashplate Mix Throttle Hold Three 5-point throttle mix curves Four 5-point mix pitch curves Revolution Mix Gyro Sensing Switch Assignable Programmable Mixes (3)

AIRPLANE SPECIFIC FEATURES

3 Wing types Elevator to Flap Mix Aileron to Rudder Mix Flap System Differential Switch Assignable Programmable Mixes (6)