Terrible RC Transmitter Made Less Terrible

It should probably go without saying that we’ve got nothing against the occasional bout of elaborate troubleshooting and repair, in fact it’s one of the most common things we cover here. As it turns out, people aren’t overly fond of being fleeced, and there are a lot of smart people out there who will put a lot of work in to keep from having to toss a favorite piece of gear into the trash. We can’t fault them for that.

But we have to say, we generally don’t see those kind of elaborate repairs for something brand new. Unfortunately, that’s exactly what [Marek Baczynski] had to do when trying to review the new iRangeX transmitter for his YouTube channel “dronelab”. He found a transmitter that was so poorly designed and constructed that he had to address a laundry list of issues to make the thing halfway tolerable. As you might expect, he’s not suggesting anyone go run and pick this one up.

The biggest problem is a fundamental flaw with how the gimbals are constructed. Due to poorly mated surfaces between the potentiometer and the stick itself, the accuracy of the controller is very low. The potentiometers don’t even return to zero when the sticks are released. Some tape was used to tighten up the connection and make the controller usable, but such poor tolerances are hard to forgive when accurate control is essentially the whole point of the device.

The other issues took a bit more debugging to figure out. The TX made an absolutely terrible screeching sound when turned on, but [Marek] was sure he was hearing a little bit of melody under the din. Putting the signal through the oscilloscope, he was able to confirm his suspicions. As it turns out, the buzzer used in the TX has a built in tone generator that was overriding the intended melody. Switching it out for a basic buzzer fixed the issue. Similarly, an issue where the radio wouldn’t turn on if it was recently turned off was tracked back to a resistor of the wrong value. Putting a higher lower value resistor in its place sorted that out as well.

It’s hard to imagine how this device made it out of the factory with so many wrong or unsuitable components, but here we are. Not that this would be acceptable at any price point, but as [Marek] points out in the video, it isn’t as if this radio is even all that cheap. For nearly $90 USD, it doesn’t seem unreasonable to expect something that actually works.

This isn’t the first time he’s put “cheap” RC hardware through the wringer. We recently covered his efforts to quantify latency in different transmitters. As the RC transmitter world gets increasingly competitive, detailed analysis like these help separate the real gear from the toys.

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RC Transmitter Hacked Into Music Player

Packed with an incredible amount of hardware, and increasingly likely to be running an open source firmware, the modern RC transmitter is effectively a little multi-purpose computer in its own right. Accordingly there is a small, but growing, community of developers coming out with software applications targeting these switch-festooned wonders. It’s only a matter of time until they are running DOOM.

One such piece of software is TaraniTunes, developed by [GilDev]. This program allows you to load your OpenTX 2.2+ equipped Taranis Q X7 or Taranis X9D with music files which can be played on the transmitter’s built-in speaker. While it likely won’t win any awards for interface design, the large LCD display coupled with the radio’s numerous physical buttons and switches makes it relatively easy to navigate your music collection.

While the software [GilDev] has written for OpenTX looks straightforward enough, getting the songs on the radio is another story. For each track you need to merge the stereo channels into mono (as the transmitter only has a single speaker), and then convert it to a 32 kHz WAV. But don’t worry about the lack of ID3 tag information, TaraniTunes allows you to create a text file containing not only the filename of each track, but its name and artist.

We’ll admit this one should be filed away in the “Because I Can” category, but it’s still an impressive hack and a clever demonstration of the current state of RC transmitter technology.

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Quantifying Latency in Cheap RC Transmitters

For those just starting out in the world of RC, a low cost transmitter like the Flysky FS-i6S can be very compelling. But is buying a cheap transmitter setting yourself up for failure down the line? The general feel in the RC community has been that cheaper transmitters have higher latency or “lag” on their inputs, which is precisely the kind of thing you want to avoid when flying along at 40+ MPH. As such, the general wisdom has been that your transmitter is one area where you don’t want to cheap out.

Wanting to put that theory to the test, [Marek Baczynski] set out to compare the response time between the Flysky FS-i6S and the more established Taranis X9D. In the video after the break, he uses his Saleae logic analyzer to time how long it takes movement on the transmitter sticks to get interpreted as servo commands at the receiver.

[Marek] connects the logic analyzer directly to the gimbals of both transmitters, allowing him to see user input before any processing is done by the electronics. It’s particularly interesting to see how the smooth analog curves of the gimbals are converted to a “staircase” digital output.

The final results of the latency test end up being fairly surprising. To put it simply: the cheaper Flysky radio not only more accurately interprets the user’s input, but does it considerably faster than the Taranis. [Marek] says he was so surprised by these results that he re-ran the test three times to verify.

But even taking into account the apparently higher fidelity of the cheap radio, he cautions you shouldn’t swap out your gear just yet. Higher end transmitters have a number of other features which make them worth hanging on to, even if the newer generation of radios is slightly faster. The real takeaway from this video is that if you’re just getting into the RC game, these cheaper transmitters aren’t necessarily the kiss of death the community makes them out to be.

Experiments like this and the recent detailed analysis of common hobby motors show just how seriously people take the world of RC. It’s unlikely this single experiment will quell the debate about “cheap” RC transmitters, but perhaps it’s a start.

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See This Slick RC Strandbeest Zip Around

Bevel gears used to mount motors vertically.

Theo Jansen’s Strandbeest design is a favorite and for good reason; the gliding gait is mesmerizing and this RC version by [tosjduenfs] is wonderful to behold. Back in 2015 the project first appeared on Thingiverse, and was quietly updated last year with a zip file containing the full assembly details.

All Strandbeest projects — especially steerable ones — are notable because building one is never a matter of simply scaling parts up or down. For one thing, the classic Strandbeest design doesn’t provide any means of steering. Also, while motorizing the system is simple in concept it’s less so in practice; there’s no obvious or convenient spot to actually mount a motor in a Strandbeest. In this project bevel gears are used to mount the motors vertically in a central area, and the left and right sides are driven independently like a tank. A motor driver that accepts RC signals allows the use of an off the shelf RC transmitter and receiver to control the unit. There is a wonderful video of the machine zipping around smoothly, embedded below.

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Can Commodity RC Controllers Stay Relevant?

Visualize some radio controlled airplane fanatic of yesteryear, with the requisite giant controller hanging from a strap, neck craned to see the buzzing dot silhouetted against the sky. It’s kind of a stereotype, isn’t it? Those big transmitters were heavy, expensive, and hard to modify, but that was just part of the challenge. Additionally, the form factor has to a degree remained rigid: the box with gimbals — or for the 3-channel controller, the pistol-grip with the big pot that looks like a cheesy race car wheel.

With so much changing in RC capabilities, and the rise of custom electronics across so many different applications, can commodity RC controllers stay relevant? We’re facing an age where the people who invest most heavily in RC equipment are also the ones most likely to want, and know how to work with customization for their rapidly evolving gear. It only makes sense that someone will rise up to satisfy that need.

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Hacking 2.4GHz Radio Control

Many modern radio control (RC) systems use frequency hopping to prevent interference. Unfortunately, hopping all over the 2.4GHz band can interfere with video or WiFi using the same frequency band. [Befinitiv] was trying to solve this problem when he realized that most of the systems used a TI CC2500 chip and a microcontroller. The microcontroller commands the chip via SPI and controls the frequency by writing into a frequency register.

Updating the microcontroller firmware was impractical. The firmware is encrypted, for one thing. In addition, the change would have to be reinserted on any future updates and repeated for every RC vendor. So [Befinitiv] took a different approach. He did a classic man in the middle attack by inserting an CPLD in between the controller and the CC2500.

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Using RC Transmitters With Flight Simulators

It’s winter, and that means terrible weather and very few days where flying RC planes and helicopters is tolerable. [sjtrny] has been spending the season with RC flight simulators for some practice time. He had been using an old Xbox 360 controller, but that was really unsuitable for proper RC simulation – a much better solution would be to use his normal RC transmitter as a computer peripheral.

The usual way of using an RC transmitter with a computer is to buy a USB simulator adapter that emulates a USB game pad through a port on the transmitter. Buying one of these adapters would mean a week of waiting for shipping, so [sjtrny] did the logical thing and made his own.

Normally, a USB simulator adapter plugs in to a 3.5mm jack on the transmitter used for a ‘buddy box’, but [sjtrny] had an extra receiver sitting around. Since a receiver simply outputs signals to servos, this provides a vastly simpler interface for an Arduino to listen in on. After connecting the rudder, elevator, aileron, and throttle signals on the receiver to an Arduino, a simple bit of code and the UnoJoy library allows any Arduino and RC receiver to become a USB joystick.

[sjtrny] went through a second iteration of hardware for this project with a Teensy 3.1. This version has higher resolution on the joystick axes, and the layout of the code isn’t slightly terrible. It’s a great project for all the RC pilots out there that can’t get a break in the weather, and is also a great use for a spare receiver you might have sitting around.