thedroneracingengineer
patreon
ImmersionRC Ghost is here. Should you ditch Crossfire?
🕑 Added 2020-09-02 17:06:01 +0000 UTCThis was sent to my email list as well as to my Patreon. Sorry if you saw it twice.
Ghost is the new long-distance, low-latency control system from ImmerisonRC. The big question everybody is asking is: why should I care? Hasn't TBS Crossfire pretty much "solved" the control link situation? Here's my take on who should choose Ghost and who might want to stick with Crossfire.
The biggest difference between Ghost and Crossfire is that Ghost uses 2.4 GHz while Crossfire uses 900 MHz. The 2.4 GHz band is much wider than the 900 MHz band, especially in Europe. This means that Ghost can have lots of pilots in the air at the same time without interference. Crossfire pilots may start to experience micro-failsafes with as few as 4 pilots flying at the same time, in extreme situations. This mostly affects races, where organizers try to include as many pilots as possible in each heat. (Some race organizers have even insinuated that Crossfire pilots may intentionally sabotague a competitor by powering up during their race.) Advantage: Ghost.
What about range? All else being equal, low frequencies travel farther and penetrate better. In the latest firmware, Crossfire can go up to 1 watt on the micro module and 2 watts on the full-size module, while Ghost caps out at 350 mW. So Crossfire's range is significantly longer than Ghost's. However, both Ghost and Crossfire have 2x or more the range of a typical 5.8 GHz video link, so the extra range of Crossfire is not going to matter to most pilots. I'm tempted to call this one a tie for 99% of people, but if you fly long-range video systems, then advantage: Crossfire.
For pilots seeking the absolute lowest latency, Ghost offers a 222 Hz "pure race" mode, while Crossfire tops out at 150 Hz. Crossfire's range is significantly reduced when in 150 Hz mode, but its higher 1W output power makes up for this. Advantage: Ghost. But only barely, since I suspect few people would notice the difference between 150 Hz (6.6 ms) and 222 Hz (4.5 ms). They're both pretty fast.
Ghost has no real solution right now for people wanting to drive servos with PWM outputs, although one is planned for the future. Even the smaller Crossfire receivers can output four PWM channels, and there are larger Crossfire receivers with 8 or more PWM outputs. Crossfire is also highly configurable, allowing re-arranging PWM outputs and re-configuring receiver outputs, such as having Crossfire output on two pins while servo channels are on other pins at the same time. Advantage: Crossfire.
Both Crossfire and Ghost have the ability to directly connect a vTX to the receiver and control the vTX channel and output power from the radio module. Crossfire connects to TBS Unfiy vTX while Ghost connects to ImmersinRC Tramp. Since there are so many different Unify vTX's, and even licensed 3rd party vTX's that support SmartAudio, advantage: Crossfire. However, many people are going to wire the vTX to the flight controller, in which case this category doesn't apply.
TBS has been aggressively marking down the retail price of Crossfire in order to compete with FrSky R9. The Crossfire Micro Starter Set with a module, three receivers, and antennas, is $120. The comparable Ghost bundle is $150. The Ghost Atto receiver runs $30, the same price as the Crossfire Nano. Advantage: Crossfire, but that advantage narrows the more receivers you buy, since the difference is mainly in the price of the initial bundle.
2.4 GHz antennas are much smaller than 900 MHz antennas. Anybody who has ever chewed up a an Immortal T will understand why, when it comes to antenna size, ease of mounting, and durability, it's advantage: Ghost. You can even install a regular 2.4 GHz "whisker" antenna on a Ghost receiver if you want. ImmersionRC also emphasizes the ease of putting a high-gain directional antenna on the radio for longer-range use.
Points have to be awarded for the fact that Crossfire has been around for several years. It's extremely stable and reliable. Most of the bugs have been worked out. When you buy Crossfire, you know what you're going to get. Ghost, being a brand new product, probably still has a few surprises in store. Advantage: Crossfire.
So then, in conclusion, which one should you get?
If you're a dedicated racer who wants the lowest latency possible, without having to worry about getting micro-failsafed during a race, I think Ghost is very compelling. Even if you're already heavily invested in Crossfire, Ghost may be worth a look.
For a more typical pilot, who seldom flies in large groups, and who doesn't care much about latency, Crossfire and Ghost seem more evenly matched. You're unlikely to push either of the systems to their limit, so the question is whether you want to go with the proven system or venture out into something new and different.
For true long-range pilots, there's no question that the lower frequency and higher output power of Crossfire, as well as the fact that it has better support for PWM servo outputs, gives it the win.
Comments
Joshua, just my 2 cents, the only reason i'm buying ghost is for my Orcas, not sure if you touched on that yet but that being said. I still have all my main gear on Crossfire.
For a toothpick, the lighter Ghost receiver and easier to mount antenna may be compelling but I just switched to CRSF. And TBS has a freaking awesome radio which Ghost doesn’t have. Advantage Ghost on first and TBS on second. For many, the Tango 2 is huge advantage especially since it is now multi protocol, double advantage! I’m sticking with CRSF since it fits my needs.
Thanks for the thorough break downs and comparison, Joshua. Have crossfire, and have no complaints. But I could see myself spending a little more to start testing the waters of ghost. Small and lighter is going to count in the coming years.
Quick fact check: You say: "Ghost has no real solution right now for people wanting to drive servos with PWM outputs" but ImmersionRC Ghost Manual 1.0 Aug 2020 says "The Atto receiver may be used for fixed-wing applications with up to 4 servos without any additional hardware". Pad S and T become channel 1 and 2 and pads for 3 and 4 are on underside. I haven't received mine yet to confirm.
Props to Tony and the ImmersionRC team for the Ghost. Having an alternative to TBS is awesome. Looking forward to see it evolving.
The micro-failsafe concerns have me worried as almost all pilots at my local clubs are on Crossfire. I really want a Tango 2 as the small form factor is very important to me - I ride to work and need to fit everything in my bag so I can get more practice in before/after work.
Redbeard The Pilot
So, how many channels does the receiver have? I can’t seem to find that info online. Probably not much of an issue for most quad pilots and JB’s “all modes on one channel” mod.
Also good for ppl that want to fly 1.3ghz video.. Might be a good time to redo my 1.3g vtx tests using ghost instead of 900mhz since I was getting interference even with a LPF on the antenna
My understanding is that firmware 3.23 and above eliminates micro-failsafes by allowing pilots to force 150Hz. A lot of the points being given to the Ghost are because of that, so I think it's important to confirm this is still a real problem. Theoretically, in most situations a 2.4GHz control link will be fine because it will outperform the VTX, but I'm eager to see if this matches up to real-world experiences over time. I'm interested to see how well Ghost can maintain its 222Hz refresh rate when flying around in something like a bando as well as Crossfire maintains 150Hz, or how more common it is for pilots to have failsafes due to minor damage to their rx antenna. In my experience an Immortal T can take quite a beating before it failsafes within VTX range, but I'm not sure the same would be true for 2.4Ghz antennas. Either way I'm glad to see more competition come to FPV market. I'd really like to see the micro-failsafe issue validated on current Crossfire firmware though. Yes, with a lot of pilots and less bandwidth you do end up on each others frequencies as they hop around, but I think the only reason pilots actually felt the micro-failsafes was because of the TX bouncing between 50 and 150Hz.
I've been trying to decide between these 2 systems. Range isn't a huge concern for me. I'm not racing yet, but think I may want to get into it. Right now I'm leaning towards ghost, mostly because I enjoy micro quads and think that the smaller antenna will make it easier. On the other hand I think crossfire has a big advantage right now because it is very often an option for BNF quads.
Just invested in a Tango2 and 2 receiver. So that I don't race and don't fly in large groups, all at the same time, I'm not really interested in Ghost or mad that I did go with Crossfire. TBS has a good and reliable system right now, Ghost first has to proof itself. Maybe, if its really that much better i can slap a module on my Tango next year, never know :) And bit off topic: DJI "yeah latency no problem for racing, I get used to it blabla...". "Oh Ghost 220hz I need for racing .... essential.." :D
