After having some troubles playing VRC, I started to look at my hardware to see if there was some gains to be had there because while I’m not a great racer in real life, I’m also not terrible 😎 I wound up doing a lot of research regarding the relative speed and latency of various tx/rx brands and models. The most concrete measurement I could come up with is the PWM frequency sent from the receiver to the ESC & servo(s). PWM signals are often much faster than PPM signals that are used by buddy-box or direct servo control systems. This is important in regards to playing VRC.
I gathered results measured by myself and others using the SkyRC Program Box. It is not a foolproof measurement of end-to-end latency – the delay from when you give a controller input and the ESC reacts to it. But it’s a clear metric, and part of the overall latency we can measure easily.
Much of this may not even matter to you. The average human reaction time is on the order of hundreds of milliseconds. For transmitter latency we’re talking about tens of milliseconds or less. Also, the transit time on the fastest servos are around 50 milliseconds, so that is another part of the equation that is difficult to reduce. But just because the measured latency is less than what we as humans can react to, it doesn’t mean these delays can’t be perceived, even if it’s just in the way something feels.
The Best – The Middle – The Rest
From my research it seems like most discerning drivers that care about latency choose Airtronics/Sanwa. Certain models have an insane 2ms latency. However, these setups are expensive and may require special servos as well. Hitec, Futaba, and Graupner also have super-fast radios and their own cult-like following.
For the middle, Spectrum seems to be the best bang for your buck. The newest DX2E (DSMR versions) are $60. They don’t advertise that it supports the fastest Spektrum response time (5.5ms). But coupled with the right receiver, like a SR3100 (even some knock-off ones), it will run at the lowest latency. The DX2E Active is an even more intriguing option – by adding a bluetooth module you can add multi-model memory, trim and end-point adjustment, even telemetry, all using their app on your smartphone.
Everything else is typically in the 10-20ms range, with the “slowest” from 20-30ms. One way radios reduce the latency and increase speed is by reducing the number of channels. It takes less time to send the information for 2-channels than it does for six, so consider that before using your 6-channel crawler radio on your touring car.
I wound up getting a used Spektrum DX3R Pro for a little more than $100 so I could have multiple model memory & settings plus 5.5ms response time. As a bonus it can switch to lefty mode if it gets bequeathed to my left-handed daughter.
Latency Data and USB Adapters
Since I started this research regarding latency to improve the feeling of my VRC gameplay, I’ve cataloged the data here under 3 different USB interfaces for playing Virtual R/C. Each USB interface has an upper limit on capture speed, but the fastest ProRace interface supports speeds that no transmitter manufacturer has reached (yet). There’s not a lot of cost difference between the USB interfaces, but the ProRace was definitely the most difficult to track down. The site milehighwings.com wouldn’t let me checkout, so I sent a private message to bluesky123 via RCGroups. He is the developer of the MHW interfaces and was able to send me a paypal request directly for one. He reported that he has stock, so you might choose to go the same route.
Here are the findings. I tried to link to the sources of information as much as possible. Ones marked with an asterisk (*) I measured myself.
- Trackstar TS3t / BER TRC1 – 49Hz / 20ms*
- Quanum – 53Hz / 18ms*
- Arrma ATX-300 – 60Hz / 17ms*
- HK-GT2 – 62mhz / 16ms*
- RadioLink RC4GS – 12ms
- Traxxas TQ 2.4GHz (Model 6516) – 10ms*
- And Every other radio above 7ms
9Turbo RX4C – Sample Rate 190 (5ms)
- Futaba 4PL – 6.8ms
- Spektrum Dx2E (DSMR versions) – 5.5ms
- Spektrum DX3R (and Pro) – 180Hz / 5.5ms*
- Airtronics/Sanwa MT-4 – 5.2ms
- Lynx 4S – 4ms
- Futaba 4PKS-R – ~3ms
- Airtronics/Sanwa MT-S – 2.6ms
- Airtronics/Sanwa MT-4S – 2.6ms
- Airtronics/Sanwa MT-44 – 2.6ms
- Airtronics/Sanwa M11x – 2.6ms
- Airtronics/Sanwa M12S – 2.6ms
- Nomadio React – 2ms
- Graupner X-8N – 1.5ms
If I missed any radios you’d like to have highlighted here, comment below. Lots of radios don’t have published PWM frame rates and I’d like to create a comprehensive list.
Extra Channels in VRC
If you want to be able to use your 3+ channel radio with VRC to use the 3rd channel for marshalling, you can do it by using the ProRace adapter for channels one and two and a VRC-3NT for the aux channel(s). Otherwise the newer RX5 looks like the best all-around option for speed and extra channels for marshalling.
Just remember that while the ProRace and RX5 will still give you the high resolution, overall latency will likely be increased by adding additional channels to the transmission.