Pleco Phase 03: Finally drivable

I wrote about Phase 02 in September 2013 and listed goals for the Phase 03.

Most of the goals are implemented and finally it is a joy to remote drive the car.

I attached a wide angle lens to the existing camera and that made a huge difference. The camera crops a bit from the 180° angle but clearly the wider the better. I also made my first 3D print to better attach the camera to the servos.

Tegra 3 based Ouya was replaced with a Tegra K1 based Jetson TK1. That made it easy to stream a low latency H264 video over the network. Due to USB 2.0 and network limitations, the best quality video stream that can be enabled from the controller application is 800×600 2 Mbps.

The Microsoft Lifecam decreases the FPS in low light conditions so I added some V4L2 controls. The brightness is set to minimum to get the maximum FPS. In addition to that, the controller application now has manual focus and manual zoom.

The latency is low enough to drive over a long distance. In local wired network, the application latency (from the controller application to the slave application and back to the controller application) is 1-2 ms. Over my local WIFI it increases to 4 ms. In the video above the car was connected to an LTE network and the communication was routed over a distance of 800 km (the relay is in Stockholm and I live near Helsinki). The latency was around 60-80 ms and it did not introduce any noticeable delay. A friend of mine even drove the car from Gold Coast (that is in Australia, almost 15000 km away!). The latency was around 450 ms and while the delay was obvious, he was still able to drive it.

I also measured the actual visual delay, i.e. how long it takes for the controller application to show what the camera sees (“photon to display”). I did that by taping a led to the camera and using an external microcontroller with two light sensors. One sensor was taped to the led on the camera and the other one was taped to the monitor showing the controller application. I then measured the difference of the two sensors.

The visual latency was about 105 ms with 1 ms network latency. The camera is supposed to be 30 FPS so that can introduce a maximum of 33 ms of latency and my monitor is 60 Hz, so it can introduce a 16 ms latency. On average something else still introduced a 80 ms latency. That 80 ms may be the sum of getting the video stream from the USB camera to the Jetson, encoding it, sending it, buffering a frame, decoding it and then finally showing it. While it might be possible to get the latency down, it is already low enough for remote driving within a 1000km range :)

The project will never end and there are already some goals for the Phase 04: