Electronics > Projects, Designs, and Technical Stuff
Are accurate clocks really the limiting factor in cheap Inertial Navigation?
barry14:
A quick Google search turned up a portable cesium clock introduced by Symmetricon in 2011 that is the size of a matchbox, weights 35 grams and uses 115 mw of power. It's based on work done by NIST.
ejeffrey:
That said, one application I can see for cheap/portable atomic clocks is not really dead reckoning, but navigation based on local beacons where a GPS clock isn't available even to the beacons. So for indoor underground positioning you could deploy fixed local beacons and allow mobile receivers to triangulate relative to those beacons. Or you could do the reverse for wireless network monitoring. In a mesh wifi network, each client can be seen by a handful of APs. They could in principle do triangulation to allow you to locate unidentified devices or rogue APs. Like GPS you would still have to periodically update the clocks due to their non-zero drift, but a cesium clock would have less drift than an OCXO.
I am still skeptical. Inexpensive portable rubidium oscillator already exist, and as I recall the stability crossover point between a Rb oscillator and a GPS signal is several hours which is plenty of leeway to keep your mesh network synchronized.
hamster_nz:
The only use I can see is to augment GPS signals - if you know the time accurately then you have one less unknown in your solution. Kalman filters and all that stuff. But going from a few ppm time error to 0 isn't going to change much.
When I was working on a system for trucks that used counting hubometers as an absolute distance reference, tire pressure and even tread wear were visible in the data. The firmware had to calibrate the tire size when travelling in a constant direction for a long enough interval and long enough distance, while GPS fix was maintained, and could then use that value when GPS was lost.
tomato:
--- Quote from: StillTrying on March 25, 2019, 08:39:03 pm ---It seems strange that a University of Sussex dept. the Prof. and phys.org don't realize that a lot more than a miniature atomic clock is needed for the none-GPS ambulance or mobile phone navigation, but we all do!
--- End quote ---
Maybe you and all the others that "know better" should read what the author wrote:
--- Quote ---Long story short, precision clocks are needed for what is called 'inertial navigation', where you map your position with time using accelerometers. ships have used for a long time, and a version of this navigation is already on our phones. it is how they get the direction when you start the navigation.
because you calculate the path by measuring time and acceleration/angular moment, if you do not have a good clock you make a lot of errors, and this is why portable atomic clocks are needed. exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.
--- End quote ---
rs20:
--- Quote from: tomato on March 25, 2019, 11:20:18 pm ---Maybe you and all the others that "know better" should read what the author wrote:
--- Quote ---Long story short, precision clocks are needed for what is called 'inertial navigation', where you map your position with time using accelerometers. ships have used for a long time, and a version of this navigation is already on our phones. it is how they get the direction when you start the navigation.
because you calculate the path by measuring time and acceleration/angular moment, if you do not have a good clock you make a lot of errors, and this is why portable atomic clocks are needed. exciting research by our colleagues on quantum gyroscopes should make this thing even better, but the first bottleneck at this point is to make a portable high accurate clock.
--- End quote ---
--- End quote ---
The problem is, read what you bolded. The first bottleneck. That implies that this innovation is immediately applicable and useful on its own.
Regardless, even if you interpret that sentence differently, the entire original article gives absolutely no hint that there's another entirely new innovation required to provide the claimed benefits. It's essentially one group claiming the credit for hypothetical future work done by someone else.
Keep in mind that if you had a choice between getting the atomic clock in your phone OR this hypothetical quantum gyro made by someone else; based on what I'm seeing in this thread, you'd absolutely want the quantum gyro. The MEMS sensors are the first bottleneck, not the clock. Hence your bolded sentence is factually wrong.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version