Hi there, I have an interesting problem where I need to measure the level of a foundation in respect to another foundation (vector normal comparison).
The part that makes this interesting is they are in a moving ship and therefore cannot be measured relative to gravity but instead must be measured instantaneously relative to one another; and are up to 100 metres apart.
The current methodology is a very outdated system that involves 100 metres of cable and a single axis accelerometer. My plan is to use two arduino's and a radio frequency transceiver. My question is how is the best method to go about communicating these numbers effectively back to the reference level?
In my mind it would be something like this:
On Slave:
average the last 0.5s of data on slave unit
send data over RF
On master
average the last 0.5s of data
display raw on oled
Wait for RF input
compare array for matching time
display delta on oled
Send delta over RF to slave
repeat
On slave
wait for RF input
display delta on oled
repeat
As i haven't delved into the use of RF yet im unsure how quickly i can send and receive data, considering i want the screen to update every 0.5s. (or at least every 1s given that the delta should be stable, and the raw should be varying)
I'm also not sure the best way to send the data or commit it to a temporary array. What would happen if the master doesn't receive the data? will the output be too slow? will waiting for a signal break the whole thing?
Also given its important that the time signatures match, i'm not too sure the best way to handle that. Is rf fast enough that both units can record, send and recieve in under 1s?
How about the idea used to measure the movement two arbitrary points on land… a laser.
Either directly, or reflected (requires only one intelligent nude),
Look up Amsterdam’s laser building measurement technology - I’m sure it’s used elsewhere. In Amsterdam, I believe it’s used to detect long term displacement of entire buildings from subsidence or structural failure.
You can bounce the light across multiple segments to traverse complex shapes and offsets within the beam spread of your specific laser.
To derive precise measurements will require more complex calculations than simple 2D maths, but it can be done - Even around multiple blind corners at different angles.
Trust me, metrology is my job. I know all there is to know about this kind of measurement.
To take a plane measurement on a mast and transfer it to a plane 3 decks below when you cannot use a gravity reference frame as the ship pitches and rolls in the water is a very cumbersome task. Almost 3 days of work, and difficult to put a number on the final accuracy.
Not interested in something they use in residential construction in Amsterdam. Please direct the response to the question asked.
Whats the difference ?
Two movable objects that you want to measure the displacement.?
Accurate to single millimeters unless there’s more to your requirements.
I accept and acknowledge your skills and experience, but don’t look past alternate strategies.
that is definitely a possibility, but first i just want to be able to develop the above code outline so the correct data is being communicated and in a timely manner.
Pretend there is no communication issue for now, what kind of "handshake" would you do to ensure the last 500ms of the slave are being compared to the last 500ms of the master?
cannot reference gravity, looking at micron accuracy, no line of sight, requires multiple on multiple instrument setups, the ship is moving much more that a couple cm over years like a building, you cannot use conventional surveying technologies.
And the big one, its completely unrelated to the question asked. Show me your video and ill tell you why you cannot use it.
im expecting to use a 0.5g 2 axis accelerometer and use the magnetometer to give a pitch direction relative to compass north; then its a simple vector comparison.
I havent used one yet, but im looking for under 0.01degree resolution and stability in the output. I can use our granite table as a reference to calibrate.
If i can at least get the proof of concept going then theres more expensive and more accurate accelerometers out there.
Let the master transmit a12 bit time stamp from a "master" clock, if the received packet at the slave didn't agree, ignore and request retransmission.
Im worried it would be in this permanent lag loop where the slave is always 1 request behind and nothing is compared?
I doubt that is possible with consumer grade magnetometers, but if so, measurements would be very slow and require extremely careful calibration to eliminate the distortions due to nearby ferrous or magnetized objects, and would likely require 1000 fold averaging to reduce the sensor noise.
AHRS packages for navigation with that level of orientation accuracy start in the general range of $50K.
