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Position jumps around a lot, could use help understanding why

Posted: Tue Feb 09, 2021 7:37 am
by theRoboticist
I have found that the tracking for my use case is usually very good, but sometimes jumps around a lot for a few seconds before returning to normal. Even if the robot is just sitting still this sometimes happens. It happens even more if the robot is moving, but it is not all the time - maybe 80-90% of the time the tracking is very good and smooth but the other 10-20% of the time it jumps around. It doesn't seem to be specific to any one beacon or location either.

I am using paired mini-TX with IMU fusion and 2 stationary mini-RX beacons. I am tracking in a large empty warehouse. I have also checked with the robot off and lights off to make sure there isn't other interference from those - there doesn't seem to be. Is it possible the noise comes from some ultrasonic reflections from the wall or ceiling?

I've attached a couple images showing the large jumping I was seeing (the robot was stationary while taking that image) as well as a few oscilloscope traces. I don't fully understand what I am looking at with the oscilloscope, but from my understanding, the ultrasonic signal from beacon 2 has some noise, which gives two readings that look plausible (8m and 10m) while the signal for beacon 1 is better and less noisy. Am I understanding that correctly?

If that is the case, how can I configure things to track better and be less jumpy? Are there some settings I can change for additional filtering or accuracy?

Re: Position jumps around a lot, could use help understanding why

Posted: Wed Feb 10, 2021 10:15 pm
by smoker77
Hello,

Please try to increase "Number of periods" setting in "Ultrasound" section from 5 to 50 for mini-Tx.
This is recommended setting for mini-Tx, it should increase amplitude of the signal.
If jumps will remain, please enable 'Show trigger' checkbox in bottom right angle of oscilloscope window.
Red line (trigger) on the oscilloscope will show detected distance. If it will jump, please share screenshots with jumping trigger.

Re: Position jumps around a lot, could use help understanding why

Posted: Mon Feb 15, 2021 7:07 am
by theRoboticist
Thank you very much for the suggestion. I changed the value from 5 to 50 and it helped quite a bit. The jumping was reduced substantially, but it didn't go away totally. I'd say the position is now stable 98-99% of the time but still with wild jumps every so often. Are there any other parameters that I could try tweaking to help improve this?

I've attached a few screenshots of the oscilloscope traces with the trigger on as requested. I tried to capture times when the position was jumping, but I'm not totally confident that I got screenshots of the scope at exactly the time it was jumping.

Please let me know if any other info would be helpful.

Re: Position jumps around a lot, could use help understanding why

Posted: Wed Feb 17, 2021 8:12 pm
by smoker77
Hello,

Currently your signal looks well.
For future, for better evaluation of signal/noise ratio try reduce 'Rx amplifier' on the right of oscilloscope window to avoid overscaling of the signal on the oscilloscope. For mini-Rx, 'Rx amplifier' affects only oscilloscope, it is not used in regular tracking mode.

The jumping can be caused by loosing line of sight between mobile and stationary beacons on some moments.
To reduce the jumps you can try to increase window of averaging in modem settings and reduce 'maximum speed' down to real maximum speed of your robot. See the settings of the attached screenshot.
Not that increasing of window of averaging will increase a latency.

Re: Position jumps around a lot, could use help understanding why

Posted: Sun Feb 21, 2021 4:14 am
by theRoboticist
Thank you for the information. I have tried those suggestions with changing the maximum speed and adjusting window of averaging, but still have problems with the position jumping - even when the robot is sitting completely still with full line of sight for all beacons. The position will be very accurate for a minute or two and then the position will jump around wildly for 20-30 seconds without me touching or changing anything.

I have attached a few more oscilloscope screenshots with the recommended changes to the RX amplifier. A couple of the stationary -> hedge pairs look like they have a very clear position signal (I only uploaded one picture of that). However, one of the other traces looks like there isn't a clear peak and another looks like the power is much lower. Are either of these indicating a problem or does this look okay? Please let me know.

Do you have other suggestions of what to try or what tests to do to help resolve the jumping problem? Thank you.

Re: Position jumps around a lot, could use help understanding why

Posted: Wed Apr 14, 2021 7:10 pm
by smoker77
Hello,

Signal from mobile beacon 2 looks more weak than signal from beacon 1.
Are you sure the stationary beacons are on line of sight?
Can you share photo of placement?
'Line of sight' means mini-Tx are covered by Rx diagram of mini-Rx (see the attachment) and no obstacles between them.