Question on Sizing + Inter-sub communication

[Kolin Szeto]

Hello!

My team and I wanted clarification on a couple of rules

1. The size limit rule, "For the RoboSub competition, each entry must fit within a six-foot long, by three-foot wide, by three-foot high “box” (1.83m x 0.91m x 0.91m)". Does this apply to sub the entire run or does this only apply to the initial size of the sub? For example, are we allowed to extend appendages outside of the sizing constraint during the middle of the run?
2. Inter-sub communication, "Teams wishing to have communication between each vehicle must post their method and frequencies on the official forum by a specified date (see forum for details). Acoustic frequencies that are always off limits for inter-sub communication are the frequency range used by the pingers." When is the deadline/when will the deadline be released for posting our communication methods if we were to attempt it?

Thanks!

[Daveman]

Kolin Szeto

1. Currently, the sub size applies to the entire run. So you can't extend appendages outside of the sizing constraint during the middle of the run. This if for the safety of the divers in the water, who might have to retrieve/return the vehicle to the start. Also for the removal of the vehicle from the water. Even if it's "easy" to stow the appendages, the diver has enough to do when trying to hook your vehicle to the hoist without having to also worrying about appendages.

2. With the current COVID-19 situation, this deadline is very fluid. If you feel like you are going to attempt the Inter-sub communication, then please post your method and frequencies.

[Boulder RoboSub]

Hi Daveman ,

Our team has two Blueprint Subsea X150 Modems that we'd like to see if we could use in the competition. They have a spreadspectrum encoding in 24-32kHz which overlaps with two of the pinger frequencies from previous years (25 & 30kHz). We haven't tested their operation alongside a pinger or how disrupting they are to a hydrophones system, but we will when non-remote operations begin up again. The Benthos pinger outputs 177dB 1uPa @1m at max power while the X150 outputs 172dB 1uPa @1m. So, if transducers in the hydrophone system have a linear response to pressure, roughly speaking the X150 signals will appear at about 1/2 the sound pressure as the pinger frequencies, so I could see that having the potential to disrupt teams attempting hydrophones on the 25 or 30kHz sections of the pool.

A couple of options that may be worth discussing
1) Since only a few teams (FEFU and Harbin to my knowledge) had hydrophone systems last year, could the pingers default off and then be turned on when a team requests? Perhaps our team could coordinate with those teams attempting hydrophones to not be in the pool at the same time or our team could always attempt to be in one of the [25,30kHz] sections and request the pinger off when we're communicating to limit probability of interfering with other teams.
2) The modems take about ~1s to send a msg. Perhaps the order and the period of the pings could be such that there's a window of time to communicate in the 24-32kHz range? This would allow for modom operation given the pingers present signficant interference and need to stay on, but wouldn't solve the interference to other teams attempting hydrophones on the 25,30kHz frequencies.

On another note, we'd also like to use a low range rf intersub comm system. It operates at 27MHz and in our divewell pool we get about 5-10m of underwater signal with it using a very bad antenna. Our plan is to re-purpose the rf system of this rc sub (https://www.ebay.com/itm/352694520495) and design better antennae for both vehicles. If both comms systems (modem and rf) work out we would love to try to attempt interesting cooperative behavior when at longer range using low bandwidth acoustic comms and then at shorter range higher throughput rf comms .
3) Would there be any considerations from the competitions perspective with using such an rf system for intersub comm?

Thanks,
-Luke

[Daveman]

Actually, there are a lot of teams that use hydrophones, it's just that they are all in various states of "working"

1,2) I agree the X150 should be quieter than the Pingers. Unfortunately they do step on some of the frequencies in use, which could interfere with the reception of the ping (there are different methods of hearing and syncing to the specific ping). The pingers could also interfere with your reception of the X150 (but that would be your problem ). Also the coordination you are hoping for would be hard to actually accomplish during the competition. The teams that are in the water can/do can change very quickly.

We do shut the pingers off when a team does not require them. Each pinger is synced to a specific time slice, and there is "quite" time in between to help cut down on the echos. So, it would be difficult to send something during that time (and how would you sync to the pinger?). Teams have a hard enough time trying to filter out the echo, much less someone else broadcasting on that same frequency.

While I appreciate your eagerness to attempt the inter-sub communication, I'm going to say no to the X150 for this year.

Something that could be done, would be to separate the pinger frequencies with the X150. So that pingers could be set to 34, 36, 38, 40. However, I'm not sure how the teams filter the signals, and therefor I'm not sure if 2 kHz is enough separation.


This is a great time for teams to discuss this potential option.


3) What a cute sub! Ah, the old 27 MHz band...
Remember, any vehicle that you wish to enter in the competition must qualify in order to be used in the semi-finals / finals.
As far as I can determine, 27 MHz should be fine to use.

[Kolin Szeto]

Daveman

Thank you for the clarification on the sizing constraints


My team is still deciding on the intersub communication method(s), but we have narrowed the choices down based on the team's capabilities to visual/light communication and acoustics, we have not decided on frequency other than not using the frequencies that will be used on the official course. We also have not decided on the transmitter/pinger yet but we will get back to you when we do.

[Daveman]

Kolin Szeto
You are very welcome. We look forward to your decisions.