Newbie, some questions pl

Help / Getting Started
1

I’m slowly approaching OpenHD, and wonder what wifi cards I should get, and what else I might need. I know, not a very original question, but …

First off, I would use OpenHD with a gopro and with full bi-directional MAVlink; it’s going to be installed on a copter with a STorM32 gimbal. For “normal” RC control I would use a 2.4GHz transmitter/receiver system in addition. I don’t need very long distances, I would be more interested in a most reliable link (as it would be used rather in urban areas than free space).

It seems to me 5.8GHz wifi cards are usually recommended for this, I find the ASUS USB-AC56 most often mentioned (if not from Aliexpress). However, in the list I also find the ALFA AWUS036ACH, which has the same chip, but has TWO antennas. So, question:

  1. Would it make sense to use a ALFA AWUS036ACH for the ground pi, i.e., would it be a substitute to using two wifi cards and yield similar redundancy/safety, or is using two wifi cards the much better option?

I came to very much trust my 2.4G RC link and the only reason for having it in addition is safety. I would control the copter via it, and only do the groundstation thing through OpenHD … very traditional setup so to say.

  1. In all seriousness and honesty, is OpenHD that reliable that an additional 2.4G RC link is not needed as fallback?

  2. If so, would it be then meaning full to choose 2.4GHz wifi cards? They are much cheaper, and I like to keep it cheaper if possible without too much disadvantage (the OpenHD thing is quite expensive already …).

I do own a RPi Zero, a RPI 3B and a RPi 3A+, as well as hdmi converter from aliexpress. Ideally I could use the RPi Zero for the air pi, for space and especially weight reasons, but the air pi would also have to function as companion computer, i.e. run some scripts as well as a dual uart expander to connect to the flight controller and a STorM32 gimbal. Difficult to say precisely, but I found that to occupy something like 25% of the RPi Zero. I found a statement that OpenHD would occupy a RPi Zero to ca. 60% or so. The RPi3A+ should be easily up to the task, but it’s really bigger and heavier.

  1. Is it realistic to use a RPi Zero as air pi, if it also has to function as companion computer?

I find quite mixed info and experience on powering. It seems that this can be a substantial issue in terms of ensuring reliability.

  1. Can I assume that a 3.5A/5.3V power supply is plenty to power all what is needed for OpenHD on the air side (rpi, wifi, hdmi converter)?

Building a OpenHD system is always made to sound easy here, like “get two pi’s and to wifi cards and you’re set”. However, more careful reading shows that it is not always as simple as that. So, please let me bluntly ask:

  1. Any “dark secrets” one should know? Any hardware items I missed? Any other typical blockers?

Many thanks, also many thx for this great work!!!
Olli

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Would it make sense to use a ALFA AWUS036ACH for the ground pi, i.e., would it be a substitute to using two wifi cards and yield similar redundancy/safety, or is using two wifi cards the much better option?

For diversity 2x cards probably works a little better, but it shouldn’t be significant enough to worry about if you’re just getting started.

In all seriousness and honesty, is OpenHD that reliable that an additional 2.4G RC link is not needed as fallback?

There are some little issues with it at the moment (it’s being rewritten to deal with them), but with RC there are no “little issues” :smiley: So if you’re happy with your existing RC setup keep using it.

If so, would it be then meaning full to choose 2.4GHz wifi cards? They are much cheaper, and I like to keep it cheaper if possible without too much disadvantage (the OpenHD thing is quite expensive already …).

You can if you like, depending on which ones you get they can be just $5-10.

Is it realistic to use a RPi Zero as air pi, if it also has to function as companion computer?

Generally no, the air pi isn’t intended for running other stuff, just a link to the ground side.

Can I assume that a 3.5A/5.3V power supply is plenty to power all what is needed for OpenHD on the air side (rpi, wifi, hdmi converter)?

Should be yes.

  1. Any “dark secrets” one should know? Any hardware items I missed? Any other typical blockers?

It’s pretty simple, the only things that trip people up are power wiring and other things causing interference, like long unshielded CSI camera cables or attaching other things on the air side that generate interference.

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many THX, steven, for taking the time and answering all these questions. Pl let me follow up

For diversity 2x cards probably works a little better, but it shouldn’t be significant enough to worry about if you’re just getting started.

so, to be clear, the dual antenna of the ALFA AWUS036ACH do indeed bring some advantage in terms of diversity = higher reliability as compared to the ASUS USB-AC56?
(so I should buy a ASUS USB-AC56 and a ALFA AWUS036ACH?)

You can if you like, depending on which ones you get they can be just $5-10.

so, is it correct to conclude that there is no intrinsic robustness advantage of 5.8GHz over 2.4GHz, if it were not for a RC link?

Generally no, the air pi isn’t intended for running other stuff, just a link to the ground side.

thx, that’s a clear statement. So I won’t try LOL

and other things causing interference, like long unshielded CSI camera cables or attaching other things on the air side that generate interference.

ok. Many thx!

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Hey Stephen.
I’m a specification writer for the building industry/architecture.
Does OpenHD need a specification written to tie up all docs? I can create one for the group as a lesson on how to do this [I’m a beginner here].

Specification general overview:
Compliance - lists all documents, goals, drawings, diagrams, and hyperlinks.
Products - describes different component scenarios
Execution - how each scenario goes together
Selections - which part goes best with what and lists options that are suitable.

I can write a draft in Word and share with you.
Email me direct to get this started.

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@stephen

as regards 5GHz wifi adapters, I have seen that there is also the AWUS036ACS, which is comparatively quite cheap. It however uses a RTL8811AU and not a RTL8812AU chip. I tried to research but couldn’t find clear answers, but I would think that the differences are so small that they are essentially compatible so that also the RTL8811AU could be used, google spits out however older reports of driver issues but also reports of it working.

Would the RTL8811AU also work?