Electronics Documentation and FAQ


#1

Hey all, I'm new so be gentle. Is there a sticky for basic electronics parameters like input voltage, max current, and common setups?

For example, in my application I would like to tether power this bad boy. I would like 24VDC at the aux power input, so I won't need the battery monitoring. I will not be using the ESC power rails. Instead, I will be using a PWM brushed controller.

From what I see so far:

1. V-Bat is energized when there is data on the tether

2. I will need to change the voltage divider and scaling for V-bat voltage monitoring

Questions:

1. What is the highest voltage people are comfortable with at the AUX power connector?

2. Has anyone considered/tried sending 24VAC down the tether and using 2 conductors for both power and data, then rectify in the ROV?

2b. Can the powerline adapters Tx/Rx on a DC line?

Sorry if these are obvious questions. I looked around a bit - maybe my keywords were off.

-R


#2

In addition, are the controller and topside board dimensions and mounting hole locations written down someplace? I can't seem to find an electronics mechanical summary. I'm happy to add to the wiki if people throw numbers and specs at me.


#3

The info you are looking for may be located here:

https://github.com/OpenROV/openrov-electronics

Currently we send +5v DC across the Tether to turn on the Control Board.

I would ask Walt if you can send 24V AC down the tether, I am sure you can but please ask Walt to confirm.

There has been some work done on this but because the batteries provide lots of dive time and for most folks it's much safer to stick with DC Batteries there has not been much more development done on this. Just do a search for AC Power in the Form and you will see lots of discussion on this topic.


#4

Hi Rob:

Glad you're thinking of experimenting with the electronics of OpenROV. As David has mentioned, the topic of power-over-tether has come up a number of times before- you should be able to find the old threads by searching through the forum.

I've looked in detail at doing this a number of times, and basically have never felt that it is worth the trouble. Your mileage may vary, especially if you have an application that requires you to be uninterrupted in the water for a very long period (say, over 4 hours). The high resistance of the tether causes large voltage swings with changes in load current, which must be dealt with on the receiving end- the ROV. You'll probably need some sort of switching power supply to convert the raw tether voltage to the battery buss voltage. That switcher will need to have some sort of maximum-power-point tracking to keep from pulling the voltage on the receiving end of the tether below the optimal point.

The documentation of the Controller Board is pretty minimal right now- basically just the schematics, Eagle design files, and the Gerbers which are posted on GitHub. I want to do a complete App Note for the board at some point- this would certainly help folks who want to tinker with bare board. Unfortunately, other projects keep getting in the way. So for the time being you're going to have to brush up on your schematic-reading skills.

As for your questions:

1. The board was designed to work with up to a 4S Lithium battery configuration, say 17 volts maximum. There's a TVS on the board that will soak up spikes over 20V (IIRC). If you want to put 24V on the battery buss, you're going to have to figure out for yourself which components are vulnerable.

2.) See above discussion.

2b.) Yes, the powerline (HomePlug) adapters work perfectly fine with a DC voltage on the output. We use a 5V signal riding on the HomePlug signal to turn the ROV on/off.

As for the mechanicals of the Controller Board, the board is 80mm by 150mm. There are 4 0.125" (3.175mm) diameter holes for mounting. The datum point for board measurements is the corner near which ESC3 is mounted. Referenced to this, the 4 hole locations are at (X,Y in mm) 3,3 27,77 147,3 and 147, 77

Hope this helps.

-W


#5

Hi Walt, it helps a lot. Thank you for the detailed response. As I move forward I will keep track of my notes and share. My rover will be an underwater wheeled vehicle, so not planning to have batteries.

I looked around for some bucking MPPT converters without battery charging with no luck. I guess this makes sense considering most applications for MPPT features would be boosting PV panel voltage for micro-inverters. Maybe having a battery would not be such a big deal, or I could brute force it with a heavy tether. I have a tether from an automated pool cleaning machine and it seems they just brute force it and use LDO's for the uP electronics. The tether I have seems to have 1mm or 0.75mm wire.

Another consideration is if I can source a module - don't want to get onto too many tangents.

If you have any suggestions off-hand let me know. Thanks again.