Request for Comments: Charging Box v2
Closed this issue · 8 comments
We need a new charging box! This issue tracks requirements and ideas for the next iteration of our charging box as well as proposed implementation options.
Requirements
- More charging ports (at least 12)
- Self-contained (handle, enough space for cables, etc.)
Nice to have
- Display with aliveness information etc.
- Interaction with connected robots (e.g. poweroff)
- No custom 230V wiring
- Low weight and small size
- Aligned LAN and charging cable ports
Size:
The chargers takes up the most space. They are also the reason why we have custom 230v wiring (which isn't that complicated).
Our own charging architecture?
If we do our own charging setup (1-2 big step down power supplies and an array of charge controllers), then displaying the charge status directly from the box would be quite easy to do.
This has been discussed before and some solutions were looked at in 2019-2020.
I assume that the safety and regulatory matters become much simpler if our custom circuitry only work with the low voltages and use an off the shelf unit for the step down conversation.
Aliveness stuff:
Good idea, I recall having a rpi in the box during initial trials for temperature monitoring, this could be extended for charge status monitoring + other functions. Maybe also a direct button to shutdown all xD.
Aligned jacks:
I guess we will need a different port than the XLR ones we use (unless we want to mess with high speed PCB design with rj45 😅 - not that hard but extra complexity).
Slimmer, robust cables:
I find the current cable setup is rather rigid and bit annoying to handle around - mainly the Lan cables. One idea I heard was to try cables with braided casing which are more flexible and apparently robust as well.
IMHO if we can expand the supported number of naos within the current size (including cable storage), I would consider it as a win.
Implementation options (electric side)
Option 1: Using the included NAO charging bricks
This is the currently used option. It is probably the simplest one but requires a lot of space and custom 230V wiring. Its space constraints may be improved by positioning the charging bricks in a different way.
Option 2: Using CC/CV boards
This option separates the AC to DC conversion and the CC/CV charging part of the NAO chargers. The first stage is shared among multiple charging ports and consists of e.g. a 30V power supply followed by CC/CV buck converter boards like the LM2596 ones. This requires much less space and potentially no 230V wiring depending on the power supply chosen.
Option 3: CC/CV on a custom PCB
This option uses the same approach as option 2 but puts all CC/CV charging electronic on a custom PCB. This requires the least amount of space and reduces wiring, but requires additional assembly time for the PCB itself.
Option 2 and 3 both sounds good. Also would be nice if they are modular, so if one module burns out, we still get to use some ports than loosing all (and easier to replace ). This is also where I wrote earlier to use 1+ 230v-30v step down units for some redundancy.
It sounds like over engineering but I'm sure we would rather have a box with half availability than no availability 😅
Connector options
XLR connector
This is the currently used one. It is quite rigid and has a nice locking mechanism. However, it takes a lot of space and results in having to sort the different cables according to their length to the missing alignment of XLR and LAN ports.
6.3mm audio jack
This one requires less space, is also quite rigid and can be aligned to the LAN ports. Additional care has to be taken to ensure no short circuits when inserting the plug, though this might be simply mitigated by using a 3-pole connector and connecting just the outermost contacts.
5.5mm barrel jack
A barrel jack requires probably the least space, but is not as rigid as the other two options and might fall out way easier. However, this would allow for symmetrical cables.
"Single Cable" connection
Concept
This is an completely different approach to the previous ones: Using the power over Ethernet 802.3bt Type 3 standard (also known as PoE++) one can transmit up to 51W via an ethernet cable. The NAO itself is not capable of charging via PoE, so a splitter with a CC/CV DC to DC step down converter which is near the NAO is used.
The charging box (except the display part) would simplify to a PoE++ capable switch, so the functional block diagram for the connection to one NAO is the following:
┌───────────────────────────────┐
NAO head ───┤ LAN out │
│ LAN (PoE) in ├───[...]─── PoE++ Switch
NAO body ───┤ DC (CC/CV) out │
└───────────────────────────────┘
This would get rid of all kind of alignment issues (since there is only one connector per NAO at the charging box), allows using more flexible cables of arbitrary lengths and easily extending the number of "charging ports" by building more splitters (assuming enough PoE++ ports left).
Implementation options
The splitter board has to handle the PoE initialization as well as the CC/CV DC to DC conversion for charging. These can either be done with two ICs or using one combining both functions as the TPS23730. This requires designing a PCB as well as R&D into the construction of the CC/CV charger.
We should also consider whether reducing the charging current is an option (~50W is just the maximum a NAO charger is able to provide, one should measure whether this is actually required), since PoE+ (802.3at Type 2) switches are more common and cheaper and the power electronic has to handle less power.
Question: yes there is an alignment problem. But why is that an issue. It is just an issue when you have to plug in the cable on the first day. But afterwards we need just the NAO side.
So no problem.
And xlr has the advantage that it would not slip out like audio Jack's could do.
And having some additional cabling next to NAO makes the wiring on the event with the Naos not better
Current idea for torso holder:
The charger cable can be integrated in the holder. A holder for the head is also planned, but maybe I will first print a torso holder and see if that works.
Box wurde gebaut