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Add a VBatt port to Misty

Request from field trial dev.

And consider adding a VBatt port please :slightly_smiling_face:

With 0.5A 5V only out, you can’t put much additional compute on the platform. And without OS-level access, I feel pretty restricted to what I can accomplish.

With a VBatt and Ethernet access to the local network, so I can call your REST APIs on wire, there’s a lot that can be done with that backpack.

As it stands, we’re limited to Arduino level compute MCUs by 0.5A.

This feature request should also be considered in the context of simultaneous operation of Misty Skills from different authors. In particular, exposing VBatt (=> higher power loads from user-added devices) would interfere with prediction of discharge rates of the battery. In turn, this might require conservative assumptions, e.g., to decide when to return to the charging pad.

Of course, if a single developer is writing all of the Misty Skills and adding extra hardware, then she can do calibration herself. However, to achieve a future where you can download and run new skills from other developers, there must be assumptions hardware performance. Exposing VBatt while maintaining off-the-shelf assumptions about hardware performance might be difficult.

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@jay.beavers Thanks for the suggestion. I agree that 0.5A @5V can be restrictive for some accessories. We intentionally limited the power available from the robot to accessories in part because of the reasons @slivingston brought up, as well as the fact that the accessory requirements range broadly. If an accessory has one or more motors, the voltage and current draw will likely be massive compared to an environmental sensor for example. Designing for many unknown use cases is a bit of a nightmare. :stuck_out_tongue:

It sounds like you are primarily interested in increasing compute. What sort of software are you thinking of running? Is it critical to run these computations on-board? Or could you offload those to a dedicated computer on the same network?

I’m thinking of piggy-backing a Google Coral or BeagleBone AI board onto the Misty. While I understand you offer a lot of onboard compute power already, as best I understand, you don’t offer the ability to run larger compute payloads like ML/CV and you don’t have a TPU onboard. So essentially I’m looking to ‘replace the brain’ with a higher end ARM board that I have root Linux access to that also has an ML accelerator.

Typically these boards require 2.0A or 3.0A which I could pull off a VBatt port.

Yes, this complicates the remaining battery lifetime predictions, though you could potentially put an ammeter on the VBatt port to help. Of course that’s not helpful if the battery load on the port is variant.

I think your best bet is to use your own battery in something like the battery holder arm designs we released here: Battery Arm Right by MistyMaker - Thingiverse

@jay.beavers that makes sense, 3A - 4A is pretty significant, but our battery could handle it. I probably shouldn’t condone splicing into the power harness, though it is possible. It would be less intrusive though to use an off-board batter like @Vlad suggested.

Another consideration is the data transfer speed on and off the robot. Unless I’m mistaken the two fastest ports on the robot are WiFi, and the USB 2.0 backpack port. If you need really low latency, then the transfer data rates may be the limiting factor, rather than the power consumption.