Using Motor Port to Power Control/Expansion Hub

[ddiaz]

This question was found on another forum and brought here for more discussion:

@FTC Q&A 325

The male XT30 connector on my Control Hub is not making a reliable connection any more. I read on an online forum a recommendation to instead use an empty motor port - instead of plugging into the XT30 to power my Control Hub, I could cut/splice a power and motor cable together to instead provide power directly into a motor port to power my Hub. Is this safe/legal?

Absolutely not. Doing so can irreversibly damage your Control Hub and can provide an overall unsafe 12V power system on the robot. The only safe and legal way to power the Control Hub or Expansion Hub is through the XT30 ports on the hubs.

If the male connector on the Hub is unreliable, use a Power Distribution Block and obtain/create a male-to-male XT30 cable to provide power to the female XT30 connector on the Control/Expansion Hub instead. Both male and female XT30 connectors on the Control/Expansion Hub are electrically connected together. Your hubs will no longer be able to be used as power passthrough, but the Power Distribution Block essentially performs the same function.

Some recommendations such as using hot glue or some other kind of glue or stabilizing method to keep the XT30 housing connected might seem like a good idea, but these are actually VERY BAD ideas. The issue is that it’s not the XT30 housing between connectors that keeps the connection stable, it’s actually the metal contacts within the housings that maintains the physical connection. If the physical connection isn’t stable, then the metal contacts within the housings very likely are not making a reliable electrical connection either. If you hot glue the housing onto the Control/Expansion Hub, any kind of physical shock could cause a momentary separation in the metal contacts. To an outsider this could look like any number of problems (ESD, a short in the cabling, etc…) but in reality it’s a poor connection hidden by hot glue. Just don’t do it.

-Danny

[pmichaud]

Our team started using WAGO lever nuts to distribute 12v power to our devices, as we’ve run into problems with reliability of the REV XT30 Power Distribution Blocks.

Here’s a photo of the basic idea:

We use some simple XT30 pigtails to send power to both the male and female XT30 ports on the Control Hub / Expansion Hub. This provides a level of redundancy in the electrical connection, as well as allowing for somewhat greater current flow to the hubs. The WAGO connectors can be connected to each other using 14AWG or even 12AWG wire for greater conductivity between the hubs.

The XT30 pigtails are available from Amazon fairly inexpensively: https://www.amazon.com/gp/product/B07C5KJX24 . These are 16AWG and silicone insulation, which makes them nicely flexible and better handle larger current draws than the typical 18AWG wires. These pigtails also seem to somehow have greater “grip” strength on the XT30 pins themselves – i.e., there’s a lot more force needed to insert/remove the plugs than what we’ve encountered with other XT30 plugs. (I have no idea why these might be better grip, they just seem to be.)

Pm