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I am trying to build an automated battery swap mechanism for drones. What I currently have in mind is a battery housing sitting on the drone which has electrical contacts on the inside, and a Li-po battery inside a third printed enclosure, which has electrical contacts on the outside, so that as my mechanical arm pushes the battery into the housing, the contacts touch for power delivery.

What kind of electrical contact should I use for this? A flat piece of copper looks unreliable to me for power delivery. I looked at pogo pins, but they usually come in small sizes for testing rigs.

Davide Andrea
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Dev Rajput
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    What current do you anticipate? – Dwayne Reid Jan 02 '23 at 20:53
  • your question might have an answer at https://drones.stackexchange.com/ – jsotola Jan 02 '23 at 21:02
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    Go gold-plated. I'd not trust copper (nor most common metals, corrosion) to be reliable over time. Otherwise you'll be cleaning them regularly. Pencil erasers contain sulphur, which cause more corrosion over time; avoid. – rdtsc Jan 02 '23 at 21:30
  • @DwayneReid since the connector recommended for my drone is an xt60, which is rated for 60Amps, I think 60Amps continuous current with intermittent spikes of over 100 Amps during acceleration but ideally these would be mostly during takeoff and in rare circumstances – Dev Rajput Jan 03 '23 at 07:39
  • I would not conclude from the XT60 that your drone consumes that much current. Can you somehow measure the current? With a clamp meter for instance? – datenheim Jan 08 '23 at 19:56

4 Answers4

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They make blade connectors especially for that purpose. You've seen them in laptop batteries.

They're not spring-loaded as you suggest, but instead the socket uses spring leaves that separate as they are penetrated by the male blade. This is more reliable and can carry more current than your proposed solution. Also, they're self-aligning, which allows for blind mating, exactly what you need.

Battery Blade Board-to-board connectors (my site).

Battery blade female connector

Battery blade male connector

You can buy them here.

Davide Andrea
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I looked at pogo pins, but they usually come in small sizes for testing rigs

Nevertheless, pogo pins might be what you are looking for: -

enter image description here

Image from here.

They come in all shapes and sizes with different shaped mating faces. And, there is no reason why multiple pins cannot be used on the same circuit connection to boost current handling capability: -

enter image description here

Image from here

Or, just go for a 30 amp pogo pin like this one: -

enter image description here

Image from here. I'm not saying this is the best or that there aren't other options. I'm saying that pogo pins can be used with sufficient care.

Andy aka
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  • The concerns is the current carrying capacity for pogo pins. The current flows through their internal spring, which is not ideal. That adds resistance. Over time, the spring overheats and loses tension. – Davide Andrea Jan 02 '23 at 23:00
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    @DavideAndrea your comment is really aimed at the op and should be under the question so that he can reveal the current handling requirements. I clearly stated in my answer that multiple pins can be used to increase current handling. I don't accept that some loss of tension leads to a problem that cannot be designed out. – Andy aka Jan 02 '23 at 23:28
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    Might also be worth noting that you can get cupped targets for pogo pins to land on, which improves contact slightly and makes them locate more easily. They don't have to just land on bare PCB targets unless you're cutting costs. – Hearth Jan 03 '23 at 06:29
  • As mentioned in another answer here, even if I try to use multiple pogo pins, it would take a lot of pogo pins to satisfy the the current requirements. Even with 2A per pogo pin I would need 30 pins to match an XT60 connector – Dev Rajput Jan 03 '23 at 12:55
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    @DevRajput Here's a 30 amp pogo pin: https://www.cfeconn.com/connector/30a-high-current-pogo-pins-spring-loaded-contacts – Andy aka Jan 03 '23 at 13:01
  • @Andyaka Cool, I didn't know such powerful pogos existed. Though a datasheet which spells "angle" as "angel" sows seeds of doubt in my mind. I wonder why Apple never managed to design something like this and instead made a connector which got a class action lawsuit for being a fire hazard. – Dmitry Grigoryev Jan 03 '23 at 14:51
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    @DmitryGrigoryev yes the spelling is always a hint of worries. – Andy aka Jan 03 '23 at 14:55
  • @Andy aka - Nice find! – Davide Andrea Jan 04 '23 at 14:32
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Toy drones typically consume single-digit amps, and consumer drones (starting at 250 gram) already need tens of amps during maneuvers. Essentially pogo pins are not an option for this, even special ones. E.g. MagSafe was a very problematic connector despite Apple's engineers best efforts, even though it was indoor-only and limited to about 2A per pin. A modest 20A battery would already need at least 20 such pins, even before you consider derating for outdoor use.

Speaking of outdoor use, bare copper contacts will oxidize in moist environment within a couple of weeks. If you then try to draw 30-50 A via such contacts, they will simply weld.

Look into commercial drone batteries to see what kind of connectors are commonly used before you try do design your own. Blade connectors are common on smaller drones, while larger ones are using XT60 and similar. You'll need significant force to mate them, but I don't think there's an easy way around this.

Dmitry Grigoryev
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Anderson Powerpole connectors are available for up to 350 ampere current and are mechanically easy to plug together. They would probably work quite well for automatic battery insertion and removal, as to connect and disconnect you only need to align the connectors and push / pull straight.

enter image description here

Pogo pins could still be a good option for auxiliary control signals, such as temperature monitoring. You may want to also monitor the voltage drop over the high-current connector, to detect any connection issues before overheating occurs.

jpa
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    Having used these, I can tell you the insertion and removal force are difficult for a human to handle, let alone a lightweight mechanical device. The higher current ones also require hydraulic crimping, not exactly ideal for small quantities. – cat40 Jan 03 '23 at 20:05
  • @cat40 Interesting - I have only used the smallest PP15 (55 A) model, and the insertion and removal felt very easy. I think that for >100A connections high-quality crimping will be necessary with any connector, as solder joints just have too much resistance. – jpa Jan 04 '23 at 06:48