Let's discuss: DOCKING solutions

[Michael Wimble]

Who has built a mobile robot docking/charging station? What hardware did you use? Did you incorporate low friction contacts? Did you worry about wear and replacement of the contacts? Did you consider sloppy robot approaches? April tags or high-reflective material for camera or LIDAR discovery of the charger? Protection from voltages higher than 12v? Interlock switches? Prevention of movement of the charger when the robot banged into it? Discuss.

[Marco Walther]

On 7/17/24 16:47, Michael Wimble wrote:
> Who has built a mobile robot docking/charging station?

I did;-)

What hardware did you use?

Brass acorn nuts & brass sheet metal;-)

Did you incorporate low friction contacts?

Kind of;-) The sheets act as kind of springs on a gantry.

Did you worry about wear and replacement of the contacts?

All the contact parts cost < $20 at HomeDepot and so far, they lasted 2+
years outside;-)

Did you consider sloppy robot approaches?

Yes, even GNSS RTK is not that accurate. My contact plates are about 2
inches wide.

April tags or high-reflective material for camera or LIDAR discovery of
the charger?

No, just GNSS approach works almost 100%.

Protection from voltages higher than 12v?

Running 29.?V into a 7S battery;-)

Interlock switches?
No, the controller/software waits a moment before turning on the 'charging'

Prevention of movement of the charger when the robot banged into it?
Discuss.

My lamb can and did move it's 'barn';-) But that usually happens when
the GNSS goes away at a bad moment and it hits the sides of the door.
This year more than last.
>

Maybe some ideas;-)

-- Marco

[Alex M]

Years ago I built a docking/charging dock for Hello Robot's Stretch robot. Here's a link with some details:

https://forum.hello-robot.com/t/auto-docking-and-charging/181/7

On Wed, Jul 17, 2024, 4:47 PM Michael Wimble <mwi...@gmail.com> wrote:

Who has built a mobile robot docking/charging station? What hardware did you use? Did you incorporate low friction contacts? Did you worry about wear and replacement of the contacts? Did you consider sloppy robot approaches? April tags or high-reflective material for camera or LIDAR discovery of the charger? Protection from voltages higher than 12v? Interlock switches? Prevention of movement of the charger when the robot banged into it? Discuss.

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[Chris Albertson]

I have not done this yet but I would think that maybe future designs would be best to use Qi “wireless” charging. I’ve been eyeing this technology for a while. We’ve all seen it used for charging phones and watches, but those are the so-called “baseline” systems that can only do 5 Watts. There is also a Qi standard that goes up to 1KW. The distance can be up to 40mm of air gap.

I see deals like the below link on Aliexpress. It’s cheap enough that I’d be willing to experiment and prototype if others wanted a to do a project

Here is one of 100 products: https://www.aliexpress.us/item/3256804469125775.html

I think using wireless woud very much reduce the mechanical complexity.

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[Dave Everett]

I have one. I don't have a picture handy. It uses 2 extension springs as the power contacts.

A DPDT relay switches them between connecting to a Nano and supplying charge voltage.

On the robot a pair of conductive strips make contact with the charger springs. Dpdt relay on the robot switches between a short circuit and connecting to the robot battery.

A single IR led on the charge produces a coded signal, the robot has 2 IR detectors that can see the IR led. AS 3d printed housing on the robot restricts the IR so the only time both sensors see the LED is when the robot isd oriented perfectly in line.

The robot backs onto the charger and the charger nano detects the short. The charger then sends a different code via IR that instructs the robot to switch the relay so the battery is connected, then when this is detected by the nano, it switches it's relay to connect the charger.

Probably overkill, but I can imagine accidental shorts happening otherwise.

All the alignment is done by the base arduino that controls the motors, clif sensors, encoders, battery monitoring and talks to the ROS computer.

Dave